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    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.

Look East in June 2014 and see if you can make the stars “pop!”

How can we make the stars pop out of the sky and into our mind’s eye?

That’s the perennial problem for me, for what we actually see is so much less than what is actually there that we can’t help but belittle the stars unintentionally. This month’s guide star, Deneb, is a prime example. It’s easy to spot using our chart as it rises in the northeast below and to the left of Vega. In terms of our bright guide star list, Deneb’s rather dim – 19th in the list of brightest stars we see with the naked eye. But that reveals much more about our point of view than about Deneb. Deneb, plain and simple, is one of the most luminous stars in our galaxy. Vega, just above and to the right of it in the northeast, looks so much brighter – but it isn’t. It’s simply so much closer. Vega is just 25 light years away.

Deneb, by one the most recent calculations, is 1,425 light years from us. (This is still open to debate and some put it nearly twice that far away!) But we’ll use the 1,425 light year figure. Put Deneb in Vega’s place – just 25 light years away –  and it would be visible in broad daylight! Does that help it “pop?”

When astronomers talk about how “luminous” a star is they don’t mean how bright it appears to us in our night sky. They mean how bright it actually is. In fact, frequently they use “luminous” to include all the radiation that comes from a star – even radiation in wavelengths that we don’t see, such as infrared and ultraviolet. They then compare a star’s luminosity with the luminosity of the Sun – the Sun being “1.” When they examine Deneb that way they get a luminosity of 54,400 Suns – awesome! (Popping yet? Can you imagine our Sun being twice as brght as it is? three times a bright? How about 54,400 times brighter?)  But when we look at Deneb we see a star that is just moderately bright – magnitude 1.25.

Prepared from Starry Nights Pro screen shot - click for larger version.

Prepared from Starry Nights Pro screen shot – click for larger version.

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

OK – let’s get serious about this popping business. When you look at Deneb, you have to use your mind’s eye to see it for what it really is, not just for what it appears to be. So what should we see when we look at Deneb? First we should see something huge. Deneb is classed as a “supergiant.” So sit back and try to imagine a star whose diameter is 108 times that of the Sun. No, wait! First imagine how big the Earth is. Then get in your mind the fact that the Sun is 109 times the diameter of the Earth. Got that? Now try to imagine that Deneb is to our Sun what our Sun is to the Earth. birdshotBut wait! I really do not want to talk about diameters. Those are for people who live in a flat world. Think in terms of volume, because that’s what a planet or star really is – a volume – a mass formed into a sphere. To get your mind around volume, picture the earth as a tiny bird shot just 2.5mm in diameter. Here’s one to give you the idea. Now picture a sphere about 10.5 inches in diameter – a basketball would be close, or this glass garden globe. See the difference? When talking diameters, the Sun is 109 Earths. But when you’re talking volume, you could fit well over a million Earths inside the Sun. sun_deneb Now think about the same thing in terms of Deneb. That little lead shot is our magnificent Sun. The blue globe is Deneb! That’s what you should see in your mind’s eye when you watch this month’s guide star rise in the northeast. Were Deneb our Sun, its surface would reach halfway to the orbit of Earth and needless to say, Earth would be in a hopelessly hot location. But there’s more, of course. Size is a great starting point, but it doesn’t equate with mass. A lot of stars are bloated – that is, their mass is spread out over a large area and they have a huge surface area from which to radiate a tremendous amount of energy. That is the case with Deneb. It is believed to be about 10-15 solar masses, but its total luminosity – the total amount of energy it radiates when compared to the Sun is a whopping 54,400 times that of the Sun! Wrap your mind’s eye around that! That’s why astronomer/author James Kaler writes that Deneb is

among the intrinsically brightest stars of its kind (that is, in its temperature or spectral class) in the Galaxy. If placed at the distance of Vega, Deneb would shine at magnitude – 7.8, 15 times more brightly than Venus at her best, be as bright as a well-developed crescent Moon, cast shadows on the ground, and easily be visible in broad daylight.

Deneb is unusual for supergiant stars for it is of spectral Class A – that means it’s your basic white star and very hot as stars go. Other very large stars, such as Betelgeuse, are in a different stage of development and quite cool and red to the eye. Deneb is believed to be just 10 million years old. That’s very young in terms of star ages. Our Sun is believed to be 5 billion years old. Deneb will never get to that ripe old age. Massive stars such as Deneb live in the fast lane, burning up their core hydrogen fuel relatively quickly. Kaler gives this analysis:

The star is evolving and has stopped fusing hydrogen in its core. However, it’s hard to know just what is going on. It might be expanding and cooling with a dead helium core and on its way to becoming a red supergiant, or it might have advanced to the state of core helium fusion. Having begun its life as a hot class B (or even class O) star of 15 to 16 solar masses just over 10 million years ago, its fate is almost certainly to explode sometime astronomically soon as a grand supernova.

Kaler certainly knows what he’s talking about, but don’t bother to keep a “death watch” on Deneb. “Astronomically soon” means some time in the next 100 million years or so 😉 Sherlock Holmes once chided his companion Watson saying “you see, but you do not observe.” With the stars, we have to take our cue from Holmes. We have to go beyond merely seeing. And in truth, we have to go beyond merely observing. We have to take the knowledge the scientists have given us and somehow apply it to what we see, so with our mind’s eye we truly observe. Only then can we pop Deneb out of that “twinkle, twinkle little star” category and see it for what it really is.

