Every Sunday evenings there are discussions on astronomy topics at ABAA, Here is a summary of discussion that took place in the middle of August. The discussion was on Magnitude system.
Apparent magnitude
Members had discussion on Magnitude
system in astronomy. Starting with Apparent magnitude, the brightness
of stars as seen from earth. Hipparchus, Greek astronomer grouped the
brightest stars as first magnitude, little fainter stars became
second magnitude, and the faintest star eye could see as sixth
magnitude. The difference in brightness from one magnitude is 2.512
times, that makes 1st magnitude star is 100time brighter
than 6th magnitude star.
|
Sirius
(brightest star)
|
-1.5
|
|
Venus
(at brightest)
|
-4.4
|
|
Full
Moon
|
-12.6
|
|
The
Sun
|
-26.8
|
|
Faintest
naked eye stars
|
6
|
|
Uranus
|
5.7
|
|
Neptune
|
8
|
|
Pluto
|
14
|
In magnitude system, negative is
brighter and positive is fainter. As negative number increases the
brightness increases, for example our sun has apparent magnitude of
-26.8 making it brightest and Uranus has apparent magnitude of +5.7
which is fainter.
Absolute Magnitude:
Apperant magnitude are brightness of
stars as seen from earth irrespective of distances. The brightness of
stars, the magnitude they appear when placed at a constant distance
is called Absolute magnitude. The magnitude that stars will appear
when placed at a distance of 32.6 light years which is 10 parsec( 1
parsec = 3.26ly).
Our Sun placed at this distance will
have magnitude of 4.8 and Sirius, brightest star in the night sky
with apparent magnitude of -1.46 will have absolute magnitude of 1.4.
Members discussed in detail on these topics like calculating
apparent magnitude of Sun.
The colour of sun, the topic was good
in the sense that most of us think it should be yellow or red as seen
from earth. But in the course of discussion it was concluded that Sun
will appear white.
The topics like Luminosity, distance modulus etc were discussed in detail.
