Geometric albedo
In
Diffuse scattering implies that radiation is reflected isotropically with no memory of the location of the incident light source. Zero phase angle corresponds to looking along the direction of illumination. For Earth-bound observers, this occurs when the body in question is at opposition and on the ecliptic.
The visual geometric albedo refers to the geometric albedo quantity when accounting for only electromagnetic radiation in the visible spectrum.
Airless bodies
The surface materials (
The geometric albedo of these bodies can be difficult to determine because of this, as their
For very bright, solid, airless objects such as
Stars
Stars shine intrinsically, but they can also reflect light. In a close binary star system polarimetry can be used to measure the light reflected from one star off another (and vice versa) and therefore also the geometric albedos of the two stars. This task has been accomplished for the two components of the Spica system, with the geometric albedo of Spica A and B being measured as 0.0361 and 0.0136 respectively.[2] The geometric albedos of stars are in general small, for the Sun a value of 0.001 is expected,[3] but for hotter or lower-gravity (i.e. giant) stars the amount of reflected light is expected to be several times that of the stars in the Spica system.[2]
Equivalent definitions
For the hypothetical case of a plane surface, the geometric albedo is the albedo of the surface when the illumination is provided by a beam of radiation that comes in perpendicular to the surface.
Examples
The geometric albedo may be greater or smaller than the Bond albedo, depending on surface and atmospheric properties of the body in question. Some examples:[4]
Name | Bond albedo | Visual geometric albedo
| ||
---|---|---|---|---|
Mercury[5][6] | 0.088 | 0.142 | ||
Venus[7][6] | 0.76 | 0.689 | ||
Earth[8][6] | 0.306 | 0.434 | ||
Moon[9] | 0.11 | 0.12 | ||
Mars [10][6] | 0.25 | 0.17 | ||
Jupiter[11][6] | 0.503 | 0.538 | ||
Saturn[12][6] | 0.342 | 0.499 | ||
Enceladus[13][14] | 0.81 | 1.38 | ||
Uranus [15][6] | 0.300 | 0.488 | ||
Neptune[16][6] | 0.290 | 0.442 | ||
Pluto | 0.4 | 0.44–0.61 | ||
Eris[17] | 0.99 | 0.96 |
See also
- Albedo
- Anisotropy
- Bond albedo
- Lambertian surface
References
- ^ See for example this discussion of Lunar albedo Archived April 13, 2009, at the Wayback Machine by Jeff Medkeff.
- ^ S2CID 131977662.
- ^ Gilbert, Lachlan (2019-04-02). "Scientists prove that binary stars reflect light from one another". UNSW Newsroom. UNSW. Retrieved 2019-04-02.
- ^ Albedo of the Earth
- arXiv:1703.02670 [astro-ph.EP].
- ^ S2CID 119307693.
- .
- ^ Williams, David R. (2004-09-01). "Earth Fact Sheet". NASA. Retrieved 2010-08-09.
- ^ Williams, David R. (2014-04-25). "Moon Fact Sheet". NASA. Retrieved 2015-03-02.
- ^ Mars Fact Sheet, NASA
- PMID 30213944.
- .
- ^ Howett, Carly J. A.; Spencer, John R.; Pearl, J. C.; Segura, M. (2010). "Thermal inertia and bolometric Bond albedo values for Mimas, Enceladus, Tethys, Dione, Rhea and Iapetus as derived from Cassini/CIRS measurements". Icarus. 206 (2): 573–593. Bibcode:2010Icar..206..573H. doi:10.1016/j.icarus.2009.07.016.
- ^ See the discussion here for explanation of this unusual value above one.
- .
- .
- ^ Verbiscer, Anne J.; Helfenstein, Paul; Porter, Simon B.; Benecchi, Susan D.; Kavelaars, J. J.; Lauer, Tod R.; et al. (April 2022). "The Diverse Shapes of Dwarf Planet and Large KBO Phase Curves Observed from New Horizons". The Planetary Science Journal. 3 (4): 31. Bibcode:2022PSJ.....3...95V. doi:10.3847/PSJ/ac63a6.
Further reading
- NASA JPL glossary
- K.P. Seidelmann, Ed. (1992) Explanatory Supplement to the Astronomical Almanac, University Science Books, Mill Valley, California.