Vital stats for Deneb (DEN-ebb), also known as Alpha Cygni:

• Brilliance: Magnitude 1.24; its luminosity is the equal of 54,400 Suns. • Distance: 1,425 light years • Spectral Types: A2 supergiant • Position: 20h:41m:26s, +45°:16′:49″

Guide star reminder

Each month you’re encouraged to learn the new “guide” stars rising in the east about an hour after sunset. One reason for doing this is so you can then see how they move in the following months. Deneb and the Northern Cross join several other guide stars and asterisms in the June sky. Again, if you have been reading these Posts for several months, be sure to find the stars, asterisms, and planets you found in earlier months. Early on a June evening these will include, from east to west, the following: Deneb, Vega, Arcturus, Spica, Saturn, Leo’s Rump (triangle),  the Sickle, Regulus, the Beehive, and in the northwest getting near the horizon, Pollux and Castor. You may also see Capella very near the horizon. For more experienced observers looking to extend their knowledge of the skies this month, I highly recommend trying to track down two more asterism – the Northern Crown and the KeystoneOK, technically the Northern Crown (Corona Borealis) is a constellation. But I always apply the name to the handful of moderately bright stars that look like a half circle – a crown. As the chart below shows, these two asterisms are located on a line between Arcturus and Vega and they sort of divide that line into thirds. As with our guide stars and other asterisms, they will help you if you advance to finding other more interesting objects int he night sky with binoculars and telescope.

keystone-crown

For a printer-friendly version of this chart, click here. The Crown itself can provide you with an interesting test of how dark your skies are since a couple hours after sunset on a June night it is well up in your eastern sky. It consists of a circlet of seven stars which can just fit within the field of view of wide-field binoculars – the example below shows an eight degree circle. It may be helpful to look at these stars with your binoculars, even if they don’t all fit in the same field of view at once. But to test how dark your skies are – and how transparent they are at the moment – wait until your vision is dark adapted, then see how many of these stars you can see. The numbers beside the stars are the magnitudes in decimals as given by Starry Nights software. However, I’ve followed the convention of not using a decimal point, since it might be mistaken for another faint star. So “41” means magnitude 4.1, for example. If you are seeing all seven stars you can be happy with your skies and these light-polluted times. In a truly dark location, however, this will be easy – but sadly such locations are rare these nights.

Read text above for explanation of how to use. Thenc lick on image to give you a larger view and luse the link below to download a printer friendly version. (Made from Starry Nights screen shot.)

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

Look North in June 2014! See the ‘North Sky Triangle’ !

Click to enlarge. (Prepared from Starry Nights Pro screenshot.)

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

Yep, that’s Deneb, the guide star that is the subject of our “Look East” Post for June, gracing our “Look North” chart as well. In fact, besides Polaris we have three key guide stars in our northern sky every June, each of which is noted for, among other things, just how far north it is.

Of the three, Capella may be the hardest to find, for it is very near the horizon in the northwest around sunset. But if you have a clear horizon in that direction, you should still pick it up, especially at the start of the month. More prominent, however, are Deneb and Vega. These stars play the key role in one of the best known sky triangles – the Summer Triangle, but that triangle becomes easier to see next month and it will be in the eastern sky. For June it is fun to link Deneb and Vega with Polaris in what we’ll call the North Sky Triangle – and the linkage has some special meaning.

We just happen to be lucky to be living in an era when we have a bright star near the North Celestial Pole – Polaris. There’s no such bright star near the South Celestial Pole, and in other eras there is none near the North Pole either. But in the distant past – and in the distant future – Deneb actually will be the bright star nearest the pole – not as near as Polaris, but still a good general guide to it.

gyroscope precessionThat’s because the Earth wobbles as it spins on its axis in much the same way as a spinning top does. So the axis of the Earth doesn’t always point to the same place. It slowly makes a great circle around the northern sky, taking roughly 25,000 years to complete. Right now our axis is pointing to within a degree of Polaris. Not precise, but good enough so it is a ready indicator of true north. A mere 18,000 years ago Deneb was within 7 degrees of the pole and will be again around the year 9800!

This wobbling of the pole is really kind of mind boggling. I look at Polaris now, and it’s a bit short of 42 degrees above my northern horizon. But in a mere 14,000 years, Polaris will be almost straight over my head, and guess what will be the pole star then? Not Deneb, but its brighter – in our skies – companion, Vega. Of course none of us is likely to witness that event, but it’s still food for thought and gives us a sense of the majestic rhythms and time frame of the heavens.

And speaking of that time frame, as I write this it occurs to me that 14,000 years really feels like a very long time from now – while the 10-million-year age of Deneb doesn’t seem that long – and it isn’t, astronomically speaking. I’m not talking now about what your mind tells you about those numbers. I’m talking about your emotional reaction to them. I wonder if it’s similar to mine? This isn’t idle speculation. It’s central to our appreciating what we are seeing. But I think 14,000 sounds like a long time because it’s a number that fits into our day-to-day experience. Huge, but we can easily imagine 1,000 of something.  So imagining 14,000 of something comes easily to us. But few of us have any experience with one million. It would take about 11 days to count one million seconds and no one in his right mind is about to try it. So when we speak of the 10-million-year age of Deneb, or the five-billion-year age of the Sun, the numbers lose their emotional impact because they don’t relate easily to our experience. But 14,000 – well, we know, in an emotional sense, just how long that is!

Look North in June 2013! We have a special ‘North Sky Triangle’ this month!

Click to enlarge. (Prepared from Starry Nights Pro screenshot.)

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

Yep, that’s Deneb, the guide star that is the subject of our “Look East” Post for June, gracing our “Look North” chart as well. In fact, besides Polaris we have three key guide stars in our northern sky every June, each of which is noted for, among other things, just how far north it is.

Of the three, Capella may be the hardest to find, for it is very near the horizon in the northwest around sunset. But if you have a clear horizon in that direction, you should still pick it up, especially at the start of the month. More prominent, however, are Deneb and Vega. These stars play the key role in one of the best known sky triangles – the Summer Triangle, but that triangle becomes easier to see next month and it will be in the eastern sky. For June it is fun to link Deneb and Vega with Polaris in what we’ll call the North Sky Triangle – and the linkage has some special meaning.

We just happen to be lucky to be living in an era when we have a bright star near the North Celestial Pole – Polaris. There’s no such bright star near the South Celestial Pole, and in other eras there is none near the North Pole either. But in the distant past – and in the distant future – Deneb actually will be the bright star nearest the pole – not as near as Polaris, but still a good general guide to it.

gyroscope precessionThat’s because the Earth wobbles as it spins on its axis in much the same way as a spinning top does. So the axis of the Earth doesn’t always point to the same place. It slowly makes a great circle around the northern sky, taking roughly 25,000 year to complete. Right now our axis is pointing to within a degree of Polaris. Not precise, but good enough so it is a ready indicator of true north. A mere 18,000 years ago Deneb was within 7 degrees of the pole and will be again around the year 9800!

This wobbling of the pole is really kind of mind boggling. I look at Polaris now, and it’s a bit short of 42 degrees above my northern horizon. But in a mere 14,000 years, Polaris will be almost straight over my head, and guess what will be the pole star then? Not Deneb, but its brighter – in our skies – companion, Vega. Of course none of us is likely to witness that event, but it’s still food for thought and gives us a sense of the majestic rhythms and time frame of the heavens.

