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STARS

Ursa Minor

Atmosphere Absorption

The nearer a star is to the horizon the fainter the star appears because of atmospheric absorption. The best spot in the sky to observe astronomical objects is the zenith which is directly overhead or when the object is closest to the zenith. Star light travels through less atmosphere at the zenith than any other direction. Star light travels through the most atmosphere when the star is at the horizon than any other direction. For example, you can look directly at a Sun set because the Sun's light has maximum atmospheric absorption at the horzion. When Sun is high in the sky it is painful and dangerous to look at the Sun with your eyes because there is less atmospheric absorption of the Sun's rays.

The following atmosphere absorption table assumes optimum atmospheric conditions. Usually local atmospheric conditions are worst and dimming will be greater.

Atmosphere Absorption

Altitude in degrees above the horzion

Dimming in terms of magnitude

1

3.0

4

2.0

10

1.0

17

0.6

21

0.4

26

0.3

32

0.2

43

0.1


Atmosphere Absorption References

Section 26 The Atmosphere and Seeing, page 437
Amateur Astronomerís Handbook, Fourth Edition by J.B.Sidgwick Revised by James Muirden

Section 26.2 The atmosphereís transmission characteristics, page 446
Amateur Astronomerís Handbook, Third Edition by J.B.Sidgwick

Atmospheric Absorption, page 282
The Amateur Astronomerís Handbook, Third Edition by James Muirden

Appendix C Air mass, atmospheric extinction and other calculations, page 268
Visual Astronomy of the Deep Sky by Roger N. Clark

Atmospheric extinction table, page 104
Through the Telescope A Guide for the Amateur Astronomer by Michael R. Porcellino

Atmospheric extinction, page 404
The Ever-Changing Sky A guide to the Celestial Sphere by James B. Kaler

Atmospheric extinction, page 51
Observerís Handbook 2000 by The Royal Astronomical Society of Canada, Editor: Roy Bishop

Atmospheric extinction, page 137
Introduction to Observing and Photographing the Solar System by Dobbins, Parker and Capen

Atmospheric extinction, page 238
A Complete Manual of Amateur Astronomy by P. Clay Sherrod

Section 19.4 The Extinction of Starlight, page 100
Challenges of Astronomy, Hands-on Experiments for the Sky and Laboratory by W. Schlosser, T. Schmidt-Kaler and E.F. Milone

Atmospheric Absorption, page 81
Astronomy Data Book by J. Hedley Robinson and James Muirden..