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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 January 2014 – King Jupiter, plus a trio of twins; Orion, man of the world; Betelgeuse, giant among giants!

January 2014 brings the usual host of bright and wondrous winter stars – and one star that isn’t  a star, but outshines them all in our skies – Jupiter. The “king of the planets” is absolutely dominant in the eastern sky this month, even though it gets a tad dimmer as the month goes on.  As we put some more distance between us and it, it drops from magnitude -2.7  at the start to -2.6 at the end of the month –  good luck on even being able to notice the change!  At magnitude 0 Capella is the brightest star we see, though in an hour or two, Sirius at Magnitude -1.5 will be up and come significantly closer to Jupiter’s brightness – but Jupiter will still dominate.

There are four new guidepost stars to meet this month and one new guidepost asterism, Orion. Orion is probably the best known figure in the heavens because it actually looks like a person and can be seen from most locations in the world since it’s centered on the celestial equator. That’s a lot for one month, but fun to think about on a dreary winter day and more fun to observe on a brilliant, winter evening. Here’s the chart for the eastern sky one hour after sunset for mid-northern latitudes. Remember, going out about 45 minutes to an hour  after sunset and looking east, you’ll see only the brightest stars as they come out. This makes it easier to identify and learn our guidepost stars. Our guidepost asterisms may not be as readily seen until a little later as the sky gets darker and more of the fainter stars come out.

The eastern sky as seen on a January evening about one hour after sunset. Click image for larger version. Use link below to download a printer-friendly, black and white version of this chart. (Chart is based on a screen shot, modified by me, of Starry Nights Pro software.)

The eastern sky as seen on a January 2014 evening about one hour after sunset. Click image for larger version. Use link below to download a printer-friendly, black and white version of this chart. (Chart is based on a screen shot, modified by me, of Starry Nights Pro software.)

Click here to download a black-on-white (printer-friendly) version of this chart

The January eastern sky – what to remember

 Castor – A trio of twins When you see Castor, think “twins” – a trio of twins. Well, in a sense there are really four pairs!

Castor is one of the Gemini Twins (Castor and Pollux), but in a small telescope we see it really is three stars, Castor A, Castor B, and Castor C - and though we can't see this in our telescopes, each of these stars is really a pair, making six stars in all!
When you spot Gemini in 2014 you will notice a brilliant Jupiter is right int he middle of it – this is shown on our “look east” chart at the beginning of this post. Click image for larger view.

But the fourth pair is just mythological – Castor is one of the “heavenly twins” of the constellation Gemini – the other twin being Pollux. This is nothing but a fanciful relationship, though, based on how the stars appear to us – and appeared to ancient cultures as well. But there is more, much more, to Castor. And, it’s what we don’t see that makes this bright star so fascinating. And seeing with your mind’s eye – your knowledge of what you are seeing – always enhances your experience under the night sky. So were you to look at Castor in a backyard telescope, you would see it has a twin – another bright star that appears quite close –  the two are known simply as Castor A and B. These two are related, orbiting one another about every 400 years.

But there’s more. Each of these two are twins! However, you can’t see this in a small telescope because in both cases the pairs of stars are extremely close to one another, orbiting one another in periods of less than 10 days. And as noted, each pair orbits the other pair in about 400 years.

But there’s more. Returning to that backyard telescope you may notice a third star, Castor C, quite a distance from the first two and significantly dimmer. This star is also part of the Castor family and it too has a twin that also is so close we can’t detect it without special instruments. In fact, Castor C consists of the closest pair of all, orbiting one another in less than a day! This pair, in turn, orbits the other four stars in the system once every 10,000 years or so. So when you look at Castor, remember that in classic mythology it has a twin, Pollux – and remember that what looks to you like a single bright star is really the combined light from six stars, all held together in one of the most complex star systems we know. (I wrote much more about the Castor system on the double-star blog. That post includes a scale model that puts Castor and company into perspective with the Earth and Sun. You’ll find it here. )

Vital stats (for just the brightest star in the Castor system):

  • Brilliance: Magnitude 1.58, the 23rd brightest star in our sky and the brightest second magnitude star. Absolute magnitude is 0.9. (Yes, we call a star “second magnitude” if it’s magnitude is between 1.5 and 2.5 – so you can see castor just slips into this category.)
  • Distance: 50 light years (not among the 200 nearest stars)
  • Spectral Type: A
  • Position: 07h:34m:36s, +31°:53′:18″
  • Compared to the Sun: Castor radiates 14 times as much energy as our Sun.

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Getting to know Pollux – the bigger, brighter twin

How Bayer saw the Gemini Twins in his 1603 atlas. (Image courtesy of Linda Hall library of Science, Engineering and Technology.)

Pollux should feel a little cheated because it’s the brightest star in the constellation of Gemini and usually the brightest star was given the designation “alpha”  by the early chart maker, Bayer. Not Pollux. It is designated “Beta Geminorum” and follows its slightly dimmer twin brother around the sky. But Pollux has its own way of standing out: It has a slight edge in brilliance in our skyit is a tad closer to us; and it is an orange giant. What’s more, in 2008 it was confirmed to have a planet orbiting it. As an orange giant, it has moved off the “main sequence,” and instead of fusing hydrogen into helium, as our Sun does, it is fusing helium into carbon and oxygen. It will eventually blow off a lot of its substance becoming a planetary nebula. It is currently about eight times the diameter of our Sun – that’s huge, but nowhere near as large as our next star, Betelgeuse. The planet that is circling Pollux is also large – “Jupiter class” – and was first detected in 1993, but not confirmed until 2008.

Vital stats:

  • Brilliance: Magnitude 1.14, the 17th brightest star in our sky. Absolute magnitude is 0.7 .
  • Distance: 34 light years (not among the 200 nearest stars)
  • Spectral Type: K
  • Position: 07h:45m:19s, +28°:01′:35″

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 Orion – A man for all to see

If you’re in the same general latitude as I am in Westport, MA, then you see Orion like this as it rises in the east on a January evening.

Orion – as seen when rising in mid-northern latitudes. (Click for larger image.)

What always sticks with me about Orion is how Robert Frost described him in his wonderful poem, “The Star Splitter.”

‘You know Orion always comes up sideways. Throwing a leg up over our fence of mountains, And rising on his hands, he looks in on me . . .

But if I lived in Sydney, Australia, I wouldn’t see it this way. What I would see is a man standing on his head!

Orion, as seen when rising in the east from Sydney, Australia. (Click image for larger version.)

