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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.

Events, June 2014 – Bright Lights Along the Ecliptic this Month

This is a great month to become familiar with the ecliptic in our sky. The ecliptic is the plane of our solar system where you will always find the Sun, Moon, and Planets.

Finding it sounds simple – and it is if you pick your time and date. The problem is it changes constantly because the Earth is tilted on its axis and revolving around the Sun.  I should stress one more thing – the ecliptic is not the path you will see the Sun, Moon, and planets take across the sky in a given night – it is the path they will follow as they change position over days, weeks, and even years. How quickly an object follows this path depends on how close it is to us – the Moon makes it completely around the ecliptic each month, the Sun each year – but a distant planet, such as Saturn, takes about 30 years.

You can trace the portion of this path visible about an hour after sunset on a June night in 2014. For the chart below I chose June 13th simply to include a nearly full Moon in the picture. It will, of course, change position each night – but the planets will stick pretty close to these general spots all month. So go out an hour or so after sunset and start your search by looking to the northwest for brilliant Jupiter. It will be brighter than any star, or any of the other planets and only about 10 degrees above the horizon – ten degrees can be measured by holding your closed fist at arms length.

Jupiter thus achors the western end of the ecliptic. We’ll move eastward to trace out the rest of it.

Click on this chart to get a much larger version. (Prepared from Starry Nights Pro screen shot.)

Click on this chart to get a much larger version. (Prepared from Starry Nights Pro screen shot.)

 

Up above Jupiter are the famous Gemini Twins – the nearer and slightly brighter one is Pollux, the other is Castor.

Turn a bit south of west you will find the bright star Regulus. While it outshines most other stars visible tonight, it is just in between Castor and Pollux in brightness and is about 30 degrees above the horizon – three fists.

Next on our list is the red planet Mars – the second brightest object on our chart. If you’re not detecting the rusty redness of it, try looking at it in binoculars. Then compare it with the next bright star on our chart, Spica. Spica is a  little lower than Mars an quite a bit dimmer. (Mats is four fist high, Spica about three and half.) Spica, however, is a very hot – and thus very blue – star. Look at the difference in color between it and Mars.

Moving eastward you’ll find Saturn, whose beautiful rings will show in even a small telescope. However, to the naked eye and binoculars Saturn simply looks like a bright star – not as bright as Mars, but certainly brighter than Spica. It has a pale, yellowish hue.

Continuing to the east is Antares, just 15-degrees – a fist and a half – above the horizon.  It’s name means “rival to Mars” and for good reason – it is a classic, red star, rivaling the color of Mars.  Again, contrast its color with that of Spica and Mars.

Oh – high overhead is the bright star Arcturus. It’s about as bright as Saturn and nearly 70 degrees above the horizon – seven fists.  Do you remember how to find Arcturus? You “follow the arc” of the Big Dipper’s handle – now high in our northern sky, to Arcturus, then “drive a spike” to Spica.

What else is going on this month?

Well, two dates to keep in mind:

The Summer Solstice is June 21 at 6:57 am EDT – and thus begins the longest day of the year.

On June 24 a thin crescent Moon will be very close to the brightest of planets, Venus in the eastern sky about an hour before sunrise. Should be a pretty sight and a nice picture opportunity.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Guide star reminder

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

keystone-crown

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

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

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

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

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

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

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

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

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

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

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

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

Events May 2014 – Four Easy Planets, Two Challenge Planets, and a Meteor Storm Watch

Click picture for larger image. (Created from a Starry Night Pro screen shot.)

Click picture for larger image. (Created from a Starry Night Pro screen shot.)

May skies have a lot to offer in 2014, for in addition to the usual parade of stars, we have four easy planets to spot, two challenging planets, and a possible “meteor storm,”  one of those once-in-a-life-time sky spectaculars -maybe! There are also a couple of special events for sky watchers in the Southern Hemisphere. Here’s the summary with  links to the details.

Mercury – the Big Tease!

Click image for larger version. (Prepared from Starry Nights Pro screen shot.)

Click image for larger version. (Prepared from Starry Nights Pro screen shot.)

Mercury is notoriously difficult to see, mainly because it demands that you know exactly when and where to look – and while you should see it with your naked eye and really quite easily, it’s much easier to find with binoculars first.  It also plays this kind of dual game with us. The first part of the game is to be so close to the Sun that it is almost always drowned in the glare of the Sun – even after sunset. (Don’t even think of looking for it with binoculars before sunset – if you accidentally catch the Sun in binoculars you will do permanent damage to your eyes.)

Start looking for Mercury 30 minutes after sunset when – from May 16 to May 28  – it will be a fist or more above the western horizon. That gets it away from the worst of the haze near the horizon and into a sky that is starting to get dark. In the next 30 minutes the sky will get darker – making it easier to see Mercury – and Mercury will get lower, making it more difficult to see.

In addition to this little game, Mercury is actually getting higher in the sky from May 16 to about May 25 – but it’s also getting dimmer – and while it’s still quite high by May 28, it is also more than a full magnitude dimmer than it was on May 16. See why I call it a tease? But you will find it, and when you do, you’ll say “that’s easy!” Yep, if you look on the right night, in the right spot, at the right time, and have an unobstructed western horizon that is also clear, Mercury is a piece of cake! 😉

Here are a couple more charts to help out – note the changes in brightness and background stars even over just a week.

mercury51914

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

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

Why is Mercury behaving this way? It’s actually getting about 25 million miles closer to us during the last two weeks of the month. However, like Venus, Mercury goes through phases which can be seen in a telescope as it approaches us because it’s also starting to go between us and the Sun. This means it changes from a disk to a crescent, so while it gets closer – which would mean brighter – there is also less of it seen by us as it moves towards becoming a crescent. So it gives us a double whammy – after the 25th it starts getting closer to the Sun and it also continues to dim.

Storm, Shower, or Drizzle – this could be really cool!

There’s some big news on the meteor front that may result in a very exciting – and ultimately unpredictable – special event in the early  morning hours of May 24th. It’s summed up nicely in the headline from the cover of the May Sky and Telescope which contains an excellent article on the subject.

‘Meteor Storm Watch – Dark with a Chance of Fireballs’

OK – that got my attention. I’ve always been fascinated by those old woodcuts depicting the incredible 1833 Leonids meteor shower. I think they’re a bit exaggerated, but that one apparently really was exceptional.

