As Mercury moves toward its passage across the Sun on Monday*, it was visible on the SOHO C3 camera. The C3 is on the SOHO spacecraft, which watches the Sun from it’s post a million miles out from Earth. The C3 has a shade to block out the Sun so it can see the Sun’s outer atmosphere. It can also see stars in the background and the occasional planet that photobombs the scene.
This month, Mercury moved in from the left side of the C3 scene, dimming as the sunlight side turns away from us. Now you can’t even see it. Venus is coming in from the right side, on the far side of the Sun, far away but still very bright. The glare from Venus overloads the sensor and makes a big ‘splash’ on the sensor.
Follow the path of Mercury on this movie of recent photos from the C3 camera. The bright streaks are where the Sun’s magnetic field heats up the Sun’s outer atmosphere. The ‘puffs’ emitted from are coronal mass ejections from the Sun.
Mercury is the tiny dot on the left moving a bit faster than the background stars (roughly on the path on the still photo above).
* Don’t view the Sun without a proper solar filter, firmly fixed to the open end of the telescope. See Sky and Telescope, or our Westchester Astronomers newsletter for details on the Transit of Mercury across the Sun.