Astronomy: The winter sky
I have been inundated with mail from my young friends. While some ask questions about astronomy and cosmology (to which I reply invariably), others have insisted upon discussion about the starry sky in winter. And how the winter stars are different from the summer stars?
Who can deny the beauty of winter night sky? It holds beautiful stars and constellations (those groups of stars that appear to form a ‘picture’ in the sky). Individual stars are interesting too, and they lend intrinsic beauty to the skies.
But there is a problem: at the end of each article I promise the contents for the next issue. Night sky, summer or winter, would have come just the same — but only after enough work on cosmology i.e. quasars, black holes and similar features of deep sky.
But now, in the face of persistence by my dear young friends, we shall go over the starry sky of winter. A typical winter evening begins a short while after sunset and as the sky darkens, first only bright stars show up. Then, about one hour after sunset, faint ones appear too.
In January, the sky is awash with stars of a wide variety. Their positions have been worked out for the whole country. Even then, I would like you to be familiar with latitudes of a few cities to help you with location of the area around your city. Latitude is your city’s position from Equator all the way up to North Pole. It is measured in degrees: zero for equator, and 90 degrees for North Pole (or South Pole, as the case may be).
There is no latitude less than zero, and none more than 90. Karachi’s latitude is 24.53 degrees north; Hyderabad’s is 25.23, Dadu 26.45, Sukkur 27.42, Quetta 30.15, Multan 30.15, Sahiwal 30.45, Lahore 31.32, Rawalpindi 33.38, Peshawar34.2, Mardan 34.2, Chitral 35.5, Shikarpur 27.57, Faisalabad 31.3, so on and so forth. Only remove the decimal points for convenience.
In December, January, February, the night sky is gorgeous: above the eastern horizon is constellation Leo (the lion), with Regulus as its main star. It is a pale-blue of great brightness. Somewhat to the west, near the zenith (top of the sky), is constellation Gemini (the Twins) with two bright stars Pollux and Castor of almost equal brightness. Further to the west is Auriga (the Charioteer) with a bright star, Capella.
Your longitude is your position on the north (or south) of equator. From this position you can study stars accurately. This is your geographical address. The address of stars is their position in the sky with relation to yours.
With change in latitude, ‘address’ in the sky will change accordingly. For example, Karachi’s latitude is about 25degrees, London’s 51.3 and Chicago’s is 41.5. All stars of northern skies are visible from these cities but their ‘heights’ in the skies from these cities would be different. Their positions will change too. From Karachi, the faintly visible Pole Star is visible at 25 degrees in the sky, from London at 51, and in Chicago at 41.5 degrees. Which means that your latitude and height of Pole Star from your city are the same. Likewise, Pole Star at North Pole is exactly overhead i.e. at 90 degrees. As for the southern sky, it is visible from the positions south of Equator.
Back to starry sky, between Gemini and Auriga, in fact a little to the south, is the sky’ most elegant and photogenic constellation, the jewel-bedecked Orion. Standing tall, erect and coldly aloof, Orion has three stars in its belt area. On its shoulder is the beautiful Betelgeuse, and on the knee, the lovely and huge, Rigel.
Also visible in the clean and pollution-free air of countryside is the star nursery, Orion nebula, the birthplace of a whole group of stars which will join the galaxy as its full-fledged members. The colorful and lovely nebula will then disappear for good.
Taurus, the bull with Aldeberan is close at hand, lending beauty to the night. Riding on the bull’s back is the one you cannot miss: Pleiades, or Seven Sisters or Surraya to us. These are in fact 50 stars that came into being from a single nebula only a few million years back. Near the zenith again is the star Algol, a member of constellation Perseus. Peeping indiscreetly in the western sky is a faintly visible galaxy (yes a galaxy!) Andromeda, more than twice the size of our home galaxy, the Milky Way.
Stars were perceived by our ancestors as gods, or heroes and they thought that by forming shapes, or figures they were trying to convey a message or something of the sort. The stars in fact convey nothing but a line of sight deception. Just as a lion or a tiger sitting in grass a mile away from you may appear in picture frame in close proximity. Nothing more, nothing less.
Enjoy your lovely winter nights watching stars and galaxies from a vantage point away from city lights, if possible. It will add beauty to your lives, I bet. More about stars of winter skies in the next issue. Warm clothes, a flask full of hot tea or coffee and if possible, a small binocular/telescope and some friends to keep you company is all I ask!