Look north in July 2014 and take the measure of your skies and eyes!

Light pollution is a big issue these days. How does it impact you? Summer is a good time to check by looking north about two hours after sunset and seeing what stars you can see in and near the Little Dipper. Why summer? Because this is when the Little Dipper should be highest in your sky – standing upwards from Polaris, the North Star. Here’s what you should see on a typical July evening when you look north from mid-northern latitudes.

In summer the faint stars of the Little Dipper are high above the North Star. Click image for larger view. (Developed from Starry Nights Pro screen shot.)

For a printer-friendly version of this chart, click here.

The Big Dipper is diving downward in the northwest but is still very high, and its handy “pointers” should get you quickly to the North Star, Polaris. Roughly opposite the Big Dipper you should see the “W” of Cassiopeia starting to make its way upward in the northeast. And unless you suffer from really terrible light pollution, you should see the two “Guardians of the Pole” – the second and third magnitude stars that mark the end of the Little Dipper. The brighter of these two is just a tad dimmer than Polaris, but since it’s higher in the sky right now and thus shining through less air to get to you, it will probably look just the same as the North Star in brightness.

To do this test you first have to wait until it is genuinely dark, and in summer that’s a bit longer than in winter. Twilight actually is divided into three steps. We have civil twilight which goes from sunset until when the Sun is six degrees below the horizon. Nautical twilight is the next period, which continues until the Sun is 12 degrees below the horizon. Then you have Astronomical Twilight until the Sun is 18 degrees below the horizon. At that point it is as dark as it will get and will remain that dark until we run the sequence in reverse as the eastern horizon nears the Sun. As a rough rule of thumb, you can consider each twilight period to last half an hour – but the exact length depends on where you are on Earth and the time of year. If you want to get precise, go to the U.S. Naval Observatory site, fill in the form you’ll find there, and you can get a table that will give you the start and end of these twilight times – or for that matter when the Moon rises, or the Sun sets. It’s very handy. (Note: the preceding link takes you to a page for US cities and towns – but there’s a second page here where you can put in the latitude and longitude for any location in the world, including in the US. )

The second thing you need to do is make sure your eyes are dark adapted. They are casually reasonably well dark adapted after you have been out for 15 minutes and have not looked at any white lights. But it can take from half an hour to an hour of protecting your eyes from any white light for them to become fully dark adapted. That doesn’t mean you have to sit around in the dark doing nothing waiting for this to happen. In the last hour or so before full darkness there are plenty of things to see – just avoid bright lights. That also means moonlight. You’re going to want to do this when the Moon is not in the sky, for it will make it difficult to see faint objects anywhere near it. In July of 2014 the last two weeks should work pretty well for the evening hours – as will the first day or two of the month.  Other evenings, the Moon will dominate the early evening sky.   (A good Moon-phase calendar can be found here, though for this purpose I find the table from the Naval Observatory for local Moon rise is also handy!)

So here’s the test:

How many stars can you see in the Little Dipper?

Remember that in the magnitude system the higher the number, the fainter the star.

The Little Dipper consists of seven stars. Three are easy – Polaris and the two “Guardians” marked “21” and “30” on the chart below. If, once you are dark adapted, you can see only one of the “Guardians,” then your skies are limited to magnitude 2 stars and brighter – very poor. If you see both, but no other stars in the Little Dipper, then your limit is magnitude 3.

On our chart below, the magnitude of each star is listed as a whole number so as not to put decimal points on the chart because they might then be confused with faint stars! So when you see a star listed as “21” that means “magnitude 2.1.”

For a printer-friendly version of this chart, click here.

Even in good, dark skies the other four stars in the Little Dipper may not be that easy to see – and the faintest ones may require averted vision – that is, don’t look exactly where the star should be. Instead, look a little to one side or the other, and the star may pop into view. That’s because the center of your eyes are not as sensitive to faint light as the outer regions of your eyes.

Here’s another little trick that may help you locate these faint stars – use binoculars. With typical, hand-held binoculars you may be able to fit all four stars of the Little Dipper’s “cup” into the same field of view. If not, get the “Guardians” in your field of view, then move just a little to where the other two stars of the “cup” should be. This does not count, of course, for the light pollution test. For that test we’re trying to determine the faintest star you can see with the naked eye. But looking first at the stars with binoculars helps assure you that they really are there! You also can trace out the handle this way, though you will have to move your binoculars to do so.

If you can locate all the stars in the Little Dipper with your naked eye, you have very dark skies – congratulations. To see how good they are – and continue to test your eyesight and dark adaption – look for the stars marked “55” and “60” on our chart.

The star marked “60” is traditionally thought of as the faintest you can see with your naked eye. That’s a magnitude 6 star. In really pristine skies, such as those over Mauna Kea in Hawaii, experienced observers with excellent eyes can detect stars down to magnitude 8 with the naked eye. Personally, I’m happy when I can see all the stars in the Little Dipper and especially happy if I can get that “55” star – I’ve never seen the “60” one with my naked eye. But relative to the heavily light-polluted eastern seaboard of the US, I have dark skies.

This is not simply a good guide to light pollution in your area. It also is a handy guide to tell you just how good  – how “transparent” – the skies are on any given night – and to show you how well you have dark adapted at any given moment. So whenever I go out to observe I frequently glance at the Little Dipper to test both my developing night vision and the clarity of the skies. (It never fails to amaze me how much and how quickly my night vision changes. )

To the casual observer all clear nights are equal. But the experienced star gazer knows they are not, and the stars in and about the Little Dipper are a good guide, especially in the summer months when they are so high in the sky.

Look east in August 2013 – kick back, lie back, look up and enjoy our home galaxy!

This is the month to meet your neighbors – a few billion of them at least!

In August we break our pattern of focusing on bright stars and instead focus on that ancient stream of stars known as the Milky Way – our own galaxy. This means observing a bit later than normal, and if you live within urban or suburban light pollution, going to where you have really dark skies. This does not mean you have to move to – or visit – Arizona. I live in one of the worst light pollution regions of the US, and I can see the Milky Way from my back yard – and see it even better if I take a 12-minute drive to a nearby wildlife sanctuary. But I do have significantly darker skies than people just a mile or two from me. You need a clear moonless night and your eyes need to be well dark adapted. Then you want to look up for a wide, faint “cloud” with a  roughly north-to-south orientation.

I’ve reduced the brightness and contrast on this image in an attempt to approximate what can be seen from an area with light to moderate light pollution. Still, a photograph always shows more – but it just can’t capture the magic of being there. In this case the photographer also caught a Perseid meteor. As you can see, the heart of the Milky Way is nicely framed by the bright Summer Triangle stars of Vega, Deneb, and Altair. Click image for larger version.

Seeing the Milky Way is worth the special effort. It is one of the most beautiful and awe-inspiring astronomical sights, and your naked eye is the best way to take it all in, though binoculars will provide a special treat as well.  In what follows, we’ll focus on where you should be to observe the Milky Way, when you should look. and finally,  where in the sky you should look.

1. Where you should be

Sadly, most people today are routinely denied this sight because of light pollution, but don’t despair! While the darker your skies are, the better, like me you may find that pretty dark skies are just a short drive away. There is an international guide to light pollution and here’s what it shows for light pollution in and around “Driftway Observatory,” my backyard. (OK – actually most of southern New England!)

On this map of light pollution for southeastern New England, Driftway Observatory is right in the center on the border of an orange/yellow area. Obviously black is the best. Blue is darned good. Green and yellow are desirable. Orange means getting poor; red and white are quite terrible. You should look for at least a yellow area – but to the south of a heavily light-polluted city if possible.