1833Leonidmeteors

This month we have a short-period comet that may produce a spectacular show for us – but not as a comet. This is Comet 209P/LINEAR and it is scheduled to cross the orbit of Earth and be totally unspectacular, even though it is quite close to us as comets go, you will need a good size telescope just to see it.

 But . . . several expert meteor observers are predicting a sudden meteor shower on the morning of May 24, and if you’re in North America above roughly latitude 40 you are at the right location to have a front row seat should this shower develop. And don’t despair if you’re in the southern US – there still could be some beautiful fire balls for you.  Some meteor experts even are predicting a possible meteor storm – something I have never seen, but would sure love to. And, of course, it may be a total fizzle, or it may be the sky spectacle of a lifetime. . . but cloudy!  You just can’t know – and that sense of anticipation and mystery is what makes these sorts of things extra fun.

Now what does a meteor shower have to do with a comet? Everything.

Meteors are pebble size or smaller generally.  When we run into one going 67,000 miles an hour – that’s our speed in orbit – they collide with our atmosphere much faster than a speeding bullet and almost always burn up before they reach the ground.

 Think about it for one moment.

Imagine something about the size of a pencil eraser 50 miles away and yet burning so brightly that you can see it. Think of whether or not you can see someone strike a match 50 miles away – or see the glow of a cigarette.  That gives you some idea of the speed these things hit with and the tremendous heat that is generated as they collide with our atmosphere.

 Now think about a Comet. Pig Pen, of Peanuts fame, is the best model I can think of for a comet – like Pigpen, a comet leaves a trail of dust behind it. That trail of dust doesn’t go away. It falls off the comet but continues to orbit the Sun. And like Pigpen’s perpetual dust cloud, it just hangs there, like droplets of water in a spacecraft – each grain of sand in its own private orbit about the Sun.

Every August 12 the Earth crosses a trail of dust left by Comet Swift Tuttle. We pass through it and we see lots of meteors, and we call this the Perseids meteor shower. If you catch it at its peak on a dark, moonless night, you may see as many as one meteor a minute.

They are called the Perseids because if you traced each meteor trail backwards, you would see they were all appearing to come from the same part of sky – a small area in the constellation of Perseus. Think of it as an open window that lets the dust of Comet Swift Tuttle tumble through.

In December there is another such shower called the Geminids. These happen every year as well – in fact, there are several more such showers, but the Perseids and the Geminids are seen as the best – most active – of the bunch.

The event this May is more complicated. I don’t know quite how they figure all this, but apparently this little, very dim, unspectacular comet has been laying down trails of dust as it goes around the Sun every five years or so. As one of the experts explains it in the May issue of Sky and Telescope, “all of the trails ejected between 1803 and 1924 cross Earth’s path on May 24.” That’s 25 trails of comet rubble all hitting at about the same time.

They know this precisely enough so that four of the experts are in agreement that this will happen right about 3 am EDT on the morning of May 24.  But they do warn the predictions could be off – generally they think this will be as good, or better, than a Perseids meteor shower. But they also grant that it may be a dud.

 The event is well-timed and placed for those of us in the northern tier of states. Those in the southern states may get a good show from especially bright meteors – but far fewer of them. The rest of the world will pretty much miss out.

 Remember, when there’s a shower, the meteor can appear anywhere in the sky, but you trace them back to their radiant – which in this case will be in the obscure – very obscure – constellation known as Camelopardalis. You all know what a Camelopardalis is, right? I’ll help you. Think giraffe. It’s in the northern sky at 3 am on May 24. To learn more about this area and see a chart, go to my post here. 

Consolation Prizes for the Southern Hemisphere

If you live south of the Equator, May always offers one of the better meteor showers of the year for you, the Eta Aquarids on May 4, 6, and 7th. A few of these may sneak north as well.

Also on the evening of May 13-14 the Moon will be near Saturn for most of us, but for folks in New Zealand and much of Australia the Moon will cross in front of the planet – what is called an occultation. This is cool to see in a telescope, but what I love is the pictures I’m sure it will generate showing Saturn near the edge of the Moon. Seeing Saturn close to the Moon, even in a picture, is a special treat that really drives home the difference in distance. Saturn, which with its ring system is so large that it would actually fill the space between us and the Moon, will look tiny next to our little moon because it is so much more distant.

On the East Coast of the US, Saturn will get within only a couple of degrees of the Moon that night – but as you move west, it gets closer – close enough to catch the two in a low power telescope field in the early morning hours.

And then there’s Uranus and Venus

I was hoping that Venus would guide binocular users right to Uranus, but no such luck. The two will be very close on the night of May 15 and 16, 2014, making it easy for small telescope users to find Uranus – but this will happen in morning twilight, and Uranus will be too faint to see against twilight background with ordinary binoculars. In fact, I think it’s going to be a challenge in a small telescope. The chart below is for an hour before sunrise – at that point Venus is only seven degrees above the eastern horizon. While it should be easily visible, assuming clear skies, spotting Uranus about 10 magnitudes fainter, won’t be easy both because it is so low and because of morning twilight.

To get both in view you need a telescope that will gather some extra light, yet also provide a 2-degree field of view, which is why I consider this a challenge – but fun to try if you enjoy mornings, as I do.

On the morning of May 25th you won’t need anything special to appreciate the Venus show – then you’ll have a beautiful crescent moon just a few degrees above Venus!

 

Look North: May is the month the North Star gets two bright flankers!

Click for larger image. (Developed from Starry Nights Pro screen shot.)

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

Is the North Star – Polaris – our brightest star? No! And it certainly won’t look that way this month as it shares the northern sky with two very bright stars. But, read on. Polaris is not nearly as dim as it looks!

If you have been learning your guidepost stars as they rise in the East, you won’t be surprised by the two bright stars which flank – and outshine – our pole star in May. To the northwest is Capella, a star we first met when it rose in the northeast in November. In May the northeast is dominated by a star that is almost Capella’s twin in brightness, Vega, a guidepost star we introduce in May. (See “Look East!” for more about Vega.) As a bonus we also have the twin guidepost stars, Castor and Pollux, making their way into the northern sky high above Capella. But let’s focus on Capella and Vega.