The real point here is that these stars do look like a man, and they can be seen from deep into both the southern and northern hemispheres. What’s more, the three distinctive stars that form Orion’s belt also mark the approximate position of the celestial equator in your sky, a handy thing to know. Of course, if you’re in the southern hemisphere, the celestial equator appears to make an arc across your sky to your north. In the northern hemisphere it appears to make an east-west arc across the sky to the south. But in either case the belt stars of Orion will rise just about due east and set due west. How high they get in your sky is calculated simply by subtracting your latitude from 90. That is, if your latitude is 42 degrees, as mine is, then Orion’s belt will be, at its highest, about 48 degrees above the horizon when it passes due south. From Sydney, Australia, the stars in the belt will cross about 56 degrees above the horizon as they pass due north. And yes, if you live on the equator these stars will cross directly over head. Anyway you look at it, Orion is a man for all latitudes – well, almost. At the north pole you would only see his top half, and at the south pole, only his feet! Return to Menu

Betelgeuse – giant among giants – and Rigel’s pretty large as well!

When you look at the eastern sky early on a January evening, get this picture in your head!

Here’s what our eastern sky would look like on a January evening if Adebaran and Rigel, two genuine giants, were as near to us as our Sun. The Sun, to scale, is also shown. Betelgeuse is NOT shown to scale.

Yes, that’s Rigel represented in the illustration, not Betelgeuse. Classified as a red supergiant, Betelgeuse is one of the largest stars you can see – and certainly up there with the biggest of all stars – yet it doesn’t look any bigger in our sky than other stars because all stars, except the Sun, are so far away they appear only as a point source of light to our eyes. Last month we showed what Aldebaran would look like if it were in our sky and the same distance from us as the Sun, and this month we’ve added Rigel to the picture. But we can’t do a similar thing with Betelgeuse – it wouldn’t be in our sky – it’s so large we would be in it if it were located where our Sun is! What’s more, it’s hard to put a number to the size of Betelgeuse, not because it can’t be measured, but because it’s hard to decide exactly what you want to measure when you’re dealing with a ball of gas – especially one like Betelgeuse. Our Sun is a little easier case. While it does not have a surface, it does appear to us to have an edge that’s fairly easy to define – it’s the place where its gases are dense enough to be opaque to our vision. Exactly how we define the size of Betelgeuse is a bit more difficult. I rely on James B. Kaler as my stellar authority. I love his books, and in one, “The Hundred Greatest Stars,” he describes the size of Betelgeuse variably as:

  • 650 times that of the Sun, or 2.8 AU (Astronomical Units – an Astronomical Unit is the distance between the Earth and the Sun – roughly 93 million miles)
  • 800 times the diameter of the Sun, or about 4 AU
  • 1600 times the Sun – about 8 AU when measured by modern observation in ultraviolet light

And on his Web site, after opting for a figure of around 8-9 AU, he writes:

However, the star is surrounded by a huge complex pattern of nested dust and gas shells, the result of aeons of mass loss, that extends nearly 20,000 AU away (Betelgeuse so far having lost over a solar mass). That, an extended atmosphere, and the pulsations make it difficult to locate an actual “surface” to tell just how large the star actually is. Moreover, because of changes in gaseous transparency, the “size” of the star depends on the color of observation.

Betelgeuse has other problems. The pulsations he refers to are a sort of puffing up that occurs from time to time and changes both size and brightness significantly. Betelgeuse is usually thought of as about magnitude 0.55, but it can be as bright as 0.3, or as dim as 1.1. All this huffing and puffing will soon lead to an explosion, and Kaler says it will then be as bright as a crescent moon! But don’t hold your breath. “Soon” in astronomical terms means sometime in the next million years or so! Its distance, too, is uncertain, but 500 light years is a good ballpark figure. Let’s focus on that 8 AU size for a moment. When we build a scale model of our solar system and reduce the Sun to something about the size of a volleyball, the tiny speck of the Earth orbits at around 75 feet away. But at 8 AU Betelgeuse would be more like 600 feet in diameter. So pause for a moment as you look at Betelgeuse on a winter evening. Imagine yourself holding an 8-inch volleyball in one hand – our Sun – while you stand next to a red, raging, unstable monster ball that is 600 feet in diameter!

Vital stats:

  • Brilliance: Magnitude 0.3 – 1.1, the 10th brightest star in our sky (sometimes). Shines with the luminosity of about 90,000 Suns.
  • Distance: 570 light years
  • Spectral Type: M
  • Position: 05h:55m:10s, +7°:24′:25″

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Rigel – Blue and brilliant

Here we go again! Like Pollux, it looks like Rigel was short-changed having been designated the “Beta” star of the constellation Orion while dimmer Betelgeuse is the Alpha. Of course, Betelgeuse, being variable, may have been brighter when Johann Bayer made his designations in 1603. Bayer’s “system” is inconsistent, however, to say the least, so there’s no sense getting too worried about this. Like Betelgeuse, Rigel is a supergiant. It’s huge and it’s brilliant too – and since it is more distant (860 light years), it is intrinsically more brilliant than Betelgeuse. Jim Kaler writes: “Only about 10 million years old, Rigel should eventually expand to become a red supergiant very much like Betelgeuse is today, by which time it will be fusing helium into carbon and beyond in preparation for its eventual explosion as a supernova.” Rigel’s radius is 74 times that of the Sun, 0.34 Astronomical Units, nearly as big as the orbit of Mercury. Rigel is a challenging double star for amateurs with moderate-sized telescopes.

Vital stats:

  • Brilliance: Magnitude 0.12, the 7th brightest star in our sky. Shines with the luminosity of about 90,000 Suns.
  • Distance: 860 light years
  • Spectral Type: B
  • Position: 05h:55m:10s, +7°:24′:25″

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Look North in January 2014 – an “engagement ring” points the way to the true celestial pole

About one hour after sunset, look north and you should see a sky similar to the one shown in our chart – assuming you live at mid-northern latitudes. The height of Polaris, the North Star, will be the same as your latitude. Polaris stays put. Everything else appears to rotate about it, so our view of all else changes in the course of the evening – and from night to night. It’s a good idea to check the north sky every time you observe to get a sense of how things are changing and to orient yourself.

Click image for larger view. Chart derived from Starry Nights Pro screen shot.

Click here to download a black-on-white (printer-friendly) version of this chart.

Of course, Polaris – the “North Star” – is really not exactly north. It’s just a very good approximation of north. True north in the sky is the North Celestial Pole – a projection of the Earth’s north pole – and it would be too much to hope that a bright star would be parked on this exact spot. But if you have binoculars, point them at Polaris on a dark, clear night – one where there’s no interference from the Moon – and you should be able to see a neat little asterism called the “Engagement Ring,” a crude ring of 7th and 8th magnitude stars with Polaris forming the diamond. Look carefully and you’ll see this ring tells you the direction and distance to the true north celestial pole.

The North Celestial Pole is to the north of Polaris (arrow), and the Engagement Ring asterism extends to the south of it. You can use the diameter of the Engagement ring as a rough guide as to how far away – in the opposite direction – the North Celestial Pole is from Polaris. Field of view here is about 4.5 degrees as seen with 15X70 binoculars. Lower power binoculars will show a larger field. Click for larger image. (Prepared from Starry Nights Pro screen shot.)

