• Choose a month

  • Rapt in Awe

    My Journey through the Astronomical Year

    Think of this as a "companion text" to this, the main web site. Not required reading, butI hope you'll find it interesting and helpful.

August 2009 – and all the planets have shown up for the party!

That’s the good news – the bad news is the “party” is an all-nighter. That is, if you really want too see all the planets – and maybe little, demoted Pluto as well – you need to start at dusk and stay at your task well into the wee hours of morning.  For Pluto, you will also need a powerful telescope and better charts than I’ll provide here, but the others can all be seen with the naked eye or binoculars.

But what I like about this situation is it makes it easy – even for those of us using nothing but the naked eye, which is really the focus of this web site  – to  see most planets on a single night and to get a sense of how their position in the sky relates to our position in the solar system and where we all are on our annual journey around  the Sun.

Astronomy is always about two realities – the reality we see and the reality we know. The trick is learning to merge these two so that when you see something in the night sky, you are familiar enough with what is really going on that what you see makes perfect sense, given what you know.

orrery_080109

The best example of this is provided by the two major planets this month – Jupiter and Saturn. The chart above shows the reality we know. It shows where all the planets are at the start of August if you could get  above the plane of the solar system and look down at them. Study it. This is from the online orrery at “Solar System Live.” (http://www.fourmilab.ch/solar/)  I drew the bar across it to represents our horizon – the line between night and day –  and the arrows show the direction the bar is moving as night progresses. To the left this shows how, from our perspective, things are setting in the west – and to the right, how they are rising in the east.

Notice that in this view Saturn is near our western horizon and Jupiter near the eastern horizon. That’s the situation right around sunset. But the sky is too bright then for us to see even bright planets. We have to wait about 45 minutes. At that point, Saturn will look like a first magnitude star about 12 degrees above the horizon almost due west – azimuth 266 degrees – in the early part of the month.

Switch to the east and Jupiter is not so shy. It is at magnitude -2.8 (nothing gets brighter than this except Venus, the Moon, and the Sun), but it is still hugging the horizon. Chances are it is too close for you to see. Give it another 45 minutes – 90 minutes after sunset – and it will be about nine degrees above the horizon a bit south of east. For my latitude – 42 degrees north – it will be at azimuth 118. But the exact position isn’t too critical, since it is so bright and there’s nothing in that general vicinity at this time that will compete with it.

This will change slowly as the month goes on – that is, Saturn gets closer to the horizon at sunset each night and Jupiter rises earlier, until on August 14th Jupiter is rising in the east as the Sun is setting in the west.

Did you notice on the solar system view that Mercury is right over there near the western horizon as well? It is, but this happens to be a fairly poor showing for what is always an elusive planet to catch. Sky and Telescope gives this instruction: “Observers near 40° north can look for it 5° above the western horizon a half hour after sunset from August 6 to August 18th.” Yep – and it will be near magnitude “0” – but you will need a very clear western horizon to see it, and I suggest you search for it with binoculars.  Earlier in the month is better than later for both Saturn and Mercury. As the month goes on Saturn not only gets  closer to the horizon, but also closer to Mercury – and this will make  both very difficult to see. By August 17 the two planets are just 3 degrees apart, but then Mercury is only 2 degrees above the horizon and Saturn about 6.

Much easier to find are our two morning planets, Venus and Mars. Both can be spotted, without strain, with the naked eye. But Venus is by far the easiest. It is a brilliant  magnitude -4 – brighter even than Jupiter, which by this time is well over in the southwest, and should be easy to see low in the east northeast by 3:30 am. By the end of the month you’ll have to wait until about 4:30 am for it to be easily seen – but that’s still two and half hours ahead of sunrise.

Mars is a bit more of a problem, though it rises well ahead of Venus. At 3 am August 1 it is a first magnitude “star” about 7 degrees to the north of Aldebaran, also first magnitude,  and both are roughly 15 degrees above the horizon, a bit north of east. Because Aldebaran is a very red star, it will be interesting to compare it with the “red” planet, but it’s best to wait another hour to do this so both are higher in the sky and not as affected by the atmosphere, which tends to make every bright object colorful.