And speaking of that time frame, as I write this it occurs to me that 14,000 years really feels like a very long time from now – while the 10-million-year age of Deneb doesn’t seem that long – and it isn’t, astronomically speaking. I’m not talking now about what your mind tells you about those numbers. I’m talking about your emotional reaction to them. I wonder if it’s similar to mine? This isn’t idle speculation. It’s central to our appreciating what we are seeing. But I think 14,000 sounds like a long time because it’s a number that fits into our day-to-day experience. Huge, but we can easily imagine 1,000 of something.  So imagining 14,000 of something comes easily to us. But few of us have any experience with one million. It would take about 11 days to count one million seconds and no one in his right mind is about to try it. So when we speak of the 10-million-year age of Deneb, or the five-billion-year age of the Sun, the numbers lose their emotional impact because they don’t relate easily to our experience. But 14,000 – well, we know, in an emotional sense, just how long that is!

Look East in June 2013 and see if you can make the stars “pop!”

How can we make the stars pop out of the sky and into our mind’s eye? That’s the perennial problem for me, for what we actually see is so much less than what is actually there that we can’t help but to either ignore or belittle the stars unintentionally.

This month’s guide star, Deneb, is a prime example. It’s easy to spot using our chart as it rises in the northeast below and to the left of Vega. In terms of our bright guide star list, Deneb’s rather dim – 19th in the list of brightest stars we see with the naked eye. But that reveals much more about our point of view than about Deneb.

Deneb, plain and simple, is one of the most luminous stars in our galaxy. Vega, just above and to the right of it in the northeast, looks so much brighter – but it isn’t. It’s simply so much closer. Vega is just 25 light years away. Deneb, by one the most recent calculations, is 1,425 light years from us. (This is still open to debate and some put it nearly twice that far away!) But we’ll use the 1,425 light year figure. Put Deneb in Vega’s place – just 25 light years away –  and it would be visible in broad daylight! Does that help it “pop?”

When astronomers talk about how “luminous” a star is they don’t mean how bright it appears to us in our night sky. They mean how bright it actually is. In fact, frequently they use “luminous” to include all the radiation that comes from a star – even radiation in wavelengths that we don’t even see, such as infrared and ultraviolet. They then compare a star’s luminosity with the luminosity of the Sun – the Sun being “1.” When they examine Deneb that way they get a luminosity of 54,400 Suns – awesome! (Popping yet? Can you imagine our Sun being 54,400 times brighter?)  But when we look at Deneb we see a star that is just moderately bright – magnitude 1.25.

lookeast_chart

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

OK – let’s get serious about this popping business. When you look at Deneb, you have to use your mind’s eye to see it for what it really is, not just for what it appears to be. So what should we see when we look at Deneb?

First we should see something huge. Deneb is classed as a “supergiant.” So sit back and try to imagine a star whose diameter is 108 times that of the Sun. No, wait! First imagine how big the Earth is. Then get in your mind the fact that the Sun is 109 times the diameter of the Earth. Got that? Now try to imagine that Deneb is to our Sun what our Sun is to the Earth.

birdshotBut wait! I really do not want to talk about diameters. Those are for people who live in a flat world. Think in terms of volume, because that’s what a planet or star really is – a volume – a mass formed into a sphere. To get your mind around volume, picture the earth as a tiny bird shot just 2.5mm in diameter. Here’s one to give you the idea.

Now picture a sphere about 10.5 inches in diameter – a basketball would be close, or this glass garden globe. See the difference? When talking diameters, the Sun is 109 Earths. But when you’re talking volume, you could fit well over a million Earths inside the Sun.

sun_deneb

Now think about the same thing in terms of Deneb. That little lead shot is our magnificent Sun. The blue globe is Deneb! That’s what you should see in your mind’s eye when you watch this month’s guide star rise in the northeast. Were Deneb our Sun, its surface would reach halfway to the orbit of Earth and needless to say, Earth would be in a hopelessly hot location.

But there’s more, of course. Size is a great starting point, but it doesn’t equate with mass. A lot of stars are bloated – that is, their mass is spread out over a large area and they have a huge surface area from which to radiate a tremendous amount of energy. That is the case with Deneb. It is believed to be about 10-15 solar masses, but its total luminosity – the total amount of energy it radiates when compared to the Sun is a whopping 54,400 times that of the Sun! Wrap your mind’s eye around that!

That’s why astronomer/author James Kaler writes that Deneb is

among the intrinsically brightest stars of its kind (that is, in its temperature or spectral class) in the Galaxy. If placed at the distance of Vega, Deneb would shine at magnitude – 7.8, 15 times more brightly than Venus at her best, be as bright as a well-developed crescent Moon, cast shadows on the ground, and easily be visible in broad daylight.

Deneb is unusual for supergiant stars for it is of spectral Class A – that means it’s your basic white star and very hot as stars go. Other very large stars, such as Betelgeuse, are in a different stage of development and quite cool and red to the eye. Deneb is believed to be just 10 million years old. That’s very young in terms of star ages. Our Sun is believed to be 5 billion years old. Deneb will never get to that ripe old age. Massive stars such as Deneb live in the fast lane, burning up their core hydrogen fuel relatively quickly.

Kaler gives this analysis:

The star is evolving and has stopped fusing hydrogen in its core. However, it’s hard to know just what is going on. It might be expanding and cooling with a dead helium core and on its way to becoming a red supergiant, or it might have advanced to the state of core helium fusion. Having begun its life as a hot class B (or even class O) star of 15 to 16 solar masses just over 10 million years ago, its fate is almost certainly to explode sometime astronomically soon as a grand supernova.

Kaler certainly knows what he’s talking about, but don’t bother to keep a “death watch” on Deneb. “Astronomically soon” means some time in the next 100 million years or so 😉

Sherlock Holmes once chided his companion Watson saying “you see, but you do not observe.” With the stars, we have to take our cue from Holmes. We have to go beyond merely seeing. And in truth, we have to go beyond merely observing. We have to take the knowledge the scientists have given us and somehow apply it to what we see, so with our mind’s eye we truly observe. Only then can we pop Deneb out of that “twinkle, twinkle little star” category and see it for what it really is.