Of course, Polaris, as with the other stars, appears to travel in a great circle around the pole. (I say “appears” because it is the Earth that is rotating, not the stars.) But, the relationship between the Engagement Ring, Polaris, and the true North Celestial Pole, remains the same, and south is defined as the direction away from the pole, north the direction towards the pole, and west is the direction the stars appear to rotate. For more on finding directions in the night sky, see this post. See the movie below, made with Starry Nights Pro software, to see how Polaris and the Engagement Ring rotate around the celestial north pole in the course of 24 hours.

High above Polaris the familiar “W” of Cassiopeia has completed its transition to an “M” as its stars roll around the pole. Off to the northwest near the horizon we see two bright guidepost stars, Vega and Deneb. To the northeast we have brilliant Capella.

The Big Dipper is easy to spot because it’s stars are bright. But folks frequently have trouble with the Little Dipper  and that’s no surprise because many of its stars are faint.  So don’t be alarmed if you can’t pick out most of the Little Dipper stars – four of them are fourth magnitude or fainter and besides, they are below Polaris this month, making them even more difficult to see since you are looking through more atmosphere when stars are low. I see them only when it has become fully dark – about 90 minutes after sunset – and when my eyes have had 10-20 minutes to dark adapt.

Look East In January 2013 – King Jupiter, plus a trio of twins; Orion, man of the world; Betelgeuse, giant among giants!

January 2013 brings the usual host of bright and wondrous winter stars – and one star that isn’t, but outshines them all – Jupiter. The “king of the planets” is absolutely dominant in the eastern sky this month, even though it gets a tad dimmer as the month goes on.  As we put some more distance between us and it, it drops from -2.7  at the start to -2.5 at the end of the month –  good luck on even being able to notice the change!  At magnitude 0 Capella is the brightest star we see, though in an hour or two, Sirius at Magnitude -1.5 will be up and come significantly closer to Jupiter’s brightness – but Jupiter will still dominate.

There are four new guidepost stars to meet this month and one new guidepost asterism, Orion. Orion is probably the best known figure in the heavens because it actually looks like a person and can be seen from most locations in the world since it’s centered on the celestial equator. That’s a lot for one month, but fun to think about on a dreary winter day and more fun to observe on a brilliant, winter evening. Here’s the chart for the eastern sky one hour after sunset for mid-northern latitudes. Remember, going out about 45 minutes to an hour  after sunset and looking east, you’ll see only the brightest stars as they come out. This makes it easier to identify and learn our guidepost stars. Our guidepost asterisms may not be as readily seen until a little later as the sky gets darker and more of the fainter stars come out.

lookeast
The eastern sky as seen on a January evening about one hour after sunset. Click image for larger version. Use link below to download a printer-friendly, black and white version of this chart. (Chart is based on a screen shot, modified by me, of Starry Nights Pro software.)

Click here to download a black-on-white (printer-friendly) version of this chart

The January eastern sky – what to remember

 Castor – A trio of twins When you see Castor, think “twins” – a trio of twins. Well, in a sense there are really four pairs!

Castor is one of the Gemini Twins (Castor and Pollux), but in a small telescope we see it really is three stars, Castor A, Castor B, and Castor C - and though we can't see this in our telescopes, each of these stars is really a pair, making six stars in all!
Click image for larger view.

But the fourth pair is just mythological – Castor is one of the “heavenly twins” of the constellation Gemini – the other twin being Pollux. This is nothing but a fanciful relationship, though, based on how the stars appear to us – and appeared to ancient cultures as well. But there is more, much more, to Castor. And, it’s what we don’t see that makes this bright star so fascinating. And seeing withy our mind’s eye – your knowledge of what you are seeing – always enhances your experience under the night sky. So were you to look at Castor in a backyard telescope, you would see it has a twin – another bright star that appears quite close –  the two are known simply as Castor A and B. These two are related, orbiting one another about every 400 years. But there’s more. Each of these two are twins! However, you can’t see this in a telescope because in both cases the pairs of stars are extremely close to one another, orbiting one another in periods of less than 10 days. And as noted, each pair orbits the other pair in about 400 years. But there’s more. Returning to that backyard telescope you may notice a third star, Castor C, quite a distance from the first two and significantly dimmer. This star is also part of the Castor family and it too has a twin that also is so close we can’t detect it without special instruments. In fact, Castor C consists of the closest pair of all, orbiting one another in less than a day! This pair, in turn, orbits the other four stars in the system once every 10,000 years or so. So when you look at Castor, remember that in classic mythology it has a twin, Pollux – and remember that what looks to you like a single bright star is really the combined light from six stars, all held together in one of the most complex star systems we know. (I wrote much more about the Castor system on the double-star blog. That post includes a scale model that puts Castor and company into perspective with the Earth and Sun. You’ll find it here. )

Vital stats (for just the brightest star in the Castor system):

  • Brilliance: Magnitude 1.58, the 23rd brightest star in our sky and the brightest second magnitude star. Absolute magnitude is 0.9. (Yes, we call a star “second magnitude” if it’s magnitude is between 1.5 and 2.5 – so you can see castor just slips into this category.)
  • Distance: 50 light years (not among the 200 nearest stars)
  • Spectral Type: A
  • Position: 07h:34m:36s, +31°:53′:18″
  • Compared to the Sun: Castor radiates 14 times as much energy as our Sun.

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Getting to know Pollux – the bigger, brighter twin

How Bayer saw the Gemini Twins in his 1603 atlas. (Image courtesy of Linda Hall library of Science, Engineering and Technology.)

Pollux should feel a little cheated because it’s the brightest star in the constellation of Gemini and usually the brightest star was given the designation “alpha”  by the early chart maker, Bayer. Not Pollux. It is designated “Beta Geminorum” and follows its slightly dimmer twin brother around the sky. But Pollux has its own way of standing out: It has a slight edge in brilliance in our skyit is a tad closer to us; and it is an orange giant. What’s more, in 2008 it was confirmed to have a planet orbiting it. As an orange giant, it has moved off the “main sequence,” and instead of fusing hydrogen into helium, as our Sun does, it is fusing helium into carbon and oxygen. It will eventually blow off a lot of its substance becoming a planetary nebula. It is currently about eight times the diameter of our Sun – that’s huge, but nowhere near as large as our next star, Betelgeuse. The planet circling Pollux is also large – “Jupiter class” – and was first detected in 1993, but not confirmed until 2008.

Vital stats:

  • Brilliance: Magnitude 1.14, the 17th brightest star in our sky. Absolute magnitude is 0.7 .
  • Distance: 34 light years (not among the 200 nearest stars)
  • Spectral Type: K
  • Position: 07h:45m:19s, +28°:01′:35″

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 Orion – A man for all to see

If you’re in the same general latitude as I am in Westport, MA, then you see Orion like this as it rises in the east on a January evening.

Orion – as seen when rising in mid-northern latitudes. (Click for larger image.)

