abbreviation of Declination, which along with Right Ascension
determines a position on the sky. Declination is measured north (+) and south (-)
from the celestial equator
and specified in degrees and minutes.
Charles Messier was a French comet hunter. His catalog (first published in 1781)
of nebulous objects was originally intended as a list of "junk" to avoid when
searching for comets.
(more info)
abbreviation of Right Ascension which along with Declination
defines a position in the sky. RA is measured eastward along the
celestial equator
with the zero point at the vernal equinox; it is specified in hours, minutes and
seconds (seconds omitted here)
Stars given a designation consisting of a letter and a number
according to the nature of their spectral lines which corresponds
roughly to surface temperature. The classes are: O, B, A, F, G, K, and M;
O stars are the hottest; M the coolest. The numbers are simply subdivisions
of the major classes. The classes are oddly sequenced because they
were assigned long ago
before we understood their relationship to temperature.
O and B stars are rare but very bright; M stars are numerous but dim.
The Sun is designated G2.
"young" for a star must be interpreted in the context of the average stellar
lifetime of billions of years. A young star is one that is no more than a
few million years old.
Glossary
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