Events January 2011: Sunrise planets, a Jupiter flyby of Uranus, and a maybe spectacular meteor shower

Three bright planets, joined by a sliver of a Moon, welcome in the New Year just before sunrise. Click image for larger view.(Some labels added to Stellarium screen shot.)

 

Quadrantid update January 4, 2011: The Quadrantids should be past their peak now, but will continue to be active through January 10. There are also several very minor showers producing some meteors this week. For an excellent meteor forecast go here. Frederik Broms captured a nice shot of a Quadrantid scooting across a beautiful backdrop of  aurora in Norway. I was observing this morning and took  about a 30-minute break to sit down,  enjoy a cup of tea,  and take in  a handful of Quandrnatids – eight to be exact – all quite bright fast, and short. The first was the brightest – about magnitude minus 2 – and seemed to be heading right towards me out of the northeast, passing below the head of Draco.   I observed other objects for a total of two hours this morning, pausing occasionally to look for Quadrantids, but saw none that way.  (More details about the Quadrantids near the end of the original post.)

And in the real world – this update as of January 1, 2011:

Clouds enhanced the sky show on January 1, revealing firstone, adn then another, of the three planets and crescent Moon. (Click image for larger view.) Picture was taken in morning twilight from Westport, MA.

For more pictures and information on what was visible from Westport, go here.

Back to the original post:

Count them! Three bright planets, plus a very thin crescent Moon will ring in 2011 just before sunrise and will mark a year that gets off with some celestial fireworks in the first week, then calms down a bit. And it’s not just a morning scene – the evening sky also holds a special treat. Jupiter and its dancing moons will continue to fascinate observers, and if you want an easy shot at Uranus, early January is as easy as it gets – until 2038!

But back to the morning: Pre-dawn viewing is fun at this time of year – at least in the northern hemisphere – for “pre-dawn” doesn’t mean getting up ridiculously early. For example, at my location in Westport, MA, the scene pictured above is best seen about 6:25 am, a very reasonable time as early observing goes. And fireworks? Well, that’s a maybe, but they could be provided by the very elusive annual Quadrantid meteor shower which can be spectacular if you’re lucky – I’m usually not, but hope blooms eternal. So here’s the basic lineup to open 2011:

• Sunrise planets
• Jupiter flyby for Uranus
• Quadrantid meteors

Sunrise planets

While the precise details of the scene at the top of this post are just for January 1, most of what you see in the scene will be there all month. The Moon, of course, is only in the scene at the start of the month – in fact, that show really starts near the end of December as the following charts will show. But if you get clouded out in the early days, don’t give up. Mercury is well placed in the morning sky from the start of the month through about January 20. It reaches its highest point in the first week when it is nearly nine degrees above the horizon about 45 minutes before sunrise. By the 18th it is about five degrees above the horizon 45 minutes before sunrise, so it’s getting pretty difficult to spot. Venus and Saturn are there all month – and Venus is nothing short of dazzling, dominating the scene as it shines at about magnitude -4.4. So as you check out the changing position of the Moon in these early charts, keep in mind that most mornings this month the pre-dawn sky to the southeast will hold a treasure of planets.

Please note: Stellarium pictures the Moon as a bright circle. In truth, on these dates it will be a crescent that gets smaller and more difficult to see as it gets lower in the sky each morning.

Three bright planets, joined by a crescent Moon, just before sunrise on December 30, 2010. Click image for larger view. (Some labels added to Stellarium screen shot.)

Three bright planets, joined by a crescent Moon, just before sunrise on December 31, 2010. Click image for larger view. (Some labels added to Stellarium screen shot.)

Three bright planets, joined by a slither of a crescent Moon - it will be difficult to see unless you have a very clear horizon - just before sunrise on January 2, 2011. (January 1 view is at the top of this post.) Click image for larger view. (Some labels added to Stellarium screen shot.)