You can get a map  for any region of the world. The simplest path is to go here. Scroll down, to the thumbnail maps and choose a region of the world that suits you and download the map for that region. Another path is limited to observers in the United States, Canada, and Mexico. For them there are “Clear Sky Charts” – astronomical viewing weather forecasts – for hundreds of locations. You can find a location near you by starting here.  Underneath your regional Clear Sky Chart you will see a short list of “Nifty links.” The last one takes you to a light pollution map for that region. It may be helpful to know your latitude and longitude first, so If you don’t know what it is, you can find it here. All of this is useful information for any sky observer to have, so if you track down a Clear Sky Clock for your region,f or example, bookmark it.

Here’s how to make sense of the light pollution maps in terms of seeing the Milky Way.

Red – “Milky Way at best very faint at zenith.”

Orange – “Milky Way washed out at zenith and invisible at horizon.”

Yellow – “Some dark lanes in Milky Way but no bulge into Ophiuchus. Washed out Milky Way visible near horizon.”

Green – “Milky Way shows much dark lane structure with beginnings of faint bulge into Ophiuchus.”

If you can get into the blue, grey, or black areas –  all of which give increasingly good views of the Milky Way – enjoy! I envy you ;-)

One critical point though: Pay attention to where there are cities. They will create light domes that will wash out at least areas fairly low in the sky. In my situation I have two small cities, Fall River to the northwest and New Bedford to the northeast. Both have populations of around 100,000 and both create light domes in those regions of the sky. Fortunately, the northern sky isn’t important for seeing the Milky Way, especially in August. But if you have a large city – or shopping mall, or anything that might create a light dome – it is better to look for an area south of it. In August in mid-northern latitudes the  Milky  Way is best from right overhead on down to the southern horizon. That’s why my best view is from a wildlife sanctuary just a few miles away and right on the north shore of  Buzzards Bay and the ocean. It means when I’m looking at the southern Milky Way – towards the very center of our galaxy – I’m seeing it over a huge expanse of water where light pollution is the least.

2. When to look

Begin looking early on a moonless, August evening and ideally, when the skies are crystal clear – frequently this comes right after a cold front passes. Although the Milky Way can be seen many months of the year, one of the best times to see it is in August, about two hours after sunset. In 2013 your best views during that time period (two hours after sunset) will come between August 1st and 12th and again after August 26th  – on other dates in August the Moon is more likely to interfere. Of course, when the Moon is young and waxing you can always wait for it to set – and when it is old and waning  you need to make sure it hasn’t risen yet. For a Moon calendar for any month go here.  If you miss it in the first two weeks of August, try again the first two weeks of September - this guide will still be useful, though everything will have moved higher and to the west a bit.

I say two hours after  sunset because it takes that long in mid-northern latitudes for it to get fully dark at this time of year, and you need full darkness. (You can find out the local time Astronomical Twilight ends – when it is fully dark – by going to this Web site. From the drop-down menu you’ll find there, choose “astronomical twilight.”) However, you can certainly start looking earlier. This is something where beach chairs or lounges are nice, and maybe even a blanket.  You can start about an hour after sunset when the brightest stars are visible. This will help you get your bearings and you can dark adapt as the skies get darker.

Finally, you need to protect your eyes from white lights. It takes 10-15 minutes for your eyes to become about 50 percent dark adapted. At that point your color vision is as good as it will get, but your sensitivity to dim light will continue to increase. In another 15 minutes or so you will reach about 90 percent dark adaption. The remaining 10 percent can take as long as four hours.  So I consider that after half an hour my eyes are about as good as I can expect them to be.  During all this time and beyond you should avoid looking at white light. You can use a red light to check a chart if you like, but keep it dim and use it sparingly. If you’re in a location where automobiles drive by, don’t look at them – close your eyes and turn away.

Where to look

When you set up your blanket or lounge chair, do your best to align it on a north-south axis with your head to the north and feet to the south. You may want to favor the east just a bit.

What you want to find as you start out is the familiar guidepost stars of the Summer Triangle – Vega, Deneb, and Altair. These were new guidepost stars in May, June, and July. If you are just starting this journey in August,they are still easy to pick out from our chart.  As the sky in the east starts to darken they will be the first stars visible, 30-45 minutes after sunset.

Click image for a larger view. (Derived from a Starry Nights Pro screen shot.)

You can download a printer friendly version of this chart here.

The brightest – and highest – of the three will be Vega, which will be approaching a point overhead. There are roughly two fists (24 degrees) between Vega and Deneb and nearly four fists (39 degrees) between  Deneb and Altair, so the Triangle is huge.

These three Summer Triangle stars roughly bracket the Milky Way – that is Vega is near the western border, Altair the eastern border, and Deneb is about at midstream.  But you need to wait, of course, for it to get darker before you can see the Milky Way.   The boundaries of the Milky Way, as with any stream, are not sharp and regular. It tends to meander a bit with little pools of light and some deep, dark areas as well.

As the skies darken and your eyes continue to dark adapt, you should try to find three distinctive asterisms that will anchor both ends of the Milky Way, plus the middle.  If you have found Deneb, then you have the first star in the Northern Cross. In fact, you may want to see this as a stick figure of the constellation Cygnus the Swan.  In that case, Deneb marks its tail; the bar of the cross, its wings, and its long neck stretch out to the south as if it were flying down the Milky Way. To the north you should locate the “W” of Cassiopeia described in detail in our “Look North” post this month. And to the south, find the “Teapot,” which we described in more detail last month. Here’s a chart showing the whole sweep of that section of sky.

Click image for larger view. (derived from Starry Nights Pro screens hot.)

You can download a printer friendly version of this chart here.

Now, if it is about two hours after sunset and if you are in a location away from light pollution and, of course, are enjoying one of those crystal clear nights with dark-adapted eyes, then you also should be seeing the Milky Way. It only takes time and patience for you to trace it out – to see areas that are brighter than others – as well as some dark patches that don’t mean the absence of stars, but the presence of obscuring dust. But don’t think of the dust as getting in the way – think of it as star stuff – for what you are seeing in many sections of the Milky Way are the parts of our galaxy where new stars are being born. Relax and explore with your binoculars – start to absorb the majesty of millions – no billions – of stars!  If conditions are right – and you have a dark sky – it will look to the naked eye like faint clouds that get brighter as your eye traces them out from north to south.

And what is it you are seeing and why does it appear this way to you? That’s the important question. And this is where you have to do some mental gymnastics.

Think of our galaxy as a large pizza pie with extra cheese and goodies heaped in the center.  Now put yourself away from that center – perhaps one-half of the way towards one edge and buried down at the level of the crust. That’s a pretty good simulation of our galaxy and our place in it. You really need to get outside it – we can only do this in our imaginations – and look at it from that perspective. If we could get outside it, here’s approximately what we would see:

Two view of our Galacy, the Milky Way. The one on the left is from  aposition above it, the one on the right shopws you the galaxy edge-on.  This is a screen shot from the wonderful, free software, "Where is  M13."

The image on the left is how we think our galaxy would look if we could get above it and look down on it – like a big pin wheel of stars.  And what if you could see it edge on? Well, that’s the picture on the right. (This is a screen shot  from a wonderful – and free – software program called “Where is M13” that helps you understand where various objects really are in relation to us and the rest of the galaxy.)

OK – focus on the edge-on image – and note how really thin most of the galaxy is. It is about 100,000 light years across, but on average just 1,000 light years thick.

plane_view_MW

Now imagine yourself on a small dot (the Earth) rotating around that small dot in our image – the Sun. Do you see a lot of stars when you look “up” – that is, look in the direction of the words  “The Sun.”

No – in fact, if you look down, you don’t see many stars either – or for that matter, if you look in just about any direction there are relatively few stars visible to you. Why? Because the disc is just 1,000 light years thick, and most of the time you’re looking right through it the short way.  But  look along the plane of the galaxy – say  directly to the right or left – and what a difference!

