Saturday, January 2, 2021

It's Perihelion Day!

Today at 8:50 am ET (1350 UTC) the distance between the Earth and Sun was the smallest it will be this year (perihelion). On July 4, 2020, we were the furthest from the Sun (aphelion). Here is a picture comparing the Sun as seen by HMI on those two days.

The left half shows what the Sun looked last July. The right half is an image from today. The Sun appears a little larger today because of our elliptical orbit around the Sun. This difference also means the telescopes on SDO were designed to fit the Sun at perihelion into the images. I made this from the images on the SDO website. You can make one yourself using the other wavelengths available there.

For every minimum distance of an orbit there is also a maximum distance. For the Earth and Sun this is called aphelion and will next occur on July 5, 2021 6:27 pm ET (2200 UTC).