Tuesday, March 3, 2009

A Crash Course in Amateur Astronomy - Lesson I

Do you know which direction is north? Anyone who wishes to become an amateur astronomer must have a good idea of compass directions. As this post is very BITS specific, it’s easy to the four directions using known landmarks. If you look in the direction of the Clock Tower, you are facing north; correspondingly if you look towards the temple it’s south. East is the direction you’d be walking, if you take the Institute road towards the IPC/Workshop. Now that we’ve established which direction is which, let’s talk about planets. In February, two planets will be very prominent on opposite sides in the sky. If you look towards the west any time before 8 PM, you’ll see (what seems to be) a star so bright that it’s been mistaken for a distant street lamp (by me). That’s good old Venus. I couldn’t help but notice that Venus sat high in the sky on the night of the 14th of February (I reserve any thoughts on implications for blossoming love). As Venus sets in the west, Saturn rises in the east. For an appreciably large duration of time you can see both Venus and Saturn in the sky. To find Saturn, face east and slowly turn your head upwards (still facing east). One bright star near the horizon (which doesn’t flicker and seems faintly yellowish) will immediately capture your attention. That’s Saturn. Continue looking higher. Further up in the Eastern sky, you’ll find two bright stars relatively close to each other in the sky. One of them is Pollux (the star with the reddish tinge) and the other is Castor (looks white, but it’s actually a six star system, incredibly), the two main stars in the constellation Gemini.


You might see another bright star in the east (again, with a distinct southward bias) that lies higher in the sky than Saturn, but not as far up as Pollux and Castor. That would be Regulus, the crown jewel in the constellation Leo. Regulus is a very interesting star. It spins so fast that its equatorial radius is 32% (or something like that) more than its polar radius.

Before moving to another celestial direction, I'll talk a bit about what the eastern sky would like later in the night, say around midnight. Obviously it is only the eastern sky that changes with time, and if you are up at midnight, you will notice an extremely bright star sitting near the horizon (but not too close). That’s Arcturus of the constellation Bootes. At the same time, if you look towards the southeastern sky you will see another reasonably bright star, again quite close to the horizon. That’s Spica, the crown jewel in the constellation Virgo. A word of warning here – the bunch of visually close stars that you see near, and a little higher in the sky than Spica, is actually another constellation called Corvus.

Now look south. Very close to the horizon lies Canopus (look for a bright star which seems to be flickering and changing colours quickly). Canopus is hard to spot because the horizon’s obscured by buildings and it never rises high in the sky. Let me take a short detour to explain why that’s the case. Everyone knows that the Earth spins from west- east, as everyone can see that the Sun rises in the east and sets in the west. But every star in the sky too rises in the east and sets in the west; more specifically, every star in the sky revolves around the North-South axis. Canopus being very close to the South Pole makes small revolutions around the N-S axis, while Polaris (the pole star) barely moves at all. One way to catch a glimpse of Canopus is to walk along the institute road (or the parallel road with the Gandhi statue) while looking South in the direction of the temple. Through gaps in the shrubbery, you can spot Canopus. Although Canopus is technically the second brightest star in the night sky, its true brightness cannot be seen in northern latitudes (Pilani’s around 28 degrees above the equator) as it’s affected strongly by the 'horizon haze'. Basically this means that stars near the horizon appear dimmer and flicker more, simply because they're closer to the lights of populated areas, and the associated wash of light population. Also, in the South lies the brightest star in the sky, Sirius. It’s easy to spot as it outshines every other object in the sky apart from Venus and the Moon. Sirius looks brilliantly white, and its parent constellation Canis Major can also be identified quite easily. Sirius seems to form one vertex in an approximately quadrilateral structure (the body of the dog); and there’s one lone star outside the quadrilateral which forms the tail of the dog.


A little higher in the Southern sky lies a very well known constellation, Orion the hunter. Orion has a host of bright stars, and the three stars which comprise the belt of the hunter are bright, visually close to each other and particularly easy to pick out.


To identify Orion, look south in the direction of the horizon and slowly turn your gaze upwards, still looking south. You’ll soon spot the belt. Now use the belt to form a trapezoid structure (of four bright stars excluding the belt) with the belt-stars in the centre. The bright reddish star on one vertex is Betelgeuse and the other bright white star on the diagonally opposite vertex is Rigel (the other two vertex stars too are bright but these two are noticeably brighter). The vertex star on the same side as Betelgeuse is Bellatrix (remember Harry Potter?) You’ve just picked out the body of the hunter.


Actually the constellation is much bigger, and includes fainter stars that form the arms of the hunter and the bow, but this will do for all those people without a 20/20 vision. Follow the line formed by the belt and a little distance away from Orion, you’ll spot another reddish, bright star. No it’s not Mars (as it’s been often mistaken to be). It’s Aldebaran, the eye of Taurus the bull. Follow the line formed by Betelgeuse and Bellatrix, in the direction of Betelgeuse and you’ll spot yet another bright star. This star looks white and is called Procyon; it’s a part of the constellation Canis Minor (the little dog). It’s time for some constellation trivia. Orion the Hunter is supposed to be fighting Taurus the bull, and is accompanied by two hunting dogs, Canis Major and Canis Minor.


I haven’t yet figured out a line pointer for this star, but since we have eliminated most other conspicuously bright stars in the area it should be easy to identify. It’s Capella and it usually lies high in the sky (all references to position are with respect to an assumed base time of 8 PM) near Orion but towards the north. Sirius, Procyon, Pollux/Castor, Capella, Aldebaran and Rigel form the Winter Hexagon. Sirius, Procyon and Betelgeuse form an approximately equilateral triangle called the Winter Triangle. Here’s some interesting information about Betelgeuse. Betelgeuse was like the bogeyman of astronomy when I was younger. Its size intimidated me. Betelgeuse is so large that its radius is something like 1000 times the radius of the Sun. If that doesn’t invoke any horror, here’s some imagery. If Betelgeuse were to be placed in the middle of the Solar System, its body would extend to cover the orbit of Mars!

To the north now… In the north lies the most famous constellation of all time, the Big Dipper (or Saptarshi, or Ursa Major, or the Great Bear, or the Great Question Mark). Unfortunately, its distinctive shape becomes prominent only when it rises high into the sky late in the night (again due to its brighter stars being obscured by horizon haze).


Then we can use the famous line pointer formed by its top two vertex stars to pick out Polaris. But at 8 PM, you can pick out another favourite constellation of mine, Cassiopeia. If you stand facing the Clock Tower from the Institute Road, Polaris will lie to its right in a relatively uncluttered portion of the sky, while Cassiopeia will lie to the left. Cassiopeia has the distinct shape of a W (inverted actually, from here in Pilani) and resembles the line structure of pentane (as it’s usually drawn).


Capella lies high in the northern sky. When Ursa Major rises, it will be in the North East, or, using our earlier notation, to the right of the clock tower.