How to find the morning planets

You won’t have any difficulty picking out Venus – there’s simply nothing brighter in the sky except the Moon and Sun. Start about an hour before sunrise and simply look to the southeast. It will be roughly 20 degrees – two fists – above the horizon, its exact height depending on when you start looking for it.

Mercury is more of a challenge. You want to look soon enough to catch it against as dark a sky as possible. But the later you look, the higher in the sky it will get. Higher is better because you’re looking through less atmosphere, so it will appear brighter. Problem is, as it gets higher, so does the pre-dawn sky, so the still-hidden Sun is washing out the sky behind Mercury, making it more difficult to see. My strategy is to start looking about an hour before local sunrise. I expect to pick up Mercury – assuming I have a clear eastern horizon – about 45-30 minutes before sunrise. If it gets much later than that, then Mercury is likely to get lost in the brightening dawn sky. Using binoculars helps, but is not necessary. With clear skies, you should see it with your naked eye. But its nearness to the Sun always makes spotting Mercury a bit challenging and not all appearances of Mercury are equal. Sometimes it takes a very low trajectory above the horizon. This month’s is a good appearance. After mid-month it gets lower and lower until it’s lost in the Sun’s glare by the last week of the month.

Saturn is easy, and you can see it much earlier. At the start of the month it rises just after midnight. This means that by an hour or two before sunrise it is well up in the south south east, about 10 degrees (one fist) above and to the right of Spica, and around 40 degrees (four fists) above the horizon. It’s easy to confuse with Spica, however, since they are nearly the same brightness – but Spica is below it, and has a bluish tint and will tend to twinkle more. Saturn has a steady, yellowish glow. You can’t see its fabled rings with binoculars, but this year it will be a delight to those using small telescopes. It’s now tilted so its rings are easily visible in the telescope -something that hasn’t been so for the past couple of years when the rings have been close to – or at – edge on from our perspective.

Jupiter flyby of Uranus

First, don’t forget that Jupiter is fun in itself with its constantly changing configuration of four Galilean moons. These are a challenge with binoculars, a joy in small telescopes, and you can learn more about them in this October post. (Just remember that the sky position in that post is for October – now Jupiter is in the southwest visible about 45 minutes after sunset.) Also, to find out which moons are where at any given moment, go here. But Jupiter serves another task this month – it guides us to Uranus – the “Georgian Star.” This is significant because it makes Uranus, which is just barely of naked eye visibility under the best of conditions, very easy for anyone to pick out using binoculars. All you have to do is find Jupiter, and since it’s the brightest “star” in the southwestern sky on January evenings this year, it’s hard to miss. Point your binoculars at it and use the charts here to identify Uranus. The charts show Jupiter’s eastward movement against the background of stars from December 25, 2010, to January 14, 2011, as it does a “fly by” of Uranus. Uranus – much more distant and orbiting much slower, hardly appears to move during this time.

This is the third such close encounter in a year, but don’t hold your breath for the next one – it’s 27 years from now!

Though at magnitude 5.9, Uranus should be visible to the naked eye if you have really dark skies and good eyes, but it will be far, far easier to see in binoculars. The circle shows a 5-degree field, typical of what you will see in binoculars, though many will show even more. The two identified stars are 20 Piscium and 24 Piscium. They are magnitude 5.5 and 5.9 respectively. They make finding Uranus even easier, for it is shining at magnitude 5.9 as well – so the three make a nice triangle of “stars” of just about equal brightness. Uranus may show a slightly blue tint. At their closest, around January 4, Uranus is less than a degree from Jupiter.

Uranus and Jupiter in the early evening of December 25, 2010. Click image for larger view. (Prepared from Starry Nights Pro screen shot.)

Uranus and Jupiter in the early evening of January 4, 2010. Click image for larger view. (Prepared from Starry Nights Pro screen shot.)

Uranus and Jupiter in the early evening of January 14, 2011. Click image for larger view. (Prepared from Starry Nights Pro screen shot.)

