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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.

The “March” of the Planets – they’re just Wild in the West in March 2012 – what you’ll see and why!

March starts off with a double-barreled planetary bang as Venus and Jupiter  meet and dance briefly, while just below them Mercury puts in its best appearance of the year zipping up for an easy look, then zipping back down.

First we’ll describe what you can see in a few simple charts, then we’ll delve into why you see it on the premise that the actual sight is much more exciting if you know what’s really going on back stage!  ( We also have a neat appearance by Mars in the eastern sky and Saturn in the morning sky, but more on that later. Oh – and while Mercury favors northern hemisphere observers this month, those in the south do see a good Jupiter/Venus show.)

What you’ ll see – March 1 -15

Go out a few minutes before sunset to a point where you have an unobstructed western horizon. Bring binoculars if you like – even a small telescope, though the naked eye gives a terrific view of this show. First, enjoy the sunset – get a sense of the Earth turning beneath your feet, and where the Sun is as it sets – though don’t look directly at it and certainly do NOT point telescope or binoculars there.  Wait 15-30 minutes and here’s what you should see in the twilight.

March gets going with a bang with this great planetary lineup in the western sky - the highlight of which is fleeting and elusive Mercury. Like all the star charts in this post, this was prepared from Starry Nights Pro screenshot. Click any star chart image for a larger view.

Yes, that’s my fist in the foreground. But you can use yours to help you find Mercury, the faintest of these three bright planets. Mercury will be about 10 degrees above the horizon, half an hour after sunset.  Hold your fist at arm’s length and you will cover about 10 degrees. (Yes, smaller people – or larger – have different size fists, but the proportions of arm length to fist size stay the same so this generally works.)  If you see this planetary line up, here are some things to notice.

First, look at the relative brightness of the three planets:

  • Venus is the brightest of the three by far. It glows at magnitude -4.3. Only the Moon and Sun are brighter.
  • Jupiter is next in brightness at -2.2 – brighter than any star gets.
  • Mercury is near its brightest at -.9 – but that makes it dimmer than the brightest star, now high in the south, Sirius – it’s about half a magnitude brighter.  And the fact that Mercury is so low and in bright twilight will make it more difficult to see. Binoculars will help find it, but it should be quite easily seen with the naked eye, especially when you know where to look.

Second. use your fist held at arms length (see chart) to note how high Mercury is above the horizon. This will change rapidly over the next 10 days.

Third, use your fist to estimate the distance between Jupiter and Venus. (One fist is 10 degrees.) This too will change rapidly over the next two weeks as Jupiter “falls” towards Venus and Venus  appears to quickly climb towards Jupiter.

Here are some charts at five day intervals to show the changes you can expect to see.

March 5, 2012

March 10, 2012

March 15, 2012

 So why do the planets appear where and when they do and why does Mercury change so rapidly in both position and brightness. Hop in your spaceship and zoom to a point well over the Sun so you can look down on our Solar System and watch the planets revolve.  That will give you the answer.

The two planets closer to the Sun than us – Venus and Mercury – revolve the fastest and have the shortest orbits.  They also pass between us and the Sun and thus go through phases like our Moon because we only see part of the sunlit portion of the planet as this happens. The outer planets, including Mars, Jupiter , and Saturn (all visible in our skies in March) don’t go through such phases and they change position more slowly – especially Jupiter and Saturn.

So let’s start with an overview showing where we and the other planets are on March 1, 2012. (All of these views are taken from the Orrery at  “Solar System Live” – a web site I heartily recommend you visit often and play with by changing the dates, etc., as encouraged at that site.)

March 1, 2012 – the entire Solar System


In this first view you need to imagine yourself on Earth. The Sun has just set, but you can see that when you look in the general direction of the Sun (west) you will see Mercury very close to it, Venus a bit farther away, and Jupiter farther away still.  If you turn around and look East you will see Mars near the Eastern horizon. Saturn is to the east as well, but will not be seen until near midnight and is really a morning sky object.

If you could look at the three bright planets in the Western sky with a small telescope, they would look something like the following picture.


To see the phases of Venus and Mercury in a small telescope it is best to catch them in twilight – start about 10 minutes after sunset -again, be careful not to look at the Sun with your telescope as your eyes would be severely damaged. Wait until the Sun is well below the horizon.  Venus gets so bright once it is fully dark that it tends to dazzle and dance and it is more difficult to see the phases then.  Mercury, on the other hand, is seldom high enough to get a good look because you are looking through so much atmosphere – but this is the best chance to see it in 2012. The relative sizes you see here are roughly the way they would appear in a telescope – they don’t represent the actual size difference of the planets because Jupiter – the largest by far – is much farther from us than either Venus or Mercury and so appears smaller than it really is.

