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.

2024 April 8
A sequence of eight images of Comet Pons-Brooks, from top
to bottom, showing the comet and its changing tail over
9 days. The ion tail looks very different in each of the
images, sometimes being much more complex than other times.
Please see the explanation for more detailed information.

The Changing Ion Tail of Comet Pons-Brooks
Image Credit & Copyright: Shengyu Li & Shaining

Explanation: How does a comet tail change? It depends on the comet. The ion tail of Comet 12P/Pons–Brooks has been changing markedly, as detailed in the featured image sequenced over nine days from March 6 to 14 (top to bottom). On some days, the comet's ion tail was relatively long and complex, but not every day, and not always on consecutive days. Reasons for tail changes include the rate of ejection of material from the comet's nucleus, the strength and complexity of the passing solar wind, and the rotation rate of the comet. Over the course of a week, apparent changes even include a change of perspective from the Earth. In general, a comet's ion tail will point away from the Sun, as gas expelled is pushed out by the Sun's wind. Today, Pons-Brooks may become a rare comet suddenly visible in the middle of the day for those able to see the Sun totally eclipsed by the Moon.

NASA Coverage: Today's Total Solar Eclipse
Tomorrow's picture: yesterday's eclipse

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