By the end of the month Mars is higher at 3 am, but Aldebaran is higher still. Mars will form an interesting triangle, though, with Aldebaran and another very red star, Betelgeuse. In fact, if you are up at that hour you get a preview of the early winter sky with the bright constellations of Auriga, Taurus, Gemni, and Orion coming into view, and Mars in the middle of them as our chart shows.

Mars early in th emorning at the end of themonth. Click for larger version. (This chart uses a screen shot from Starry Nights software which I have then annotated.)

Mars early in th emorning at the end of themonth. Click for larger version. (This chart uses a screen shot from Starry Nights software which I have then annotated.)

Returning to the evening sky, this remains a good year to track down Neptune and Uranus with binoculars. Both are relatively easy to find, but offer special challenges.

Notice on the solar system chart how Neptune is roughly in line with Jupiter as we view both from Earth. On August first a careful study of the Jupiter region with binoculars around 10 pm will reveal Neptune at about magnitude 8 and only two degrees to the north (left) – but finding it can be tricky.  Try putting Jupiter in the right-hand edge of your field – or even move your binoculars so Jupiter just drops out of the right hand edge. That way the glare from it won’t interfere with your view.  At that point Neptune should be pretty close to the center of your field of view. There are several stars nearby and both Neptune and Jupiter are changing position as the month goes on. Here’s a chart for August 1.

Neptune and Jupiter at the first of August, 2009. (Clickfor larger view.) (This chart uses a screen shot from Starry Nights software which I have then annotated.)

Neptune and Jupiter at the first of August, 2009. (Clickfor larger view.) (This chart uses a screen shot from Starry Nights software which I have then annotated.)

By the middle of the month, they have drifted a bit farther apart, and there’s a row of sixth magnitude stars in a gentle arc between them. If you compare the first chart and this second one you will see these stars and how the position of the planets change relative to them.

Neptune and Jupiter near the middle of August, 2009. (This chart uses a screen shot from Starry Nights software which I have then annotated.)

Neptune and Jupiter near the middle of August, 2009. (This chart uses a screen shot from Starry Nights software which I have then annotated.)

By the end of the month these same stars are closer to Neptune and the gap between Neptune and Jupiter is almost five degrees. That means they both probably fit in the same binocular field, but just barely.

If you look at the horizon line on our solar system chart – especially the eastern one – and note the direction it is moving, then you can see how our view will change during the night. As Jupiter and Neptune get higher we eventually get to a point where Uranus comes into view, then, well after midnight, Mars and Venus put in an appearance.

Uranus is easier to see than Neptune because it’s significantly brighter – about magnitude 6.  We also get a special break this month, for Uranus will form a wide “double star” with 20 Piscium, a star that is just a tad brighter than the planet. But this makes it easy to identify.  Here’s my way to locate it. First, trace out a few asterism in the sky south of east. (The following chart is for 11 pm EDT, August 1, at 40° North – but should serve as a general guide for almost any location.)

This charts helps you locate thegeneral area inw hich to find Uranus. Click forlarger version. (This chart uses a screen shot from Starry Nights software which I have then annotated.)

This charts helps you locate thegeneral area inw hich to find Uranus. Click forlarger version. (This chart uses a screen shot from Starry Nights software which I have then annotated.)

Next, you want to zero in on the Circlet of Pisces and an unnamed trapezoid below it.

Tracking down Uranus with binoculars. (This chart uses a screen shot from Starry Nights software which I have then annotated.)

Tracking down Uranus with binoculars. (This chart uses a screen shot from Starry Nights software which I have then annotated.)

The Circlet will not fit quite in the typical binocular field of view. The trapezoid should fit and maybe Uranus at the same time – but the way I find Uranus is to find the trapezoid in my binoculars, then move up so that only its top two stars are visible in the bottom of my field of view. Now up and to the right are two almost identical stars – the higher one is Uranus. It is about half a degree above 20 Piscium, a star that is just a tad brighter, though you will be challenged to tell the difference.  (The charts show only those stars you can expect to see with your binoculars – but depending on the binoculars and conditions, you may not see all of these stars.) Uranus is on the brighter side of magnitude 6 and at this point, at least 10 degrees above the horizon. Waiting until later in the night – or later in the month, this will only get easier as Uranus will get higher.  But as the month goes on it will pull away a little from 20 Piscium. By August 30 they are a degree apart and instead of Uranus being directly above 20 Piscium, it will have moved above and to the right – westward.