March 5, 2012 – dance of the inner planets

In the following sequence you will see the Orrery view of Earth and the inner planets, as well as a view of what we see in the sky on each date  and how the phases of Mercury are changing. These changes in phase should make clear why the planet appears dimmer with each day after  March 5. On March 15 it will be quite difficult to see, as it will not only be close to the horizon, but it will have fallen in brightness almost two full magnitudes – that’s roughly the same difference in brightness you see between Jupiter and Venus – quite a change!

Western sky planets March 5, 2012 with inset showing how Mercury would appear in a small telescope.

Notice how Mercury is getting between us and the Sun - soon it will be lost in the Sun's glare.

Mercury is now (March 15) quite low, quite faint, and very difficult to see - and no wonder - just a slither of its sunlit face is visible to us as it comes near to passing between us and the Sun.

Mars and Saturn

Mars is an easy shot, visible in the east right after sunset, though it will be easier to see if you wait an hour or two. Use the chart in the “Look East” post here.  Mars gets close to us every two years, but not all “close” approaches are the same. Mars has an eliptical orbit and sometimes we hit it – as we are in 2012 – when it is closest to us, yet about as far as it gets from the Sun. That means it’s around 65 million miles form us this month. In some years it can be almosy half that distance from us, so while amateur astronomers will train their telescopes on it this month, it will appear relatively small.

Saturn is a wonderful sight in a small telescope and you can easily find it in the morning sky with the naked eye. Here’s a chart for a couple hours before sunrise at mid-month. Note that it is pretty close to one of our bright, guidepost stars, Spica, and they are roughly equal in brightness.

The early morning sky to the southwest is rich in bright stars and planets. Prepared from screenshot of Starry Nights Pro software. Click image for larger version.

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

If you studied the “Look East” post this month you met  Regulus, Mars, the Sickle and Triangle of Leo in the early evening sky. Now as Sunrise approaches they are nearing the Western horizon.  Saturn and Spica make a nice pair in the southwest that are hard to miss, with bright Arcturus above them and the brilliant, reddish guidepost star, Antares about due south.

Look East: March 2012 – with Mars – Roars in like a sickle and triangle! (Huh?)

Sure, I’d like to tell you March roars in like a lion – but honestly it’s easier to point to the sickle and the triangle and the “Little King” we call Regulus, this last being the new guidepost star for March. But there is a lion there, too. Let’s look at the sickle and triangle first, though, because they’re two very easy asterisms you’ll see in the east about an hour or so after sunset. The Big Dipper off to the northeast gives you an idea of size for comparison.

This is the eastern sky as it will appear about an hour after sunset from mid-northern latitudes. The circle represents a typical field of view for low power binoculars. While you should see the brightest stars easily, in twilight - or in typical light pollution - you'll find that binoculars will show some of the fainter stars nearby and help you be sure you have identified the correct bright star. The Mars position is for the 15th, but it will change a little each night. Click image for larger view. Prepared from Starry Nights Pro screen shot.

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

OK – so can you make this into a lion? I find it fairly easy if I consider the sickle his head and mane – and I consider the triangle his rear haunches. I leave the rest to my imagination and don’t really attempt to connect the dots.

Leo does look much like the Lion depicted inthe 1603 Bayer catalog.  Click image for larger version.
The stars of Leo do indeed trace out some key parts of the Lion depicted in this plate from the 1603 Bayer atlas. (Click image for larger view.) Note that the bright star that marks the tail is named “Denobola,” which in Arabic really does mean “tail.” We encounter this also in the tail of Cygnus the Swan where the bright star is named “Deneb.” The Arabic star names are frequently descriptive. (Image courtesy of Linda Hall library of Science, Engineering and Technology.)


Regulus, our new bright guidepost star for this month, means “little king,” or “prince,” in Latin. That fits right in with the lion‘s reputation as King of the Beasts. And what a lovely image to have a prince leading a lion onto the night-time stage this month!

Is Regulus memorable in its own right? Well yes. It’s a star that is spinning so fast that if we could see its disc, it would look like a beach ball that someone sat on. It takes Regulus about 16 hours to make one rotation – in comparison, our Sun, a smaller star, takes about a month to rotate. In fact, if Regulus were spinning just a bit faster, it would spin itself apart!

The rapid spinning gives Regulus an equatorial diameter that is about one-third bigger than its polar diameter. This also results in the polar regions of Regulus being much hotter than its equator.

