Scrutable

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.

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. I suggest that one of the sessions was in optical range, and one in the near IR where Hubble has some capability.

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.

Someone here has done a nice Webb / Hubble overlay https://twitter.com/luckytran/status/15 ... e2L1NRD_bQ

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.)

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.
I take it this counts as 'Astronomy and Space'?

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.

I really can't see how people can say 'look how big the supermoon is' in pictures taken with a telephoto lens

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.

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.

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.

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?

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.

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.

Stayed up reading and eating crisps tonight because the aurora forecast was pretty good. The clouds cleared about 1.45am, and

That's an unedited phone photo btw.

It was even better about 20 minutes before that but I was running around outside gobsmacked in the car park rather than faffing about with pics.

I hope the crisps were as good as that.

I've never seen the aurora. Whenever it's shown on the telly it rolls and shimmers and ripples and I think "surely that's a timelapse". But they never say "here it is speeded up about 30 times" they just say it's the aurora. So after all these years I still don't know how fast it really moves.

Martin Y wrote: ↑

Sun Aug 21, 2022 2:09 pm

I hope the crisps were as good as that.

I've never seen the aurora. Whenever it's shown on the telly it rolls and shimmers and ripples and I think "surely that's a timelapse". But they never say "here it is speeded up about 30 times" they just say it's the aurora. So after all these years I still don't know how fast it really moves.

Same. Can anyone enlighten us?

So what I should have done in the first place is just go to YouTube and search for "aurora borealis in real time".

https://www.youtube.com/watch?v=T75IKSXVXlc

Compered to that I think the stuff I thought was time lapse really was time lapse, but the real thing does have features which move and change really quite quickly.

Yes, sorry - busy day.

The closest thing I can liken it to is watching a large flag or muslin curtain blowing in a moderate breeze. Last night there were some periods when it seemed to be wafting rather slowly, with a silvery wash across most of the sky, and other moments of more intense, quick fluttery type movements.

I'd seen some videos but really wasn't prepared for how impressive it was in real life. I'd seen it once before, but that was just a single silvery line waving about slowly.

No idea why anyone feels the need to speed it up tbh.

Anyway, cloudy tonight unfortunately, but tomorrow night I'll be out catching birds so fingers crossed.

Bird on a Fire wrote: ↑

Sun Aug 21, 2022 2:58 am

Stayed up reading and eating crisps tonight because the aurora forecast was pretty good. The clouds cleared about 1.45am, and

You are lucky to see aurora this early in the arriving autumn. The amount of sufficiently dark night is only about 2-3 hrs - though that now increases rapidly. And Iceland is so cloudy that getting breaks in the clouds sufficient to see them makes it hard at any time of year, let alone in such a narrow window of proper darkness.

I've been to Iceland a couple of times in later August when there might have been a chance. On one of those trips, I was camping at Myvatn at this precise date in August, and someone told me in the morning that if I'd gone for a look at 1am, I'd have seen the aurora. Irritatingly, I had got up for a pee at that time, but didn't think to walk away from the floodlights by the loo block and look up. Being sodding freezing under the clear sky - there was a frost - was a disincentive. The next night it snowed - Myvatn is quite high at 300m; people had to be rescued from Askja in the NE interior. And the night after that a storm blew in - by now we were by the coast in the Eastfjords - and we had to abandon a day to sitting in the tent and a coffee-shop. The weather can keep you entertained in Iceland.

Cool picture of Jupiter from JWT, with auroras - clicky.

I also liked that article made it pretty clear that the image was false colour, but I think that was just to avoid people emailing in saying "Jupiter's The Red Planet. Red. That's not red." Could've done better though, They missed it in one of the captions.

monkey wrote: ↑

Tue Aug 23, 2022 3:54 pm

Cool picture of Jupiter from JWT, with auroras - clicky.

I also liked that article made it pretty clear that the image was false colour, but I think that was just to avoid people emailing in saying "Jupiter's The Red Planet. Red. That's not red." Could've done better though, They missed it in one of the captions.

A colleague of mine claimed that because it was false colour that meant the image was made up.

Grumble wrote: ↑

Tue Aug 23, 2022 3:56 pm

monkey wrote: ↑

Tue Aug 23, 2022 3:54 pm

Cool picture of Jupiter from JWT, with auroras - clicky.

I also liked that article made it pretty clear that the image was false colour, but I think that was just to avoid people emailing in saying "Jupiter's The Red Planet. Red. That's not red." Could've done better though, They missed it in one of the captions.

A colleague of mine claimed that because it was false colour that meant the image was made up.

Here's a true color version of that image for them.

(JWST can observe at wavelengths as short as 600nm/Yellow/Orange, but didn't for this image)