For a few days before and after a new moon, light from the Sun, reflecting off Earth and onto the Moon’s dark side, is just powerful enough to make the whole portion of the Moon facing Earth visible (see Figs. 1 and 2). This doubly reflected light (once from Earth’s surface, then from the lunar surface into our eyes) goes by the name earthshine. In the present note we discuss some features of earthshine and of the reciprocal phenomenon termed as moonshine.
References
1.
Peter
Thejll
, Chris
Flynn
, Hans
Gleisner
, and Andrew
Mattingly
, “Earthshine: Not just for romantics
,” Astron. Geophys.
49
, 15
–20
(2008
).2.
The eccentricity of an elliptical orbit determines its closeness to a circle; it is the ratio of the distance between its two focal points to length of its major axis.
3.
P. R.
Goode
, J.
Qiu
, V.
Yurchyshyn
, J.
Hickey
, M-C.
Chu
, E.
Kolbe
, C. T.
Brown
, and S. E.
Koonin
, “Earthshine observations of the Earth’s reflectance
,” Geophys. Res. Lett.
28
, 1671
–74
(2001
).4.
“
Reflectivity values of reflective surfaces
,” The Encyclopedia of Earth
, https://editors.eol.org/eoearth/wiki/File:Table_1.jpg.5.
The Moon’s phase angle is simply that angle at the Moon that is subtended by Earth and the Sun.
6.
The expression for earthshine or moonshine luminous flux would be Here REarth = 6.37 × 106 m is the radius of the Earth, RMoon = 1.74 × 106 m is the radius of the Moon, = 3.82 × 108 m is the mean distance between Earth and the Moon, κEarth (10%-90%) and κMoon (12%) are albedos of Earth and Moon, respectively; here moonlight flux is
© 2018 American Association of Physics Teachers.
2018
American Association of Physics Teachers
AAPT members receive access to The Physics Teacher and the American Journal of Physics as a member benefit. To learn more about this member benefit and becoming an AAPT member, visit the Joining AAPT page.