New star watchers frequently assume the North Star, Polaris, will be the brightest star in the sky. It isn’t even close! It is bright, but its fame comes because it’s very, very close to where the axis of the Earth points to the north celestial pole. So it serves anyone trying to find true north as a very good guide. But when it comes to brightness, it’s in the same league as the stars in the Big Dipper. Quite bright, but it can’t hold a candle to Capella and Vega. When you look at a list of the brightest stars, Vega is number 5 and Capella number 6. Polaris, our North Star, is number 48!

As simple as one, two, three!

That doesn’t mean Polaris is a slouch, though. First, in the eastern sky in May you meet Spica. (That’s on our chart for the east.) One distinction of Spica is that it’s as close to being magnitude 1 as any star gets. A distinction of Polaris is, as Spica defines magnitude 1, Polaris defines magnitude 2. (To be precise it’s magnitude 2.02.) Vega and Capella are extremely close to magnitude 0. Vega is 0.03 and Capella 0.08. Good luck on telling the difference! This month, if you look north 90 minutes after sunset, you may think Capella is a bit brighter actually – but if it appears that way it will be because it’s a bit higher in the sky and thus is not dimmed by having to fight its way through as much of our atmosphere as Vega is doing at the moment. So don’t try to split hairs. And yes, you’re right – they are NOT really as “simple as one, two, three” – on the magnitude scale they are as simple as zero, one, two – but that doesn’t sound as good! (Vega and Capella are zero; Spica is magnitude one, and Polaris, magnitude two.)

So which is really the brightest star of these four? Are you ready for this? Polaris! That’s right – if you put all four stars at the same distance, Polaris would appear to be the brightest. Remember, that the lower the magnitude number, the brighter the star. In absolute magnitude – the brightness we give to a star if they are all shining from the same distance  – these four stars line up this way:

  • Polaris -3.4
  • Spica -3.2
  • Capella 0.1
  • Vega 0.3

And those absolute magnitudes also reflect their order in distance from us.

  • Polaris 433 light years
  • Spica 250 light years
  • Capella 45 light years
  • Vega 25 light years

So sometimes a star is very bright because it’s – well, very bright. But sometimes it only appears to be very bright because it is very close to us. If you put our closest star into this group, our Sun – remember, it is just 8 light minutes from us – in absolute magnitude it would be by far the dimmest of this group – absolute magnitude 4.9! So while Polaris doesn’t look all that bright, it really is a very bright star! Another way to think about this is if you move our Sun out to where Polaris is, it would be about magnitude 10! You would need binoculars or a telescope to see it!

Click image for larger view of this chart. Yellow circle represents typical field of view for low power binoculars, such as 10X50.

To get an idea of the difference between Polaris and our Sun, point your binoculars towards Polaris.  You should be able to make out the “Engagement Ring” asterism – granted, a crude ring with Polaris as the diamond.  This asterism points you towards the true north celestial pole  – just avery short distance to the other side of Polaris –  and also gives you a good idea of about how far Polaris is from that pole.  Small binoculars will not show you the companion of Polaris, but to get an idea of how bright our Sun would be at the same distance, look for the star labelled 9.8 – and if you can’t see it, see if you can see the star that’s a bit brighter labelled “9.”  Don’t expect to see these instantly. Sit calmly, relax, and keep looking for at least a minute.

And here’s one more cool secret about Polaris. It has a companion that just happens to be quite dim – magnitude 9. It’s fun to see the two of them if you have a small telescope, though it’s not all that easy because Polaris is so much brighter than its companion. But if you get a chance to see Polaris and its companion in a telescope, remind yourself that the very faint companion is still a bit brighter than our Sun would look at this distance. This companion, known as Polaris B, was discovered in 1780 by William Herschel, and for many years Polaris was thought to be a binary star – that is, a system of two stars orbiting about a common center of gravity. But Polaris was holding one more surprise – it’s really a triple star.

The top image shows Polaris and its faint companion that can be seen in any decent backyard telescope. The bottom image shows the second companion, Polaris Ab, which has only been seen by using the Hubble Space Telescope.

This has been known for some time, but no one could see the third star until they turned the Hubble Space telescope on it in 2006. That’s when NASA released the first image of this third companion. The accompanying press release explained it this way:

By stretching the capabilities of NASA’s Hubble Space Telescope to the limit, astronomers have photographed the close companion of Polaris for the first time. They presented their findings  in a press conference at the 207th meeting of the American Astronomical Society in Washington, D.C.

“The star we observed is so close to Polaris that we needed every available bit of Hubble’s resolution to see it,” said Smithsonian astronomer Nancy Evans (Harvard-Smithsonian Center for Astrophysics). The companion proved to be less than two-tenths of an arc second from Polaris — an incredibly tiny angle equivalent to the apparent diameter of a quarter located 19 miles away. At the system’s distance of 430 light years, that translates into a separation of about 2 billion miles.

“The brightness difference between the two stars made it even more difficult to resolve them,” stated Howard Bond of the Space Telescope Science Institute (STScI). Polaris is a supergiant more than two thousand times brighter than the Sun, while its companion is a main-sequence star. “With Hubble, we’ve pulled the North Star’s companion out of the shadows and into the spotlight.”

So as I said, Polaris is no slouch. It not only is a very bright star, but it also has two companions, and scientists are still studying it because it is unusual in other respects. We’ll talk about those other differences another month.

Look East! Drive a Spike to Spica (pronounced Spy-ka) and two planets in May 2014!

If you followed “the arc” of the Big Dipper ‘s handle last month to find Arcturus, then you “drive a spike”  this month to find Spica –  pronounced Spy-ka – plus Mars and Saturn. It’s like taking a long, cool slide from the Dipper – and the “Arc-to-Arcturus” and “Spike-to-Spica” relationships hold true as long as these stars are in our skies – which will be right through August.

Here’s how it looks – remember: look east  starting about an hour after Sunset.  Arcturus, Spica, and Mars should all be visible as the first stars emerge, but Saturn will have to wait a bit. At the start of the month it may be too low until about two hours after sunset – but each night it rises earlier and earlier. On May 10 it is in opposition, rising as the sun sets.

Click to enlarge. (Prepared from Starry Nights Pro screen shot.)

Click to enlarge. (Prepared from Starry Nights Pro screen shot.)