I like to call Uranus the “Georgian Star” even though folks seldom know what I’m talking about! The point is, “Georgian Star” beats the heck out of the adolescent giggles you get if you’re not very careful about how you pronounce Uranus – and “Georgian Star” was the name it went by in England when first discovered. For more on the Georgian Star see the Spetember post here.

Quadrantids – the most elusive of meteor showers

If you love morning, if you love cold weather, and if you love gambling – then the Quadrantid meteor shower is for you! For me – I’m usually up early and out early observing if it’s clear, so in early January I remind myself to look north for a while to see if I can spot some Quadrantid meteors. This January that advice is particularly good on January 3rd and 4th for North American observers – and especially good on January 3rd if you happen to live in Europe. Why? The Quadrantids can produce as many as 100 meteors an hour, but everything has to be just right for that to happen. But even if they don’t produce many, the ones that do show can be spectacular.

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

For one thing, while Quadrantid meteors may appear essentially any time during the first 10 days of the year, the Quadrantids have an incredibly sharp peak (just 2-4 hours long) that according to the American Meteor Society will happen near 0100 Universal Time on January 4th. (Go here to convert Universal Time to your time.) This is 8 pm EST, and there will be no interference from the Moon, but before you East Coast folks get too excited, the radiant point (see chart above) for the Quadrantids is very low in the northwest at that time of night. The American Meteor Society (AMS) says this about observing when the Quadrantid radiant is low:

Rates would only be a small fraction of what could be seen with the radiant high in the sky. This timing is best suited for Eastern Europe and Central Asia where the radiant is favorably placed high in the sky during the morning hours. Even under ideal circumstances this display is quite variable. Observers should witness 30-50 shower members per hour at maximum but occasionally these rates can exceed 100 Quadrantids per hour from rural locations.

However, don’t despair. Sky and Telescope in the January issue acknowledges that very few meteors appear when the radiant is low:

But those that do are spectacular “earthgrazers” that skim along the upper atmosphere far across the sky. Just one of those can make your night. So keep an eye out on the evening January 3rd.

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.

Because of this, the AMS urges North American observers to view on both the mornings of January 3 and January 4 – especially the last few hours before dawn. They also give a piece of advice about meteor watching that is new to me – don’t look straight up – focus on a slice of sky from the horizon, upwards. Here’s more advice from their web site about this year’s Quadrantids:

The best strategy is to face toward the north or eastern portion of the sky. This way you can have the Quadrantid radiant within your field of view and easily determine shower association for Quadrantids and non-Quadrantids. Do not face directly at the radiant as the meteors seen in the region of the sky are short and easily missed. Meteors seen further from the radiant are longer and more noticeable. It is advised to face as low as possible without looking at the ground. Therefore, have the bottom of your field of view on the horizon. You may have thought that facing straight up is best but the sky directly above you presents a thin slice of the atmosphere and you see only meteors that are relatively close to you. Facing more toward the horizon allows you to see a larger portion of the atmosphere and meteors that occur much further away.

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, through out some constellations, and agreed upon official boundaries for the remaining 88. The Quadrans Muralis is no more. But they do still appear on sky charts printed before that time.

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

Update: January 1, 2011

I got up this morning, saw clouds, and was tempted to go back to bed. I should know by now that Mark Twain had it right when he penned his famous essay on New England weather . . .

I reverently believe that the Maker who made us all makes everything in New England but the weather. I don’t know who makes that, but I think it must be raw apprentices in the weather-clerk’s factory who experiment and learn how, in New England, for board and clothes, and then are promoted to make weather for countries that require a good article, and will take their custom elsewhere if they don’t get it.

There is a sumptuous variety about the New England weather that compels the stranger’s admiration-and regret. The weather is always doing something there; always attending strictly to business; always getting up new designs and trying them on the people to see how they will go. . .  .