Vital stats for Deneb (DEN-ebb), also known as Alpha Cygni:

• Brilliance: Magnitude 1.24; its luminosity is the equal of 54,400 Suns.
• Distance: 1,425 light years
• Spectral Types: A2 supergiant
• Position: 20h:41m:26s, +45°:16′:49″

Guide star reminder

Each month you’re encouraged to learn the new “guide” stars rising in the east about an hour after sunset. One reason for doing this is so you can then see how they move in the following months.

Deneb and the Northern Cross join several other guide stars and asterisms in the June sky. Again, if you have been reading these Posts for several months, be sure to find the stars, asterisms, and planets you found in earlier months. Early on a June evening these will include, from east to west, the following: Deneb, Vega, Arcturus, Spica, Saturn, Leo’s Rump (triangle),  the Sickle, Regulus, the Beehive, and in the northwest getting near the horizon, Pollux and Castor. You may also see Capella very near the horizon.

For more experienced observers looking to extend their knowledge of the skies this month, I highly recommend trying to track down two more asterism – the Northern Crown and the KeystoneOK, technically the Northern Crown (Corona Borealis) is a constellation. But I always apply the name to the handful of moderately bright stars that look like a half circle – a crown. As the chart below shows, these two asterisms are located on a line between Arcturus and Vega and they sort of divide that line into thirds. As with our guide stars and other asterisms, they will help you if you advance to finding other more interesting objects int he night sky with binoculars and telescope.

keystone-crown

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

The Crown itself can provide you with an interesting test of how dark your skies are since a couple hours after sunset on a June night it is well up in your eastern sky. It consists of a circlet of seven stars which can just fit within the field of view of wide-field binoculars – the example below shows an eight degree circle. It may be helpful to look at these stars with your binoculars, even if they don’t all fit in the same field of view at once. But to test how dark your skies are – and how transparent they are at the moment – wait until your vision is dark adapted, then see how many of these stars you can see. The numbers beside the stars are the magnitudes in decimals as given by Starry Nights software. However, I’ve followed the convention of not using a decimal point, since it might be mistaken for another faint star. So “41” means magnitude 4.1, for example. If you are seeing all seven stars you can be happy with your skies and these light-polluted times. In a truly dark location, however, this will be easy – but sadly such locations are rare these nights.

Read text above for explanation of how to use. Thenc lick on image to give you a larger view and luse the link below to download a printer friendly version. (Made from Starry Nights screen shot.)

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

Events – June 2013 – Venus chases Mercury, Saturn is due south, and the Summer Solstice arrives

This is a delightful time to find the ever elusive Mercury because through the first two weeks of June it puts on its best show of the year for those in the Northern Hemisphere and it’s relatively easy to find because brilliant Venus points the way.

Look west about 30 minutes after Sunset on June 1, 2013 and you can find three planets ina row. Venus should be obvious to the naked eye. Find it and put it int he bottom of your low-power binocular field and you should see Mercury near the top of the field of view. Move Venus to the top and you should pick up Jupiter near the bottom of the field of view. Jupiter is brighter than Mercury, but may not appear to be because it will belower and more impacted by looking through the atmosphere and the twilight which will be brightest near the horizon.

Look west about 30 minutes after sunset on June 1, 2013 and you can find three planets in a row. Venus should be obvious to the naked eye. Find it and put it in the bottom of your low-power binocular field and you should see Mercury near the top of the field of view. Move Venus to the top and you should pick up Jupiter near the bottom of the field of view. Jupiter is brighter than Mercury, but may not appear to be because it will be lower and more impacted by looking through the atmosphere and the twilight which will be brightest near the horizon. Jupiter will soon drop out of sight but for the next two weeks Venus and Mercury will make easy targets.

Special June 2013 dates for viewing Mercury, Venus, Jupiter and the Moon:

  • 1 – Mercury at its brightest and Jupiter still in view.
  • 9 – A very thin crescent Moon little more than one day old will be roughly 10 degrees – one fist – beneath the pair of planets – Venus and Mercury.
  • 10 – A much easier to see – and quite pleasing – will be a 2-day lunar crescent  beside the pair (just south)  and almost fitting in the same binocular field of view.
  • 11 – The 3-day crescent Moon will have climbed well past the pair, but still make a nice show.
  • 18 – Mercury has reached its peak and started back down and on this date drawing within a couple degrees of Venus – just south. The two will be quite high – about 11 degrees half an hour after sunset, but Mercury will have faded to magnitude 1.1 making it a challenge to pick out in the twilight.

Also this month:

But let’s start with Mercury because the speedy little planet is always a challenge to see. Why? First, because it is very fast. Earth chugs along at a “mere”  66,000 miles an hour in its annual journey around our star, the  Sun. (Doesn’t feel like we’re going that fast, does it?) But Mercury, being closer to the Sun, moves much faster –  it covers a much smaller orbit at a blazing 107,000 miles an hour. So that means when it is well placed for observing it doesn’t stay that way long and it’s easy for the weather and the rest of life to get in the way of seeing it.

What’s more, because it is so near the Sun we only see it as it pulls out to one side or the other  of the Sun and it does that for relatively brief intervals.

And even these quick glimpses vary considerably because it’s orbit is much more lopsided than most. At one point it can be as much as 43.6 million miles from the Sun – and at another it may be as little as 28.6 million miles. (In comparison, Earth can vary from roughly 94.5 million miles from the Sun to 91.4 million miles.)

How far it is from the Sun impacts how easy it is for us to see. If close to the Sun it either rises or sets in strong twilight – and since it seldom gets much brighter than magnitude -1, it can be  quite difficult to pick out in the twilight. And even when it gets pretty far away from the Sun, it’s so small that it never becomes as bright as Venus – in fact, in June it will be easily outshone by Jupiter and Venus.  This June, Mercury will reach a maximum brightness of -0.4 and that on the first day – it grows a bit dimmer each night thereafter, though this will be hard to judge because it also puts more distance between it and the Sun, so that means we see it against a darker background each night.

Cool, huh? I mean it moves a little bit more into darker sky each night – but at the same time it dims a little each night – doesn’t want to make things too easy for us!  😉

But sometimes several factors combine to give us an especially good look at Mercury and this June is such a case – with the added bonus that the much brighter Venus will be near it and thus point the way to finding Mercury.  The basic routine is simple. You want to start looking about 30 minutes after sunset and when you spot Venus, turn your binoculars on it – about any binoculars will do – and for much of the month Mercury will fit  in the same field of view looking like a significantly dimmer star.  As it gets darker you should be able to pick it out with your naked eye – though if you wait too long it will be too close to  the Western horizon – so timing really counts.

