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.
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!
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.
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.