And seldom have I scene anything quite so sumptuous as the weather that started out 2011, threatening to overcome, yet in the end, enhancing tremendously the parade of planets the Universe had planned to start the year.  At least that’s the way it was at Gooseberry this morning.

I had been up observing from 3-4 am under clear skies.  At 5 am it was totally overcast at my home, 10 minutes from Gooseberry where I can watch the sun rise over Buzzard’s Bay. At 5:30 it was still cloudy, but I went to Gooseberry anyway because the satellite images hinted at some remote possibility it would clear again.  At about 6 am Jennifer and Sybil arrived. It was totally overcast, but their spirits were high. Sybil said she had scene a lovely crescent Moon from her home a few minutes before getting in the car.  That was an encouraging sign.

Then as we stood there in the cool air, a star or two started to pop out overhead. Hope! Off on the eastern horizon there was a clear band between two cloud banks. “What’s that?” asked Jennifer? “A planet?” Yep!  Mercury. The one I expected to see last, if at all, for even under perfectly clear conditions mercury was so close to the horizon I knew it would be difficult to pick out. but there it was sandwiched between the dark clouds.

Next Saturn popped out  above Spica – and about the same time Arcturus put in an appearance and over in the west, Regulus. So we had two planets with some serious hope that the clouds would continue to move. But it was quite a while before we started catching glimpses of brilliant Venus.  And the last to emerge was the beautiful crescent Moon.  The pictures give some idea of what we saw, but nothing can capture the experience of simply being there. A scene like this really is enhanced by the clouds. They add an element of mystery and motion to what is already a wonder-full show. of course, they can also frustrate the heck out of you – but the fact they didn’t is perhaps a good sign – a good way to begin 2011.

Last to be revealed by the shifting clouds were Venus and the crescent Moon. (Click image for larger view.)

A picture can only hint at the richness of the varioed pastel colors in the morning twilight, and the awesome emtional impact of seeing the crescent Moon and Venus framed so beautifully. (CLick image for larger view.)

Having trouble picking out Venus in the above photo. The enlarged version might help -or take a look at this “enhanced version. ”

Click image for larger view.

Look East In January 2011 – 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. 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
• Pollux – The bigger, brighter twin
• Orion – A man for all to see
• Betelgeuse – a giant among giants
• Rigel – Blue and brilliant

Castor – A trio of twins

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

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. But there is more, much more, to Castor. And, it’s what we don’t see that makes this bright star so fascinating.

Were you to look at Castor in a backyard telescope, you would see it has a twin – another bright star that appears quite close – so the two are 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.
• 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

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.” 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 sky; it 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 in your sky to your north. In the northern hemisphere it appears to make an arc in 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

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. What isn't shown to scale is Betelgeuse. That's because we couldn't see it as a star if it were the same distance from us as the Sun - for we would be buried deep inside it, and Betelgeuse would be everywhere.

If the Sun looks smaller than you think it should in the above image. 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 won’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. We can’t do a similar thing with Betelgeuse – it wouldn’t be in our sky – we would be in it!

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 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 – an ‘Engagement Ring” points the way and ‘W” becomes an ‘M’

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 project 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 we see two bright guidepost stars, Vega and Deneb. To the northeast we have brilliant Capella. 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.

Luna-see: Your own Earth/Moon(s) model

Yes, that’s “Moons” plural because in this little project we make two just as a matter of convenience.

The idea here is simple. I believe that concrete demonstrations stick with us and allow us to internalize abstractions – so I found the time invested in developing a simple Earth/Moon model deepened my understanding of why we see what we see, and I hope it will do the same for you. So here it is. The major abstract ideas that are made concrete here include:

• The relative sizes not only in diameter, but volume, of the Earth and Moon.
• The phases of the Moon and why it changes from night to night and changes position in our sky as well.
• The true-to-scale distance between the Earth and Moon and why this simply isn’t shown in most books.
• The reason why eclipses of the Moon do not occur at each full Moon, but are relatively rare.