As the month progresses Mercury will be a bit higher each night 30 minutes after sunset and Venus will appear to chase it – but Jupiter will drop out of view in just a few days.

Your first challenge, of course,is to merely find the planets in your evening sky and that require an unobstructed western horizon, good clear skies, and appropriate timing – and binoculars sure help, but aren’t absolutely necessary.

But what are you really seeing?

Or maybe the better question is: Why do you see the planets this way?

For the answer we turn to an Orrery – and there’s one online that can be found here. I used it – and modified the view with labels and arrows – to produce the two images that follow.  Essentially this is a view from overhead showing the counter-clockwise motion of the planets around the Sun.  It is only very roughly proportional and your challenge is to look at the Orrery view, then mentally place yourself on the Earth and imagine what your view at sunset would look like. Remember – now you’re getting down in the plane of the solar system and looking outward and what you see is a two-dimensional view that  cancels out the huge distances between the planets.

This June 1 view holds true for Mercury and Venus formost of the month. Jupiter quickly gets too close to the Sun. What we see at sunset are theplanets to the left of the arrow pointing west. As the Earth rotates, the arrow sweeps to the left and theplanets vanish from our view - although Saturn, seen int he southeast at the start of the evening, appears to climn higher in our sky as we turn towards it.  But, of course, nothing stands still. The Planets also revolve around the Sun, so from night to night Venus and Mercury will close the distance between themselves and Earth. The result in 30 days is shown in the next image.

This June 1 view holds true for Mercury and Venus for much of the month. Jupiter quickly gets too close to the Sun. What we see at sunset are the planets to the left of the arrow pointing west from the Earth. As the Earth rotates, the arrow sweeps to the left and the planets set – although Saturn, seen in the southeast at the start of the evening, appears to climb higher in our sky as we turn towards it. But, of course, nothing stands still. The planets also revolve around the Sun, so from night to night Venus and Mercury will close the distance between themselves and Earth. The result in 30 days is shown in the next image.

By the end of the month our view tot he west at Sunset shows us only Venus. Jupiter has long vanished fromt he scene and infact, may just becoming visible inthe pre-dawn sky with Mars.  Venus remain in view,  and Staurn is the dominant planet for much of the Summer night in 2013.

By the end of the month our view to the west at Sunset shows us only Venus. Jupiter has long vanished from the scene and in fact, may just be coming visible in the pre-dawn sky with Mars. Venus remains in view, and Saturn is the dominant planet for much of the Summer night in 2013.

As I watch this wonderful dance of the planets from night to night – and the changes are especially obvious with the swiftly moving inner planets of Mercury and Venus –  I try to get a picture in my minds eye of what’s really happening. Do this enough and when you look at a planet or the Moon in the sky, you can easily sense exactly where they are  in their orbits around the Sun – and where you are in respect to them. I find this a very satisfying piece of mental gymnastics – that we little creatures on our tiny little spaceship Earth, whirling and hurtling about the Sun at incredible speeds, have been able to figure this out. Don’t get me wrong – I take no c edit for that – just one of those special moments when I feel proud to be one of the billions of homo sapiens  here and feel maybe we have earned that name – sapiens indeed! 😉

One last piece of dynamics at work. As mentioned, Mercury is at its brightest at the start of the month.  By the 14 it has dropped about one whole magnitude to 0.76, by the 21st it’s magnitude 1.5, and by the 28th magnitude 2.6. So it will be getting harder and harder to see as it drops more and more into the twilight zone and as it loses brightness. Why does it get dimmer? Look at the Orrery charts – it is moving to a position between us and the Sun and just like the Moon, as it gets between us and the Sun it goes through phases. By the 28th it is a thin crescent and so is reflecting very little light our direction. (These phases can be seen with a small telescope, but you will not detect them with binoculars.)

Mercury and Venus week by week

The following chart shows you the changing positions of Venus and Mercury during June 2013. All are for 30 minutes after sunset for mid-northern latitudes, and all are prepared from Starry Nights Pro screen shots with labels added. Venus never gets much higher than 10 degrees above the horizon – not only throughout June, but essentially for the rest of the year it will be a pretty constant western star – slipping southward somewhat and eventually, in late fall, rising some , before going off stage in January 2014. Mercury’s appearance int he West is strictly for June and as you can see, by the end of the month it’s heading quickly for the horizon and is quite faint.

mvj_2

mv_3

mb_4

mv_5

Saturn – a southern star!

Wait until about an hour after sunset during June 2013, then look due south.  Almost four fists above the horizon (from mid-northern latitudes)  and about one fist apart are two bright “stars.” The slightly brighter one on the left (east) is Saturn. The other – which should appear bluer – is the first magnitude guidepost star  Spica. Down to the  lower left is another star of about the same brightness, Antares. Compare these three – they are roughly the same brightness, but Antares is tinted red, Saturn yellow, and Spica blue.  They  make a good introduction to noting star colors – which to my eye are more tints, but certainly detectable.

saturn_1

Who can resist the Solstice magic?

We’re fascinated with extremes and since the Sun is responsible for maintaining all life on Earth it’s rather natural to want to track its movements in our sky and mark its extremes. There’s no better time to do so than when it reaches it’s most northern point – the Summer solstice. And if you want to be really accurate that happens at 1:04 am EDT on the morning of June 21. So the time to greet the astronomical start of Summer is to mark the sunrise on June 21.

That said, this is more for those who are fond of records. Truth is you will be hard pressed to tell the difference of where exactly where the sun rises or sets a couple days before that date, or a couple days afterwards. The changes are just too small for us.  So you have to take the word of those who track such things with sophisticated math and instruments – 1:04 am June 21 is the time and date when the Sun reaches its most northerly point.  And the shortest night of the year is June 20-21.

All of this, of course, is for northern hemisphere observers. Our friends Down Under are marking the start of winter.

And speaking of special events . . .

On the night of June 22-23 we have a full Moon – the largest full Moon of the year.