What always sticks with me about Orion is how Robert Frost described him in his wonderful poem, “The Star Splitter.”

‘You know Orion always comes up sideways. Throwing a leg up over our fence of mountains, And rising on his hands, he looks in on me . . .

But if I lived in Sydney, Australia, I wouldn’t see it this way. What I would see is a man standing on his head!

Orion, as seen when rising in the east from Sydney, Australia. (Click image for larger version.)

The real point here is that these stars do look like a man, and they can be seen from deep into both the southern and northern hemispheres. What’s more, the three distinctive stars that form Orion’s belt also mark the approximate position of the celestial equator in your sky, a handy thing to know. Of course, if you’re in the southern hemisphere, the celestial equator appears to make an arc across your sky to your north. In the northern hemisphere it appears to make an east-west arc across the sky to the south. But in either case the belt stars of Orion will rise just about due east and set due west. How high they get in your sky is calculated simply by subtracting your latitude from 90. That is, if your latitude is 42 degrees, as mine is, then Orion’s belt will be, at its highest, about 48 degrees above the horizon when it passes due south. From Sydney, Australia, the stars in the belt will cross about 56 degrees above the horizon as they pass due north. And yes, if you live on the equator these stars will cross directly over head. Anyway you look at it, Orion is a man for all latitudes – well, almost. At the north pole you would only see his top half, and at the south pole, only his feet! Return to Menu

Betelgeuse – giant among giants – and Rigel’s pretty large as well!

When you look at the eastern sky early on a January evening, get this picture in your head!

Here’s what our eastern sky would look like on a January evening if Arcturus and Rigel, two genuine giants, were as near to us as our Sun. The Sun, to scale, is also shown. Betelgeuse is NOT show to scale.

Yes, that’s rigel represented inthe illustration, not Betelgeuse. Classified as a red supergiant, Betelgeuse is one of the largest stars you can see – and certainly up there with the biggest of all stars – yet it doesn’t look any bigger in our sky than other stars because all stars, except the Sun, are so far away they appear only as a point source of light to our eyes. Last month we showed what Aldebaran would look like if it were in our sky and the same distance from us as the Sun, and this month we’ve added Rigel to the picture. But we can’t do a similar thing with Betelgeuse – it wouldn’t be in our sky – it’s so large we would be in it if it were located where our Sun is! What’s more, it’s hard to put a number to the size of Betelgeuse, not because it can’t be measured, but because it’s hard to decide exactly what you want to measure when you’re dealing with a ball of gas – especially one like Betelgeuse. Our Sun is a little easier case. While it does not have a surface, it does appear to us to have an edge that’s fairly easy to define – it’s the place where its gases are dense enough to be opaque to our vision. Exactly how we define the size of Betelgeuse is a bit more difficult. I rely on James B. Kaler as my stellar authority. I love his books, and in one, “The Hundred Greatest Stars,” he describes the size of Betelgeuse variably as:

  • 650 times that of the Sun, or 2.8 AU (Astronomical Units – an Astronomical Unit is the distance between the Earth and the Sun – roughly 93 million miles)
  • 800 times the diameter of the Sun, or about 4 AU
  • 1600 times the Sun – about 8 AU when measured by modern observation in ultraviolet light

And on his Web site, after opting for a figure of around 8-9 AU, he writes:

However, the star is surrounded by a huge complex pattern of nested dust and gas shells, the result of aeons of mass loss, that extends nearly 20,000 AU away (Betelgeuse so far having lost over a solar mass). That, an extended atmosphere, and the pulsations make it difficult to locate an actual “surface” to tell just how large the star actually is. Moreover, because of changes in gaseous transparency, the “size” of the star depends on the color of observation.

Betelgeuse has other problems. The pulsations he refers to are a sort of puffing up that occurs from time to time and changes both size and brightness significantly. Betelgeuse is usually thought of as about magnitude 0.55, but it can be as bright as 0.3, or as dim as 1.1. All this huffing and puffing will soon lead to an explosion, and Kaler says it will then be as bright as a crescent moon! But don’t hold your breath. “Soon” in astronomical terms means sometime in the next million years or so! Its distance, too, is uncertain, but 500 light years is a good ballpark figure. Let’s focus on that 8 AU size for a moment. When we build a scale model of our solar system and reduce the Sun to something about the size of a volleyball, the tiny speck of the Earth orbits at around 75 feet away. But at 8 AU Betelgeuse would be more like 600 feet in diameter. So pause for a moment as you look at Betelgeuse on a winter evening. Imagine yourself holding an 8-inch volleyball in one hand – our Sun – while you stand next to a red, raging, unstable monster ball that is 600 feet in diameter!

Vital stats:

  • Brilliance: Magnitude 0.3 – 1.1, the 10th brightest star in our sky (sometimes). Shines with the luminosity of about 90,000 Suns.
  • Distance: 570 light years
  • Spectral Type: M
  • Position: 05h:55m:10s, +7°:24′:25″

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Rigel – Blue and brilliant

Here we go again! Like Pollux, it looks like Rigel was short-changed having been designated the “Beta” star of the constellation Orion while dimmer Betelgeuse is the Alpha. Of course, Betelgeuse, being variable, may have been brighter when Johann Bayer made his designations in 1603. Bayer’s “system” is inconsistent, however, to say the least, so there’s no sense getting too worried about this. Like Betelgeuse, Rigel is a supergiant. It’s huge and it’s brilliant too – and since it is more distant (860 light years), it is intrinsically more brilliant than Betelgeuse. Jim Kaler writes: “Only about 10 million years old, Rigel should eventually expand to become a red supergiant very much like Betelgeuse is today, by which time it will be fusing helium into carbon and beyond in preparation for its eventual explosion as a supernova.” Rigel’s radius is 74 times that of the Sun, 0.34 Astronomical Units, nearly as big as the orbit of Mercury. Rigel is a challenging double star for amateurs with moderate-sized telescopes.

Vital stats:

  • Brilliance: Magnitude 0.12, the 7th brightest star in our sky. Shines with the luminosity of about 90,000 Suns.
  • Distance: 860 light years
  • Spectral Type: B
  • Position: 05h:55m:10s, +7°:24′:25″

Return to Menu

Look North in January 2013 – an “engagement ring” points the way to the true celestial pole

About one hour after sunset, look north and you should see a sky similar to the one shown in our chart – assuming you live at mid-northern latitudes. The height of Polaris, the North Star, will be the same as your latitude. Polaris stays put. Everything else appears to rotate about it, so our view of all else changes in the course of the evening – and from night to night. It’s a good idea to check the north sky every time you observe to get a sense of how things are changing and to orient yourself.

Click image for larger view. Chart derived from Starry Nights Pro screen shot.

Click here to download a black-on-white (printer-friendly) version of this chart.