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

While the Dipper is easy to recognize, its stars are second magnitude – bright, but easily out-shone by the triangle of Arcturus, Mars, and Saturn. Even Spica, almost exactly magnitude 1, is brighter than the Dipper stars. Still, the Dipper stars will be very high in the northeast and easy to spot as it gets dark.  The brightest star in this section of the sky is Arcturus at magnitude minus 0.04. (Remember, the lower the magnitude number, the brighter the object – minus magnitude are brighter still.) The next brightest star you’ll see is over to your left, low in the northeast – Vega at magnitude 0.04. So Vega is barely on the plus side of  magnitude  zero and Arcturus is barely on the minus side, a difference that is next to impossible to detect with the eye. This year both these stars will be out shone by Mars, almost magnitude -1,  and Saturn is just a tad dimmer than Arcturus and Vega, though about a full magnitude dimmer than Mars.  Together these  five –  Mars, Arcturus, Vega, Saturn, and Spica will give you a good sense of the magnitude scale. In fact, throw in Polaris – the North Star, which is almost exactly magnitude 2 and you have a range of four magnitudes represented – quite a brilliant display.

The color contrast is exceptional here too. As these stars and planets get higher in the sky, you will notice that Mars is definitely reddish, Spica is a rich blue, while Saturn has a yellow tint.

We dealt with Arcturus last month. Saturn will be in our sky all night and as always is a treat for the small telescope user. From a naked eye perspective,  it’s fun to remember that the name “planet” means “wanderer” in Greek, but all “wanderers” are not created equal. Mars, Venus, and Mercury move  so quickly in our night sky that you can easily mark their changes over a period of a few days -certainly a week.  Saturn is much more sluggish.

Saturn changes position over the course of an entire year by roughly 12 degrees.  To see this in the sky , find Saturn. Hold your fist at arms length so Saturn is just below it. Just above your fist is where Saturn was last year. Put Saturn on top of your fist and just below your fist is where it will be next year. So how long will it take Saturn to get around the sky to roughly the same position? Well, 360/12 = about 30 years!  Now if you think a moment, the Moon takes about 30 days to get around our sky – and that means the Moon moves each day about 12  degrees –  the same apparent distance covered by Saturn each year.  All of which should tell you that it would be reasonable to assume Saturn is much farther away from us than the Moon – which, of course, it is.

None of this is rocket science, but I find it interesting to contemplate as I look up and see Saturn. I measure that distance it will travel in the next year and in my mind’s eye I stand above the Solar System and I see a long thin pie slice reaching from me to Saturn’s distance orbit and this helps me keep things in perspective – gives me a better intuitive feel for the neighborhood in which we live.  OK – for the record Saturn is moving at about 22,000 miles an hour, Mars about 54,000 miles an hour in a much shorter orbit, and we’re whipping right along close to 67,000 miles an hour – and we don’t even feel the wind in our face! Oh – and Saturn’s actual orbital period is 29.458 years.

On to this month’s new guidepost stars!

Vega and Spica are each fascinating stars, but let’s start with Vega. Shining brightly not far above the northeastern horizon as the evening begins, Vega comes about as close to defining the word “star” as you can get. In “The Hundred Greatest Stars” James Kaler calls it “the ultimate standard star” because its magnitude is about as close to zero as you can get  and its color is about as close to white as you can get. (If you’re one of those who assumed all stars are white, you’re forgiven. Individuals vary in their ability to see different colors in stars and for everyone the color differences are subtle – in fact I think of them as tints rather than colors. )

It’s hard not to be attracted to Vega when you read Leslie Peltier’s wonderful autobiography, “Starlight Nights.” Vega was central to his astronomical observing throughout his career because he began with it when he first started reading the book from which I got the idea for this web site, “The Friendly Stars” by Martha Evans Martin. Peltier wrote:

According to the descriptive text Vega, at that very hour in the month of May, would be rising in the northeastern sky. I took the open book outside, walked around to the east side of the house, glanced once more at the diagram by the light that came through the east window of the kitchen, looked up towards the northeast and there, just above the plum tree blooming by the well, was Vega. And there she had been all the springtimes of my life, circling around the pole with her five attendant stars, fairly begging for attention, and I had never seen her.

Now I knew a star! It had been incredibly simple, and all the stars to follow were equally easy.

Vega went on to be the first target of the 2-inch telescope he bought with the $18 he made by raising and picking strawberries. (This was around 1915.) And Vega became the first target for every new telescope he owned until his death in 1980. If you still don’t know a star, go out and introduce yourself to Vega early on a May evening. Even without a plum tree to look over, you can’t miss her! And once you’ve done that you’re well on your way to making the night sky your own.  (And yes, Vega is the star from which the message comes in Carl Sagan’s book/movie “Contact.”)

Vital stats for Vega, also known as Alpha Lyrae:

• Brilliance: Magnitude .03 ; a standard among stars; total radiation is that of 54 Suns.
• Distance: 25 light years
• Spectral Type: A0 Dwarf
• Position: 18h:36m:56s, +38°:47′:01″

Spica, a really bright star – honest!

Spica is truly a very bright star, but the numbers you may read for its brightness can have you pulling your hair. That’s because there are at least four common ways to express the brightness of Spica and other stars, and writers don’t always tell you which way they’re using. So let’s look at these four ways and see what they mean for Spica.

The first is the most obvious. How bright does it look to you and me from our vantage point on Earth using our eyes alone? We then assign it a brightness using the magnitude system with the lower the number, the brighter star. (For full discussion of this system, see “How bright is that star?”)

By this measure Spica is 16th on the list of brightest stars and is about as close as you can come to being exactly magnitude 1. (Officially 1.04) Though I should add here that the number really marks the midpoint of a magnitude designation – that is, any star that is in the range of magnitude .5 to magnitude 1.5 is called “magnitude 1” and so on for the other numbers on the scale.

But that scale talks about what we see. It doesn’t account for distance. Obviously if you have two 60-watt light bulbs and one is shining 6 feet away from you and the other 1,000 feet away, they are not going to look the same brightness. But if we put them both at the same distance – say 100 feet – they would look the same. So it is with stars. To compare them we pretend they all were at the same distance – in this case 10 parsecs, which is about 32.6 light years. Put our Sun at that distance and it would be magnitude 4.83. (That’s about as faint as the fainest stars we see in the Little Dipper.) We call that its absolute magnitude.

The absolute magnitude for Spica is -3.55 – not quite as bright as dazzling Venus.