And Pluto? I wouldn’t try to hunt it down even with my 15-inch telescope.  Although it is relatively high in the south once it gets really dark, it is much too faint to see in anything except large amateur scopes. And to make matters worse, it has lots of competition, for it is above the Teapot in the middle of the Milky Way, and at magnitude 14, just a faint, faint dot among many, many other faint dots. Better to spend your time exploring the Milky Way itself. See: August Guideposts: Asterisms guide you along the Milky Way.

This is the general area within which you can find Pluto this month. But theplanet is faint and buried with the faint stars of the Milky Way.  (This chart uses a screen shot from Starry Nights software.)

This is the general area within which you can find Pluto this month. But theplanet is faint and buried with the faint stars of the Milky Way. (This chart uses a screen shot from Starry Nights software.)

August Guideposts: Asterisms guide you along the Milky Way

Editor’s note: There’s a companion project to this post  – build a scale model of the Milky Way – here.

One of the most beautiful and awe-inspiring astronomical sights is the Milky Way. Sadly, most people today are denied this sight because of light pollution, but don’t despair! With a little knowledge and just about any pair of binoculars, you should be able to easily spot our galaxy – the Milky Way –  and yes, even travel (with your eyes and binoculars)  toward its core.

We’re going to use our guidepost stars and three easily recognizable asterisms to do just that. Of course, if you can get out, away from light pollution, do so.  I live in one of the most light-polluted parts of the world, the northern half of the Eastern Seaboard of the United States, yet I have just enough rural countryside and ocean nearby to allow me to  regularly enjoy the Milky Way from my backyard, and I see it even better if I take a 15-minute drive to a site nearer the ocean. So this guide is for those at dark sites using just the naked eye, as well as for those who live in more light-polluted suburbs.

Here’s when and where and how to look.

When? Early on a moonless, August evening 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 is in August, about two hours after sunset.

Where? I would say anywhere except the city – and if there is a city nearby, try to orient yourself so it is to your north. Do your best to leave your southern sky free of light pollution.  The more free of light pollution, the better – but you don’t have to make a big expedition in order to do this.  While I can see the Milky Way from my backyard, my favorite viewing location is at a bird sanctuary with the ocean to its south about 10 minutes drive away. This spot also has the advantage of an almost clear horizon for 360 degrees!

How? Lie down, look up, nurture your night vision, and put your best binoculars to work.  A blanket, or better yet, a lawn lounge chair will help make this comfortable; otherwise, you’ll find the Milky Way a pain in the neck, and there’s no need for that! “Best binoculars” for this purpose means the ones with the largest diameter lens that you can comfortably hand hold, and that usually means something in the order of 50 mm. But smaller will do the job too. After all, Galileo was the one who showed us the real nature of the Milky Way – the fact that it was actually millions of distant stars and not a faint cloud – and just about any binocular you have will do a better job than the telescope he used. (For more on binoculars for astronomy see this post.)

Most important – guard your night vision! I’m going to suggest you start this exploration early – about 45 minutes after sunset, then stay at it for the next hour or more as the sky darkens above you. If you do this – and if you avoid white light, such as the headlights of cars and the beam of a flashlight – your eyes will naturally dark adapt, and about 45 minutes after you began you should start to pick up the Milky Way, though it may take another 15-30 minutes for you to be able to see it in its full glory.

One more critical “when” note. Choose a time several days after full Moon. When the Moon is waxing – getting larger and brighter each night – it will drown out the Milky Way.  You want to do your early evening Milky Way observing when the moon is waning. This is the couple of weeks after full and really up to the point where the Moon is about two  or three days  old. You need to wait five or six days after full Moon because you don’t want the Moon rising just as full darkness sets in and thus spoiling your view. (In 2009 full Moon is August 5 and good Milky Way observing begins August 11 and continues to about August 23, 2009.)