Of course, Polaris – the “North Star” – is really not exactly north. It’s just a very good approximation of north. True north in the sky is the North Celestial Pole – a projection of the Earth’s north pole – and it would be too much to hope that a bright star would be parked on this exact spot. But if you have binoculars, point them at Polaris on a dark, clear night – one where there’s no interference from the Moon – and you should be able to see a neat little asterism called the “Engagement Ring,” a crude ring of 7th and 8th magnitude stars with Polaris forming the diamond. Look carefully and you’ll see this ring tells you the direction and distance to the true north celestial pole.

The North Celestial Pole is to the north of Polaris (arrow), and the Engagement Ring asterism extends to the south of it. You can use the diameter of the Engagement ring as a rough guide as to how far away – in the opposite direction – the North Celestial Pole is from Polaris. Field of view here is about 4.5 degrees as seen with 15X70 binoculars. Lower power binoculars will show a larger field. Click for larger image. (Prepared from Starry Nights Pro screen shot.)

Of course, Polaris, as with the other stars, travels in a great circle around the pole. But, the relationship between the Engagement Ring, Polaris, and the true North Celestial Pole, remains the same, and south is defined as the direction away from the pole, north the direction towards the pole, and west is the direction the stars appear to rotate. For more on finding directions in the night sky, see this post. See the movie below, made with Starry Nights Pro software, to see how Polaris and the Engagement Ring rotate around the celestial north pole in the course of 24 hours.

High above Polaris the familiar “W” of Cassiopeia has completed its transition to an “M” as its stars roll around the pole. Off to the northwest near the horizon we see two bright guidepost stars, Vega and Deneb. To the northeast we have brilliant Capella.

The Big Dipper is easy to spot because it’s stars are bright. But folks frequently have trouble with the Little Dipper  and that’s no surprise because many of its stars are faint.  So don’t be alarmed if you can’t pick out most of the Little Dipper stars – four of them are fourth magnitude or fainter and besides, they are below Polaris this month, making them even more difficult to see since you are looking through more atmosphere when stars are low. I see them only when it has become fully dark – about 90 minutes after sunset – and when my eyes have had 10-20 minutes to dark adapt.

Quadrantids! This year – 2012 – it’s ‘our’ turn! (And mark the date for the coming Venus transit too!)

Really special astronomical events are rare – not only because they’re – well – rare, but because they are made rarer by having all the right conditions line up for your particular location, the final one being your personal schedule and, of course, the unpredictable weather.

In 2012, however, there will be at least two such events, both of which favor the US, though the first  ( the Quadrantids meteor shower) favors the East Coast a bit more than the West Coast (which is why I say it’s “our” turn since I live on the East Coast) – and the second, a transit of Venus in June, favors the West Coast a bit more than the East Coast.

Venus Transit  – See it in 2012, or wait for more than a century

In June, you say? Tell me about it later – say May.

And I will do so then in detail – but it’s not too early to mark your calendar now and thus keep it in your personal planning. So circle June 5, 2012. What is a transit of Venus? It’s a time when we can see Venus as a black dot cross the disc of the Sun – a time when Venus is actually between us and the Sun – and it happens rarely.  There have been just seven such transits since the invention of the telescope! And – of course – be careful! You will need special equipment to observe such a transit. Never look at the sun either with your naked eye or any  binocular or telescope unless it is one especially equipped just for looking at the Sun.  Such equipment isn’t expensive, though, and if you already have a telescope, would be a good investment to consider for this event and to regularly see  sunspots. I’m sure there will be several public observation points set up for those who don’t have such a telescope.

For me these are equally exciting events to witness, but the Venus transit carries the added bonus of happening in warm weather at a reasonable hour and has a whole bunch of science history associated with it – plus it isn’t going to happen again in our lifetime – unless in the coming years we find really wondrous ways to add to lifespan. Why historical?  Because scientists a couple hundred years ago lead dangerous and adventure-filled expeditions to observe a similar transit which was seen as a sort fo Rosetta Stone that would unlock all the important numbers of the solar system, giving us all planet distances and sizes.  At that time Kepler’s wonderful laws had given them the proportions of the Solar System – but they had no specific figures to plug in and no obvious way to measure any key one, such as the distance from the Earth to the Sun.  No way except this wonderful idea of observing a transit of Venus from two widely separated places on Earth – creating a baseline for a huge triangle –  and then using relatively simple math to derive the right numbers.

In Westport I will have only a couple hours to watch a portion of the transit before the sun sets, but that’s enough if the weather is clear. Here’s a simulation created using Starry Nights Pro software, of what I expect to see. It takes about a minute. Watch the top of the Sun for the entry of the dot that represents Venus.

Ok – enough – the date to reserve for Venus and the Sun is June 5. If you’re eager now for more details, go here.

Here come the Quadrantids – I mean right now!

As for the Quadrantids, I gave a head’s up on those last month because the date is right at the beginning of the year – the night of January 3-4 – which in this case really means the early morning of January 4.  Yes, I know for most locations it’s really cold at that time – this is mostly a northern hemisphere event – and morning isn’t everyone’s cup of tea – but as meteor showers go this can be really special.

The rarely seem Quandrantids (I’ve caught them once in over half a century and not at their best) are predicted to peak around 2-3 am EST on January 4.  (For the rest of the world that’s 7-8 hours Universal time January 4, 2012. Go here to convert Universal Time to your time.) This is a shower where the peak can be spectacular – 60-200 meteors an hour– but it lasts only a couple of hours. So it’s rare to have the peak come in the early morning hours for your section of the world when the showers radiant is also at or near its highest point and when the Moon offers little or no interference.

For me in Massachusetts a fairly bright 10-day-old Moon sets at 2:55 am – weather permitting – and it will be cold, I’m sure – I’ll start watching about 2 am and plan to stick at it until about 5 am. (Earlier when the moon is still up , it will be in the opposite corner of the sky to the shower’s radiant, so won’t offer much interference for those who would prefer to start around midnight.)

These links will take you to a couple of good examples of bright Quadrantids in previous years. This is a great individual meteor and ina serie sof images shows the trail it left.This leads to a nice series of photos of last year’s Quadrantids which peaked over Europe.

Where to look

So, if you love morning, if you love cold weather, and if you love gambling –  the Quadrantid meteor shower is for you!  Even if they don’t produce many, the ones that do show can be very bright so I wouldn’t discourage those in other parts of the Northern Hemisphere from looking – they’ll just see a lot fewer than those in a lucky location.

Quadrantid radiant point as it appears at 3 am January 4 from 42° N latitude. Click image for larger version. (Chart is screen shot from Starry Night Pro.)

What’s more, the Quadrantids are known for producing fireballs – the very brightest of meteors – ones that can even outshine Venus!

So how will you know a Quadrantid when you see it. After all, on any given night there can be several random meteors. The key is to note its direction. If you’re in North America, Quadrantids will generally come from the north northwest in the early evening, from north about the time of the shower’s peak, and from the north northeast later. As with so many good showers, the time to see the most Quadrantids will be in the early morning – essentially from about 1 am January 4, 2011, on.

