Observational Stellar Astronomy

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Observational Stellar Astronomy - an Astronomy Net Article

Observational Stellar Astronomy
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by
G. Sanjith
October 21, 2004

Abstract

Think that stellar astronomy cannot be done with a small telescope or a pair of binoculars? Think the study of stars is best left to professional astronomers? Think again.

INTRODUCTION:

"We are made of star stuff": Carl Sagan

Stars are an integral part of the universe. There are very prominent in the night sky only next to the moon. But even people with a small telescope prefer to observe the moon rather than stars. They think that real stellar astronomy can't be done with a small telescope but the fact is even a good pair of binoculars would do. The immediate question that arises is "How?".

That is what this article ventures to explain. Also, telescope optics required for good stellar observation is provided.

TEMPERATURE OF A STAR:

There are different parameters of a star. One of them is its temperature. The temperature of a star can be found out easily by simple observations. The colour of a star and its temperature are related. Once the colour of a star is known, its temperature can be found by using some laws such as Wiens Law.

STAR COLOUR	STAR TEMPERATURE (K)
Strong blue	40000
Light blue	18000
Bluish white	10000
White	7000
Yellow-white	5500
Orange	4000
Red	3000

SPECTRAL CLASS:

All the stars in this universe are divided in to spectral classes based on their spectral lines. There are 10 spectral classes. The spectral class of a star and the temperature of a star are related. So the spectral class can be found for a star since we know its temperature. The ten spectral classes are:

O, B, A, F, G, K, M, R, N, S.

TEMPERATURE(K)	SPECTRAL CLASS
50000	O
25000	B
11000	A
7600	F
6000	G
5100	K
3600	M
3000	R, N, S

The spectral classes are based on the spectrum lines of the star. So, the elements present in the star can be known once the spectral class is known.

O- Ionized helium and metals, weak hydrogen
B- Neutral helium, ionized metals, hydrogen stronger
A- Hydrogen, singly ionized metals
F- Hydrogen weaker, neutral metals
G- Hydrogen, singly ionized calcium, neutral metals
K- Neutral metals
M- Titanium oxide, neutral metals
R, N, S- Zirconium oxide and neutral metals

TELESCOPE OPTICS FOR STELLAR OBSERVATION:

There are different types of stars in the universe. We shall broadly classify them into two:

Variables
Binary stars

Observing Variable stars: Variables are those stars which show some degree of variability in their luminosity and magnitude.Sometimes, the degree of variability may be high.So, for best observation a telescope needs to collect a lot of light from the star i.e., its light gathering power should be high which can be achieved by using an objective lens of large diameter in case of a refractor. A reflecting telescope too requires this.
Observing Binary stars:: Binary stars are a pair of stars which revolve around a common centre. The closest star to the sun Proxima Centauri is a binary star.For observing a binary star, the resolving power of a telescope needs to be high which is its ability to distinguish between two close objects having a small angular separation.

CONCLUSION:

This article was written with the aim that people should not think that stellar astronomy is something beyond them and not be content with identifying constellations and gazing at them. All the parameters of stars have not been covered here. Many like magnitude and stellar distance have been left out. The reader can devise some innovative methods to measure these parameters as well.

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