I have a new Apogee Podcast out on the 365DaysOfAstronomy network. You can check that out here, or just go to the main webpage and listen to the other great astronomy podcasts put out every single day.
I finally figured out the directions to the Earth and Sun in the new graphic that I've been trying to re-introduce into my daily podcast. I'm glad to have this different perspective so the motions of the Galilean moons can be seen.
Here it is for my next podcast for 13 January 2015:
|Figure 1: New JT graphic showing the motions of the four Galilean moons over the next 24 hours|
First, the x and y axes are in units of kilometers. The furthest away any moon gets (Callisto) is about 1.8 million km. You can see the lines and dots representing the positions of the moons. The dots indicate its position at 0h, 6h, 12h, 18h, and 0h UTC. The blue line is the line of site from Jupiter to Earth. The gray line is the line of site from Jupiter to the Sun. So you can see in the graphic above that both Io and Europa are going to transit Jupiter (moving between Jupiter and the Earth), but slightly before that they cast their shadows onto Jupiter (moving between Jupiter and the Sun). The quadrant system I've developed is, as far as I know, my own invention. It just allows me to easily know where the moon are and how they're moving. In quadrants 1 and 4, the moons are always moving eastward from Earth's point of view, and in quadrants 2 and 3 the moons are moving westward.
All of these plots are created with data taken from the JPL Horizons website.
You can see and hear my latest podcast by going here, or click on the link on the right.