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.

2010 September 23
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Equinox and the Iron Sun
Credit: NASA / Goddard / SDO AIA Team

Explanation: Today, the Sun crosses the celestial equator heading south at 03:09 Universal Time. Known as an equinox, this astronomical event marks the first day of autumn in the northern hemisphere and spring in the south. Equinox means equal night. With the Sun on the celestial equator, Earth dwellers will experience nearly 12 hours of daylight and 12 hours of darkness. Of course, in the north the days continue to grow shorter, the Sun marching lower in the sky as winter approaches. To celebrate the equinox, consider this view of the Sun in extreme ultraviolet light from the Sun staring Solar Dynamics Observatory. Recorded yesterday, the false-color image shows emission from highly ionized iron atoms. Loops and arcs trace the glowing plasma suspended in magnetic fields above solar active regions.

Tomorrow's picture: equinox moon

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