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A few people seemed quite keen on the astronomical observations in Chris C's diary, so I thought I'd start a separate thread for astropics.

I haven't really got the camera for it, but to kick off, all four Galilean moons of Jupiter are beautifully spread out tonight and I'm sure someone can do better than this:



They are, from top left to bottom right, Callisto, Ganymede, Io and Europa. They look wonderful in binoculars right now!

Guy

This is a great thread, Guy, I'll look forward to seeing other peoples' observations.

yeah you rabble cluttering up my diary was actually just pleased someone was looking
what camera are you using guy?
"I'm sure someone can do better than this" I very much doubt better but i must say doing this in the dark without a torch has made me very aware of where the controls are on the new camera so not a wasted excercise. despite the cold i'll give it a go.

That's a fantastic picture Guy and great timing. I was out last week with a telescope looking at the night sky with my kids and we saw Jupier and its moons just like that! I wasn't sure for definite if it was the moons I was looking at or some other stars, or even some sort of reflection in the telescope! Thanks for clearing up our astronomical queries as well as our butterfly ones!

I gave my telescope away when I moved house, but there's a lot you can do with binoculars - and, it seems, with a simple camera (mine is a Canon compact).

I tried for the Andromeda galaxy tonight, but although I did technically get a photo of it, it was rather disappointing (a slightly hazy sky with high ice crystals probably didn't help):



The galaxy - over 2000 000 light years away - is the fuzzy thing on the right. This is what that picture should have looked like (courtesy of Stellarium):



The problem is, you can't take a really long exposure photograph of the sky unless you have a motor synchronised with the sky's relative motion. It's a bit silly really, trying things like this with a compact camera alone, but it's fun!

That galaxy is easily visible with binoculars - and even with the naked eye.

I've also tried the Orion Nebula. A tiny bit of nebulosity is visible in this picture (taken on New Year's Eve):



And I've been getting portraits of some of the constellations. Here is Orion:



And here is Lepus:



Those were also taken on New Year's Eve.

Guy

the only recognisable one i got tonight before it disappeared over the roof was this one.

and you only use compact Guy? blimey i have alot to learn.

Chris

I know I sound like a numpty, but are you using tripods to take these pictures? I tried to take one myself last night but the 10 second exposure looked like an asteroid trail because my hand clearly hadn't been steady for the duration of the shot.

Yes, a tripod is essential! I also use a time delay, so the shutter doesn't open until 2 secs after I press the release. That eliminates the immediate handshake of operating the camera. For wide angle shots, an exposure of 15 seconds gets good results. With 12 x zoom that is far too long because the sky moves. Much more than one second exposure will leave visible tracks on the stars at that zoom. However, that does depend on the distance of the stars from the North celestial pole. Orion is on the celestial equator, so its stars cover a significantly greater distance across the sky in 15 seconds than, say, those of Cassiopeia or Ursa Minor.

Guy

padfield wrote: Yes, a tripod is essential! I also use a time delay, so the shutter doesn't open until 2 secs after I press the release. That eliminates the immediate handshake of operating the camera. For wide angle shots, an exposure of 15 seconds gets good results. With 12 x zoom that is far too long because the sky moves. Much more than one second exposure will leave visible tracks on the stars at that zoom. However, that does depend on the distance of the stars from the North celestial pole. Orion is on the celestial equator, so its stars cover a significantly greater distance across the sky in 15 seconds than, say, those of Cassiopeia or Ursa Minor.

Guy

Interesting stuff, Guy, which will no doubt come in highly useful if I ever get round to buying a tripod!

The moon last night:



Guy

padfield wrote:I also use a time delay, so the shutter doesn't open until 2 secs after I press the release.

Shutter. What shutter?
That is one plus side for the compact.

Good point, JKT!

I think I'll still call it the shutter release, though.

Guy

I have been searching without success for image pairs of the Moon taken from widely separated places on the Earth so that a 3-D effect can be obtained.

Working on human eye spacing of around 7 centimetres and 3-D effect apparent out to around 7 metres, this points to a baseline of at least 4,000 kilometres being needed to image the Moon in 3-D. So with England-Switzerland distance being only around 800 kilometres, I doubt that simultaneous pictures taken in England and Switzerland could be used to make 3-D.

But this could be worth a try. Exact synchronization of the taking of the pictures would be essential to avoid unwanted differences in the Moon’s phase.

Jack

That's a brilliant idea, Jack! I'd be willing to give it a try during the next waxing phase of the moon, when it is in the sky at civilised times of the night! It will be trivial to resize our pictures to the same number of pixels across. They would have to be rotated carefully too.

I would suggest we pick a fixed time on a succession of nights - say, over a week - and each take a photo at that time when the cloud cover permits.

Like you, I doubt there'd be any discernible effect, but it sounds a fun project. I'll do my own detailed calculations when I get a moment - I'm in the middle of something else right now, that I need to get on with.

Guy

OK - I reckon the 3D effect will be equivalent to looking normally at an object 33m away (which agrees with your estimation, Jack). At that distance, the parallax is enough to make things stand out against the background but I doubt enough to make parts of them stand out against other parts (and there will be no background visible in the photographs). The moon is about half a degree across, so the appropriate object to imagine at 33m is a (slightly small) basketball.

Guy

If from a fixed location, the Moon were photographed just after rising and then just before setting, you could get a much bigger baseline. At Earth’s equator, this would be around 12,000 kilometres. But at higher latitudes, eg Switzerland or Britain, the baseline would be less (Guy – by a factor of cosine latitude???)

The Moon’s phase would change during the period it was above the horizon so it’s hard to say how significant that might turn out to be in terms of 3-D effect.

Jack

Jack Harrison wrote:If from a fixed location, the Moon were photographed just after rising and then just before setting, you could get a much bigger baseline. At Earth’s equator, this would be around 12,000 kilometres. But at higher latitudes, eg Switzerland or Britain, the baseline would be less (Guy – by a factor of cosine latitude???)

Good maths, Jack! Go to the top of the class! Around full moon, in winter, the moon behaves like the sun in summer, spending more than 12 hours above the horizon, so your plan might work. The phase difference would, I think, be significant, but if this were a long-term project you could wait several lunar cycles until the same phase occurred at the appropriate time.

Guy

Does libation make a difference to these calculations? The slight "wobble" that means that we can actually see rather more than half the Moon from the Earth. I speak from a position of almost complete ignorance - I have no idea of how much this wobble is, or over what kind of period it happens.

Dave

I think that should be "libration"...

Dave

Libation adds a very pleasant wobble to everything, I find!

In fact, this whole project is probably a product of libation and all the calculations are very approximate anyway.

Guy