Looking to the left you see many stars – in fact, a thin river of stars. Looking this direction, you’re looking through about 20,000 light years of star-filled space. We are looking along the plane, generally towards the outer rim, when we look at the W of Cassiopeia. Look along the plane to the right, and you see even more stars in a much wider river. Now you’re looking through about 30,000 light years of star-filled space and then right at the star-rich, galaxy core. And this, in a general way, is what we are doing when we look toward the Teapot of Sagittarius. That’s why the Milky Way is so much brighter and denser in that direction.

Not too difficult to understand – but this is only a rough sketch. As recently as 2008 scientists came up with a much different perspective of our galaxy than we had had up until then. Prior to the latest study, we thought the galaxy was a spiral with a bulge in the center and four main arms. Now they see it as a barred spiral – that is, the bulge in the center looks more like a bar that spills into two – not four – main spiral arms. There are other smaller arms in the spiral, and it all gets quite complex.

The problem, of course, is there is no way we can get outside our galaxy and look in. The distances are incredibly vast. Even if we could send a space probe at the speed of light, it would be thousands of years before it got outside our galaxy, took some pictures of us, and sent those pictures back. So we have to try to decide what the galaxy really looks like from the outside by studying it from the inside. Imagine, for a moment, being inside your body and trying to figure out what you look  like by what you can see from the inside, and you get an idea of the problem. Fortunately we can see other galaxies, and in later months we’ll be looking at one that looks a lot like what we think ours would look like if we could only get outside it and look back.

Meanwhile, relax – look up – and dream of all  the wonders that are out there and sending their messages back to you in the form of millions of tireless photons that have traveled thousands of years to reach your eyes and ping your brain on this dreamy August evening.  Harvest some of those photons by surfing the Milky Way with your binoculars. You will notice that in some areas it is quite dense and you may even discover some tiny, tight clusters of new stars – or a globular cluster of old stars, or even a little hazy patch where new stars are being born.  You need a telescope to see these well, but you can just discern some of them with binoculars, and with telescope or binoculars, what you really need to see with is your mind’s eye. Knowing what you are looking at is what brings this faint cloud alive and turns it into the awesome collection of billions of stars – and more billions of planets –  that it is.

Look east in August 2012 – kick back, lie back, look up and enjoy our home galaxy!

This is the month to meet your neighbors – a few billion of them at least!

In August we break our pattern of focusing on bright stars and instead focus on that ancient stream of stars known as the Milky Way – our own galaxy. This means observing a bit later than normal, and if you live within urban or suburban light pollution, going to where you have really dark skies. This does not mean you have to move to – or visit – Arizona. I live in one of the worst light pollution regions of the US, and I can see the Milky Way from my back yard – and see it even better if I take a 12-minute drive to a nearby wildlife sanctuary. But I do have significantly darker skies than people just a mile or two from me. You need a clear moonless night and your eyes need to be well dark adapted. Then you want to look up for a wide, faint “cloud” with a  roughly north-to-south orientation.

I’ve reduced the brightness and contrast on this image in an attempt to approximate what can be seen from an area with light to moderate light pollution. Still, a photograph always shows more – but it just can’t capture the magic of being there. In this case the photographer also caught a Perseid meteor. As you can see, the heart of the Milky Way is nicely framed by the bright Summer Triangle stars of Vega, Deneb, and Altair. Click image for larger version.

Seeing the Milky Way is worth the special effort. It is one of the most beautiful and awe-inspiring astronomical sights, and your naked eye is the best way to take it all in, though binoculars will provide a special treat as well.  In what follows, we’ll focus on where you should be to observe the Milky Way, when you should look. and finally,  where in the sky you should look.

1. Where you should be

Sadly, most people today are routinely denied this sight because of light pollution, but don’t despair! While the darker your skies are, the better, like me you may find that pretty dark skies are just a short drive away. There is an international guide to light pollution and here’s what it shows for light pollution in and around “Driftway Observatory,” my backyard. (OK – actually most of southern New England!)

On this map of light pollution for southeastern New England, Driftway Observatory is right in the center on the border of an orange/yellow area. Obviously black is the best. Blue is darned good. Green and yellow are desirable. Orange means getting poor; red and white are quite terrible. You should look for at least a yellow area – but to the south of a heavily light-polluted city if possible.

You can get a map  for any region of the world. The simplest path is to go here. Scroll down, to the thumbnail maps and choose a region of the world that suits you and download the map for that region. Another path is limited to observers in the United States, Canada, and Mexico. For them there are “Clear Sky Charts” – astronomical viewing weather forecasts – for hundreds of locations. You can find a location near you by starting here.  Underneath your regional Clear Sky Chart you will see a short list of “Nifty links.” The last one takes you to a light pollution map for that region. It may be helpful to know your latitude and longitude first, so If you don’t know what it is, you can find it here. All of this is useful information for any sky observer to have, so if you track down a Clear Sky Clock for your region,f or example, bookmark it.

Here’s how to make sense of the light pollution maps in terms of seeing the Milky Way.

Red – “Milky Way at best very faint at zenith.”

Orange – “Milky Way washed out at zenith and invisible at horizon.”

Yellow – “Some dark lanes in Milky Way but no bulge into Ophiuchus. Washed out Milky Way visible near horizon.”

Green – “Milky Way shows much dark lane structure with beginnings of faint bulge into Ophiuchus.”

If you can get into the blue, grey, or black areas – enjoy! I envy you ;-)

One critical point though: Pay attention to where there are cities. They will create light domes that will wash out at least areas fairly low in the sky. In my situation I have two small cities, Fall River to the northwest and New Bedford to the northeast. Both have populations of around 100,000 and both create light domes in those regions of the sky. Fortunately, the northern sky isn’t important for seeing the Milky Way, especially in August. But if you have a large city – or shopping mall, or anything that might create a light dome – it is better to look for an area south of it. In August in mid-northern latitudes the  Milky  Way is best from right overhead on down to the southern horizon. That’s why my best view is from a wildlife sanctuary just a few miles away and right on the north shore of  Buzzards Bay and the ocean. It means when I’m looking at the southern Milky Way – towards the very center of our galaxy – I’m seeing it over a huge expanse of water where light pollution is the least.

2. When to look

Begin looking early on a moonless, August evening and ideally, when the skies are crystal clear – frequently this comes right after a cold front passes. Although the Milky Way can be seen many months of the year, one of the best times to see it is in August, about two hours after sunset. In 2012 your best views will come between August 6th and 22nd – on other dates the Moon is more likely to interfere. Of course, when the Moon is young and waxing you can always wait for it to set – and when it is old and waning  you need to make sure it hasn’t risen yet. For a Moon calendar for any month go here.  If you miss it in the first two weeks of August, try again the first two weeks of September - this guide will still be useful, though everything will have moved higher and to the west a bit.

I say two hours after  sunset because it takes that long in mid-northern latitudes for it to get fully dark at this time of year, and you need full darkness. (You can find out the local time Astronomical Twilight ends – when it is fully dark – by going to this Web site. From the drop-down menu you’ll find there, choose “astronomical twilight.”) However, you can certainly start looking earlier. This is something where beach chairs or lounges are nice, and maybe even a blanket.  You can start about an hour after sunset when the brightest stars are visible. This will help you get your bearings and you can dark adapt as the skies get darker.

Finally, you need to protect your eyes from white lights. It takes 10-15 minutes for your eyes to become about 50 percent dark adapted. At that point your color vision is as good as it will get, but your sensitivity to dim light will continue to increase. In another 15 minutes or so you will reach about 90 percent dark adaption. The remaining 10 percent can take as long as four hours.  So I consider that after half an hour my eyes are about as good as I can expect them to be.  During all this time and beyond you should avoid looking at white light. You can use a red light to check a chart if you like, but keep it dim and use it sparingly. If you’re in a location where automobiles drive by, don’t look at them – close your eyes and turn away.

Where to look

When you set up your blanket or lounge chair, do your best to align it on a north-south axis with your head to the north and feet to the south. You may want to favor the east just a bit.

