Here’s a program that will show you the positions of the 4 largest moons of Jupiter and the Great Red Spot. Before you run the code, enter your time difference from GMT in offset at the start of the code. My offset is 4. When the program starts, it shows you the current GMT and your local time (if you set the correct offset value). It also shows the positions of the 4 largest moons and the Great Red Spot (if it’s on this side of Jupiter). You can enter a date (mmddyyyy) or date and hour (mmddyyyyhr) or date, hour, and minutes (mmddyyyyhrmn) then tap “Calc new date”. The parameter window will close and you’ll be in full screen mode. You can also change the month, day, hour, minute with the sliders. Slide right to increase, left to decrease. You can also just tap the sliders to increment or decrement each by 1. Tap on the left side to decrement, right side to increment. Above each moon is its identification letter. Below the moon names is the Central Meridian value. That’s the current longitude of Jupiter that’s crossing the middle of Jupiter. With the parameter window open, there’s a View slider that alters the viewing position of the moons. View 1 is for binoculars or a terrestrial telescope. That view is normal. View 2 is for a reflecting telescopes that show up side down. View 3 is for SCT that just reverses the image right to left. Use the “Close print area” to flip back to full screen. That’s used so I can recalculate the values for full screen. The positions are not exact, but close enough for just knowing which moon is which. I show the moons going across Jupiter and hide them when they go behind. I don’t have any code to account for the moon shadows on Jupiter or to hide the moons in Jupiter’s shadow. I think I explained everything. If not I’ll add them. The program and text was too big, so I had to zip the code.
PS. Tapping near the top of the screen resets the date and time to current.
Here’s an updated version for the moons of Jupiter. I added a visual at the bottom of the screen to show the direction of the Sun. This will give you an idea of where the shadows of the moons will fall on Jupiter (I don’t show the shadows) or the direction of the shadow of Jupiter might be to hide a moon that was behind it. The yellow circle will vary from side to side as the Earth circles the Sun. The value shown is the angular separation of the Earth and Sun as seen from Jupiter. I also added an option to give you a birds eye view from above Jupiter that shows the positions of the moons in their orbit. Just tap the Show/Hide Orbit to see the view.
@dave1707 - checked this out, would be nice to place a backdrop image from sky box of our local system to place the derived image with a zoom option to emphasise the orientation. Are you into astronomy?
@Bri_G I’m not sure what you mean for the backdrop. The purpose of this program is to give you an idea of what you’ll see if you go out to observe Jupiter. It’s not meant to be a pretty program, just informative. You’ll be able to identify which moon is which, the direction they’re going and if you’ll be seeing a moon shadow on Jupiter, a moon passing across Jupiter, or if a moon will be eclipsed by Jupiter. Also, you’ll get an idea of the position of the Great Red Spot (now kind of dull). As for Astronomy, I got my first telescope, a 60mm refractor in 1960. I used that for several years and seen a lot of things with it. I still have it, but I don’t use it. My main scope is an 8” Celestron that I got in 1975. It’s still in perfect condition. I have a permanent polar aligned mount that I put the C8 on. I also have a computer controlled 4” NexStar that fits on the same mount. I could always get the Jupiter info from the internet, but I thought I’d try writing my own so I had what I wanted in one place.
@dave1707 - the backdrop suggestion was just to provide a scrollable night sky view as a backdrop with Jupiter highlighted so that, on tapping, a zoomed out image showing current orientation would zoom out. May be impractical but I thought it may help people locate Jupiter easier in the night sky.
@Bri_G There’s a lot of apps that can be downloaded so that if you hold your iPhone/iPad up towards the sky, it will show you what you’re pointing at. As for Jupiter, right now it’s the brightest thing in the southeast sky a little after sunset. And a little ways to the left of it is Saturn. Well, that’s from my location, 41 degrees north latitude. I keep forgetting that everyone who reads this could be anywhere in the world, so the southeast or left could be something else.