This chart, taken from the American Meteor Society page here, is an excellent depiction of Quadrantids (the dark, straight lines) and for me drive homes the point that while the radiant is in the Northeast, the meteors can appear anywhere in the sky – afterall, that’s what the word “radiant” sure implies.

Click image for larger version. (From the American Meteor Society website.)

Here’s good advice from the American Meteor Society on this year’s Quandrantids:

Maximum rates for this shower are difficult to predict. Most observers across North America can expect to see a maximum of 40 Quadrantids per hour on the morning of January 4th. If you are lucky it could be several times higher.

A good observing strategy for observers in North America would be to begin observations near midnight. This will allow eastern observers to catch the maximum should it arrive a bit early. Pacific observers may want to start around 2300 (11pm) on the 3rd. While rates would most likely be low for western observers, any Quadrantid activity would be in the form of earth-grazing meteors, which are long-lasting and produce long trails as they graze the upper atmosphere. Face anywhere in the north to east quadrant, with your field of view half way up in the sky. This will keep the moon at your back. Quadrantid meteors will shoot upward from the northeastern horizon until it [the radiant] gains sufficient height when it can produce meteor shooting in all directions.

Observers located in the northern hemisphere other than North American can expect to see approximately 25 Quadrantids per hour between moon set and dawn. Due to the high northern declination (celestial latitude) of the Quadrantid radiant, observers in the southern hemisphere will see very few Quadrantids. As seen from the southern hemisphere the Quadrantid radiant lies low in the north, if it clears the horizon at all before dawn.

 And why are they called Quadrantids? Other meteor showers are named for the constellation in which their radiant is located – the Perseids in Perseus, the Geminids in Gemini, etc. But who knows of a constellation named Quadran…??? Well, think Pluto! There once was a constellation named Quadrans Muralis, and that’s where they appear to radiate from. But in 1932 the International Astronomical Union cleaned up sky maps, threw out some constellations, and agreed upon official boundaries for the remaining 88. Like Pluto’s full planet status, the Quadrans Muralis is no more.

Its name is Latin for is mural quadrant and refers to an instrument that was very important to astronomy before the time of telescopes. Check out this description.

And then there’s Jupiter, Mars, Saturn – and of course, Venus!

We’ve a wonderful planet show going on this month with the actors changing  positions on the celestial stage, but Jupiter still dominant with Venus on the rise and Mars and Saturn beginning to arrive early enough to catch the night owls and give us early morning-types a real treat.

Jupiter is still high in the south and in evening twilight will rival Venus in brightness. Well, not really, but it will appear that way because Venus, beaming in the western sky, will occupy a section of sky with a much brighter background.  Venus is actually about magnitude -4 and Jupiter  magnitude -2.6. Venus will get higher in the western sky each night – Jupiter will move slowly towards it.

Mars  and Saturn are still mainly morning objects, but that is changing rapidly. Mars comes up in the evening in January – but isn’t well placed for observing until later. As the Earth overtakes Mars in its orbit the two draw closer which for the naked eye observer means Mars gets a lot brighter (doubles in the course of the month) and for the telescope observer its disc gets significantly larger making it easier to detect some features.

Saturn rises close to midnight, but doesn’t become well placed for observing until the early morning. It still makes a spectacular naked eye sight, however, looking like a natural companion to the bright guidepost star, Spica.  In fact, when I first saw this pair a few weeks ago  my initial reaction was “what the heck are the Gemni twins , Castor and Pollux, doing low in the southeast!?” But while the brightness and spacing reminded me of Castor and Pollux, I knew it was the wrong section of sky and I also could see that one – Saturn – gave off a yellowish hue while Spica is the bluest of blues.

Finding Saturn and Spica is easy – you follow the arc of the Big Dipper’s handle and that will lead you first to another bright star, Arcturus and then t0 Saturn and Spica. Observing Saturn with a telescope is now a real treat because the rings are tipped to give us an excellent view of them – something that hasn’t been the case for the past few years.

Looking behind the scenes – what the actors are really doing

Watching the planet show is like watching a play where the real action is hidden from us and what we see gives us an impression of bright stars which wander – “planet” means “wanderer” – among the “fixed” and generally dimmer stars. But lets lift up the curtain and go back stage.

The following series of images – click on each to get a much larger version – focuses on the motions of Venus between now and the June 5th transit of the Sun.  The larger image shows the western sky about 30 minutes after sunset at the start of each month. It is a screen shot from SkySafari Pro software. I have added to it a screen shot that uses the online Orrery found here to show the actual position of the inner planets as seen from a vantage point above the Sun. I love this sort of thing. It’s simply cool to stand outside, see a planet, and really be able to visualize where you are and where it is. Afterall, astronomy is largely a game of such mental gymnastics and understanding these things makes your observing experience more meaningful.

So if you study the changing Orrery view you can see how the motions of the planet all relate to what we actually see in the sky.  Draw an imaginary line from the Earth through the Sun and that line marks the difference between evening and morning. From our vantage point on earth as we rotate and approach a view of the Sun each morning we see the planets that are in our morning sky – and once we pass the Sun  – as night falls – what we see is in our evening sky. That’s why I marked an “evening” and “morning” side for each Orrery view.

With that in mind, here are the images leading up to the Venus transit for the first of each month, starting with January 1, 2012. (Be sure to click on each image for the larger version.)

Looking west,  half an hour after Sunset, January 1, 2012

Looking west, half an hour after Sunset, January 1, 2012 Click image for larger version. Prepared from SkySafari Pro screen shot.

Looking west,  half an hour after Sunset, February 1, 2012

Looking west, half an hour after Sunset, February 1, 2012 Click image for larger version. Prepared from SkySafari Pro screen shot.

Looking west,  half an hour after Sunset, March 1, 2012

Looking west, half an hour after Sunset, March 1, 2012 Click image for larger version. Prepared from SkySafari Pro screen shot.

Looking west,  half an hour after Sunset, April 1, 2012

Looking west, half an hour after Sunset, April 1, 2012 Click image for larger version. Prepared from SkySafari Pro screen shot.

Looking west,  half an hour after Sunset, May 1, 2012

Looking west, half an hour after Sunset, May 1, 2012 Click image for larger version. Prepared from SkySafari Pro screen shot.

Looking west,  at Sunset, June 1, 2012

Looking west, at Sunset, June 1, 2012 Click image for larger version. Prepared from SkySafari Pro screen shot.

Look East In January 2012 – a trio of twins; Orion, man of the world; Betelgeuse, giant among giants!

January brings a host of bright and wondrous winter stars. There are four new guidepost stars to meet this month and one new guidepost asterism, Orion. Orion is probably the best known figure in the heavens because it actually looks like a person and can be seen from most locations in the world since it’s centered on the celestial equator. That’s a lot for one month, but fun to think about on a dreary winter day and more fun to observe on a brilliant, winter evening.