What you want to find as you start out is the familiar guidepost stars of the Summer Triangle – Vega, Deneb, and Altair. These were new guidepost stars in May, June, and July. If you are just starting this journey in August,they are still easy to pick out from our chart.  As the sky in the east starts to darken they will be the first stars visible, 30-45 minutes after sunset.

Click image for a larger view. (Derived from a Starry Nights Pro screen shot.)

You can download a printer friendly version of this chart here.

The brightest – and highest – of the three will be Vega, which will be approaching a point overhead. There are roughly two fists (24 degrees) between Vega and Deneb and nearly four fists (39 degrees) between  Deneb and Altair, so the Triangle is huge.

These three Summer Triangle stars roughly bracket the Milky Way – that is Vega is near the western border, Altair the eastern border, and Deneb is about at midstream.  But you need to wait, of course, for it to get darker before you can see the Milky Way.   The boundaries of the Milky Way, as with any stream, are not sharp and regular. It tends to meander a bit with little pools of light and some deep, dark areas as well.

As the skies darken and your eyes continue to dark adapt, you should try to find three distinctive asterisms that will anchor both ends of the Milky Way, plus the middle.  If you have found Deneb, then you have the first star in the Northern Cross. In fact, you may want to see this as a stick figure of the constellation Cygnus the Swan.  In that case, Deneb marks its tail; the bar of the cross, its wings, and its long neck stretch out to the south as if it were flying down the Milky Way. To the north you should locate the “W” of Cassiopeia described in detail in our “Look North” post this month. And to the south, find the “Teapot,” which we described in more detail last month. Here’s a chart showing the whole sweep of that section of sky.

Click image for larger view. (derived from Starry Nights Pro screens hot.)

You can download a printer friendly version of this chart here.

Now, if it is about two hours after sunset and if you are in a location away from light pollution and, of course, are enjoying one of those crystal clear nights with dark-adapted eyes, then you also should be seeing the Milky Way. It only takes time and patience for you to trace it out – to see areas that are brighter than others – as well as some dark patches that don’t mean the absence of stars, but the presence of obscuring dust. But don’t think of the dust as getting in the way – think of it as star stuff – for what you are seeing in many sections of the Milky Way are the parts of our galaxy where new stars are being born. Relax and explore with your binoculars – start to absorb the majesty of millions – no billions – of stars!  If conditions are right – and you have a dark sky – it will look to the naked eye like faint clouds that get brighter as your eye traces them out from north to south.

And what is it you are seeing and why does it appear this way to you? That’s the important question. And this is where you have to do some mental gymnastics.

Think of our galaxy as a large pizza pie with extra cheese and goodies heaped in the center.  Now put yourself away from that center – perhaps one-half of the way towards one edge and buried down at the level of the crust. That’s a pretty good simulation of our galaxy and our place in it. You really need to get outside it – we can only do this in our imaginations – and look at it from that perspective. If we could get outside it, here’s approximately what we would see:

Two view of our Galacy, the Milky Way. The one on the left is from  aposition above it, the one on the right shopws you the galaxy edge-on.  This is a screen shot from the wonderful, free software, "Where is  M13."

The image on the left is how we think our galaxy would look if we could get above it and look down on it – like a big pinwheel of stars.  And what if you could see it edge on? Well, that’s the picture on the right. (This is a screen shot  from a wonderful – and free – software program called “Where is M13” that helps you understand where various objects really are in relation to us and the rest of the galaxy.)

OK – focus on the edge-on image – and note how really thin most of the galaxy is. It is about 100,000 light years across, but on average just 1,000 light years thick.

plane_view_MW

Now imagine yourself on a small dot (the Earth) rotating around that small dot in our image – the Sun. Do you see a lot of stars when you look “up” – that is, look in the direction of the words  “The Sun.”

No – in fact, if you look down, you don’t see many stars either – or for that matter, if you look in just about any direction there are relatively few stars visible to you. Why? Because the disc is just 1,000 light years thick, and most of the time you’re looking right through it the short way.  But  look along the plane of the galaxy – say  directly to the right or left – and what a difference!

Looking to the left you see many stars – in fact, a thin river of stars. Looking this direction, you’re looking through about 20,000 light years of star-filled space. We are looking along the plane, generally towards the outer rim, when we look at the W of Cassiopeia. Look along the plane to the right, and you see even more stars in a much wider river. Now you’re looking through about 30,000 light years of star-filled space and then right at the star-rich, galaxy core. And this, in a general way, is what we are doing when we look toward the Teapot of Sagittarius. That’s why the Milky Way is so much brighter and denser in that direction.

Not too difficult to understand – but this is only a rough sketch. As recently as 2008 scientists came up with a much different perspective of our galaxy than we had had up until then. Prior to the latest study, we thought the galaxy was a spiral with a bulge in the center and four main arms. Now they see it as a barred spiral – that is, the bulge in the center looks more like a bar that spills into two – not four – main spiral arms. There are other smaller arms in the spiral, and it all gets quite complex.

The problem, of course, is there is no way we can get outside our galaxy and look in. The distances are incredibly vast. Even if we could send a space probe at the speed of light, it would be thousands of years before it got outside our galaxy, took some pictures of us, and sent those pictures back. So we have to try to decide what the galaxy really looks like from the outside by studying it from the inside. Imagine, for a moment, being inside your body and trying to figure out what you look  like by what you can see from the inside, and you get an idea of the problem. Fortunately we can see other galaxies, and in later months we’ll be looking at one that looks a lot like what we think ours would look like if we could only get outside it and look back.

Meanwhile, relax – look up – and dream of all  the wonders that are out there and sending their messages back to you in the form of millions of tireless photons that have traveled thousands of years to reach your eyes and ping your brain on this dreamy August evening.  Harvest some of those photons by surfing the Milky Way with your binoculars. You will notice that in some areas it is quite dense and you may even discover some tiny, tight clusters of new stars – or a globular cluster of old stars, or even a little hazy patch where new stars are being born.  You need a telescope to see these well, but you can just discern some of them with binoculars, and with telescope or binoculars, what you really need to see with is your mind’s eye. Knowing what you are looking at is what brings this faint cloud alive and turns it into the awesome collection of billions of stars – and more billions of planets –  that it is.

Look North in March 2012 – Oops, there’s a big hole in the sky!

Well, not really – but unless you live in an area with very dark skies, free of light pollution, you’re going to have a hard time seeing the faint stars above Polaris, the North Star, at this time of year. Here’s what our March north sky star chart looks like.

Our northern sky is quite dark above Polaris, but the Big Dipper is prominent in the northeast and serves as our primary guide to finding the North Star. Click image for larger view. (Prepared from a screen shot of Starry Nights software.)

Click here to download a printer-friendly version of this chart.

Notice the emptiness? The area labeled “Dark Hole?” Mind you, this is not a black hole – just an area of our sky that looks quite empty – unless your viewing location is free of light pollution and your eyes are thoroughly dark adapted. If you can see all seven stars of the Little Dipper, then you should see several stars in this area. But even then I doubt if you will be able to trace out the constellation which goes there. It’s known as Camelopardalis. My copy of Urania’s Mirror, published in 1832, says Camelopardalis consists:

. . . of 58 stars, but none larger than the fourth magnitude. . . .The Camelopard is an Abysinian animal, taller than the elephant, but not so thick. He is so named because he has a head and neck like a camel, and is spotted like a leopard; but his spots are white upon a reddish brown ground. The Italians call him giraffa. To Hevelius, who formed the constellation, he owes his celestial honors.

Ah, giraffe! Thank you, Italians. Here’s how he is pictured in full color on one of the constellation cards that came with Urania’s Mirror (The scan is © Ian Ridpath.)