Step 1

First you need to gather a few simple materials and tools. Here’s what I used, but for the wood you could easily substitute cardboard – or some other material – and use clay for the Earth ball as well as the two moons. I just like wood and found what I wanted in a local craft store that’s part of a national chain and so I assume, commonly available. Clay for the Moon balls works best because shaping them to size is a learning experience and because they cling to the wires that are used as stands – no glue needed, and you can adjust their position quickly.

Tools and materials for model - click image for larger view.

Materials needed:

1 large disc approximately 6 inches in diameter
2 small discs about 3/4-inch in diameter
1 small disc about 1/2-inch in diameter
1 1-inch ball
1 piece of string 30 inches long
2 thin, stiff wires such as used in floral arrangements – one should
be 1-inch long, the other 3-inches long
clay

Tools needed:

protractor
pen or pencil
black felt-tipped pen (fine or very fine tip works best for writing)
ruler
small flashlight

Step 2 – Prepare a “month disc”

Using a pencil or fine ballpoint pen and protractor, carefully mark off 15 points along the perimeter of the disc, each 12 degrees apart, starting at “0”. These marks will cover half the disc.

Putting marks every 12 degrees starting at 0 and going a full 180 degrees.

Use the ruler to draw 15 lines on your disc, each going from a mark at the perimeter, through the center and clear to the other edge – this will divide the disc into 30 equal spaces, separated by 12 degrees each. Twelve degrees is the approximate amount the Moon covers in our sky each 24 hours, and the 30 divisions mark out a lunar month from New Moon through First Quarter, Full, Last Quarter and back to New.

Choose one line as your zero point, and about halfway between the perimeter and the center, place an arrowhead pointing towards the center (see highlighted area on picture above) – on this line
write “SUN” – the arrowhead indicates the direction of sunlight which for our purposes will remain constant through the month.

Considering the line just labeled as your zero point, the other lines can be numbered going counterclockwise 1-29 – the days of a lunar month – the period between two “new” Moons.

The space either side of this “0” line can be labeled “NEW.” On the other side of this line, near the perimeter, you can label the space either side of it “FULL” – Notice “NEW” moon is between the Earth and Sun; the “FULL” Moon is always opposite the Sun. You can label space 7 “FIRST QUARTER,” and on the opposite side to it, “LAST QUARTER.”

Step 3 – Adding the Earth

In the center of the disc put a small mound of clay about half-an-inch high and about an inch in diameter – take care to center this – and using the ball that is the Earth, make a depression in the top of this mound to hold the “Earth” in position at the center. (You could make the Earth ball of clay, in which case the raised mound isn’t necessary – it’s just there to keep the Earth ball from rolling away.)

If you’re satisfied everything is marked correctly, you may want to go over your labels with the black, felt tip pen to make them more prominent.

Step 4 – Adding the Moons

Make two Moons.

Take a small pinch of clay and roll it into a ball 1/4-inch in diameter. Repeat so you have two small clay balls. These represent scale models of the Moon. (The Earth is about 8,000 miles in diameter, the Moon about 2,160.) Did have trouble estimating how little clay you would need to come out at exactly one-quarter-inch in diameter? Many people do. It’s a good lesson in the difference between the diameter of a sphere and the volume.)

Put another small mound of clay about half-an-inch high on the 1/2-inch disc.

Place the short wire in the center of this mound so it is sticking straight up.

Place one of your Moons on this wire.

Step 5 – And now the shadow

Make an Earth-shadow disc

Take a 3/4-inch disc and using a marker, crayon, or whatever – color it black on both sides. This disc represents the Earth’s shadow at the distance of the Moon from the Earth.

Position the shadow by placing a small mound of clay about half-an-inch tall on the line marked “FULL” about 3/4 of the way between the “Earth” and the perimeter of the month disc.

Stand your Earth shadow on its edge in this clay.