Here’s the chart for the eastern sky one hour after sunset for mid-northern latitudes. Remember, going out about 45 minutes after sunset and looking east, you’ll see only the brightest stars as they come out. This makes it easier to identify and learn our guidepost stars. Our guidepost asterisms may not be as readily seen until a little later as the sky gets darker and more of the fainter stars come out.

The eastern sky as seen on a January evening about one hour after sunset. Click image for larger version. Brilliant Jupiter is just off the chart, above and to the right, but still dominant in the early evening eastern sky in 2012. Use link below to download a printer-friendly, black and white version of this chart. (Chart is based on a screen shot, modified by me, of Starry Nights Pro software.)

Click here to download a black-on-white (printer-friendly) version of this chart.

The January eastern sky – what to remember

 Castor – A trio of twins

When you see Castor, think “twins” – a trio of twins. Well, in a sense there are really four pairs!

Castor is one of the Gemini Twins (Castor and Pollux), but in a small telescope we see it really is three stars, Castor A, Castor B, and Castor C - and though we can't see this in our telescopes, each of these stars is really a pair, making six stars in all!
Click image for larger view.

But the fourth pair is just mythological – Castor is one of the “heavenly twins” of the constellation Gemini – the other twin being Pollux. This is nothing but a fanciful relationship, though, based on how the stars appear to us – and appeared to ancient cultures as well. But there is more, much more, to Castor. And, it’s what we don’t see that makes this bright star so fascinating. And seeing withy our mind’s eye – your knowledge of what you are seeing – always enhances your experience under the night sky.

So were you to look at Castor in a backyard telescope, you would see it has a twin – another bright star that appears quite close –  the two are known simply as Castor A and B. These two are related, orbiting one another about every 400 years. But there’s more. Each of these two are twins! However, you can’t see this in a telescope because in both cases the pairs of stars are extremely close to one another, orbiting one another in periods of less than 10 days. And as noted, each pair orbits the other pair in about 400 years. But there’s more.

Returning to that backyard telescope you may notice a third star, Castor C, quite a distance from the first two and significantly dimmer. This star is also part of the Castor family and it too has a twin that also is so close we can’t detect it without special instruments. In fact, Castor C consists of the closest pair of all, orbiting one another in less than a day! This pair, in turn, orbits the other four stars in the system once every 10,000 years or so.

So when you look at Castor, remember that in classic mythology it has a twin, Pollux – and remember that what looks to you like a single bright star is really the combined light from six stars, all held together in one of the most complex star systems we know. (I wrote much more about the Castor system on the double-star blog. That post includes a scale model that puts Castor and company into perspective with the Earth and Sun. You’ll find it here. )

Vital stats (for just the brightest star in the Castor system):

  • Brilliance: Magnitude 1.58, the 23rd brightest star in our sky and the brightest second magnitude star. Absolute magnitude is 0.9. (Yes, we call a star “second magnitude” if it’s magnitude is between 1.5 and 2.5 – so you can see castor just slips into this category.)
  • Distance: 50 light years (not among the 200 nearest stars)
  • Spectral Type: A
  • Position: 07h:34m:36s, +31°:53′:18″
  • Compared to the Sun: Castor radiates 14 times as much energy as our Sun.

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Getting to know Pollux – the bigger, brighter twin

How Bayer saw the Gemini Twins in his 1603 atlas. (Image courtesy of Linda Hall library of Science, Engineering and Technology.)

Pollux should feel a little cheated because it’s the brightest star in the constellation of Gemini and usually the brightest star was given the designation “alpha”  by the early chart maker, Bayer. Not Pollux. It is designated “Beta Geminorum” and follows its slightly dimmer twin brother around the sky. But Pollux has its own way of standing out: It has a slight edge in brilliance in our skyit is a tad closer to us; and it is an orange giant. What’s more, in 2008 it was confirmed to have a planet orbiting it.

As an orange giant, it has moved off the “main sequence,” and instead of fusing hydrogen into helium, as our Sun does, it is fusing helium into carbon and oxygen. It will eventually blow off a lot of its substance becoming a planetary nebula. It is currently about eight times the diameter of our Sun – that’s huge, but nowhere near as large as our next star, Betelgeuse. The planet circling Pollux is also large – “Jupiter class” – and was first detected in 1993, but not confirmed until 2008.

Vital stats:

  • Brilliance: Magnitude 1.14, the 17th brightest star in our sky. Absolute magnitude is 0.7 .
  • Distance: 34 light years (not among the 200 nearest stars)
  • Spectral Type: K
  • Position: 07h:45m:19s, +28°:01′:35″

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 Orion – A man for all to see

If you’re in the same general latitude as I am in Westport, MA, then you see Orion like this as it rises in the east on a January evening.

Orion – as seen when rising in mid-northern latitudes. (Click for larger image.)

What always sticks with me about Orion is how Robert Frost described him in his wonderful poem, “The Star Splitter.”

‘You know Orion always comes up sideways.

Throwing a leg up over our fence of mountains,

And rising on his hands, he looks in on me . . .

But if I lived in Sydney, Australia, I wouldn’t see it this way. What I would see is a man standing on his head!

Orion, as seen when rising in the east from Sydney, Australia. (Click image for larger version.)

The real point here is that these stars do look like a man, and they can be seen from deep into both the southern and northern hemispheres. What’s more, the three distinctive stars that form Orion’s belt also mark the approximate position of the celestial equator in your sky, a handy thing to know. Of course, if you’re in the southern hemisphere, the celestial equator appears to make an arc across your sky to your north. In the northern hemisphere it appears to make an east-west arc across the sky to the south.

But in either case the belt stars of Orion will rise just about due east and set due west. How high they get in your sky is calculated simply by subtracting your latitude from 90. That is, if your latitude is 42 degrees, as mine is, then Orion’s belt will be, at its highest, about 48 degrees above the horizon when it passes due south. From Sydney, Australia, the stars in the belt will cross about 56 degrees above the horizon as they pass due north. And yes, if you live on the equator these stars will cross directly over head. Anyway you look at it, Orion is a man for all latitudes – well, almost. At the north pole you would only see his top half, and at the south pole, only his feet! Return to Menu

Betelgeuse – giant among giants – and Rigel’s pretty large as well!

When you look at the eastern sky early on a January evening, get this picture in your head!

Here’s what our eastern sky would look like on a January evening if Arcturus and Rigel, two genuine giants, were as near to us as our Sun. The Sun, to scale, is also shown. Betelgeuse is NOT show to scale.

Yes, that’s rigel represented inthe illustration, not Betelgeuse. Classified as a red supergiant, Betelgeuse is one of the largest stars you can see – and certainly up there with the biggest of all stars – yet it doesn’t look any bigger in our sky than other stars because all stars, except the Sun, are so far away they appear only as a point source of light to our eyes. Last month we showed what Aldebaran would look like if it were in our sky and the same distance from us as the Sun, and this month we’ve added Rigel to the picture. But we can’t do a similar thing with Betelgeuse – it wouldn’t be in our sky – it’s so large we would be in it if it were located where our Sun is!

What’s more, it’s hard to put a number to the size of Betelgeuse, not because it can’t be measured, but because it’s hard to decide exactly what you want to measure when you’re dealing with a ball of gas – especially one like Betelgeuse. Our Sun is a little easier case. While it does not have a surface, it does appear to us to have an edge that’s fairly easy to define – it’s the place where its gases are dense enough to be opaque to our vision.

Exactly how we define the size of Betelgeuse is a bit more difficult. I rely on James B. Kaler as my stellar authority. I love his books, and in one, “The Hundred Greatest Stars,” he describes the size of Betelgeuse variably as:

  • 650 times that of the Sun, or 2.8 AU (Astronomical Units – an Astronomical Unit is the distance between the Earth and the Sun – roughly 93 million miles)
  • 800 times the diameter of the Sun, or about 4 AU
  • 1600 times the Sun – about 8 AU when measured by modern observation in ultraviolet light

And on his Web site, after opting for a figure of around 8-9 AU, he writes:

However, the star is surrounded by a huge complex pattern of nested dust and gas shells, the result of aeons of mass loss, that extends nearly 20,000 AU away (Betelgeuse so far having lost over a solar mass). That, an extended atmosphere, and the pulsations make it difficult to locate an actual “surface” to tell just how large the star actually is. Moreover, because of changes in gaseous transparency, the “size” of the star depends on the color of observation.

Betelgeuse has other problems. The pulsations he refers to are a sort of puffing up that occurs from time to time and changes both size and brightness significantly. Betelgeuse is usually thought of as about magnitude 0.55, but it can be as bright as 0.3, or as dim as 1.1. All this huffing and puffing will soon lead to an explosion, and Kaler says it will then be as bright as a crescent moon! But don’t hold your breath. “Soon” in astronomical terms means sometime in the next million years or so! Its distance, too, is uncertain, but 500 light years is a good ballpark figure.

Let’s focus on that 8 AU size for a moment. When we build a scale model of our solar system and reduce the Sun to something about the size of a volleyball, the tiny speck of the Earth orbits at around 75 feet away. But at 8 AU Betelgeuse would be more like 600 feet in diameter. So pause for a moment as you look at Betelgeuse on a winter evening. Imagine yourself holding an 8-inch volleyball in one hand – our Sun – while you stand next to a red, raging, unstable monster ball that is 600 feet in diameter!

Vital stats:

  • Brilliance: Magnitude 0.3 – 1.1, the 10th brightest star in our sky (sometimes). Shines with the luminosity of about 90,000 Suns.
  • Distance: 570 light years
  • Spectral Type: M
  • Position: 05h:55m:10s, +7°:24′:25″

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Rigel – Blue and brilliant

Here we go again! Like Pollux, it looks like Rigel was short-changed having been designated the “Beta” star of the constellation Orion while dimmer Betelgeuse is the Alpha. Of course, Betelgeuse, being variable, may have been brighter when Johann Bayer made his designations in 1603. Bayer’s “system” is inconsistent, however, to say the least, so there’s no sense getting too worried about this.

Like Betelgeuse, Rigel is a supergiant. It’s huge and it’s brilliant too – and since it is more distant (860 light years), it is intrinsically more brilliant than Betelgeuse. Jim Kaler writes: “Only about 10 million years old, Rigel should eventually expand to become a red supergiant very much like Betelgeuse is today, by which time it will be fusing helium into carbon and beyond in preparation for its eventual explosion as a supernova.”

Rigel’s radius is 74 times that of the Sun, 0.34 Astronomical Units, nearly as big as the orbit of Mercury.

Rigel is a challenging double star for amateurs with moderate-sized telescopes.

Vital stats:

  • Brilliance: Magnitude 0.12, the 7th brightest star in our sky. Shines with the luminosity of about 90,000 Suns.
  • Distance: 860 light years
  • Spectral Type: B
  • Position: 05h:55m:10s, +7°:24′:25″

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Look North in January 2012 – an “engagement ring” points the way to the true celestial pole

About one hour after sunset, look north and you should see a sky similar to the one shown in our chart – assuming you live at mid-northern latitudes. The height of Polaris, the North Star, will be the same as your latitude. Polaris stays put. Everything else appears to rotate about it, so our view of all else changes in the course of the evening – and from night to night. It’s a good idea to check the north sky every time you observe to get a sense of how things are changing and to orient yourself.

Click image for larger view. Chart derived from Starry Nights Pro screen shot.

Click here to download a black-on-white (printer-friendly) version of this chart.

Of course, Polaris – the “North Star” – is really not exactly north. It’s just a very good approximation of north. True north in the sky is the North Celestial Pole – a projection of the Earth’s north pole – and it would be too much to hope that a bright star would be parked on this exact spot. But if you have binoculars, point them at Polaris on a dark, clear night – one where there’s no interference from the Moon – and you should be able to see a neat little asterism called the “Engagement Ring,” a crude ring of 7th and 8th magnitude stars with Polaris forming the diamond. Look carefully and you’ll see this ring tells you the direction and distance to the true north celestial pole.

The North Celestial Pole is to the north of Polaris (arrow), and the Engagement Ring asterism extends to the south of it. You can use the diameter of the Engagement ring as a rough guide as to how far away – in the opposite direction – the North Celestial Pole is from Polaris. Field of view here is about 4.5 degrees as seen with 15X70 binoculars. Lower power binoculars will show a larger field. Click for larger image. (Prepared from Starry Nights Pro screen shot.)

Of course, Polaris, as with the other stars, travels in a great circle around the pole. But, the relationship between the Engagement Ring, Polaris, and the true North Celestial Pole, remains the same, and south is defined as the direction away from the pole, north the direction towards the pole, and west is the direction the stars appear to rotate. For more on finding directions in the night sky, see this post. See the movie below, made with Starry Nights Pro software, to see how Polaris and the Engagement Ring rotate around the celestial north pole in the course of 24 hours.

High above Polaris the familiar “W” of Cassiopeia has completed its transition to an “M” as its stars roll around the pole. Off to the northwest near the horizon we see two bright guidepost stars, Vega and Deneb. To the northeast we have brilliant Capella.

The Big Dipper is easy to spot because it’s stars are bright. But folks frequently have trouble with the Little Dipper  and that’s no surprise because many of its stars are faint.  So don’t be alarmed if you can’t pick out most of the Little Dipper stars – four of them are fourth magnitude or fainter and besides, they are below Polaris this month, making them even more difficult to see since you are looking through more atmosphere when stars are low. I see them only when it has become fully dark – about 90 minutes after sunset – and when my eyes have had 10-20 minutes to dark adapt.

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