Regulus is also a multiple star system, but as such rather dull visually. The second star in the system is much fainter, so it can barely be detected by a skilled observer using binoculars – and in a telescope it’s so far away from the primary star that the two stars don’t seem like a pair at all. Both these stars are spectroscopic doubles – meaning the companions are so close we can’t see them with a telescope.

Though a relatively young star – about 250 million years as compared to the five-billion-year age of our Sun – Regulus is apparently nearing the end of its normal life as a “main sequence” star. That is, it’s about to finish burning hydrogen, which means it will soon go into the last stages of its life. But according to Jim Kaler, Regulus is also a curious case. It appears to have a very close white dwarf companion which scientists believe once was much larger and brighter than Regulus. But the gases were drawn from the white dwarf into Regulus, making Regulus both huge and bright and causing it to spin the way it does.

In total, Regulus is another example of how what looks like a common star to us, is quite fascinating when seen in the light of modern science.

Vital stats for Regulus:

• Brilliance: Magnitude 1.35, 22nd among the brightest stars in our sky; shines with the luminosity of about 150 Suns.
• Distance: 77 light years
• Spectral Type: B7V
• Position: 10h:08m:22s, +11°:58′:02

The buzz about the Beehive (M44) and Leo’s whiskers – a binocular treat!

In ancient times the constellation Leo extended much farther east and west, and M44 was considered to be its whiskers.

from “The Next Step – Finding and Viewing Messier Object” by Ken Graun

Whiskers indeed! I like that. It’s a great way to remember where to look for M44, for if you can find the Sickle – the huge head and mane of Leo – then all you have to think is “now where would his whiskers be?” Scan 2-3 binocular fields in that direction – westward – and you should soon stumble upon M44, the Beehive. Here is a chart you can use to find it. Do wait  until about two hours after sunset when it is really dark and M44 is well up in the sky.

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

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

M44 also is known as “the Beehive,” and Praesepe, which is Latin for manger. And if you have dark skies, away from light pollution, you will see this as a small, wispy cloud, perhaps suggestive of Leo’s whiskers. It is, in fact, a beautiful star cluster as binoculars or a small telescope will reveal. Galileo first discovered its true nature, and in this hazy patch counted more than 40 stars. You should see about that many with your binoculars. This is one of the nearest star clusters to us, and although there is still debate over its exact distance, it is around 580 light years. That compares with about 400 light years for the Pleiades. The two clusters are pretty close to the same size, but M44 is considered much older. M45 – the Pleiades – is estimated to be 78 million years old, while M44 is thought to be about 660 million years old. As star ages go, they’re both quite young. But open clusters, such as these, do not last too long – the members stars tend to get drawn off by close encounters with other stars as the whole clusters moves about our Milky Way galaxy.

The Latin name, Praesepe, is worth examining because it explains the names of two relatively bright stars which flank it – Asellus Borealis and Asellus Australis. Borealis means “northern” and Australis means “southern.” Asellus means “ass” – as in donkey – and Praesepe means “crib” or “manger.” In other words, the Beehive apparently looked to some like a pile of hay in a manger, and these two flanking stars were donkeys eating that hay, one to the north and one to the south. In binoculars the scene should look something like this.

M44 and surroundings as it would appear in binoculars with a 5-degree field of view. Click image for larger view. (Chart derived from Starry Nights software screen shot.)

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

The two donkeys are about as bright as the stars in the handle of the Little Dipper, so under dark skies should be faintly visible to the naked eye with the northern one the dimmest. The third star, Eta Cancri, is dimmer still. Its name, however, indicates that it, the Beehive, and other stars shown here are all part of the rather obscure constellation known as Cancer, the crab.

Look North in March 2012 – Oops, there’s a big hole in the sky!

Well, not really – but unless you live in an area with very dark skies, free of light pollution, you’re going to have a hard time seeing the faint stars above Polaris, the North Star, at this time of year. Here’s what our March north sky star chart looks like.

Our northern sky is quite dark above Polaris, but the Big Dipper is prominent in the northeast and serves as our primary guide to finding the North Star. Click image for larger view. (Prepared from a screen shot of Starry Nights software.)

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

Notice the emptiness? The area labeled “Dark Hole?” Mind you, this is not a black hole – just an area of our sky that looks quite empty – unless your viewing location is free of light pollution and your eyes are thoroughly dark adapted. If you can see all seven stars of the Little Dipper, then you should see several stars in this area. But even then I doubt if you will be able to trace out the constellation which goes there. It’s known as Camelopardalis. My copy of Urania’s Mirror, published in 1832, says Camelopardalis consists:

. . . of 58 stars, but none larger than the fourth magnitude. . . .The Camelopard is an Abysinian animal, taller than the elephant, but not so thick. He is so named because he has a head and neck like a camel, and is spotted like a leopard; but his spots are white upon a reddish brown ground. The Italians call him giraffa. To Hevelius, who formed the constellation, he owes his celestial honors.

