A Galilean Night (Oct 23rd)

[salientNZ]

Hi,

Looking at the photo supposedly showing the Gallilean moons of Jupiter, I was immediately struck by the fact that the moons are in the wrong plane. Surely they should line up with the moon since the Earth and its moon, and Jupiter and its moons are all in the plane of the planets. So the photo is either doctored, or those points of light are background stars.

I think it unlikely that the camera would be able to see the Galilean moons at all, especially with the glare of the full moon. Only 6 other stars are visible in the shot. If the moons were visible (magnitude ~5) then I think a lot more other stars would also be visible.

Also, the bottommost "moon" is about 25 arcminutes from Jupiter (measured by comparing it with the Moon's 30 arcminutes), which is about 2 and a half times the greatest separation, which, according to Wikipedia, is 10 arcminutes.

Lastly, at least 4 of the other stars in the shot are short streaks showing that this was quite a slow exposure. However, the "moons" do not show this at all.

So I think that the photo was doctored, with the Galilean moons being added in later.

Cheers,
Brent.

[bystander]

Actually, Jupiter and Earth (and all the other planets) are somewhat off the ecleptic. In addition, Earths equator and the Moon's orbital plane is tilted from the ecleptic, as is Jupiter and its moons.

http://apod.nasa.gov/apod/ap091023.html

[salientNZ]

Actually, Jupiter and Earth (and all the other planets) are somewhat off the ecleptic. In addition, Earths equator and the Moon's orbital plane is tilted from the ecleptic, as is Jupiter and its moons.

So you think that the moon being 2 degrees higher in the sky is due to these aberrations, and the line through the Galilean moons is likely to be the actual ecliptic (or close to it) ?

How do you explain the apparent distance of the moons from Jupiter ?

Cheers,
Brent.

[bystander]

See APOD: 2009 July 14 - Moons and Jupiter
and Asterisk*: Moons of Jupiter (2009 July 14)
especially Chris Peterson's posts
http://asterisk.apod.com/vie ... 76#p108276
http://asterisk.apod.com/vie ... 77#p108277

[Chris Peterson]

So you think that the moon being 2 degrees higher in the sky is due to these aberrations, and the line through the Galilean moons is likely to be the actual ecliptic (or close to it) ?

How do you explain the apparent distance of the moons from Jupiter ?

This looks just about right for the evening of August 6. The ecliptic is almost horizontal (sloping slightly upwards to the right, nearly parallel to Jupiter's moons) and almost bisects the Moon and Jupiter (it's actually just above the star visible between the two). On the right side of Jupiter you have Europa and Ganymede, on the left side you have Callisto. Io is nearly on top of Jupiter, and can't be seen. The "moon" a bit farther to the left is actually a magnitude 6 star. The bright star between Jupiter and the horizon is mag 2.85 delta Capricorn.

The locations of the stars, Moon, and Galilean satellites are exactly as they ought to be.

[salientNZ]

The "moon" a bit farther to the left is actually a magnitude 6 star.

Thank you: that explains it for me.

Thanks a lot for taking the time to address my concerns. My apologies for insinuating that the picture was doctored.

Cheers,
Brent.