Where do you look? Up, in a word.

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.

What you want to see as you start out is the familiar guidepost stars of the Summer TriangleVega, Deneb, and Altair. These should be familiar because you learned them in June or July. If not, you can learn them now.  They are easy to pick out because as the sky starts to darken they will be the first stars visible, and they will be high in the east. Here’s a chart of what you will see.

Orient yourself north-south, then locate the Summer Triangle high in the east. Click for larger charts. (All charts use screen shots of Starry Nights software which I have then annotated.)

Orient yourself north-south, then locate the Summer Triangle high in the east. Click for larger chart. (All charts use screen shots of Starry Nights software which I have then annotated.)

The brightest – and highest – of the three will be Vega which will be approaching a point overhead. There’s roughly two fists (24 degrees) between Vega and Deneb and nearly four fists (39 degrees) between  Deneb and Altair, so the Triangle is huge. (Our chart is about 90 degrees wide covering from northeast on the left, to southeast on the right. And that real bright “star” near the horizon? That’s the planet Jupiter – at least in 2009. It won’t be in this position other years in August.)

These three Summer Triangle stars roughly bracket the Milky Way – that is Vega roughly marks the western border, Altair roughly denotes 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.   Right now you’re learning where to look. Do keep in mind that 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.

But it is early yet. At this point the Milky Way is beyond your reach and probably your binoculars as well. If you have located the Summer Triangle, though, it is time to find the first of our three August asterisms. Remember that an asterism, while it may be part of a constellation, is different. It is a small collection of bright stars and unlike a constellation, it actually will look like the object its name implies.

Use Deneb to start your identification of the Northern Cross. (This chart uses a screen shot from Starry Nights software which I have then annotated.)

Use Deneb to start your identification of the Northern Cross. (This chart uses a screen shot from Starry Nights software which I have then annotated.)

The first of these asterisms we’ll use is the Northern Cross, which also serves as a good rough outline of Cygnus the Swan, the constellation which it inhabits.  You find it by starting with Deneb, the middle – and faintest – star in the Summer Triangle. I am assuming it is now more than an hour after sunset and other bright stars are starting to appear. Our Summer Triangle stars are magnitude zero and one – very bright. The Northern Cross stars are magnitude 2 and 3 – dimmer, but about as bright as the stars in the familiar Big Dipper. If you don’t find all these stars immediately, be patient. It may just need to be a little darker. But start with Deneb. It marks the top of the cross, which lies in a general north-south direction. Here’s a chart of the bright stars in this asterism.

Deneb, and the three stars that form the cross bar, should be easy to see.  The fifth star, Albireo, is the dimmest of the group, but note how it is roughly on a line halfway between Vega and Altair, and you should be able to locate it using those two as a guide.  Albireo is magnitude 3 and marks the tip of the cross and even if it is now quite dark, you may have difficulty seeing it in light polluted skies. If so, use your binoculars – and do notice that it does not quite make a straight line with the center star and Deneb.  Also, almost halfway between the center star and Albireo you may notice another, still fainter star that’s a little off this line.

If you want to see this as the swan of the constellation Cygnus, that’s easy enough. Deneb is Arabic for “tail” and marks the tail of the swan. The three bright stars of the cross-bar are the Swan’s wings and the other two stars extending to the south are the Swan’s long neck. Deneb is flying right down the Milky Way – which is what we will do as well, after we locate two more helpful asterisms.

For the first of these next two asterisms, reorient yourself so you are now looking north.

We want to locate  the W of Cassiopeia as it rises in the northeast.  This is a very helpful asterism that also will help you locate the North Star.  Much of the time, of course, we use the Dipper and its “Pointer” stars to find Polaris, the North Star. But as we move into the fall the Dipper gets lower and lower in the northwest. In my backyard it eventually sinks beneath trees. But no worry – as the Dipper goes down the W  of Cassiopeia rises and it is a perfect counterpoise to the Dipper. Like the Pointer stars, it is about 30  degrees –  roughly three fists – from Polaris, so I think of it as marking the other side of a huge circle going around the North Star. The Dipper marks one side of that circle, the W the other. Here’s the appropriate chart. (To see an animation of how these stars move around the North Star, see this post.)