Wow! That’s pretty bright compared to our Sun! Yes it is. Sun 4.83; Spica -3.55. Don’t miss the “minus” sign in front of Spica’s number! That means there’s more than eight magnitudes difference between the Sun and Spica. And that relates to the next figure you are likely to see quoted. Something that is called its luminosity. Luminosity compares the brightness of a star to the brightness of our Sun. Unfortunately, the term is often misused – or poorly defined. Thus in the Wikipedia article I just read on Spica it said that “Spica has a luminosity about 2,300 times that of the Sun.” Yes, but what does that mean? It means that if we were to put the two side by side, Spica would appear to our eyes to be 2,300 times as bright as our Sun.

That is bright! But there’s more, much more. Spica is also a very hot star – in fact one of the brightest hot stars that we see with our naked eyes. But we miss most of that brightness because most of it is being radiated in forms of energy that our eyes don’t detect. In the case of Spica, that is largely ultraviolet energy. The Wikipedia article actually listed Spica’s luminosity twice, and the second time it gave it as “13,400/1,700.”

Oh boy – now we have Spica not 2,300 times as bright as the Sun, but more than 13,000 times as bright. Now that IS bright – but is it right? Yes! So why the difference? Again, the first “luminosity” given – 2,300 times that of the Sun – is measuring only what we can see with our eyes. The second is measuring total amount of electromagnetic radiation a star radiates and is properly called the “bolometric luminosity.” And why two numbers for that last figure? 13,400/1,700? Because while Spica looks like one star to us, it is really two stars that are very close together and one is much brighter than the other. So what we see as one star is really putting out energy in the neighborhood of 15,100 times as much as our Sun.

This can get confusing, so I suggest you remember three things about Spica.

1. It defines first magnitude, having a brightness as it appears to us of 1.04.

2. It is really far brighter (magnitude -3.55), but appears dim because it is far away – about 250 light years by the most recent measurements.

3. It is very hot – appearing blue to our eyes – and because it is very hot it is actually radiating a lot more energy in wavelengths we don’t see, so it is far, far brighter than our Sun.

Spica is the brightest star in the constellation Virgo, one of those constellations where you can not really connect the dots and form a picture of a virgin unless you have an over abundance of imagination. Besides, the remaining stars are relatively faint. That’s why we focus on the bright stars and sometimes those simple patterns known as “asterisms” and use them as our guides.

Vital stats for Spica, also known as Alpha Virgo:

• Brilliance: Magnitude 1.04; a close double whose combined radiation is the equal of 15,100 Suns.
• Distance: 250 light years
• Spectral Types: B1,B4 Dwarfs
• Position: 13h:25m:12s, -11°:09′:41″

Guideposts reminder

Each month you’re encouraged to learn the new “guidepost” stars rising in the east about an hour after sunset. One reason for doing this is so you can then see how they move in the following months. If you have been reading these posts for several months, you may want to relate Spica to two earlier guidepost stars with which it forms a right triangle, Arcturus and Regulus.

Once you have identified the Right Triangle, note carefully the positions of Spica and Regulus. They pretty much mark the “ecliptic.” This is the path followed by the Sun. Also, within a few degrees north or south of it, you will find the planets and the Moon. That’s well illustrated in 2014 by the presence of both Saturn and Mars, very near the ecliptic, as noted on our chart.

Arcturus and Regulus are not the only guidepost stars and asterisms in the May sky. Again, if you have been reading these posts for several months, be sure to find the stars and asterisms you found in earlier months. Early on a May evening these will include, from east to west, the following: Arcturus, Spica, Saturn, Leo’s Rump (triangle), The Sickle,  Mars, Regulus, the Beehive, Procyon, Sirius, Pollux, Castor, and in the northwest near the horizon, Capella, and the Kite. Venus will be a bright evening “star” in the west, and if you look early in the month you may catch a glimpse of Sirius and Betelgeuse before they set.

Events April 2014: Mars, the Moon, and the Earth’s Shadow – Yes, a Total Lunar Eclipse !

 

anatomy-of-a-lunar-eclipse-graphic

Love those Lunar eclipses, but who was in charge of the scheduling for this one? Some insomniac like me, no doubt, for on the East Coast of the USA where I live this thing really doesn’t pick up steam until about 2 am April 15, then continues until near when the Moon sets just before dawn. The West coast residents get a somewhat more timely view.

Here’s the schedule for those in the Eastern Daylight Time zone on the morning of April 15:

1:57 am partial eclipse begins

3:06 am totality begins

3:45 am mid-eclipse

4:25 am totality ends

5:33 am partial ends

The Moon sets about the time the Sun rises, which varies according to location. (Eclipses happen at the same time all over the world – but of course what time that is for your location depends on your time zone – and for some, the Moon simply won’t be in your sky during the eclipse hours.  For a complete guide to where this eclipse can be seen and when for your location, see the NASA eclipse pages.

There’s an incredible NASA eclipse Javascript on this page that delivers all sorts of eclipse data and time for anywhere in the world – however, I did notice that the times were  standard – so you need to adjust for daylight savings if relevant.

What adds a special touch to this eclipse is that Mars will be pretty close to the Moon from the time the Moon rises near sunset. I always like watching the fainter stars come out as the Moon goes into total eclipse, then slowly vanish as it comes back. But with this eclipse, Mars will provide a special treat with it’s ruddy hue shining brighter than any of the nearby stars – though Arcturus and Spica will both rival it.  Here’s a chart for my location – the same relationships will apply anywhere, but those farther west will see the orientation of the chart shift since the Moon and stars will be higher in their sky at this point.

 

eclipsed_moon

Click image for larger version. (Prepared from Starry Nights Pro screen shot.)

 

The Scorpion should be beautiful on the southern horizon. For me the Moon is about 22 degrees above the southwest horizon at this point. If you have trouble finding it – eclipses vary on how dark they get, then simply look for Mars and Spica – if you get Spica in binoculars the Moon will be in the same field about 2 degrees east of it.

April Planet Parade

Click image for larger view. (Made from screen shot of Starry Nights Pro.)

No, you can’t see the Moon – it’s eclipsed! (Actually, it can be quite red and fairly easy to see – or it can be quite dark and difficult to see during totality. ) Click image for larger view. (Made from screen shot of Starry Nights Pro.)

Jupiter is high in the western sky all month, setting in the wee hours of the morning; by the end of the month it sets closer to midnight, but is still brighter than any star or any other planet in the evening sky.