Why is this larger than other full Moons? Because it is closer to us at this particular full Moon. How much larger is it? Significantly – but not so much that you really can tell the difference. To do that you need to see a larger full moon next to a small full Moon – and you can do that by going to this web site which gives a wonderfully detailed explanation.

Meanwhile, just sit back and enjoy it – and don’t confuse this with the Moon illusion phenomena – that is simply our eyes and brain playing tricks on us to make the Moon (or the Sun) look much larger when it is near the horizon, than when it is high in the sky.

Look north in July 2012 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 2012 the middle of the month – roughly the 10th to the 24th – should work pretty well.   (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.

June 2012 Events – Venus at the start, Venus at the end – and lots of cool stuff in between

Here’s a quick summary of June 2012 highlights:

All month – Mars and Saturn

Mars and Saturn put on a continuing display in the southwest – they are near equal in brightness and very close – in brightness – to the first magnitude guide stars, Regulus and Spica.

Mars, Saturn, Regulus, and Spica are the bright “stars” we see in the southwestern sky on a June evening. Can you put them in order of brightness? (Answer at the end of this post.) Click image for larger view. Prepared from Starry Nights Pro screen shot.

June 4 – Partial eclipse of the Moon

This event favors the western United States and Australia – but some parts of the eastern US can see some of it. First contact for the penumbra- the faint part of Earth’s shadow – is at  08:48:09 UT; the umbra makes contact at 09:59:53 UT, and the umbral phase is over at 09:59:53 UT. The penumbral phase ends at 13:18:17 UT.

For a map showing visibility of this event throughout the world, as well as other details, please go here.  To convert Universal Time (GMT) to your local time, please go here. GMT is selected as the default and eclipse times are in 24-hour format.

June 5-6 – Transit of  Venus

Historic  Transit of Venus – you don’t want to miss this one. Of course, you need the weather to be on your side, plus proper safety precautions for viewing the Sun. Go here for all the details.

June 20 – The Summer Solstice

The sun rises and sets as far north as it can; twilight seems to last forever; and the really dark night is darned short. Here in Westport, MA, the Sun sets at 8:22 pm EDT, but astronomical twilight doesn’t end until 10:34 pm EDT. That’s when it’s truly dark. And the morning phase of astronomical twilight begins at 02:59 am EDT. That gives us just four hours, 25 minutes of full darkness that night.

June 15 to early July – Catch the elusive planet Mercury in the evening sky – special treat June 21!

For many years I thought Mercury was really difficult to see. It isn’t, but it has that reputation for a reason. The problem with seeing Mercury is you have to know exactly when and where to look, but every year there are two or three good opportunities. This year one of them comes in the last couple of weeks of June.  During that period Mercury will be roughly 10 degrees above the horizon (one fist held at arm’s length –  to the north of west. The planet will be playing tag with the familiar Castor and Pollux – the Heavenly Twins – and will make a fine group with them and the crescent Moon on June 21.

Here are three  charts that should help you find it – but pay attention to the time. That is critical. You have to catch Mercury after sunset when the sky is dark enough for it to be seen, yet not too long after sunset or the planet will be too close to the western horizon and difficult to see through all the atmosphere. I suggest you start searching with binoculars about 15 minutes after sunset. Mercury should be visible to the naked eye around 30 minutes to an hour after sunset depending on local conditions. It’s easier to see with the naked eye once you spot it in binoculars, and it will be a bit brighter than the Twins.

All the named stars will be roughly the same brightness as Mercury, but it is hard to make comparisons in a twilight sky because the nearer to the horizon a star (or planet), the lighter the background against which you’ll see it. Click image to see a larger version. Prepared from Starry Nights Pro screen shot.

Click image to see a larger version. Prepared from Starry Nights Pro screen shot.

Click image to see a larger version. Prepared from Starry Nights Pro screen shot.

Last week of June – Jupiter and Venus vie for the title “Morning Star”

The giant planet Jupiter is back with its four bright moons and will be with us for many months to come.  It starts out the month rising just before the Sun, but by the end of the month will rise a full two hours before dawn. What’s more, it will be joined by a crescent Venus, fresh from its historic transit of the Sun at the start of the month.  And if that’s not enough, this all takes place in one of the most beautiful sections of the night sky with the charming cluster of the Pleiades hanging above the scene and the  Hyades just coming into view below it.

To see this you need an unobstructed eastern horizon; binoculars will make it much more enjoyable, and I plan to start looking about two hours before sunrise when the Pleiades are visible in a dark sky. Jupiter and Venus may not pop into view for another hour, and by then morning twilight will be getting strong – but they are so brilliant it shouldn’t matter.  However,  if you don’t see them on June 29, by all means give it a try any of several days before or after that date. From morning to morning Venus will appear to be trying to overtake Jupiter – and will get a bit closer in early July.

Capella, one of the brightest stars is near magnitude 0 – Jupiter about -2 and Venus a dazzling -4.4. Use binoculars to see the Pleiades. Click image for larger version. Prepared from Starry Nights Pro screen shot.

Answers to the brightness question

On June 15 Saturn shines at magnitude .61 and thus is the brightest, but Mars is extremely close at magnitude .7. (Extra pat on the back if you got these two correct! ) Spica is next at .98 and then Regulus at at 1.34. As the month goes on both Mars and Saturn will get a tad dimmer, but the order of brightness will remain the same – Saturn, Mars, Spica, and Regulus.

Look East in June 2012 and see if you can make the stars “pop!”

How can we make the stars pop out of the sky and into our mind’s eye? That’s the perennial problem for me, for what we actually see is so much less than what is actually there that we can’t help but to either ignore or belittle the stars unintentionally.

This month’s guide star, Deneb, is a prime example. It’s easy to spot using our chart as it rises in the northeast below and to the left of Vega. In terms of our bright guide star list, Deneb’s rather dim – 19th in the list of brightest stars we see with the naked eye. But that reveals much more about our point of view than about Deneb.

Deneb, plain and simple, is one of the most luminous stars in our galaxy. Vega, just above and to the right of it in the northeast, looks so much brighter – but it isn’t. It’s simply so much closer. Vega is just 25 light years away. Deneb, by the most recent calculations, is 1,425 light years from us. Put Deneb in Vega’s place and it would be visible in broad daylight! Does that help it “pop?”