Time to demonstrate lunar phases

For these demonstrations we use just the month disc, Earth, and the Moon on the one-inch wire – oh, and you’ll need a flashlight, and while the room doesn’t need to be pitch black, it’s good to lower the lights.

There are two keys here:

1. Always point your flashlight -which represents the Sun – in the same direction – the direction indicated by the arrowhead you put on the New Moon line.
2. Always position yourself as if you were standing on the side of the Earth looking up at the Moon in your sky. Another way to think of this is if the Moon is placed at Day 3, you should place yourself so you are looking along the line that connects Day 18 and Day 3 and runs through the Earth.

Move your Moon around the perimeter of the disc. To see its phase on any given night, shine the flashlight on it to simulate sunlight – and sight along the line from the Earth to the Moon for that particular night.

Position yourself so you are looking in the direction of the arrowhead, and you will see a "new" Moon - completely dark and lost in the glare of the Sun!

The person holding this flashlight is positioned to see a 2-day-old crescent Moon - the photographer was at a somewhat different angle and so saw a larger crescent. Remember - keep flashlight pointed in the same direction and position yourself along the line that is nearest to where you have placed the Moon.

Now here we are at full Moon - oops, but we forgot the earth's shadow!

Put the Earth's shadow in place and it should be clear that - ooops, the shadow is blocking the Moon! But if it does that we would have an eclipse every full Moon - every month! Clearly we don't, so ...

You should notice one problem. When you get to full Moon, the shadow of the Earth blocks the Moon from view. This would mean there would be an eclipse every month at full Moon – but we know there isn’t. What’s wrong with our model?

Step 6 – Going full scale and setting things right!

Our model is convenient for showing the phases of the Moon – and actually keeping track of them each month by advancing the Moon on the monthly disc each day. But it has two problems. First, it doesn’t show the distance between the Earth and Moon to scale – and second, it doesn’t show that the Moon’s orbit is tilted about five degrees to the orbit of the Earth!

So here’s how we’ll correct that situation.

Take the second 3/4-inch disc and place a clay mound on it about half-an-inch high.

Place the long wire (3 inches) vertically in this piece of clay.

Place your second clay Moon on top of this wire.

Now use the string to place your new model of the Moon 30 inches from the Earth. You have now created a scale model of the Earth/Moon system. But why is the Moon so much higher than the Earth in this model? Actually, the Moon could be that much lower than the Earth as well – we are showing it in one direction only because we’re building our model on a table. The Moon, at any given moment, could be just as far below the tabletop as it is above it – or anywhere in between these two extremes!.

To show the distance to scale, place the Moon about 30 inches from the Earth.

Placing the Moon 3 inches above the table seems high – does a five-degree tilt in the Moon’s orbit really amount to that much at the distance of the Moon from the Earth?

If the table edge represents the plane of the Earth's orbit, then the string will represent the plane of the Moon's orbit, tilted five degrees to the orbit of the Earth.

Five degrees doesn’t sound like much – but this is how much the Moon’s orbit tilts with respect to the Earth. You can get a rough idea of what this means on the scale of the Earth/Moon system by using your protractor and the string. Line your protractor up with the edge of a table. Then have your string come out at five degrees from the center of the protractor. Thirty inches later you’ll find that five degrees is now represented by about three inches – the height of our second model of the Moon.

That’s why our second wire was three inches long.

And now it should be clear why we don’t have an eclipse each month. Place your Earth’s shadow out near your Moon, and you can see that most of the time the Moon is going to miss the shadow – it will either be above it or below it.

At full the Moon may be well above the Earth's shadow, well below it, or on relatively rare occasions, pass right through it - and at those time we see an eclipse of the Moon.

You can also see that the Moon might pass through the shadow briefly, or it may take nearly three hours to get through it. But it won’t take 24 hours. Three is about the maximum. And so when an eclipse occurs at full Moon, the Moon for those few hours may, or may not, be in your night sky. That’s why eclipses are visible from only part of the Earth, and they may occur at any time of the day or night.