Ah, giraffe! Thank you, Italians. Here’s how he is pictured in full color on one of the constellation cards that came with Urania’s Mirror (The scan is © Ian Ridpath.)

Camelopardalis as depicted on the card from Urania’s Mirror, 1832. Notice the Pointer Stars of the Big Dipper are near the upper left and Polaris is just to the right of the giraffe’s head, so at this time of year the giraffe would appear upside down in our northern skies.

If you put him in the sky at this time of year his head would be down near Polaris. . . . Hmmm… the illustrator seems to have forgotten the spots mentioned in the text, and the animal’s neck got a bit longer than a camel’s. Ah well – while the 1830s had some advantages in terms of simplicity, I don’t think I would like to be trying to learn the night sky with Urania’s Mirror as my only guide.

Oh – but speaking of long necks, one of the things that has always fascinated me is some of the early attempts at astronomical telescopes and particularly the one in the following woodcut. This was an instrument built by Johann Hevelius in the mid-17th century at his observatory in Poland. The tube was about 150 feet long – befitting, in a strange way, for the man who put a giraffe in the northern sky!

Click image for larger view.
There was a logic to this giraffe-like telescope.
At the time a telescope’s lens could not bring the different colors of light to a single focus, so bright objects were always fringed with color and nothing was in really sharp focus. This negative effect, however, could be lessened by making the telescope’s focal length longer – so to get a really good telescope you had to go to these ridiculous extremes – which, of course, made it a nearly impossible telescope to use in any practical way.
Impressive to look at – difficult to aim and look through.
Fortunately the achromatic lens – combining two different types of glass – was invented and this reduced the problem considerably even in a relatively short telescope. We still use such achromatic lenses today ins mall refractor, though if you want to get a really sharp, color-free image you pay considerably more money for an apochromatic lens. Or, you listen to Newton who figured way back int he 1600s that the way around this was to design a telescope that used a mirror to collect the light rather than a lens. Trouble was, it took a long time to learn how to make mirrors that didn’t tarnish quickly when exposed to the night air. Nothings easy!
Now – about or “hole” in the northern sky. Get to a place where light pollution is at a minimum and it will fill with stars – relatively faint, but they are there. Just scan around with binoculars and you’ll find some even through the typical light pollution most people today are forced to endure. 

Events in February 2012: Look West! Can you see the faintest – and the brightest?

Looking west this month after sunset offers a study in contrast. For one thing, the two brightest planets – in fact, the two brightest objects in our skies after the Sun and Moon – Venus and Jupiter, will be drawing together night-by-night until at the end of the month you could nearly cover the pair with your fist.

Why? Because in a very real sense we live in two worlds. One is the world of the ancients. The world they saw and we still see. In it the planets are wandering stars that  change positions in irregular patterns, while the fixed stars change position in our sky – but hold their positions relative to one another.

That is one world. It is an obvious world, but one many of us have lost touch with because our artificial light and homes hide the night sky from us.  The other world is the one revealed by the past four centuries of science.  In that world the planets are nearby, solid bodies, shining by reflected light and all revolving around a single star – our Sun. How they appear to us is governed by the laws uncovered by the work of Copernicus, Galileo, Kepler, and Newton.

To me the  fun is to live in both worlds – to appreciate the night sky as the ancients saw it – and at the same time to appreciate the night sky as revealed by the great minds of science.  And this February gives us a perfect opportunity to do so. For what really fascinates me is that the Jupiter and Venus show is the brightest part of two western light shows, one involving the largest object in our solar system after the Sun – Jupiter – and the other some of the smallest things we will see – the zillions of dust specs (roughly one millimeter in size) – that make up the Zodaical Light.

So when you are through being dazzled by photons reflecting off of huge bunches of stuff, relax, and see if you can find one of the most delicate reflection features of our solar system – in fact, one of the more subtle things you’ll ever see in the night sky – the Zodaical Light. It, too, is at its prime this month, but you need a genuinely dark sky, especially to the west, to see it.

Much more about that in a moment – but first the easy shot that goes on all month – the Jupiter and Venus Show!

This one you can’t miss, even if you live in a region where most of the stars are washed out by local light pollution. There’s a wonderful symmetry to this show and it’s so simple to see. Just go out about 45 minutes after sunset any night in February and look up in the southwest. Roughly overhead the brightest “star” you will see is Jupiter. And high in the west at this hour will be an even brighter “star,” Venus.