Camelopardalis as depicted on the card from Urania’s Mirror, 1832. Notice the Pointer Stars of the Big Dipper are near the upper left and Polaris is just to the right of the giraffe’s head, so at this time of year the giraffe would appear upside down in our northern skies.

If you put him in the sky at this time of year his head would be down near Polaris. . . . Hmmm… the illustrator seems to have forgotten the spots mentioned in the text, and the animal’s neck got a bit longer than a camel’s. Ah well – while the 1830s had some advantages in terms of simplicity, I don’t think I would like to be trying to learn the night sky with Urania’s Mirror as my only guide.

Oh – but speaking of long necks, one of the things that has always fascinated me is some of the early attempts at astronomical telescopes and particularly the one in the following woodcut. This was an instrument built by Johann Hevelius in the mid-17th century at his observatory in Poland. The tube was about 150 feet long – befitting, in a strange way, for the man who put a giraffe in the northern sky!

Click image for larger view.
There was a logic to this giraffe-like telescope.
At the time a telescope’s lens could not bring the different colors of light to a single focus, so bright objects were always fringed with color and nothing was in really sharp focus. This negative effect, however, could be lessened by making the telescope’s focal length longer – so to get a really good telescope you had to go to these ridiculous extremes – which, of course, made it a nearly impossible telescope to use in any practical way.
Impressive to look at – difficult to aim and look through.
Fortunately the achromatic lens – combining two different types of glass – was invented and this reduced the problem considerably even in a relatively short telescope. We still use such achromatic lenses today ins mall refractor, though if you want to get a really sharp, color-free image you pay considerably more money for an apochromatic lens. Or, you listen to Newton who figured way back int he 1600s that the way around this was to design a telescope that used a mirror to collect the light rather than a lens. Trouble was, it took a long time to learn how to make mirrors that didn’t tarnish quickly when exposed to the night air. Nothings easy!
Now – about or “hole” in the northern sky. Get to a place where light pollution is at a minimum and it will fill with stars – relatively faint, but they are there. Just scan around with binoculars and you’ll find some even through the typical light pollution most people today are forced to endure. 

Look east! In August 2011 – kick back, lie back, look up and enjoy our home galaxy!

This is the month to meet your neighbors – a few billion of them at least!

In August we break our pattern of focusing on bright stars and instead focus on that ancient stream of stars known as the Milky Way – our own galaxy. This means observing a bit later than normal, and if you live within urban or suburban light pollution, going to where you have really dark skies. This does not mean you have to move to – or visit – Arizona. I live in one of the worst light pollution regions of the US, and I can see the Milky Way from my back yard – and see it even better if I take a 12-minute drive to a nearby wildlife sanctuary. But I do have significantly darker skies than people just a mile or two from me. You need a clear moonless night and your eyes need to be well dark adapted. Then you want to look up for a wide, faint “cloud” with a  roughly north-to-south orientation.

I've reduced the brightness and contrast on this image in an attempt to approximate what can be seen from an area with light to moderate light pollution. Still, a photograph always shows more - but it just can't capture the magic of being there. In this case the photographer also caught a Perseid meteor. As you can see, the heart of the Milky Way is nicely framed by the bright Summer Triangle stars of Vega, Deneb, and Altair. Click image for larger version.

Seeing the Milky Way is worth the special effort. It is one of the most beautiful and awe-inspiring astronomical sights, and your naked eye is the best way to take it all in, though binoculars will provide a special treat as well.  In what follows, we’ll focus on where you should be to observe the Milky Way, when you should look. and finally,  where in the sky you should look.

1. Where you should be

Sadly, most people today are routinely denied this sight because of light pollution, but don’t despair! While the darker your skies are, the better, like me you may find that pretty dark skies are just a short drive away. There is an international guide to light pollution and here’s what it shows for light pollution in and around “Driftway Observatory,” my backyard.

On this map of light pollution for southeastern New England, Driftway Observatory is right in the center on the border of an orange/yellow area. Obviously black is the best. Blue is darned good. Green and yellow are desirable. Orange means getting poor; red and white are quite terrible. You should look for at least a yellow area - but to the south of a heavily light-polluted city if possible.

You can get a map  for any region of the world. The simplest path is to go here. Scroll down, to the thumbnail maps and choose a region of the world that suits you and download the map for that region. Another path is limited to observers in the United States, Canada, and Mexico. For them there are “Clear Sky Charts” – astronomical viewing weather forecasts – for hundreds of locations. You can find a location near you by starting here.  Underneath your regional Clear Sky Chart you will see a short list of “Nifty links.” The last one takes you to a light pollution map for that region. It may be helpful to know your latitude and longitude first, so If you don’t know what it is, you can find it here. All of this is useful information for any sky observer to have, so if you track down a Clear Sky Clock for your region,f or example, bookmark it.

Here’s how to make sense of the light pollution maps in terms of seeing the Milky Way.

Red – “Milky Way at best very faint at zenith.”

Orange – “Milky Way washed out at zenith and invisible at horizon.”

Yellow – “Some dark lanes in Milky Way but no bulge into Ophiuchus. Washed out Milky Way visible near horizon.”

Green – “Milky Way shows much dark lane structure with beginnings of faint bulge into Ophiuchus.”

If you can get into the blue, grey, or black areas – enjoy! I envy you ;-)

One critical point though: Pay attention to where there are cities. They will create light domes that will wash out at least areas fairly low in the sky. In my situation I have two small cities, Fall River to the northwest and New Bedford to the northeast. Both have populations of around 100,000 and both create light domes in those regions of the sky. Fortunately, the northern sky isn’t important for seeing the Milky Way, especially in August. But if you have a large city – or shopping mall, or anything that might create a light dome – it is better to look for an area south of it. In August in mid-northern latitudes the  Milky  Way is best from right overhead on down to the southern horizon. That’s why my best view is from a wildlife sanctuary just a few miles away and right on the north shore of  Buzzards Bay and the ocean. It means when I’m looking at the southern Milky Way – towards the very center of our galaxy – I’m seeing it over a huge expanse of water where light pollution is the least.

2. When to look

Begin looking early on a moonless, August evening and ideally, when the skies are crystal clear – frequently this comes right after a cold front passes. Although the Milky Way can be seen many months of the year, one of the best times to see it is in August, about two hours after sunset. In 2010 your best views will come between August 1st and 15th – after that the Moon will offer more and more interference each night for the next two weeks.  However, by the 31st, you should get in a solid hour of Milky Way treat before the waning, gibbous Moon rises. If you miss it in the first two weeks of August, try again the first two weeks of September - this guide will still be useful, though everything will have moved higher and to the west a bit.

I say two hours after  sunset because it takes that long in mid-northern latitudes for it to get fully dark at this time of year, and you need full darkness. (You can find out the local time Astronomical Twilight ends – when it is fully dark – by going to this Web site. From the drop-down menu you’ll find there, choose “astronomical twilight.”) However, you can certainly start looking earlier. This is something where beach chairs or lounges are nice, and maybe even a blanket.  You can start about an hour after sunset when the brightest stars are visible. This will help you get your bearings and you can dark adapt as the skies get darker.

Finally, you need to protect your eyes from white lights. It takes 10-15 minutes for your eyes to become about 50 percent dark adapted. At that point your color vision is as good as it will get, but your sensitivity to dim light will continue to increase. In another 15 minutes or so you will reach about 90 percent dark adaption. The remaining 10 percent can take as long as four hours.  So I consider that after half an hour my eyes are about as good as I can expect them to be.  During all this time and beyond you should avoid looking at white light. You can use a red light to check a chart if you like, but keep it dim and use it sparingly. If you’re in a location where automobiles drive by, don’t look at them – close your eyes and turn away.

Where to look

When you set up your blanket or lounge chair, do your best to align it on a north-south axis with your head to the north and feet to the south. You may want to favor the east just a bit.

