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View Full Version : Ganymede with your unaided eye... anyone?



mapguy
2016-Feb-05, 10:19 PM
With Jupiter approaching opposition, I thought it might be interesting to discuss this. With a maximum brightness of mag. 4.4 (but with a maximum elongation of only 350 seconds from its much brighter host planet), some people say it's not possible to see Ganymede without optical aid, while others claim they've done it. Has anyone here had success?

antoniseb
2016-Feb-05, 10:50 PM
I have made a serious effort to do it under ideal conditions and do not believe I could distinguish it. I was able to see it with only a small amount of help (1.5 power glasses).

tony873004
2016-Feb-05, 11:11 PM
I think I did it once, but it wasn't Ganymede alone. I waited for Ganymede and Callisto to align when Ganymede was near max separation.
I thought it was obvious, but maybe I imagined it because I was expecting to see it.

Here's a simulation of the Galilean moons as seen from San Francisco. It shows a few alignments between Ganymede and (Europa or Callisto) during the next few weeks. Don't trust the sim for longer than that. It doesn't take into account Jupiter's non-spherical shape, so the positions of the moons noticeably drift from reality after about 6 weeks.

Press P or [>] on the Time Step interface to play or pause, and [<<] on the Time Step interface to reverse time.

http://orbitsimulator.com/gravitySimulatorCloud/simulations/1454711729688_Gmoons.html

Solfe
2016-Feb-05, 11:14 PM
Every summer I go camping with the kids and try to see the moons of Jupiter. On several occasions, I have seen something that looks about right but I have never had a telescope or charts to tell for sure. I am 99% certain I haven't seen a moon but actually saw a background star because it seemed too easy.

On one occasion, I had a nice telescope loaned to me. Of course, that time, I definitely could NOT make out anything that looked remotely like a moon with just my eyes. In the scope I could see two, but didn't have any way to know which ones.

One of these years, I am going to pack up everything I need to verify and bring it with me.

Hornblower
2016-Feb-06, 04:00 AM
I have never been able to see any of them without optical aid, but I read a charming piece in Sky and Telescope about a 7-year-old child who did see either Ganymede or Callisto. Her father was getting ready to show her the view in his telescope and told her that the moon would be above Jupiter in the field of view. She replied with something like, "No, it is below Jupiter." He turned and saw her staring at the planet, and he concluded that she really was seeing something, because she had no prior knowledge of the inverted field in the scope. This little girl was blessed with very sharp vision.

Romanus
2016-Feb-06, 04:57 AM
Unaided viewings of Callisto and maybe even Callisto have been reported for some time. Supposedly it's also possible to see Venus's crescent (or rather, roughly elongated appearance) with the naked eye near inferior conjunction, though the cases I've heard of have also often been children.

Solfe
2016-Feb-06, 05:41 AM
I've had cub scouts report seeing shadows from Venus on snow. As near as I can tell, you have to be way out in the country-side, in a treed area, and in a valley. Personally, I see nothing at all, but my sons and their friends can see it.

StupendousMan
2016-Feb-06, 02:05 PM
<offtopic>

I once saw a shadow cast (at least in part) by Venus. I was observing at the Apache Point Observatory in New Mexico, at an altitude of about 9,000 feet, on a clear night. I stood in front of the clean, white exterior surface of a door, and waved my arm slowly. I could see a shadow clearly, in the direction opposite to Venus, but it's possible that some skyglow from that portion of the sky was contributing.

</offtopic>

DaveC426913
2016-Feb-06, 02:59 PM
I've had cub scouts report seeing shadows from Venus on snow. As near as I can tell, you have to be way out in the country-side, in a treed area, and in a valley. Personally, I see nothing at all, but my sons and their friends can see it.

Yes. Just last autumn, Venus was so bright it cast shadows. I tried to get pics of it, but my camera couldn't handle it.

I was not out in the country; in fact I was in my backyard, in a major metropolis.

I hardly believe it myself, but it was unmistakable. I could hold up something in front of a white card and move it around and see a shadow.

DaveC426913
2016-Feb-06, 03:03 PM
What is the angular spread of the Galilaean moons as seen from Earth? I've often looked at Jupiter with the naked eye and wondered how far they are from Jupiter.

(calculate calculate, carry the one...)
Looks like it's about .5 degrees at conjunction and .38 at opposition?

So, about half to a third the width of my pinky at arm's length.

Fiery Phoenix
2016-Feb-06, 03:55 PM
I don't think I've ever seen the moons unaided. However, I have heard on several occasions that it is in fact possible to pick out some of them with the naked eye under ideal conditions.

tony873004
2016-Feb-06, 08:48 PM
What is the angular spread of the Galilaean moons as seen from Earth? I've often looked at Jupiter with the naked eye and wondered how far they are from Jupiter.

(calculate calculate, carry the one...)
Looks like it's about .5 degrees at conjunction and .38 at opposition?

So, about half to a third the width of my pinky at arm's length.
On September 2, 2016, the crescent moon will occult Jupiter while Jupiter is near conjunction, so you can directly observe it then with a pair of binoculars.
Here's a simulated view.
http://orbitsimulator.com/gravitySimulatorCloud/simulations/1454791027799_a.html
The spread of ALL Jupiter's moons is even greater. Zoom out from 128000 to 4000 to see the whole family.

George
2016-Feb-08, 06:11 PM
The brightest Ganymede will get, according to JPL Horizons calculations, will be 4.83, which will be during opposition on March 8th.

When he was 18 or so of age, I confirmed my son's sighting of at least two moons of Jupiter one night. [I could not see them and didn't believe him until confirmed using Starry Night.]