|Image exposure: |
25.4 ms per frame @ zero gain
Best 10% of 1500 video frames
|Image date: |
2021-09-01 (10.28 pm AEST)
Jupiter has nearly eighty natural satellites, the largest of which are the four Galilean Moons: Io, Europa, Ganymede and Callisto – all easily visible in binoculars or a small telescope. Io is rocky, inhospitable and highly active geologically with hundreds of active volcanoes, caused by the tidal forces induced by its proximity to Jupiter itself.
Because it orbits very close to Jupiter, Io’s orbit of the planet is quick and lively – a mere 1.77 days – and so it regularly transits across the face of Jupiter as seen from Earth. When this occurs, Io itself is not seen – but its shadow on Jupiter is very prominent to astronomers.
It just so happened that one of these transits was in progress while I was taking the video which I used to create the feature image above. The shadow is clearly visible on Jupiter and in the unlikely event that any creature existed on Jupiter, they would experience an eclipse of the Sun as the shadow passed across them.
I would like to say that this observation was planned but to be quite honest I’ve taken a number of shots of Jupiter over the years and never recorded a transit, so my success this time was due more to the law of averages than any foresight on my part.
I took a total of six videos over the course of about fifteen minutes and converted each to a single still image using Autostakkert software. I then combined the resulting six still images to a single gif image as seen below:
Here is an animated orbital diagram borrowed from Wikimedia Commons, which show how the four Galilean Moon orbits are arranged:
Here is a single still image which I took during Io’s transit of Jupiter. The transit is obscured because Jupiter was deliberately over-exposed to show the other three Galilean Moons:
Transits not only occur across Jupiter, they also occur across the face of the Sun, so here is an image I took of the Transit of Venus in 2012 to prove it.
Thanks for reading 🙃
Cosmic Focus Observatory
Above us only sky….
|Telescope:||SkyWatcher Esprit 120 mm apochromatic 3-element refractor; 840 mm f/l @ f/7.|
|Optics:||Field flattener; Astronomik light pollution filter, 2x Powermate.|
|Mount & Guiding:||SkyWatcher EQ6-R Pro mount.|
|Imaging camera:||ZWO ASI 071 MC cooled.|
Images © Roger Powell
I’m one of the founder members of Macarthur Astronomical Society and current webmaster.
Cosmic Focus Observatory, 34° S