What you want to find as you start out is the familiar guidepost stars of the Summer TriangleVega, Deneb, and Altair. These were new guidepost stars in May, June, and July. If you are just starting this journey in August,they are still easy to pick out from our chart.  As the sky in the east starts to darken they will be the first stars visible, 30-45 minutes after sunset.

Click image for a larger view. (Derived from a Starry Nights Pro screen shot.)

You can download a printer friendly version of this chart here.

The brightest – and highest – of the three will be Vega, which will be approaching a point overhead. There are roughly two fists (24 degrees) between Vega and Deneb and nearly four fists (39 degrees) between  Deneb and Altair, so the Triangle is huge.

These three Summer Triangle stars roughly bracket the Milky Way – that is Vega is near the western border, Altair the eastern border, and Deneb is about at midstream.  But you need to wait, of course, for it to get darker before you can see the Milky Way.   The boundaries of the Milky Way, as with any stream, are not sharp and regular. It tends to meander a bit with little pools of light and some deep, dark areas as well.

As the skies darken and your eyes continue to dark adapt, you should try to find three distinctive asterisms that will anchor both ends of the Milky Way, plus the middle.  If you have found Deneb, then you have the first star in the Northern Cross. In fact, you may want to see this as a stick figure of the constellation Cygnus the Swan.  In that case, Deneb marks its tail; the bar of the cross, its wings, and its long neck stretch out to the south as if it were flying down the Milky Way. To the north you should locate the “W” of Cassiopeia described in detail in our “Look North” post this month. And to the south, find the “Teapot,” which we described in more detail last month. Here’s a chart showing the whole sweep of that section of sky.

Click image for larger view. (derived from Starry Nights Pro screens hot.)

You can download a printer friendly version of this chart here.

Now, if it is about two hours after sunset and if you are in a location away from light pollution and, of course, are enjoying one of those crystal clear nights with dark-adapted eyes, then you also should be seeing the Milky Way. It only takes time and patience for you to trace it out – to see areas that are brighter than others – as well as some dark patches that don’t mean the absence of stars, but the presence of obscuring dust. But don’t think of the dust as getting in the way – think of it as star stuff – for what you are seeing in many sections of the Milky Way are the parts of our galaxy where new stars are being born. Relax and explore with your binoculars – start to absorb the majesty of millions – no billions – of stars!  If conditions are right – and you have a dark sky – it will look to the naked eye like faint clouds that get brighter as your eye traces them out from north to south.

And what is it you are seeing and why does it appear this way to you? That’s the important question. And this is where you have to do some mental gymnastics.

Think of our galaxy as a large pizza pie with extra cheese and goodies heaped in the center.  Now put yourself away from that center – perhaps one-half of the way towards one edge and buried down at the level of the crust. That’s a pretty good simulation of our galaxy and our place in it. You really need to get outside it – we can only do this in our imaginations – and look at it from that perspective. If we could get outside it, here’s approximately what we would see:

Two view of our Galacy, the Milky Way. The one on the left is from  aposition above it, the one on the right shopws you the galaxy edge-on.  This is a screen shot from the wonderful, free software, "Where is  M13."

The image on the left is how we think our galaxy would look if we could get above it and look down on it – like a big pinwheel of stars.  And what if you could see it edge on? Well, that’s the picture on the right. (This is a screen shot  from a wonderful – and free – software program called “Where is M13” that helps you understand where various objects really are in relation to us and the rest of the galaxy.)

OK – focus on the edge-on image – and note how really thin most of the galaxy is. It is about 100,000 light years across, but on average just 1,000 light years thick.

plane_view_MW

Now imagine yourself on a small dot (the Earth) rotating around that small dot in our image – the Sun. Do you see a lot of stars when you look “up” – that is, look in the direction of the words  “The Sun.”

No – in fact, if you look down, you don’t see many stars either – or for that matter, if you look in just about any direction there are relatively few stars visible to you. Why? Because the disc is just 1,000 light years thick, and most of the time you’re looking right through it the short way.  But  look along the plane of the galaxy – say  directly to the right or left – and what a difference!

Looking to the left you see many stars – in fact, a thin river of stars. Looking this direction, you’re looking through about 20,000 light years of star-filled space. We are looking along the plane, generally towards the outer rim, when we look at the W of Cassiopeia. Look along the plane to the right, and you see even more stars in a much wider river. Now you’re looking through about 30,000 light years of star-filled space and then right at the star-rich, galaxy core. And this, in a general way, is what we are doing when we look toward the Teapot of Sagittarius. That’s why the Milky Way is so much brighter and denser in that direction.

Not too difficult to understand – but this is only a rough sketch. As recently as 2008 scientists came up with a much different perspective of our galaxy than we had had up until then. Prior to the latest study, we thought the galaxy was a spiral with a bulge in the center and four main arms. Now they see it as a barred spiral – that is, the bulge in the center looks more like a bar that spills into two – not four – main spiral arms. There are other smaller arms in the spiral, and it all gets quite complex.

The problem, of course, is there is no way we can get outside our galaxy and look in. The distances are incredibly vast. Even if we could send a space probe at the speed of light, it would be thousands of years before it got outside our galaxy, took some pictures of us, and sent those pictures back. So we have to try to decide what the galaxy really looks like from the outside by studying it from the inside. Imagine, for a moment, being inside your body and trying to figure out what you look  like by what you can see from the inside, and you get an idea of the problem. Fortunately we can see other galaxies, and in later months we’ll be looking at one that looks a lot like what we think ours would look like if we could only get outside it and look back.

Meanwhile, relax – look up – and dream of all  the wonders that are out there and sending their messages back to you in the form of millions of tireless photons that have traveled thousands of years to reach your eyes and ping your brain on this dreamy August evening.  Harvest some of those photons by surfing the Milky Way with your binoculars. You will notice that in some areas it is quite dense and you may even discover some tiny, tight clusters of new stars – or a globular cluster of old stars, or even a little hazy patch where new stars are being born.  You need a telescope to see these well, but you can just discern some of them with binoculars, and with telescope or binoculars, what you really need to see with is your mind’s eye. Knowing what you are looking at is what brings this faint cloud alive and turns it into the awesome collection of billions of stars – and more billions of planets –  that it is.

Look north in July 2011 and take the measure of your skies and eyes!

Light pollution is a big issue these days. How does it impact you? Summer is a good time to check by looking north about two hours after sunset and seeing what stars you can see in and near the Little Dipper. Why summer? Because this is when the Little Dipper should be highest in your sky – standing upwards from Polaris, the North Star. Here’s what you should see on a typical July evening when you look north from mid-northern latitudes.

In summer the faint stars of the Little Dipper are high above the North Star. Click image for larger view. (Derived from Starry Nights Pro screen shot.)

For a printer-friendly version of this chart, click here.

The Big Dipper is diving downward in the northwest but is still very high, and its handy “pointers” should get you quickly to the North Star, Polaris. Roughly opposite the Big Dipper you should see the “W” of Cassiopeia starting to make its way upward in the northeast. And unless you suffer from really terrible light pollution, you should see the two “Guardians of the Pole” – the second and third magnitude stars that mark the end of the Little Dipper. The brighter of these two is just a tad dimmer than Polaris, but since it’s higher in the sky right now and thus shining through less air to get to you, it will probably look just the same as the North Star in brightness.