However, Mars rivals Jupiter, taking over in the eastern sky in the early evening hours and remaining visible all night throughout April. It’s in retrograde motion this month, which means it appears to climb a bit higher in our sky as the month goes on, moving west against the background of stars. This is the best opportunity for two years for telescope users to get a good look at Mars.

Saturn gets high enough to view in the eastern sky about three hours after sunset at the start of the month, and two hours after sunset by the end of the month.

Venus is best seen low in the east about 45 minutes before sunrise, and on April 25th has a nice pairing with the crescent Moon. While Jupiter is brighter than any star, Venus is two magnitudes brighter than Jupiter, so it shows up well even though it is well into morning twilight before it is high enough to see easily. I like finding pretty spots to try to capture the crescent Moon, Venus, and foreground landscape  in twilight.  Here’s a shot I got at the Town Farm in Westport MA when there was a similar  arrangement of the Moon and Venus in March 2014.

venus_moon_farm

Click image for larger view.

 

A Meteor Sprinkle

The annual Lyrids meteor “shower” is not nearly as intense as the Perseids in August or the Geminids in December, but if the night is clear it could be fun. It is supposed to peak (roughly 20 meteors per hour) on April 23 when a  waning crescent Moon will rise after 3 am and start to interfere some.

I must admit that with a shower like this I take it casually. That is, I go out and observe other things, but I keep an eye out for meteors, and if I see one, I try to trace its path backwards to see if it points in the general direction of the constellation Lyra – if it does, I assume it’s part of the shower and not a random meteor. You might see a shower meteor a few days before or after the peak, and it might come at any time of night in any part of the sky, but if I were going to pick an hour to keep a sharp eye out for Lyrids, it would be between 2 am and 3 am on the morning of April 23.

The Lyrids are believed to be remnants of Comet Thatcher, which orbits the Sun about every 415 years.

 

 

Look North in April 2014! See Mizar – the best thing since – well, since sliced bread!

In April the Big Dipper is climbing high overhead in the northeast and starting to pour its contents into the Little Dipper – not a very good idea, but fun to contemplate. Meanwhile, the only double star pair where both stars have proper names – Mizar and Alcor – is high in the northeast and ready to challenge your eyesight and boggle your mind.

Mizar is the middle of the three stars that form the handle of the Big Dipper – the same three that we use as an arc to trace a path to Arcturus. (That reference is explained in this month’s “Look East” post.) Wait until an hour or more after sunset, then focus on that center star. Is it one star – or two? For my old eyes, it is one. And since my eyes are not that bad, I question those who say this is an “easy” test of eyesight. But lots of people do indeed see two stars there when they look carefully. Maybe you’re one of them. If you’re not sure, or can see just one, take a look with your binoculars. Now you certainly should see two.

The brighter of the two is Mizar, the fainter one Alcor. More on that in a minute. First, here’s our northern sky for this month.

Arrows indicate directions in the sky where north is always the direction towards the north celestial pole, and west is always the direction the stars appear to move. Click image for larger view. (Developed from Starry Nights Pro screen shot.)

Download a printer-friendly version of this chart here.

And here’s what you should see when you look with binoculars at the Big Dipper’s handle.

Zooming in on the center star in the Big Dipper’s handle using binoculars, you should see it is really two stars – Mizar and Alcor. Click image for larger view. (Developed from Starry Nights Pro screen shot.)

The words “double star” simply mean that a star that appears as one to our naked eyes, is seen as two when optical aid is used. But they may simply be two stars that are closely aligned, yet in reality very far apart and have no real connection to one another. “Binary star” is the term used for two stars that are gravitationally linked to one another. So here’s the double rub with Mizar:

  • When you are looking at Mizar and Alcor, you probably are looking at six stars, not two!
  • Scientists still dispute whether Mizar and Alcor are a true double, even though they have been observing this system with telescopes since 1650!

My “sliced bread” reference figures into the Mizar/Alcor picture in a roundabout way. I have trouble remembering things. So when I wanted to remember the approximate distance to Mizar – 80 light years – I asked myself what interesting thing was going on 80 years ago that can help me remember the distance to these stars? And the answer – given a little research – was that about 80 years ago America was introduced to sliced bread all packaged neatly. Actually, sliced bread was first introduced in 1928, according to Wikipedia, but it was in 1930 that the first national marketing campaign began for “Wonder Bread.” Wonderful. So about 80 years ago the light you see left Mizar and Alcor to begin its journey to your eye.  Don’t let the different dates bother you because an approximation is close enough.

And Mizar alone is a lot more interesting than sliced bread.

Even a small telescope reveals that Mizar itself is a beautiful double! That’s what was revealed when a telescope was turned on it in 1650. But no telescope can reveal to the eye that these two stars are in fact, each a double! The stars in each pair are so close to one another that only an instrument known as an interferometer can reveal them. So what we see as Mizar is in fact four stars. (Double stars are a special love of mine, and I wrote about observing Mizar  in the double star blog I share with John Nanson here.)

But what about Alcor? The Hipparchos satellite, the best modern source for star distances, found Mizar to be 78.1 light years away and Alcor to be 81.1. Those are great ball park figures and good enough for the sliced bread reference. But they may be wrong. The astronomer James Kaler wrote a few years ago in his book “The Hundred Greatest Stars” that these distances may be wrong – in fact, some evidence suggested then that Mizar was actually farther away than Alcor. Kaler concluded in his book that they are “probably paired.”

But now comes more evidence as reported in the current (2014) Wikipedia reference to Mizar:

. . .In 2009, it was independently reported by two groups of astronomers (Eric Mamajek et al., and Zimmerman et al.) that Alcor actually is itself a binary, consisting of Alcor A and Alcor B (a red dwarf star), and that this binary system is most likely gravitationally bound to Mizar, bringing the full count of stars in this complex system to six.

So what our naked eye reveals as one or two stars, may indeed be a complex system of six stars! Which in my mind says that slicing up Mizar and Alcor this way may be – well, may be the best thing since sliced bread and just the sort of thing that makes observing the stars such a treat for the eye and mind!

Look East in April 2014 – take a simple slide to the World’s Fair Star and bump into Mars as a bonus!

 

uhhh

The name”Arcturus” derives from Ancient Greek and means “Guardian of the Bear.” It is the brightest star in the constellation Boötes. Click image for a much larger version. (Prepared from Starry Nights Pro screen shot.)