Look north and you'll see the W of Cassiopeia rising in the northeast. The last star of the W - the one closest to the horizon - is the faintest and may no tbe visible at first. Click to enlarge this chart. (This chart uses a screen shot from Starry Nights software which I have then annotated.)

Look north and you'll see the W of Cassiopeia rising in the northeast. The last star of the W - the one closest to the horizon - is the faintest and may no tbe visible at first. Click to enlarge this chart. (This chart uses a screen shot from Starry Nights software which I have then annotated.)

But for our purposes on this August night we shall see the W as marking the northern extremity of the Milky Way. Oh the Milky Way  continues up here – but it does get fainter and a little harder to pick out.  Still, you should think in your mind of a river running through the W of Cassiopeia through the Northern Cross – or Swan – and on southward past Altair, the southern-most star in the Summer Triangle.

And where does it go? Why into the Teapot of course!  For those in mid-northern latitudes, which is where I am, the Teapot asterism tends to sit on our southern horizon – and some of the best and brightest parts of the Milky Way look like steam coming out of its spout! So turn around now and face south. For me, the Teapot is just 15-20 degrees off the horizon – roughly two fists – but if you live farther south, say about latitude 25 degrees, then it will be significantly higher.

Here’s what you should be  looking for:

You canbt hink of the Milky Way as streaming into the Teapot - or you can think of it as the steam coming out of the Teapot - which ever helps you remember best where to look.  Click for a larger chart. (This chart uses a screen shot from Starry Nights software which I have then annotated.)

You can think of the Milky Way as a river streaming into the Teapot - or you can think of it as the steam coming out of the Teapot - which ever helps you remember best where to look. Click for a larger chart. (This chart uses a screen shot from Starry Nights software which I have then annotated.)

The Teapot is the core of the constellation Sagittarius, and it follows the familiar scorpion of Scorpius. You may have found that last month when you located another of our guidepost stars, Antares. Now, as you look south –  it also should be quite dark by now – you should have no trouble seeing the second and third magnitude stars that form the Teapot, or for that matter, the wonderful curves of the scorpion to its west.

Now, if it is more than 90 minutes 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! Here’s an overview from the W through the Northern Cross to the Teapot. 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.

The August Milky Way appears as a cloudy area in this sweeping overview  showing a fully dark sky. By all means, click for a larger image of this chart.  (This chart use

The August Milky Way appears as a cloudy area in this sweeping overview showing a fully dark sky. By all means, click for a larger image of this chart. (This chart use

But what if you are in a typical, light-polluted, suburb? You’ re looking in the right spot, but you see no star clouds, only a handful of bright stars. Don’t despair. If you have located  the three asterisms – the W to the north, the Northern Cross overhead, and the Teapot to the south, then you are looking at the Milky Way even if you can’t see it.  Assuming it is at least 90 minutes after sunset, now is the time to start exploring with your binoculars. (You should do this even if you can see the Milky Way well with your naked eye.)

Start with the center of the Northern Cross and sweep from left to right – east to west – across the three stars that mark its cross arm.  When you’re on the center star of these three you should see lots of fainter stars in your binoculars – but as you get out beyond the stars that mark the ends of the crossbar, you should see fewer. Do broard sweeps with your binoculars being conscious of the background hue.  Away from the Milky Way it should be darker – if you notice it lightening as you move across the Milky Way – wall, that’s the Milky Way.  Remember to think of the Milky Way as a river running roughly north to south from the W to the Teapot – to find its borders, keep sweeping across it in an east-to-west direction as you also move slowly southward. (Looking at the background hue, however can be deceptive. You have to separate the change caused by the Milky Way from the change of say the light dome of a nearby city, or other source of bright light. The sky, for example, will appear lighter as you approach the moon. But then, trying to find the Milky Way with the moon in the sky isn’t a real good idea as mentioned earlier.

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."

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 we 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 travelled thousands of year to reach your eyes and ping you 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.

Something big has hit Jupiter again

New dark spot on Jupiter taken with Hubble's Wide-Field Camera 3 on July 23.