To do this test you first have to wait until it is genuinely dark, and in summer that’s a bit longer than in winter. Twilight actually is divided into three steps. We have civil twilight which goes from sunset until when the Sun is six degrees below the horizon. Nautical twilight is the next period, which continues until the Sun is 12 degrees below the horizon. Then you have Astronomical Twilight until the Sun is 18 degrees below the horizon. At that point it is as dark as it will get and will remain that dark until we run the sequence in reverse as the eastern horizon nears the Sun. As a general rule of thumb, you can consider each twilight period to last half an hour – but the exact length depends on where you are on Earth and the time of year. If you want to get precise, go to the U.S. Naval Observatory site, fill in the form you’ll find there, and you can get a table that will give you the start and end of these twilight times – or for that matter when the Moon rises, or the Sun sets. It’s very handy. (Note: the preceding link takes you to a page for US cities and towns – but there’s a second page here where you can put in the latitude and longitude for any location in the world, including in the US. )

The second thing you need to do is make sure your eyes are dark adapted. They are casually dark adapted after you have been out for 15 minutes and have not looked at any white lights. But it can take from half an hour to an hour of protecting your eyes from any white light for them to become fully dark adapted. That doesn’t mean you have to sit around in the dark doing nothing waiting for this to happen. In the last hour or so before full darkness there are plenty of things to see – just avoid bright lights. That also means moonlight. You’re going to want to do this when the Moon is not in the sky, for it will make it difficult to see faint objects anywhere near it. In July of 2011 the first five days or the last 10 days should work pretty well.  In the middle of the month, the Moon will dominate the evening sky.   (A good Moon-phase calendar can be found here, though for this purpose I find the table from the Naval Observatory for local Moon rise is also handy!)

So here’s the test:

How many stars can you see in the Little Dipper?

The Little Dipper consists of seven stars. Three are easy – Polaris and the two “Guardians” marked “21” and “30” on the chart below. If you can see only one of the “Guardians,” then your skies are limited to magnitude 2 stars and brighter – very poor. If you see both, but no other stars in the Little Dipper, then your limit is magnitude 3.

On our chart below, the magnitude of each star is listed as a whole number so as not to put decimal points on the chart that might then be confused for faint stars! So when you see a star listed as “21” that means “magnitude 2.1.”

For a printer-friendly version of this chart, click here.

Even in good, dark skies the other four stars in the Little Dipper may not be that easy to see – and the faintest ones may require averted vision – that is, don’t look exactly where the star should be. Instead, look a little to one side or the other, and the star may pop into view. That’s because the center of your eyes are not as sensitive to faint light as the outer regions of your eyes.

Here’s another little trick that may help you locate these faint stars – use binoculars. With typical, hand-held binoculars you may be able to fit all four stars of the Little Dipper’s “cup” into the same field of view. If not, get the “Guardians” in your field of view, then move just a little to where the other two stars of the “cup” should be. This does not count, of course, for the light pollution test. For that test we’re trying to determine the faintest star you can see with the naked eye. But looking first at the stars with binoculars helps assure you that they really are there! You also can trace out the handle this way, though you will have to move your binoculars to do so.

If you can locate all the stars in the Little Dipper with your naked eye, you have very dark skies – congratulations. To see how good they are – and continue to test your eyesight and dark adaption – look for the stars marked “55” and “60” on our chart.

The star marked “60” is traditionally thought of as the faintest you can see with your naked eye. That’s a magnitude 6 star. In really pristine skies, such as those over Mauna Kea in Hawaii, experienced observers with excellent eyes can detect stars down to magnitude 8 with the naked eye. Personally, I’m happy when I can see all the stars in the Little Dipper and especially happy if I can get that “55” star – I’ve never seen the “60” one with my naked eye. But relative to the heavily light-polluted eastern seaboard of the US, I have dark skies.

This is not simply a good guide to light pollution in your area. It also is a handy guide to tell you just how good the skies are on any given night – and to show you how well you have dark adapted at any given moment. So whenever I go out to observe I frequently glance at the Little Dipper to test both my developing night vision and the clarity of the skies. (It never fails to amaze me how much and how quickly my night vision changes. )

To the casual observer all clear nights are equal. But the experienced star gazer knows they are not, and the stars in and about the Little Dipper are a good guide, especially in the summer months when they are so high in the sky.

Look east! In August 2010 – kick back, lie back, look up and enjoy our home galaxy!

This is the month to meet your neighbors – a few billion of them at least!

In August we break our pattern of focusing on bright stars and instead focus on that ancient stream of stars known as the Milky Way – our own galaxy. This means observing a bit later than normal, and if you live within urban or suburban light pollution, going to where you have really dark skies. This does not mean you have to move to – or visit – Arizona. I live in one of the worst light pollution regions of the US, and I can see the Milky Way from my back yard – and see it even better if I take a 12-minute drive to a nearby wildlife sanctuary. But I do have significantly darker skies than people just a mile or two from me. You need a clear moonless night and your eyes need to be well dark adapted. Then you want to look up for a wide, faint “cloud” with a  roughly north-to-south orientation.

I've reduced the brightness and contrast on this image in an attempt to approximate what can be seen from an area with light to moderate light pollution. Still, a photograph always shows more - but it just can't capture the magic of being there. In this case the photographer also caught a Perseid meteor. As you can see, the heart of the Milky Way is nicely framed by the bright Summer Triangle stars of Vega, Deneb, and Altair. Click image for larger version.

Seeing the Milky Way is worth the special effort. It is one of the most beautiful and awe-inspiring astronomical sights, and your naked eye is the best way to take it all in, though binoculars will provide a special treat as well.  In what follows, we’ll focus on where you should be to observe the Milky Way, when you should look. and finally,  where in the sky you should look.

1. Where you should be

Sadly, most people today are routinely denied this sight because of light pollution, but don’t despair! While the darker your skies are, the better, like me you may find that pretty dark skies are just a short drive away. There is an international guide to light pollution and here’s what it shows for light pollution in and around “Driftway Observatory,” my backyard.

On this map of light pollution for southeastern New England, Driftway Observatory is right in the center on the border of an orange/yellow area. Obviously black is the best. Blue is darned good. Green and yellow are desirable. Orange means getting poor; red and white are quite terrible. You should look for at least a yellow area - but to the south of a heavily light-polluted city if possible.

You can get a map  for any region of the world. The simplest path is to go here. Scroll down, to the thumbnail maps and choose a region of the world that suits you and download the map for that region. Another path is limited to observers in the United States, Canada, and Mexico. For them there are “Clear Sky Charts” – astronomical viewing weather forecasts – for hundreds of locations. You can find a location near you by starting here.  Underneath your regional Clear Sky Chart you will see a short list of “Nifty links.” The last one takes you to a light pollution map for that region. It may be helpful to know your latitude and longitude first, so If you don’t know what it is, you can find it here. All of this is useful information for any sky observer to have, so if you track down a Clear Sky Clock for your region,f or example, bookmark it.

Here’s how to make sense of the light pollution maps in terms of seeing the Milky Way.

Red – “Milky Way at best very faint at zenith.”

Orange – “Milky Way washed out at zenith and invisible at horizon.”

Yellow – “Some dark lanes in Milky Way but no bulge into Ophiuchus. Washed out Milky Way visible near horizon.”

Green – “Milky Way shows much dark lane structure with beginnings of faint bulge into Ophiuchus.”

If you can get into the blue, grey, or black areas – enjoy! I envy you ;-)

One critical point though: Pay attention to where there are cities. They will create light domes that will wash out at least areas fairly low in the sky. In my situation I have two small cities, Fall River to the northwest and New Bedford to the northeast. Both have populations of around 100,000 and both create light domes in those regions of the sky. Fortunately, the northern sky isn’t important for seeing the Milky Way, especially in August. But if you have a large city – or shopping mall, or anything that might create a light dome – it is better to look for an area south of it. In August in mid-northern latitudes the  Milky  Way is best from right overhead on down to the southern horizon. That’s why my best view is from a wildlife sanctuary just a few miles away and right on the north shore of  Buzzards Bay and the ocean. It means when I’m looking at the southern Milky Way – towards the very center of our galaxy – I’m seeing it over a huge expanse of water where light pollution is the least.

