CMEs, Comet Captured in SOHO/LASCO Imagery 2/20/2015

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The Earth-facing solar disk has been relatively quiet for the last week. Yesterday, however, SOHO LASCO instruments imaged a pair of CMEs. Concurrent with those CMEs, a comet was visible looping around the Sun in the same images. In this post, we’ll take a look at a time lapse of LASCO imagery and guide you through what is going on. Here’s the video:

Where the images come from: SOHO is the Solar and Heliospheric Observatory. It is a spacecraft run jointly by NASA and ESA (European Space Agency) that orbits near L1 – that’s the same stable place DSCOVR is headed. It’s primary missing is to image the Sun and Solar atmosphere. It has several cameras aboard, one of those is LASCO.

LASCO stands for Large Angle and Specrometric Cornograph. Effectively, It is a camera pointed at the Sun that is focused such that the Sun is in the center and it is a wide enough angle that it captures an image of space up to 8 sun-diameters in each direction (32 radii total). In order to actually capture the atmosphere of the sun, an arm holds a circular disk in front of the lens to block the Sun itself. In the video, you can see the result – a narrow blocked bar (the arm) from bottom left to center, and the dark circle in the middle. This leaves just the Corona, stars behind, and planets behind the Sun visible.

Lasco is particularly useful for spotting plasma eruptions (CMEs) from the Sun. As the ejecta lifts off the surface of the Sun it becomes visible as bright plumes around the blocked disk. Scientists can measure how large, how wide, and how fast the ejections are moving by studying their signature on the coronagraph.

In this video, the first CME is visible in the Northeast limb between :09 and :12. This is a fairly narrow CME, and given the timelapse, it lasted about 4 hours. The Second CME is much more impressive and launches from the Southwest limb. It is brighter, and it is much wider, appearing to emerge from almost 90 degree of the disk. The second CME can be seen starting around :38 and continuing to the end of the sequence.

Finally, and arguably most interesting, if you watch carefully, you will see a comet looping around the Sun in this image. It is small. The easiest way to see it is by watching the left side of the screen towards the end of the video, you will see it and it’s small tail moving from right to left and slightly up. Now, watch the video again, and see if you can watch it swing from the upper right down around behind the larger CME, and emerge to the South of the sun, then progress behind the Arm, and emerge again.

We’ve taken a screen grab and circled the comet below:

Comet SOHO 2875 in LASCO
ScreenGrab from LASCO timelapse with Comet 2875 identified

Happy Hunting!

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