Astronomy Picture of the Day

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

January 11, 1999
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Perihelion Sun
Credit: ISAS, Yohkoh Project, SXT Group

Explanation: The Earth's orbit is not a perfect, sun-centred circle. At aphelion, the most distant point in Earth's orbit, the Sun is 150 million kilometres away and at perihelion, the closest point, Earth approaches the Sun to within about 147 million kilometres. While aphelion occurs in July, perihelion for planet Earth comes in January. In fact, inhabitants of the Northern Hemisphere, particularly those wearily weathering winter storms, may be surprised to learn that Earth reached its closest point to the Sun on January 3rd this year. This false-colour picture recorded near perihelion is from the earth-orbiting Yohkoh Solar Observatory. It shows an increasingly active Sun in the light of X-rays. A negative colour scheme is used, darker colours representing more intense X-ray light.

Tomorrow's picture: The Wind on Mars

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Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (USRA)
NASA Technical Rep.: Jay Norris. Specific rights apply.
A service of: LHEA at NASA/ GSFC
&: Michigan Tech. U.