2. When to look

Begin looking early on a moonless, August evening and ideally, when the skies are crystal clear – frequently this comes right after a cold front passes. Although the Milky Way can be seen many months of the year, one of the best times to see it is in August, about two hours after sunset. In 2010 your best views will come between August 1st and 15th – after that the Moon will offer more and more interference each night for the next two weeks.  However, by the 31st, you should get in a solid hour of Milky Way treat before the waning, gibbous Moon rises. If you miss it in the first two weeks of August, try again the first two weeks of September - this guide will still be useful, though everything will have moved higher and to the west a bit.

I say two hours after  sunset because it takes that long in mid-northern latitudes for it to get fully dark at this time of year, and you need full darkness. (You can find out the local time Astronomical Twilight ends – when it is fully dark – by going to this Web site. From the drop-down menu you’ll find there, choose “astronomical twilight.”) However, you can certainly start looking earlier. This is something where beach chairs or lounges are nice, and maybe even a blanket.  You can start about an hour after sunset when the brightest stars are visible. This will help you get your bearings and you can dark adapt as the skies get darker.

Finally, you need to protect your eyes from white lights. It takes 10-15 minutes for your eyes to become about 50 percent dark adapted. At that point your color vision is as good as it will get, but your sensitivity to dim light will continue to increase. In another 15 minutes or so you will reach about 90 percent dark adaption. The remaining 10 percent can take as long as four hours.  So I consider that after half an hour my eyes are about as good as I can expect them to be.  During all this time and beyond you should avoid looking at white light. You can use a red light to check a chart if you like, but keep it dim and use it sparingly. If you’re in a location where automobiles drive by, don’t look at them – close your eyes and turn away.

Where to look

When you set up your blanket or lounge chair, do your best to align it on a north-south axis with your head to the north and feet to the south. You may want to favor the east just a bit.

What you want to find as you start out is the familiar guidepost stars of the Summer TriangleVega, Deneb, and Altair. These were new guidepost stars in May, June, and July. If you are just starting this journey in August,they are still easy to pick out from our chart.  As the sky in the east starts to darken they will be the first stars visible, 30-45 minutes after sunset.

Click image for a larger view. (Derived from a Starry Nights Pro screen shot.)

You can download a printer friendly version of this chart here.

The brightest – and highest – of the three will be Vega, which will be approaching a point overhead. There are roughly two fists (24 degrees) between Vega and Deneb and nearly four fists (39 degrees) between  Deneb and Altair, so the Triangle is huge.

These three Summer Triangle stars roughly bracket the Milky Way – that is Vega is near the western border, Altair the eastern border, and Deneb is about at midstream.  But you need to wait, of course, for it to get darker before you can see the Milky Way.   The boundaries of the Milky Way, as with any stream, are not sharp and regular. It tends to meander a bit with little pools of light and some deep, dark areas as well.

As the skies darken and your eyes continue to dark adapt, you should try to find three distinctive asterisms that will anchor both ends of the Milky Way, plus the middle.  If you have found Deneb, then you have the first star in the Northern Cross. In fact, you may want to see this as a stick figure of the constellation Cygnus the Swan.  In that case, Deneb marks its tail; the bar of the cross, its wings, and its long neck stretch out to the south as if it were flying down the Milky Way. To the north you should locate the “W” of Cassiopeia described in detail in our “Look North” post this month. And to the south, find the “Teapot,” which we described in more detail last month. Here’s a chart showing the whole sweep of that section of sky.

Click image for larger view. (derived from Starry Nights Pro screens hot.)

You can download a printer friendly version of this chart here.

Now, if it is about two hours after sunset and if you are in a location away from light pollution and, of course, are enjoying one of those crystal clear nights with dark-adapted eyes, then you also should be seeing the Milky Way. It only takes time and patience for you to trace it out – to see areas that are brighter than others – as well as some dark patches that don’t mean the absence of stars, but the presence of obscuring dust. But don’t think of the dust as getting in the way – think of it as star stuff – for what you are seeing in many sections of the Milky Way are the parts of our galaxy where new stars are being born. Relax and explore with your binoculars – start to absorb the majesty of millions – no billions – of stars!  If conditions are right – and you have a dark sky – it will look to the naked eye like faint clouds that get brighter as your eye traces them out from north to south.

And what is it you are seeing and why does it appear this way to you? That’s the important question. And this is where you have to do some mental gymnastics.

Think of our galaxy as a large pizza pie with extra cheese and goodies heaped in the center.  Now put yourself away from that center – perhaps one-half of the way towards one edge and buried down at the level of the crust. That’s a pretty good simulation of our galaxy and our place in it. You really need to get outside it – we can only do this in our imaginations – and look at it from that perspective. If we could get outside it, here’s approximately what we would see:

Two view of our Galacy, the Milky Way. The one on the left is from  aposition above it, the one on the right shopws you the galaxy edge-on.  This is a screen shot from the wonderful, free software, "Where is  M13."

The image on the left is how we think our galaxy would look if we could get above it and look down on it – like a big pinwheel of stars.  And what if you could see it edge on? Well, that’s the picture on the right. (This is a screen shot  from a wonderful – and free – software program called “Where is M13” that helps you understand where various objects really are in relation to us and the rest of the galaxy.)

OK – focus on the edge-on image – and note how really thin most of the galaxy is. It is about 100,000 light years across, but on average just 1,000 light years thick.

plane_view_MW

Now imagine yourself on a small dot (the Earth) rotating around that small dot in our image – the Sun. Do you see a lot of stars when you look “up” – that is, look in the direction of the words  “The Sun.”

No – in fact, if you look down, you don’t see many stars either – or for that matter, if you look in just about any direction there are relatively few stars visible to you. Why? Because the disc is just 1,000 light years thick, and most of the time you’re looking right through it the short way.  But  look along the plane of the galaxy – say  directly to the right or left – and what a difference!

Looking to the left you see many stars – in fact, a thin river of stars. Looking this direction, you’re looking through about 20,000 light years of star-filled space. We are looking along the plane, generally towards the outer rim, when we look at the W of Cassiopeia. Look along the plane to the right, and you see even more stars in a much wider river. Now you’re looking through about 30,000 light years of star-filled space and then right at the star-rich, galaxy core. And this, in a general way, is what we are doing when we look toward the Teapot of Sagittarius. That’s why the Milky Way is so much brighter and denser in that direction.

Not too difficult to understand – but this is only a rough sketch. As recently as 2008 scientists came up with a much different perspective of our galaxy than we had had up until then. Prior to the latest study, we thought the galaxy was a spiral with a bulge in the center and four main arms. Now they see it as a barred spiral – that is, the bulge in the center looks more like a bar that spills into two – not four – main spiral arms. There are other smaller arms in the spiral, and it all gets quite complex.

The problem, of course, is there is no way we can get outside our galaxy and look in. The distances are incredibly vast. Even if we could send a space probe at the speed of light, it would be thousands of years before it got outside our galaxy, took some pictures of us, and sent those pictures back. So we have to try to decide what the galaxy really looks like from the outside by studying it from the inside. Imagine, for a moment, being inside your body and trying to figure out what you look  like by what you can see from the inside, and you get an idea of the problem. Fortunately we can see other galaxies, and in later months we’ll be looking at one that looks a lot like what we think ours would look like if we could only get outside it and look back.

Meanwhile, relax – look up – and dream of all  the wonders that are out there and sending their messages back to you in the form of millions of tireless photons that have traveled thousands of years to reach your eyes and ping your brain on this dreamy August evening.  Harvest some of those photons by surfing the Milky Way with your binoculars. You will notice that in some areas it is quite dense and you may even discover some tiny, tight clusters of new stars – or a globular cluster of old stars, or even a little hazy patch where new stars are being born.  You need a telescope to see these well, but you can just discern some of them with binoculars, and with telescope or binoculars, what you really need to see with is your mind’s eye. Knowing what you are looking at is what brings this faint cloud alive and turns it into the awesome collection of billions of stars – and more billions of planets –  that it is.

Follow

Get every new post delivered to your Inbox.

Join 42 other followers

%d bloggers like this: