How many of Jupiter's moons can you see?

[Elp]

Was outside observing for once. Upon seeing Jupiter I was surprised to be able to see 6 moons, normally I can only see the four main ones, even when imaging. At first I thought it was an optical error, but changing eyepieces and viewing it later also presented 6 moons. So the question is, how many can you see or have managed to see?

[Richard N]

I thought that I could see 5 yesterday but one was a star aligned on the same plane as the moons. Might you have seen stars too?

[Mandy D]

34 minutes ago, Elp said:

Was outside observing for once. Upon seeing Jupiter I was surprised to be able to see 6 moons, normally I can only see the four main ones, even when imaging. At first I thought it was an optical error, but changing eyepieces and viewing it later also presented 6 moons. So the question is, how many can you see or have managed to see?

It seems rather unlikely that you have seen Amalthea, as it is mag 14.1 and very close to Jupiter. You need very, very dark skies and large aperture to stand a chance at this one. Himalia orbits much further out (beyond Callisto) and shines at 14.6, so a little more within the realms of possibility in a large telescope. I think you likely saw stars. Have you checked on Stellarium or similar?

[Elp]

This is what I saw, I didn't manage to photo the one on the opposite side close to the planet (as per my sketch), and then around 1-2 hours later it was arranged as per my rudimentary markup on the RHS of the image, if it were background stars I wouldn't have seen all six again hours later?

Edited August 21, 2023 by Elp

[Nik271]

The extra 'moons' are field stars. Apart from the Galilean moons the rest are near impossible with small telescopes. The next brightest, Amalthea was only discovered in 1882 with the 32 inch Lick refractor. The star close to Jupiter and opposite Io is magnitude 13, quite impressive if you saw that one. Or it could be the 10-th magnitude star further to the right, Jupiter was passing closer to it around midnight.

 

Edited August 21, 2023 by Nik271
typo corrected

[Mandy D]

@Elp This is what you would have seen at 02:00 UTC. Your image is mirrored. The blue star is a star.

[Elp]

Thanks both, thought I was going mad.

[Mandy D]

@Elp I've gone a bit deeper in Stellarium with this next screenshot, which shows the positions of Amalthea (JV, mag 14.1 ) and Thebe (JXIV, mag 15.7).  For visual you would need 12 inches of aperture for Amalthea and a whopping 24 inches for Thebe.

[John]

The most I've seen are the 4 Galilean moons, even with my 12 inch dob.

I have seen Neptunes moon Triton with my 12 inch dob and my 5.1 inch refractor and also the two Uranian moons Titania and Oberon. 

I've still not managed to see Phobos or Deimos at Mars. 

 

Edited August 21, 2023 by John

[cajen2]

I did see an 'extra moon' some while ago through my 8" dob. Obviously a field star, but it was on exactly the same plane as the usual four.

[John]

I found this information posted on another forum, which seems helpful:

"There are two problems with Jupiter's smaller moons. First, they are small, so don't reflect much light. Secondly, they are close to one of the brightest objects in the sky, so tend to be washed out by Jupiter's brilliance. So you need a large aperture to even see the tiny specks of light, and then good quality, high contrast optics that won't be overwhelmed by stray light from Jupiter.

The Galilean moons range in brightness from 4.6 to 5.6 magnitude. The next brightest moons are Amalthea (14.1) and Himalia (14.6). Stars of magnitude 14.1 to 14.6 require at least an aperture of 250mm (10-inch) to be visible, and even then they require perfectly dark skies, high magnification, and a trained eye. Amalthea orbits very close to Jupiter, 181,400 km as compared to 421,800 km for Io, so it will be completely overwhelmed by Jupiter except in the largest telescopes. Himalia orbits much farther away, 11,461,000 km, nearly 10 times farther than Callisto (1,883,000 km). As a result, Himalia is the most frequently observed non-Galilean moon. All the other moons of Jupiter are 16th magnitude or fainter, making them very difficult to see visually. Most have been discovered photographically."

[Mandy D]

@John Not your mistake, as what you posted is a direct quote, but, in what universe is 11 461 000 "nearly 10 times further" than 1 833 000? My calculator says about 5 times further or six times as far.

[John]

8 hours ago, Mandy D said:

@John Not your mistake, as what you posted is a direct quote, but, in what universe is 11 461 000 "nearly 10 times further" than 1 833 000? My calculator says about 5 times further or six times as far.

I missed that minor detail. Luckily I'm not trying to navigate between Callisto and Himalia currently !

 

[Mutley]

Sigma Aries. Caught me out the other night too