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Re: Astronomy and Space

Posted: Tue Jul 12, 2022 9:40 am
by jaap
plodder wrote:
Tue Jul 12, 2022 8:53 am
The slidey thing here: https://www.theguardian.com/science/202 ... axy-images

It's not lined up right, right? These are two different bits of space?
The same bit of space but they are not lined up. The JW one is rotated about 1/6 of a turn anticlockwise and zoomed in a bit.

Re: Astronomy and Space

Posted: Tue Jul 12, 2022 9:59 am
by Gfamily
jaap wrote:
Tue Jul 12, 2022 9:40 am
plodder wrote:
Tue Jul 12, 2022 8:53 am
The slidey thing here: https://www.theguardian.com/science/202 ... axy-images

It's not lined up right, right? These are two different bits of space?
The same bit of space but they are not lined up. The JW one is rotated about 1/6 of a turn anticlockwise and zoomed in a bit.
The HST image itself is a composite from at least two imaging sessions as well - you can tell because there are 8 spikes on the brightest star's image - 4 very clear, and 4 offset by about 20 degrees.
HST offset.png
HST offset.png (87.92 KiB) Viewed 357 times
I suggest that one of the sessions was in optical range, and one in the near IR where Hubble has some capability.

Re: Astronomy and Space

Posted: Tue Jul 12, 2022 11:09 am
by dyqik
Gfamily wrote:
Tue Jul 12, 2022 9:06 am
For an idea of the scale, imagine the photo on your phone's screen.
Now imagine you're a goalkeeper and the other goalkeeper is showing you this image from their goalline (I don't know why they have your phone, but bear with me). That's the area of the image* on the sky.


*Appx 7cm at 100 metres.
Or the goalie holding a tennis ball, if you want a purely sports* analogy.

Which is really big compared to one bit of what I do, which is more like a tennis ball on the moon. Or 7cm at 380,000,000 meters. This is the size of the ring in the EHT images.

And really small compared to the other bit if what I do, which is like 7cm at 10cm for the field of view (45° on the sky, sine rather than tangent because we're working on a sphere). This is roughly the size of the full map that makes up Gfamily's avatar.

Although the main thing I do has about the same image sizes as JWST.

*A sport with goals 100m apart that uses tennis balls. Or we could go to cricket, I guess.

Re: Astronomy and Space

Posted: Tue Jul 12, 2022 3:48 pm
by Stranger Mouse
Someone here has done a nice Webb / Hubble overlay https://twitter.com/luckytran/status/15 ... e2L1NRD_bQ

Re: Astronomy and Space

Posted: Fri Aug 05, 2022 12:06 pm
by shpalman

Re: Astronomy and Space

Posted: Fri Aug 05, 2022 6:14 pm
by Sciolus
Anyone got one of these self-assembly brass orreries? They look rather nice, but at 60 cm across I'm not sure where I'd put it.

(If anyone's tempted, there's a widely advertised code for £100 off.)

Re: Astronomy and Space

Posted: Sat Aug 13, 2022 2:33 pm
by Aitch
Missed the Perseids last night (OK, I forgot) and only remembered the Big Moon this morning. Still looked pretty big, though it's hard to tell from a photograph. :(
10803-cess.jpg
10803-cess.jpg (94.93 KiB) Viewed 110 times
I take it this counts as 'Astronomy and Space'?

Re: Astronomy and Space

Posted: Sat Aug 13, 2022 5:36 pm
by Gfamily
Aitch wrote:
Sat Aug 13, 2022 2:33 pm
Missed the Perseids last night (OK, I forgot) and only remembered the Big Moon this morning. Still looked pretty big, though it's hard to tell from a photograph. :(

10803-cess.jpg

I take it this counts as 'Astronomy and Space'?
The moon would have reduced the visibility of the Perseids, so it wouldn't have been a great display. They are spread over a longish period though, so keep looking while it's clear. The moon will be rising about 45 minutes later each evening, so you'll soon be able to get some dark skies before n it rises and spoils things.

The talk of the s****moon is mostly bollocks, each year we'll inevitably get one full moon where it's nearer than any other (and thus seemingly larger). However, unless you were told, you wouldn't know which full moon it is by looking at it.

Re: Astronomy and Space

Posted: Mon Aug 15, 2022 8:35 am
by Trinucleus
I really can't see how people can say 'look how big the supermoon is' in pictures taken with a telephoto lens

Re: Astronomy and Space

Posted: Mon Aug 15, 2022 8:55 am
by Aitch
Trinucleus wrote:
Mon Aug 15, 2022 8:35 am
I really can't see how people can say 'look how big the supermoon is' in pictures taken with a telephoto lens
That's why I included the chimney stack.

Re: Astronomy and Space

Posted: Mon Aug 15, 2022 9:35 am
by jaap
Aitch wrote:
Mon Aug 15, 2022 8:55 am
Trinucleus wrote:
Mon Aug 15, 2022 8:35 am
I really can't see how people can say 'look how big the supermoon is' in pictures taken with a telephoto lens
That's why I included the chimney stack.
That does not help. Without knowing exactly how far away the chimney stack is, and how large the stack really is, such a photo leaves you as confused as Father Dougal. It is easy to make E.T.-style huge moon silhouette pictures just by being far enough away from the comparison object.

I suppose you could work out what angle you are looking up to the stack at, make an assumption about how many floors the building has, and work out the distance from that. Or work out the distance from the paralax on the three pairs of pipes. But the uncertainty in all of that as well as the uncertainty in the actual size of the stack far outweighs any apparent change of the size of the moon in the sky.

Re: Astronomy and Space

Posted: Mon Aug 15, 2022 9:53 am
by Gfamily
The full moon always looks big as it rises - it's an optical illusion thingy - probably because the brain knows that clouds near to the horizon look smaller than clouds overheard (because they are further away), so it scales them up accordingly, and the same applies when judging the size of the Moon near to the horizon.

In addition, across the summer months, the moon stays nearer to the horizon overnight, and we're more likely to be sitting out under a moonlit night in the summer.

Don't get me started on the stupid names they give to the full moon each month either - the acorn moon and the screwfix moon or whatever.

Re: Astronomy and Space

Posted: Mon Aug 15, 2022 1:58 pm
by Trinucleus
Aitch wrote:
Mon Aug 15, 2022 8:55 am
Trinucleus wrote:
Mon Aug 15, 2022 8:35 am
I really can't see how people can say 'look how big the supermoon is' in pictures taken with a telephoto lens
That's why I included the chimney stack.
But is it a supermoon at 30x zoom or an ordinary moon at 32x?

Re: Astronomy and Space

Posted: Mon Aug 15, 2022 2:02 pm
by monkey
Gfamily wrote:
Mon Aug 15, 2022 9:53 am
The full moon always looks big as it rises - it's an optical illusion thingy - probably because the brain knows that clouds near to the horizon look smaller than clouds overheard (because they are further away), so it scales them up accordingly, and the same applies when judging the size of the Moon near to the horizon.
The most fun thing about the moon illusion is that the effect disappears if you look at it through your legs.

Re: Astronomy and Space

Posted: Mon Aug 15, 2022 2:23 pm
by Gfamily
monkey wrote:
Mon Aug 15, 2022 2:02 pm
Gfamily wrote:
Mon Aug 15, 2022 9:53 am
The full moon always looks big as it rises - it's an optical illusion thingy - probably because the brain knows that clouds near to the horizon look smaller than clouds overheard (because they are further away), so it scales them up accordingly, and the same applies when judging the size of the Moon near to the horizon.
The most fun thing about the moon illusion is that the effect disappears if you look at it through your legs.
As does your dignity. 😄