New dark spot on Jupiter taken with Hubble's Wide-Field Camera 3 on July 23.

Apparently a comet smashed into Jupiter recently and the result – a “black eye” – was discovered by an Australian amateur. It’s visible in backyard telescopes, but you have to know just when to look – Jupiter rotates pretty quickly and you’re only going to see this if that side of the planet is turned right towards you. You also probably need to wait unti close to midnight when Jupiter is fairly high int he southeast.

Or, you can check out this shot from Hubble and read the New York Times story about it.

I got one look at Jupiter since the spot appeared – but I didn’t know it was there and got interrupted by a love-sick fox. (See my post here.)

Back in 1993 we all got excited as we watched the reports pour in  from observatories over that new thing, the World Wide Web,  as a comet smashed into Jupiter. That one was predicted well in advance and observatories all over the world were tuned into the event.

OK – how to see this one: First, find Jupiter – brightest star in the southeast rising just after sunset. Now go to this page at Sky and Telescope which predicts when the Great Red Spot will be front and center. Add two hours six minutes to any of those times and that when this new black eye should be best seen.

Build an inexpensive, simple, one-tooth-pick, global, equatorial, elegant and smaller than an iPod, wristdial!

A day in the Sun – a brief timelapse video of the garden-size version of the wristdial in action. (See if you can discover what time did the bird land on the dial, casting it’s shadow on the face!)  This is the same basic design as the wrist dial, only larger.

Is the wristdial really all those things – inexpensive, simple, one-tooth-pick, global, equatorial, elegant and smaller than an iPod? Yes, and with no moving parts to break. Instead it depends on the motion of the Earth which, ponderous as it is (6.6 sextillion tons) moves like – well, like clockwork!

And simple?

Yep! Here’s an image of the final product in action in the northern hemisphere early on a summer morning.  (Oh, it can also find north for you, so it can double as a compass. More on this in the full directions in PDF format 😉

composite_main

Click for larger image.

The wristdial travels in a neat, folded package (see inset at upper left). The toothpick is inserted at a right angle to the dial face, and this can be checked with the “setting triangle.” The same triangle is then used to set the dial face so its plane points to the celestial equator. Get those two set correctly, and the dial works anywhere on Earth that the Sun is shining.  clay_winterThe dial has two faces, the one shown in the preceding picture is for use in spring and summer. The other side –  shown in the picture at right – is for use in fall and winter. The design can easily be scaled up and faces are included for a larger version, or you can use the instruction included here to design your own.

Sundials are simple things that point to profound truths about the motions of Earth and Sun. They’ll teach you about your position on this rapidly spinning sphere and put you in direct touch with some awesome forces of nature. That’s what I love about them. But right now you’re probably more interested in how to make your own wristdial, so let’s do it!

You can download the full directions – with many color photos – from the link below. This is a large Acrobat PDF file, so allow several minutes for it to download.  Because of the numerous color image, I suggest you read  it on screen – but you’ll want to print either page 4 or page 5, depending on the hemisphere in which you will use the dial.

Download complete directions for wrist dial here: directions_wristdial_f4

You might want to get a jump on things by first finding and jotting down a few useful facts.

Latitude and longitude (http://www.getlatlon.com/) – You don’t have to be super precise. All can be rounded to the nearest degree. For Westport, MA I round my latitude to 42° N, and my longitude to 71° W.

Central meridian (http://www.travel.com.hk/region/timezone.htm) – Time zones are set every 15 degrees of longitude so you’ll see the central meridian for yours at the top of the map on the web page linked above. Westport, MA, is in the Eastern Standard time zone which is centered on 75 degrees longitude.

Compass deviation (http://www.geo-orbit.org/sizepgs/magmapsp.html) – I suggest you find your compass deviation only because I’m assuming you might use a magnetic compass to find north. If you have another way to determine north, you can ignore this. But a magnetic compass is not precise. In the case of Westport, MA the deviation is 16° east, which means that if my magnetic compass says it is pointing north, it is really pointing 16 degrees to the west of north, so to point true north I have to correct by pointing 16 degrees to the east of what it says is north. Of course, I might use a GPS, or call the local airport to learn the compass deviation.

