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Nonthermal sources can have very high brightness temperatures. In pulsars the brightness temperature can reach 10 30 K. [9] For the radiation of a helium–neon laser with a power of 1 mW, a frequency spread Δf = 1 GHz, an output aperture of 1 mm 2, and a beam dispersion half-angle of 0.56 mrad, the brightness temperature would be 1.5 × 10 10 ...
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 ...
In contrast, the term brightness in astronomy is generally used to refer to an object's apparent brightness: that is, how bright an object appears to an observer. Apparent brightness depends on both the luminosity of the object and the distance between the object and observer, and also on any absorption of light along the path from object to ...
Brightness is the polar opposite of darkness. ... Scientific. Luminosity; Brightness (sound) Brightness temperature; Surface Brightness; Artistic. The Brightness, ...
As defined by the US Federal Glossary of Telecommunication Terms , "brightness" should now be used only for non-quantitative references to physiological sensations and perceptions of light. [3] Brightness is an antonym of "dimness" or "dullness". With regard to stars, brightness is quantified as apparent magnitude and absolute magnitude.
"Early" is a synonym for hotter, while "late" is a synonym for cooler. Depending on the context, "early" and "late" may be absolute or relative terms. "Early" as an absolute term would therefore refer to O or B, and possibly A stars. As a relative reference it relates to stars hotter than others, such as "early K" being perhaps K0, K1, K2 and K3.
More luminous Cepheids are cooler and larger and have longer periods. Along with the temperature changes their radii also change during each pulsation (e.g. by ~25% for the longer-period l Car), resulting in brightness variations up to two magnitudes. The brightness changes are more pronounced at shorter wavelengths. [13]
Nevertheless, very hot main-sequence stars are still sometimes called dwarfs, even though they have roughly the same size and brightness as the "giant" stars of that temperature. [ 21 ] The common use of "dwarf" to mean the main sequence is confusing in another way because there are dwarf stars that are not main-sequence stars.