 

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

Arcturus isn’t universally known as the “World’s Fair Star,”  but  it should be.  Its light bridged two World’s Fairs, making an astronomical link between the one in 1893  and a second in 1933 – both held in Chicago.  It’s intriguing that  the general public was excited enough about science – in the middle of the Great Depression – to make such a link attractive to the Fair’s promoters. Light from Arcturus  – believed at that time to be 40 light years away – was captured by the 40-inch refractor at Yerkes Observatory and its energy used to turn on the lights for the 1933 Fair.

This put the public spotlight not only on Arcturus, but it raised consciousness about the vast distance between us and that star, since the light being used had started its journey during the 1893 Fair and arrived just in time to start the next Fair. When you know light can circle the Earth more than seven times in a single second, you start to understand just what an incredible journey that was.

Of course Arcturus has many other distinctions. For one thing, it makes a perfect connection with the best known asterism in the sky, the Big Dipper.  To find it, all you have to remember is “follow the arc to Arcturus.

And in 2014 you get a bonus – keep following that arc and you’ll quickly come toa slightly brighter “star,” the planet Mars! More about that in our “events” post for April, but I did add Mars to this month’s “look east” chart. It forms a nice triangle with Arcturus and Spica, another bright star we’ll meet next month as it’s quite low this month.

Getting back to Arcturus – another way to remember where to find Arcturus is its name, derived from ancient Greek, which can be translated as “Bear Watcher.”  That’s because Arcturus looks like it’s keeping an eye on the “Great Bear,” Ursa Major, as both circle the northern pole.

You can also think of the magnitude system by which we rate the brightness of stars as starting near Arcturus. At magnitude minus .04 it’s about as close to zero as you can get – the minus sign indicating it is a tad brighter than zero.  Its absolute magnitude is also pretty close to zero since absolute magnitude is defined as how bright a star would be if it were about 33 light years from us, and by modern measurement Arcturus is now believed to be about 37.6 light years from us.  That makes its absolute magnitude -.29.

Arcturus has the distinction of being the brightest star in the northern celestial hemisphere, but this is splitting hairs in several ways. It means it’s the brightest star north of the celestial equator. Sirius, now over in the southwest, is obviously  brighter. But Sirius is south of the celestial equator. Both stars are located close enough to the celestial equator so they can be seen from most places on Earth.

It’s interesting to note, however, that Mars is outshining it this month- by quite a bit. In round numbers, Arcturus is zero, Mars is minus 1.2 and Sirius, setting in the est early on April evenings, is minus 1.5.

But Arcturus (-.04) also wins the “brightest star in the northern hemisphere” distinction by another hair. Remember that the lower the magnitude number, the brighter the star. Both Vega (.03) and Capella (.08) are north of the celestial equator, and the difference in brightness between Arcturus (-.04), Vega (.03), and Capella (.08) is roughly a tenth of a magnitude.  For practical purposes, they all look the same.  But in practical terms, making the comparison by naked eye is – well –  very impractical. Capella is currently fairly high in the northwest. But next month, when Vega is high enough in the east to see well,  Capella will be rather low in the northwest. At that time Arcturus should look brighter – but its actual brightness will be aided by the fact that it is high over head at that time, so you are seeing it while looking through a lot less air than you will be when looking at Vega or Capella. Besides, visually trying to compare stars that are this far apart in our sky is next to impossible since you have to look away from one to see the other. I simply think of all three as magnitude zero and leave the hair splitting to the scientists and their instruments.

Oops – we interrupt this program for a bulletin from 1907!

Yes, having just written how impractical the naked eye comparison is, I found this passage in “The Friendly Stars” by Martha Evans Martin, a book that was published more than a century ago:

Arcturus and Capella are so nearly equal in brightness that astronomers differ as to which outranks the other, even when they measure  their light with a supposedly accurate  instrument and a trained eye. To my own eye Arcturus outshines Capella, and on asking various inexperienced persons for off-hand opinions as to the relative brightness of the two stars, I have invariably had an answer in favor of Arcturus. The best authorities, however, make Capella a shade brighter.

Oh my! And now with 100 years of scientific progress, the verdict is that Martha Evans Martin and her causal observer friends were correct – and the “best authorities”  wrong. Arcturus is the brightest.  So much for my idea that you can’t tell the difference with the naked eye! Give it a try and see what you think. (You can find a chart for Capella and more details about that star  in this post.) Since we’re ranking stars, however, Arcturus is actually fourth on the list of brightest stars – two others that are ahead of it, Canopus and Rigel Kentaurus, are not seen by observers in mid-northern latitudes. Sirius, of course, is.

While Arcturus radiates a lot of energy, much of it is not in the form of visible light. It has what’s known as a “peculiar spectrum” and radiates much of its energy in the infrared portion of the spectrum.  This means that to our eyes it doesn’t look as bright as it really is.

Orange-ish Arcturus is 215 times as bright as our Sun and 25 times the Sun’s diameter. (Image courtesy of  Windows of the Universe.)

One more deception of sorts: This brightness is not because Arcturus is so big – well , yes it is, but not big in terms of the amount of stuff in it, but big in terms of surface area. If you’re measuring the amount of stuff that makes up Arcturus – its mass – it is about the same size as our Sun. But Arcturus has a much greater surface area, so think of it as a hugely bloated version of our Sun. (Keep that in mind when you look at the comparison sketch above.) It is a much older star and is now going through its red giant phase, something our Sun will probably do several billion years from now, burning the Earth to a cinder in the process.

Hmmm . . . to get an idea of how much impact that large surface area has, if you put our Sun out near Arcturus it would be barely visible to the naked eye – and then under truly dark –  not light polluted – skies.

Vital stats for Arcturus, also  known as Alpha Bootes:

•    Brilliance: Magnitude  -.04, brightest star in the celestial northern hemisphere; shines with the luminosity of 215 Suns.

•    Distance: 37 light years

•    Spectral Type: K1 Giant

•    Position: 14h:15m:38s, +19°:10′:5

Guideposts reminder

Each month you’re encouraged to learn the new “guidepost” stars and asterisms rising in the east about an hour after sunset. One reason for doing this is so you can then see how they move in the following months. So if you have been following – even if this is just your second month – look for the previous guidepost stars and asterisms that you have learned and that are still with us in April. Here’s the list from east to west.

