Thursday, January 5, 2023

Perihelion Interrupts Instrument Calibrations

SDO executed the EVE FOV and HMI/AIA Flatfield instrument calibration maneuvers yesterday, 04 Jan 2023, at 1415 UTC (9:15 am ET) and 1730 UTC (12:30 pm ET), respectively. During these maneuvers, at 1617 UTC (11:17 am ET) the Earth reached perihelion, the point in its orbit when it is closest to the Sun. Here is a picture comparing AIA 1600 images at 1649 UTC (10:49 am ET, right) and 04 Jul 2022, 0711 UTC (03:11 am ET, during DST, on left) when the Earth is farthest from the Sun.

The blues lines are drawn to touch the poles of the Sun in the image from last July. You can see that the Sun appears to be a bit larger near perihelion than at apohelion. The SDO telescopes cannot change the size of their images and HMI in particular had to allow for this change in apparent size when designing the optics.

Happy Perihelion 2023!