When astronomers talk about how “luminous” a star is they don’t mean how bright it appears to us in our night sky. They mean how bright it actually is. In fact, frequently they use “luminous” to include all the radiation that comes from a star – even radiation in wavelengths that we don’t even see, such as infrared and ultraviolet. They then compare a star’s luminosity with the luminosity of the Sun – the Sun being “1.” When they examine Deneb that way they get a luminosity of 54,400 Suns – awesome! (Popping yet? Can you imagine our Sun being 54,400 times brighter?)  But when we look at Deneb we see a star that is just moderately bright – magnitude 1.25.

Click image for a larger version. The full “Summer Triangle” asterism will be easier to see as the month goes on, and the key stars get higher earlier in the evening. The key focus this month is the guide star Deneb.

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

OK – let’s get serious about this popping business. When you look at Deneb, you have to use your mind’s eye to see it for what it really is, not just for what it appears to be. So what should we see when we look at Deneb?

First we should see something huge. Deneb is classed as a “supergiant.” So sit back and try to imagine a star whose diameter is 108 times that of the Sun. No, wait! First imagine how big the Earth is. Then get in your mind the fact that the Sun is 109 times the diameter of the Earth. Got that? Now try to imagine that Deneb is to our Sun what our Sun is to the Earth.

birdshotBut wait! I really do not want to talk about diameters. Those are for people who live in a flat world. Think in terms of volume, because that’s what a planet or star really is – a volume – a mass formed into a sphere. To get your mind around volume, picture the earth as a tiny bird shot just 2.5mm in diameter. Here’s one to give you the idea.

Now picture a sphere about 10.5 inches in diameter – a basketball would be close, or this glass garden globe. See the difference? When talking diameters, the Sun is 109 Earths. But when you’re talking volume, you could fit well over a million Earths inside the Sun.

sun_deneb

Now think about the same thing in terms of Deneb. That little lead shot is our magnificent Sun. The blue globe is Deneb! That’s what you should see in your mind’s eye when you watch this month’s guide star rise in the northeast. Were Deneb our Sun, its surface would reach halfway to the orbit of Earth and needless to say, Earth would be in a hopelessly hot location.

But there’s more, of course. Size is a great starting point, but it doesn’t equate with mass. A lot of stars are bloated – that is, their mass is spread out over a large area and they have a huge surface area from which to radiate a tremendous amount of energy. That is the case with Deneb. It is believed to be about 10-15 solar masses, but its total luminosity – the total amount of energy it radiates when compared to the Sun is a whopping 54,400 times that of the Sun! Wrap your mind’s eye around that!

That’s why astronomer/author James Kaler writes that Deneb is

among the intrinsically brightest stars of its kind (that is, in its temperature or spectral class) in the Galaxy. If placed at the distance of Vega, Deneb would shine at magnitude – 7.8, 15 times more brightly than Venus at her best, be as bright as a well-developed crescent Moon, cast shadows on the ground, and easily be visible in broad daylight.

Deneb is unusual for supergiant stars for it is of spectral Class A – that means it’s your basic white star and very hot as stars go. Other very large stars, such as Betelgeuse, are in a different stage of development and quite cool and red to the eye. Deneb is believed to be just 10 million years old. That’s very young in terms of star ages. Our Sun is believed to be 5 billion years old. Deneb will never get to that ripe old age. Massive stars such as Deneb live in the fast lane, burning up their core hydrogen fuel relatively quickly.

Kaler gives this analysis:

The star is evolving and has stopped fusing hydrogen in its core. However, it’s hard to know just what is going on. It might be expanding and cooling with a dead helium core and on its way to becoming a red supergiant, or it might have advanced to the state of core helium fusion. Having begun its life as a hot class B (or even class O) star of 15 to 16 solar masses just over 10 million years ago, its fate is almost certainly to explode sometime astronomically soon as a grand supernova.

Kaler certainly knows what he’s talking about, but don’t bother to keep a “death watch” on Deneb. “Astronomically soon” means some time in the next 100 million years or so 😉

Sherlock Holmes once chided his companion Watson saying “you see, but you do not observe.” With the stars, we have to take our cue from Holmes. We have to go beyond merely seeing. And in truth, we have to go beyond merely observing. We have to take the knowledge the scientists have given us and somehow apply it to what we see, so with our mind’s eye we truly observe. Only then can we pop Deneb out of that “twinkle, twinkle little star” category and see it for what it really is.

Vital stats for Deneb (DEN-ebb), also known as Alpha Cygni:

• Brilliance: Magnitude 1.24; its luminosity is the equal of 54,400 Suns.
• Distance: 1,425 light years
• Spectral Types: A2 supergiant
• Position: 20h:41m:26s, +45°:16′:49″

Guide star reminder

Each month you’re encouraged to learn the new “guide” stars rising in the east about an hour after sunset. One reason for doing this is so you can then see how they move in the following months.

Deneb and the Northern Cross join several other guide stars and asterisms in the June sky. Again, if you have been reading these Posts for several months, be sure to find the stars, asterisms, and planets you found in earlier months. Early on a June evening these will include, from east to west, the following: Deneb, Vega, Arcturus, Spica, Saturn, Leo’s Rump (triangle),  the Sickle, Regulus, the Beehive, and in the northwest getting near the horizon, Pollux and Castor. You may also see Capella very near the horizon.

For more experienced observers looking to extend their knowledge of the skies this month, I highly recommend trying to track down two more asterism – the Northern Crown and the KeystoneOK, technically the Northern Crown (Corona Borealis) is a constellation. But I always apply the name to the handful of moderately bright stars that look like a half circle – a crown. As the chart below shows, these two asterisms are located on a line between Arcturus and Vega and they sort of divide that line into thirds. As with our guide stars and other asterisms, they will help you if you advance to finding other more interesting objects int he night sky with binoculars and telescope.

keystone-crown

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

The Crown itself can provide you with an interesting test of how dark your skies are since a couple hours after sunset on a June night it is well up in your eastern sky. It consists of a circlet of seven stars which can just fit within the field of view of wide-field binoculars – the example below shows an eight degree circle. It may be helpful to look at these stars with your binoculars, even if they don’t all fit in the same field of view at once. But to test how dark your skies are – and how transparent they are at the moment – wait until your vision is dark adapted, then see how many of these stars you can see. The numbers beside the stars are the magnitudes in decimals as given by Starry Nights software. However, I’ve followed the convention of not using a decimal point, since it might be mistaken for another faint star. So “41” means magnitude 4.1, for example. If you are seeing all seven stars you can be happy with your skies and these light-polluted times. In a truly dark location, however, this will be easy – but sadly such locations are rare these nights.