  • Arcturus
  • Leo’s Rump  (triangle)
  • The Sickle
  • Regulus
  • the Beehive
  • Procyon
  • Sirius
  • Pollux
  • Castor
  • Betelegeuse
  • Orion’s Belt
  • Rigel
  • Capella
  • the Kite
  • Aldebaran
  • the Winter Hexagon
  • the Pleiades 

Events for March 2014: Planet Sandwich Seasoned with a Sprinkling of Zodiacal Dust

Two realities - The image above gives you an idea of the true size and look of the planets visible in March skies. (From left, Venus, Earth, Mars, Jupiter, Saturn) That's one reality. What you see with your naked eye looks like stars - though very bright ones.

Two realities – The image above gives you an idea of the true size and look of the planets visible in March skies. (From left, Venus, Earth, Mars, Jupiter, Saturn) That’s one reality. What you see with your naked eye is much different.  Planets look like stars – though very bright ones  and some with distinctive hues.

At dusk Jupiter dominates the night sky high overhead –  think of it as one slice of bread for our sandwich. During morning twilight Venus dominates the sky low in the east – that’s the other slice. Between we have Mars on the evening side of midnight and Saturn on the morning side of midnight.

The “seasoning” – Zodiacal Light  – is interplanetary dust that forms a soft cone of light rising out of the west about 80 minutes after sunset – but is only visible if your skies are dark enough.

In total this makes a tasty show at any time of night to supplement the annual,  ever-advancing march of the stars. Here’s where and when to look.

The Zodiacal Light is the most challenging and can’t compete with the Moon’s light, so it’s available for the first two nights of the month, then comes into view again starting on the 18th and going for the rest of March, 2014.  To see it you need a clear sky to the west with no light pollution in that direction. You also need to allow your eyes to dark adapt. for 20 minutes. What you’re looking for is something roughly akin to the Milky Way in brightness, but in a soft pyramid shape that starts out wide as it rises from the horizon and leans to the south as it reaches one-third or more up the sky in the general direction of Jupiter. It’s really quite an amazing feature.

If you see it, reflect on this explanation from Wikipedia:

The material producing the zodiacal light is located in a lens-shaped volume of space centered on the Sun and extending well out beyond the orbit of Earth. This material is known as the interplanetary dust cloud. Since most of the material is located near the plane of the Solar System, the zodiacal light is seen along the ecliptic. The amount of material needed to produce the observed zodiacal light is amazingly small. If it were in the form of 1 mm particles, each with the same albedo (reflecting power) as Earth’s Moon, each particle would be 8 km from its neighbors.

For the metrically-challenged (that includes me) that means one dust particle every five miles! In the light of that information, it’s absolutely awesome if you see any thing at all!

Jupiter dominates the stars of Gemini, including the two bright twins to the left, Castor and Pollux.  In the midst of the brightest stars in our skies - the Winter Hexagon - it is the brightest of them all.

Highly recommended that you click this image for larger version. Hard to see the stars otherwise.

Jupiter  is on top these March nights, sharing the same general area of sky as the Gemini Twins. I took the picture (above) of it in late February – it’s position in March won’t change much, though it will get a little dimmer, it will still be much brighter than any star. As always, it’s fun to see if you can hold your binoculars steady enough to detect one of its four largest Moons. When it’s high like this you’re looking through less air and they may be easier to spot – but then, it’s a  bit hard on the neck to look so high in the sky while holding binoculars.

Again. to see any of Jupiter’s Moons your eyes have to be dark adapted, its best to use the largest, most powerful binoculars you can hold, such as 10X50, and you need an idea what to expect. The moons will be roughly in line with Jupiter’s equator – but at any given moment the number visible will vary, as will their distance from the planet, and which side they may be on. (They can all be on one side, they can be split two to a side, etc.) Jupiter together with its Moon – even when they are most distant, are only going to take up about 1/20th of the typical binocular field.

Here’s the sort of thing you are hoping to see:

How Jupiter’s moon might appear at one specific moment – in this case a moment when they were all on the same side of the planet. Of course the next night the view could be quite different. The letters stand for Europa, Io, Ganymede, and Callisto.

If this is your first time looking for the moons, do yourself a favor. Go to this page at the Sky and Telescope Web site and open the JavaScipt utility. It will tell you right where the moons are – and which is which – for any given moment.

As Jupiter dims a bit during the month, Mars becomes quite bright reaching magnitude -1.3 by the end of the month, and shines with a distinctive reddish hue. That’s  almost as bright as Sirius, but is no challenge to Jupiter, both of which appear white.

Click image for larger version. (Prepared from Starry Nights Pro screen shot.)

Click image for larger version. (Prepared from Starry Nights Pro screen shot.)

It rises about 3.5 hours after Sunset at the start of the month, but comes up during evening twilight at the end of the month. Generally it will be well placed for naked eye observing about an hour after it rises – those with small telescopes may want to wait another hour or two for a better view. That’s why I see it primarily as a late evening object.

You’ll find it by looking to the east about four hours after sunset as March begins. The Big Dipper will be high in the northeast. Follow the curve of it’s handle down to the bright star Arcturus. Continue this curve and you will come to Mars, roughly five degrees from the bright blue star, Spica. (Remember: When low on the horizon bright stars and planets will appear to sparkle and change color because you are looking through so much air.) While these relationships will remain the same, as the month goes on Mars will be rising earlier and earlier.

Click image for larger version. (Prepared from Starry Nights Pro screen shot.)

Click image for larger version. (Prepared from Starry Nights Pro screen shot.)

Saturn still is best seen in the early morning hours, though it rises just before midnight in the southeast. I think the best guide to it is the triangle it forms with Arcturus and Mars. Of the three corners of this triangle, Saturn is dimmest, shining with a soft yellowish light. However, it still outshines the stars in its vicinity.

You can’t miss Venus if you’re up an hour before sunrise. It actually comes up a couple hours before sunrise and in morning twilight is well above the southeast horizon an hour before sunrise. At about magnitude -4.7 (it gets a bit dimmer towards the end of March) it simply outshines everything except the Sun and Moon, so there’s no mistaking it and no difficulty finding it. Just look in the right general direction at the right time.

On March 27, 2014 a very thin, waning crescent Moon should fit in the same binocular field with Venus roughly three degrees up and to the left.

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