Nightskywatching
by
Kamal Lodaya

November Sky
The map shows stars seen at 9 pm on 1st November (31st October was Full Moon, so we are now in the month of Kartika), 8 pm on 15th November (New Moon, amavasya) and 7 pm on 30th November (Full Moon, Kartika purnima). 

Last issue's star map showed the huge rectangle of Pegasus or Mahashwa, the flying horse. Below it was a striking line of stars, Andromeda or Devayani. Parallel to it was the little Ashwini nakshatra in the constellation of Aries or Mesha. Going from Ashwini towards Pegasus you will find the bright planet Mars or Mangala. If you watched it last month, you will find it a little less bright. If you saw it with a telescope last month and see it again now, you will see that Mars is smaller: it has moved farther away from us. Last month the Earth, which moves faster around the Sun, overtook Mars. This month Earth has left Mars behind.
This time we look at the northern sky to find an interesting M-shaped constellation called Cassiopeia or Sharmishtha. As you can see from the map, following the highest stroke of the M takes you to Hamsa or Cygnus. The first star is called Kaf and the second one is Schedar. Both names come from Arabic astronomy. So you follow Schedar to Kaf to reach Hamsa.

If you are seeing this away from city lights, you may see that there is a faint cloud here, this is the Milky Way. If you saw the Milky Way in Sagittarius (Dhanu) in summer, you will find it much fainter here. This is because in Sagittarius we are looking in the direction of the centre of the Milky Way, here we are looking in a direction away from its centre.

The next star at the centre of the M was named Navi by an astronaut whose name was Ivan. Officially its name is Gamma Cassiopeiae, that is, the third brightest star in Cassiopeia. It is not difficult to guess why the Arabs saw Kaf-Schedar-Navi as a camel's hump.

Following the stroke Navi-Schedar upwards takes you to Pegasus. Following this same stroke Schedar-Navi downwards and curving a bit inwards you come to a small star called Polaris or Dhruva.

Most people are disappointed to find that the pole star (Dhruva) is not very bright. It is 433 light years away, which is more than a dozen times the distance of bright stars like Vega (Abhijit) and Altair (Shravana). It is a triple star system, two bright stars going around each other, and a third faint star going around them.

What makes Dhruva special is that it stays where it is. If you wake up at night or before dawn and see the night sky, all the other stars in the East will have gone higher and higher and be seen setting towards the West. Cassiopeia will now look like a W. But following the same stroke, curving inwards, you will find the pole star at the same place.

Today it is easy to understand why this happens. We know that the Earth rotates once in 24 hours. So it is not the stars that are rising in the East and setting in the West. It is we on the Earth who are turning around, and watching different parts of the space around us from different angles.

On 11 November 1572, 448 years ago, the Danish night sky observer Tycho Brahe was surprised to find that the "camel hump" Kaf-Schedar-Navi was completed to form a diamond shape with a fourth star brighter than the planet Jupiter. He named it Nova (new), today it is called a supernova, a star which exploded.

Over the next year it faded and became invisible. With other European observers, Tycho found that it was at the same position with respect to the other stars of Cassiopeia seen from everywhere. This is unlike the Moon, which is seen slightly differently with respect to the background stars from different parts of the Earth. He concluded that it was farther than the Moon, that is, it was in the "unchanging heavens". (Today we know it was 7500 light years away.)

This changed Tycho's life, he became an astronomer. The 1572 supernova changed astronomy from an observation based discipline to a physics based one, because it showed that although the stars do not appear to change, they do change over time. In 1952, British observers Hanbury Brown and Cyril Hazard found the remnant of the supernova using a radio telescope (one which collects radio waves instead of optical light) at Jodrell Bank, Manchester.