Read text above for explanation of how to use. Thenc lick on image to give you a larger view and luse the link below to download a printer friendly version. (Made from Starry Nights screen shot.)

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

Look North in June 2012! We have a special ‘North Sky Triangle’ this month!

Click to enlarge. (Prepared from Starry Nights Pro screenshot.)

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

Yep, that’s Deneb, the guide star that is the subject of our “Look East” Post for June, gracing our “Look North” chart as well. In fact, besides Polaris we have three key guide stars in our northern sky every June, each of which is noted for, among other things, just how far north it is.

Of the three, Capella may be the hardest to find, for it is very near the horizon in the northwest around sunset. But if you have a clear horizon in that direction, you should still pick it up, especially at the start of the month. More prominent, however, are Deneb and Vega. These stars play the key role in one of the best known sky triangles – the Summer Triangle, but that triangle becomes easier to see next month and it will be in the eastern sky. For June it is fun to link Deneb and Vega with Polaris in what we’ll call the North Sky Triangle – and the linkage has some special meaning.

We just happen to be lucky to be living in an era when we have a bright star near the North Celestial Pole – Polaris. There’s no such bright star near the South Celestial Pole, and in other eras there is none near the North Pole either. But in the distant past – and in the distant future – Deneb actually will be the bright star nearest the pole – not as near as Polaris, but still a good general guide to it.

gyroscope precessionThat’s because the Earth wobbles as it spins on its axis in much the same way as a spinning top does. So the axis of the Earth doesn’t always point to the same place. It slowly makes a great circle around the northern sky, taking roughly 25,000 year to complete. Right now our axis is pointing to within a degree of Polaris. Not precise, but good enough so it is a ready indicator of true north. A mere 18,000 years ago Deneb was within 7 degrees of the pole and will be again around the year 9800!

This wobbling of the pole is really kind of mind boggling. I look at Polaris now, and it’s a bit short of 42 degrees above my northern horizon. But in a mere 14,000 years, Polaris will be almost straight over my head, and guess what will be the pole star then? Not Deneb, but its brighter – in our skies – companion, Vega. Of course none of us is likely to witness that event, but it’s still food for thought and gives us a sense of the majestic rhythms and time frame of the heavens.

And speaking of that time frame, as I write this it occurs to me that 14,000 years really feels like a very long time from now – while the 10-million-year age of Deneb doesn’t seem that long – and it isn’t, astronomically speaking. I’m not talking now about what your mind tells you about those numbers. I’m talking about your emotional reaction to them. I wonder if it’s similar to mine? This isn’t idle speculation. It’s central to our appreciating what we are seeing. But I think 14,000 sounds like a long time because it’s a number that fits into our day-to-day experience. Huge, but we can easily imagine 1,000 of something.  So imagining 14,000 of something comes easily to us. But few of us have any experience with one million. It would take about 11 days to count one million seconds and no one in his right mind is about to try it. So when we speak of the 10-million-year age of Deneb, or the five-billion-year age of the Sun, the numbers lose their emotional impact because they don’t relate easily to our experience. But 14,000 – well, we know, in an emotional sense, just how long that is!

Venus transit June 5/6, 2012 – you don’t want to miss this one!

UPDATE – The transit went well for many folks throughout the world. For a personal observing report and a few pics I took, go here. For lots and lots of pictures , go here.  And for other transit observing experiences, go here.

 

Transit as seen from Westport, MA through a hole in the clouds.

Study this NASA map to see whether you are slated to see all of the transit of Venus on June 5/6, 2012, or part near the time of local sunrise, or part near local sunset. (Click image for larger version.)

On June 5/6, 2012, most of the world will have the chance to see all – or part – of a once-in-a-lifetime  event – a transit of Venus across the face of the Sun.  CAUTION: To view this, even with the naked eye, you must use proper protective filters. Binoculars and telescopes must be equipped with such filters and if not, used only to safely project an image of the event – not looked through.

That said, here are three shots simulating the event as seen from Westport, MA. From this East Coast location we will see only the first couple of hours of the transit, then our view will be interrupted by sunset. Notice that Venus will appear to enter near the “top” of the Sun, This location and path vary with your position on Earth. (At the end of this post are several links. The second of these links gives you specific information on the time and the path of Venus across the Sun as seen from your location. In the images below, the Sun is festooned with sunspots and other features. Such features may or may not be seen depending on what is happening on the Sun at the time of the transit and on the type of solar filter used to view the event.

Predicted path of Venus transit across the face of the sun as seen in astronomical telescope (flips image horizontally) from Westport, Ma. Click image for larger view. (Prepared from Starry Nights Pro screen shots.)

Did you find the images exciting? Probably not. But it should give you some idea of what to look for on June 5, and there is no substitute for seeing the real thing as it happens.  There’s also no substitute for understanding what it is you’re viewing and why – besides the fact that there won’t be another such transit for more than a century. No wonder so many people are very excited about seeing it. I’ve already seen one such transit – as have many others – for these events come in pairs fairly close together, and the last one was visible just eight years ago.  But I still will make every effort to see this one, and if the weather forecast says my local view is likely to be obscured by clouds, I’m ready to drive a couple of hundred miles to get to some place that’s clear.

Here, in a nutshell, is why I find this event so exciting:

  • There won’t be another chance to see a transit of  Venus until 2117.
  • On display will be the full majesty  – and magic – of our gravitationally-powered solar system where Venus – a body almost as large as the Earth – passes directly between us and the Sun at a distance of bout 30 million miles.
  • More than 200 years ago many scientists risked life and limb to travel to distant locations on the Earth in attempts to view the transit and accurately time it.  Such observations, they hoped, would unlock the secrets of the size of our solar system – secrets that despite their best efforts remained hidden. As noted in the New York Times, “Sea travel was so risky in 1761 that observers took separate ships to the same destination to increase the chances some of them would make it alive.”
This event is covered in so many different ways with wonderful graphics, wonderfully accessible details about when you can see it from your location, and terrific stories, that I would be trying to reinvent the wheel to repeat it all here.  Instead, I urge you to take advantage of the links below.

Some useful transit links

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