Venus is about six times brighter than Jupiter, but this difference may not be quite that obvious because Jupiter will be seen high in the sky where it has to get through less of our atmosphere – and the sky will be darker near Jupiter. Venus will still be basking against a twilight background.

There are subtle changes in the brightness of each planet as the month goes on. Venus starts the month at magnitude – 4.1. (Remember, the lower the magnitude number, the brighter the object.) By the end of the month it is magnitude – 4.3. Why? Well, in our travels – and it – about the Sun we get closer to it. At the start of the month we’re about 102,858,000 miles apart. At the end of the month this gap has closed to 85,002,000 miles.

That’s really significantly closer,so you might think the change in brightness would be even greater. However, as we draw closer to Venus, Venus is also inserting itself between us and the Sun and so we see less of it – that is, it goes through phases like our Moon and at the start of the month we’re seeing light reflected from 71% of its surface, while at the end of the month we’re seeing just 64% of its surface. (I’m indebted, by the way, to Sky and Telescope magazine which publishes all this data about the planets each month.)

Jupiter, since it’s orbit is well beyond us, doesn’t go through these dramatic phases. We see 99% of it at the start of the month and 99% at the end. But we are drawing apart – essentially the Earth in it’s much smaller orbit is quickly widening the gap between us and Jupiter – and that gap is much larger than the one between us and Venus, so even though Jupiter is much larger, it is so far away, it is still dimmer.

At the start of the month Jupiter shines at magnitude -2.3 and at the end of the month it is magnitude -2.2. That’s a change that will only be noticeable to those with lots of experience at evaluating brightness – to most of us, it will look the same. But in terms of distance Jupiter starts the month about 468,162,000 miles from us and by the end of the month this gap is 507,036,000 miles.

In other words Jupiter is nearly 40 million miles farther away, yet dims in light by just one-tenth of a magnitude.

I know these numbers might just be bouncing off your mind with a sense of irrelevancy, but they fascinate me simply because they reveal some of the inner gurglings of what are the constantly changing dynamics of our solar system – dynamics that result in us seeing in the night sky two very bright lights appearing to approach one another night-by-night.

Think of how that must have looked to people in other times when we didn’t spend so much time indoors, dazzled by artificial lights and we knew nothing about what these bright lights in the night really were, nor how they’re relationships changed as each moved about the Sun at different speeds in orbits of vastly different lengths.

And with that in mind let’s switch gears now and consider some very tiny objects that are orbiting the Sun as well and displaying a soft glow in our western sky as they do so.

Basking in the Zodiacal Light of Almost Spring

The last 10 days or so of February 2011 will be a good time to start looking for the Zodiacal Light.

Planets shine by reflected light, planets are found in the plane of our solar system – and thus in a certain section of sky, marked by the wide band of the zodiac – and so are these minute dust particles. They’re just hard to get your mind around because they don’t consist of the cloud of dust that is anything like our common experience of dust. That is, these dust particles are minute, but they are also far apart. So to get a picture of them, imagine a bunch of them about half the size of a BB shot and each separated from the other by about five miles! Five miles! That’s what we mean by “cloud” in this case.

But, of course, space is so huge and we’re so far from these dust particles that even with that separation, from our distance they look like a cloud and when the sun shines on them, this cloud creates a soft glow in our western sky.

You don’t need a totally clear horizon to see the zodiacal light, or binoculars, but you do need total darkness and that means little-to-no light pollution and no Moon. So you want to wait until a few days after full Moon to begin this quest. I feel I have a good shot at it from my favorite ocean-front observing point where I have a clear horizon to the west with no cities to create light domes there. Evenings in February and March – and mornings in September and October – are the best time for folks at mid-northern latitudes to look for this.

The zodiacal light is roughly the same intensity as the Milky Way, so if you can see the Milky Way from your chosen location, then you should be able to pick up this faint glow. Like the Milky Way, it stretches over a good deal of sky. It is widest near the horizon and gets narrower as it rises towards the zenith. You want to look for this roughly 80 minutes after sunset. You can check for an exact time for your location by getting information from here on when astronomical twilight ends. (The drop-down menu on that page specifies the times for astronomical twilight.) As astronomical twilight ends you want to start looking. As with any faint object, your eyes need to be dark adapted, so I am assuming you have been out for at least 15 minutes with no white light to dazzle you. If you try to look for this earlier, you may confuse it with twilight. Much later and it is not as bright, since what we are seeing is sunlight reflecting off interplanetary dust particles – dust particles that orbit in the same plane as the planets – the area we call the zodiac – and thus the name for this phenomena, zodiacal light.

If you see it, reflect on this more detailed 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 about one dust particle every five miles! And that causes all that light?! Awesome!

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