Thursday, November 14, 2013

The Perihelion Passage of Comet ISON

Comet C/2012 S1 (ISON) will be at its perihelion (the closest it gets to the Sun) on November 28, 2013. It will then move back out into the solar system, becoming a night-sky comet and then fading from view. But watch now because Comet ISON will never return! It came from the Oort cloud and it will fly out of the solar system in a few million years.

When they are close to the Sun, sungrazing comets can be seen in the EUV channels of SDO and other solar satellites as their debris lights up the Sun's magnetic field. As Comet ISON moves through perihelion, SDO will point at three places away from the Sun to track the comet. This figure describes what we will do.

About 100 minutes before perihelion we will point SDO at the “Approach” position. It takes about 5 minutes for SDO to point to a new place in space and allow the fuel to stop moving (“Move, settle”). We allow for that in the timing of the moves. SDO will then observe that part of space for one hour. The Sun will appear in the upper right corner of the images and Comet ISON will move through the images from the lower right to the upper left. Images should be available on the SDO Comet ISON website after 12:30 pm ET.

At 1:09 pm ET, SDO will be pointed to the “Perihelion” position and observe that part of space for an hour. This location includes the perihelion, which happens at about 1:44 pm ET. At 2:14 pm ET, SDO will point at the “Departure” and observe for another hour. We will see Comet ISON moving away from the Sun in this box. At 3:19 pm ET SDO will point back at the Sun and we will resume our solar studies.

You can also see this in a movie.

The Oort cloud is many, many comets orbiting very far from the Sun. Kind of the paint splatter from making the Solar System. We think it starts about 0.1 lightyears from the Sun and extends to 0.8 lightyears — about halfway to the next star. Comet ISON is the first Oort-cloud, sungrazing comet in quite a while. It has fallen thousands of AU to just barely miss the Sun and make its escape. Join us at the SDO Comet ISON website from 1700 to 2024 UTC (noon to 3:24 pm ET) on November 28, 2013 (Thanksgiving Day in the USA) to watch this unique event.