Expert: Jayendra Upadhye - 7/25/2008

Question
Hello
When I hear the term "first magnitude star" I have figured in the past that the star would be at least a 1.OO or above (until we reach 2.00.  What do we call the stars BEFORE the 1.00 - all those up to Spica?  Do we cal them Zero Magnitude stars?   Thanks for any help.

Curtis

Answer
Hi Curtis,
I believe, when one says "a first magnitude star", one means magnitude 1 and above, until 2.

Its all about conveying the non-decimal parts.

thus a star 11.4 in magnitude would be called as a star of magnitude 11.

the scale is actually logarithmic, and ofcourse one gets decimal fractions in the real magnitude values.

All a matter of convention to me really.
refer to how the fractions are "rounded off" while referring to a magnitude range, in link number 2 on wikipedia.

THAT is your answer (link 2).
for example:-
0 magnitude is actually −0.50 to 0.49.

refer:-
1 - http://www.prc68.com/I/Mag.shtml
2 - http://en.wikipedia.org/wiki/Apparent_magnitude

regards
jayen