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Beyond Earthly Skies

On Worlds Where Day Dominates Night

16 Feb 2015, 22:00 UTC
On Worlds Where Day Dominates Night
(200 words excerpt, click title or image to see full post)

For most planets including Earth, it is reasonably accurate to assume that the nightside begins at a zenith angle of about 90°, which means approximately half the planet’s surface is in daylight while the other half experiences night. A zenith angle of 0° corresponds to the spot on the planet where its host star appears directly overhead (i.e. the sub-stellar point). However, for planets that orbit very close to their host stars, the large apparent size of the stellar disk means that an irradiance distribution which assumes the nightside begins at a zenith angle of 90° becomes inaccurate. On these planets, the nightside begins at a zenith angle significantly larger than 90°. This means the dayside covers a much greater extent than the nightside.Planets that orbit close to their host stars are quite likely tidally-locked, where the same side of the planet always faces its host star, resulting in a permanent dayside and nightside. Extreme examples include COROT-7b, Kepler-10b and Kepler-78b. These planets orbit so close to their host stars that they each complete a year in a matter of hours. Temperatures at the sub-stellar point are expected to reach 2,500 K or more. Such temperatures are high enough to ...

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