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This is a consequence of the logarithmic magnitude scale, in which brighter objects have smaller (more negative) magnitudes than dimmer ones. For comparison, the whitish Sun has a B−V index of 0.656 ± 0.005, [2] whereas the bluish Rigel has a B−V of −0.03 (its B magnitude is 0.09 and its V magnitude is 0.12, B−V = −0.03). [3]
The diagram also shows considerable evolution through time. The red sequence earlier in the evolution of the universe was more constant in color across magnitudes and the blue cloud was not as uniformly distributed but showed sequence progression. One of five patches of sky covered by the COMBO-17 survey. [4]
The apparent magnitudes of stars in the system are often used to determine the color indices B−V and U−B, the difference between the B and V magnitudes and the U and B magnitudes respectively. [1] The system is defined using a set of color optical filters in combination with an RMA 1P21 photomultiplier tube. [2]
The typical axes for infrared color–color diagrams have (H–K) on the horizontal axis and (J–H) on the vertical axis (see infrared astronomy for information on band color designations). On a diagram with these axes, stars which fall to the right of the main sequence and the reddening bands drawn are significantly brighter in the K band ...
The Sun is found on the main sequence at luminosity 1 (absolute magnitude 4.8) and B−V color index 0.66 (temperature 5780 K, spectral type G2V). The Hertzsprung–Russell diagram (abbreviated as H–R diagram , HR diagram or HRD ) is a scatter plot of stars showing the relationship between the stars' absolute magnitudes or luminosities and ...
Below there are lists the nearest stars separated by spectral type.The scope of the list is still restricted to the main sequence spectral types: M, K, F, G, A, B and O.It may be later expanded to other types, such as S, D or C.
A truly dark sky has a surface brightness of 2 × 10 −4 cd m −2 or 21.8 mag arcsec −2. [ 9 ] [ clarification needed ] The peak surface brightness of the central region of the Orion Nebula is about 17 Mag/arcsec 2 (about 14 milli nits ) and the outer bluish glow has a peak surface brightness of 21.3 Mag/arcsec 2 (about 0.27 millinits).
An online star chart; Monthly sky maps for every location on Earth Archived 2007-09-13 at the Wayback Machine; The Evening Sky Map – Free monthly star charts and calendar for northern hemisphere, southern hemisphere, and equatorial sky watchers. Sky Map Online – Free interactive star chart (showing over 1.2 million stars up to magnitude 12)