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Stars that have magnitudes between 1.5 and 2.5 are called second-magnitude; there are some 20 stars brighter than 1.5, which are first-magnitude stars (see the list of brightest stars). For example, Sirius is magnitude −1.46, Arcturus is −0.04, Aldebaran is 0.85, Spica is 1.04, and Procyon is 0.34.
The scale used to indicate magnitude originates in the Hellenistic practice of dividing stars visible to the naked eye into six magnitudes. The brightest stars in the night sky were said to be of first magnitude (m = 1), whereas the faintest were of sixth magnitude (m = 6), which is the limit of human visual perception (without the aid of a ...
An object's absolute magnitude is defined to be equal to the apparent magnitude that the object would have if it were viewed from a distance of exactly 10 parsecs (32.6 light-years), without extinction (or dimming) of its light due to absorption by interstellar matter and cosmic dust. By hypothetically placing all objects at a standard ...
Sky brightness refers to the visual perception of the sky and how it scatters and diffuses light. The fact that the sky is not completely dark at night is easily visible. If light sources (e.g. the Moon and light pollution ) were removed from the night sky , only direct starlight would be visible.
In between the two distributions is an underpopulated space known as the green valley which includes a number of red spirals. Like the comparable Hertzsprung–Russell diagram for stars, galaxy properties are not necessarily completely determined by their location on the color–magnitude diagram. The diagram also shows considerable evolution ...
The famed "devil comet," officially known as 12P/Pons-Brooks, on April 21 made it closest approach to the sun in its 71-year orbit of the massive star.. Earning its nickname from its distinctive ...
C-R – Formerly its own class (R) representing the carbon star equivalent of late G- to early K-type stars. C-N – Formerly its own class representing the carbon star equivalent of late K- to M-type stars. C-J – A subtype of cool C stars with a high content of 13 C. C-H – Population II analogues of the C-R stars.
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