Southern hemisphere dial at work in winter.

Southern hemisphere dial at work in winter.

The wristdial has now been tested in the southern hemisphere by my friend Dom in Sydney, Australia. Dom took some photos of his wristdial in action, next to a larger, traditional garden sundial in Centennial Park.  You will note three things about these photos. First, the shadow is on the underside of the dial face because when these photos were taken in mid-July it was winter in the southern hemisphere. Second, the time indicated by the dial is almost exactly the same as the time indicated by Dom’s watch. That’s because Sydney is not on daylight savings time in the winter. Also. Sydney’s longitude is just one degree – four minutes – east of the central longitude for its time zone.   Because of that the time should be four minutes fast. But, the equation of time for July  is six minutes slow. When you apply the equation of time,  the four minutes “fast” caused by a difference in longitude is subtracted from the six minutes “slow” of the equation of time and the dials solar time is within about two minutes of standard clock time.  (This kind of calculation is described in detail  for your location in the directions you can download. )

Southern hemisphere wristdial showing solar time as compared to clock time while sitting on a traditional sundial in a park in Sydney, Australia.

Southern hemisphere wristdial showing solar time as compared to clock time while sitting on a traditional sundial in a park in Sydney, Australia.

July’s Guidepost Stars: Look east – look south!

July offers an eyeful, and if you are just starting to learn the sky this month, you have four new guidepost stars to meet. However, those who were out in June already met Vega and perhaps the rest of the Summer Triangle – if not, by all means get out about 45 minutes after sunset on a July evening and look to the east. In the twilight you should see something like the simulation below with Vega the highest and brightest of the trio. Altair is next in brightest and the most southerly. Deneb is the least bright of the three and most northerly. This triangle is huge – roughly 20 degrees (two fists) in height and 40 degrees (four fists) in width. And you’ll have plenty of time to get familiar with it, for it’s prominent in northern latitudes right into winter.

 

Summer triangle in twilight, as depicted in Starry Nights software. Be sure to click for larger image.

Summer triangle in twilight, as depicted in Starry Nights software. Be sure to click for larger image.

 

 

But once you feel confident you have this triangle identified, face South and look for our other July guidepost star, Antares. The name “Antares” can be translated as “rival of Mars” and is an indication of the star’s redness. If this isn’t immediately apparent to you, compare it to blue/white Vega. Or, if you have been studying the sky for several months, compare it to the icy blue of Spica, now in the southwest sky. (Remember – you reach Spica by following the arc of the Big Dipper’s handle first to Arcturus, then continuing on to Spica. 

 

Stellarium's depiction of the twilight sky looking due south in July from mid-northern latitudes. Antares is the bright star to the left (east) and Spica the other one. Click for a much larger image.

Stellarium's depiction of the twilight sky looking due south in July from mid-northern latitudes. Antares is the bright star to the left (east) and Spica the other one. Click for a much larger image.

 

 

The image above shows how the twilight sky to the south looks in early July. The lower star on the left is Antares, the one to the right is Spica. There’s about 45 degrees between these two, so as it gets fully dark you’ll notice Antares is almost due South. In northern latitudes Antares is quite low – here in Westport, MA. it is only 22 degrees above the southern horizon when it transits (about 10 pm in early July) – just half as high as Polaris which, of course, anchors the northern sky. (No – Antares is not the southern pole star. It is a long way from it. In fact, there is no bright star marking the southern celestial pole, but if there were you would have to be in the southern hemisphere to see it. Antares is less than one third of the way to the South Celestial Pole. )

As the sky gets fully dark on a July evening, Antares will be due South and be the core of one of the constellations that really does resemble it’s name – Scorpius, the scorpion.

Antares at the heart of Scorpius.

Antares at the heart of Scorpius.

The stick figure charted at right doesn’t really do justice to the graceful curves of its body and tail. Sadly, for me this constellation is largely hidden by trees. My best view of Scorpius comes when I look to the south over the bay or ocean, though I can see it early on a July evening if I step out into the road in front of my house, for the road heads south and at that time Scorpius dominates my southern sky from the horizon to about one third of the way up.

%d bloggers like this: