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Re: Astronomy and Space

Posted: Sat May 15, 2021 1:35 pm
by Pishwish
China has landed a rover on Mars. Not much information, I expect pictures will be released over the next week or so.

Rocketlab, the small payload rocket company, has suffered another failure as its second stage only briefly ignited. The company is trialling reuse and was also hoping to recover its first stage, not sure if they have achieved that.

SpaceX has submitted plans for an orbital (ish) test of its starship/super heavy rocket after June 20.

Re: Astronomy and Space

Posted: Mon May 24, 2021 1:35 am
by bmforre
dyqik wrote:
Thu Nov 19, 2020 5:16 pm
The Arecibo Telescope can't be repaired after it's last hurricane damage, and will now be decommissioned.

https://www.nsf.gov/news/news_summ.jsp?cntn_id=301674
But Joy to Astronomy World:
-- China's Five-hundred-meter Aperture Spherical Radio Telescope (FAST), the world's largest filled-aperture and most sensitive radio telescope, has officially opened to the world starting Wednesday.

-- Astronomers globally can submit their observation applications for evaluation till May 15 and the results will be announced on July 20. Observations by overseas scientists will begin in August.

-- The opening of FAST demonstrates that China is seriously expanding the circle of friends in basic research and sharing FAST with the rest of the world, said Li Di, chief scientist of the telescope.
Hurrah!

Re: Astronomy and Space

Posted: Mon May 24, 2021 1:42 am
by basementer
I guess they wanted to stress Spherical rather than Radio. Wouldn't want it to become known as the FART.

Re: Astronomy and Space

Posted: Wed May 26, 2021 9:07 am
by basementer
The moon's entering the penumbra and it's already quite high in the sky. Fingers crossed for continuing clear weather.

Re: Astronomy and Space

Posted: Wed May 26, 2021 12:14 pm
by basementer
I think this is my best pic of tonight's eclipse (it's 3k*2k, more detail comes out when you download the file and open it in an image editor - I have a 6k*4k jpeg too if anyone's interested, but it's over the forum's file size limit.)

Re: Astronomy and Space

Posted: Wed May 26, 2021 12:30 pm
by Gfamily
Nice one.
One of my astro friends is despairing of someone in his local club (in Shropshire) who is posting on their Facebook group about "seeing the eclipse".

Still, we have our partial solar eclipse due in a couple of weeks.

Re: Astronomy and Space

Posted: Wed May 26, 2021 6:16 pm
by basementer
We had a good partial solar visible from Wellington a few years ago. The light shining through trees projected lots of little crescent suns onto the ground. Hope you have clear weather.

Re: Astronomy and Space

Posted: Fri Jun 11, 2021 11:06 am
by shpalman

Re: Astronomy and Space

Posted: Tue Jun 15, 2021 5:52 pm
by Gfamily
This is quite fun, an app that will show you the galactic locations of various stars and deep space objects.

Free, and ad free
"Our Galaxy"
https://otherwise.com/

Re: Astronomy and Space

Posted: Wed Jul 21, 2021 6:51 pm
by Gfamily
People who do astro imaging know that one of the key things is being able to get your mount as stable as possible.
This often involves digging a big hole and filling it with concrete so you can have a very solid pier.

Putting your telescope on your decking just doesn't work if people are moving around.

So, how ridiculous to think you could just dangle a telescope on a cable below a balloon 40km up in the atmosphere (75% of the height of Branson's recent flight)
And yet, that can get a better than 1 arc second precision on exposures up to an hour, so almost satellite-level imaging at down-to-earth costs (and repairs are easier too).

We're are very clever apes in many ways.
https://www.theguardian.com/science/202 ... w-of-space?

Re: Astronomy and Space

Posted: Wed Jul 21, 2021 8:12 pm
by bolo
Its final test flight in 2019 demonstrated “extraordinary pointing stability”, the SuperBIT team says, “with variation of less than one thirty-six thousandth of a degree for more than an hour”. That should allow a telescope to obtain images as sharp as those from the Hubble space telescope.
That pointing stability is impressive, and they'll get nice clear viewing at that altitude, but the diffraction limit says they're not getting images as sharp as Hubble's with a primary mirror 0.5 meters in diameter.

Definitely still cool, though.

Re: Astronomy and Space

Posted: Wed Jul 21, 2021 10:06 pm
by monkey
bolo wrote:
Wed Jul 21, 2021 8:12 pm
Its final test flight in 2019 demonstrated “extraordinary pointing stability”, the SuperBIT team says, “with variation of less than one thirty-six thousandth of a degree for more than an hour”. That should allow a telescope to obtain images as sharp as those from the Hubble space telescope.
That pointing stability is impressive, and they'll get nice clear viewing at that altitude, but the diffraction limit says they're not getting images as sharp as Hubble's with a primary mirror 0.5 meters in diameter.

Definitely still cool, though.
Maybe they meant before the fixed the Hubble mirror?

Re: Astronomy and Space

Posted: Thu Jul 22, 2021 11:47 am
by dyqik
bolo wrote:
Wed Jul 21, 2021 8:12 pm
Its final test flight in 2019 demonstrated “extraordinary pointing stability”, the SuperBIT team says, “with variation of less than one thirty-six thousandth of a degree for more than an hour”. That should allow a telescope to obtain images as sharp as those from the Hubble space telescope.
That pointing stability is impressive, and they'll get nice clear viewing at that altitude, but the diffraction limit says they're not getting images as sharp as Hubble's with a primary mirror 0.5 meters in diameter.

Definitely still cool, though.
I'm not sure if Hubble is strictly primary mirror diffraction limited - the corrector that was installed, tertiary and instrumental optics and things like the secondary support also contribute to the point spread function of the optical system. The actual diffraction limit will be set by an aperture stop in the optical system, chosen to prevent any residual aberrations from the corrector and other optics building up at the edge of the primary.

The diffraction limit also depends on the wavelength - Hubble observes between 2.5 um and 0.1 um, so you can beat it with a 0.5m mirror at 25nm deep in the UV.

Looking it up, Hubble's effective primary diameter in terms of resolution at 500nm is about 1.5m.

With my millimeter wave optical stuff, the aperture field distribution is also tapered significantly, so that the resolution is lower than the diffraction limit, by a factor of two or so. This is to reduce spillover from the edge of the primary (which is a concern even in refracting systems). This isn't nearly as useful a thing at optical wavelengths though.

In any case, they are only talking about the pointing stability here, not diffraction. Scaling up the telescope to a Hubble sized primary would likely make pointing more stable.

Re: Astronomy and Space

Posted: Thu Jul 22, 2021 12:04 pm
by dyqik
I've found conflicting numbers for Hubble's best resolution now. I think 1.25m is a better diameter to use for an equivalent diffraction limited resolution - equivalent to 0.1 arcsecond resolution at 500nm.

Re: Astronomy and Space

Posted: Thu Jul 22, 2021 12:57 pm
by dyqik
Anyway, here are some observations with slightly higher resolution than Hubble - showing a disc around a planet that is likely in the process of forming moons:

https://www.eso.org/public/news/eso2111/?lang

Image

Nominative determinists will be pleased to see that one of the authors is a Miriam Keppler.

Re: Astronomy and Space

Posted: Thu Jul 22, 2021 5:21 pm
by monkey
dyqik wrote:
Thu Jul 22, 2021 12:04 pm
I've found conflicting numbers for Hubble's best resolution now. I think 1.25m is a better diameter to use for an equivalent diffraction limited resolution - equivalent to 0.1 arcsecond resolution at 500nm.
I did a quick search and I found a figure comparing resolutions of various telscopes at various wavelengths. It suggests Hubble's best resolution is about 0.07 arcsecond at 500 nm (eyeball), so you're not far off, if this figure is correct.
telescope resolution.png
telescope resolution.png (140.58 KiB) Viewed 169 times
The figure is 4-2 on page 49 of this report clicky

Re: Astronomy and Space

Posted: Thu Jul 22, 2021 6:05 pm
by dyqik
It depends on which instrument you are using, as well as the current pointing stability of Hubble, whose gyros have been going on and off line. I got 100 mas from ESO, as NASA stuff I found seemed out of date. Go to STScI for the real numbers, I guess.

That figure cuts off some of the stuff I've been involved in, over on the bottom right. Event Horizon Telescope gets to 60 microarcseconds at ~1 mm wavelength.

Re: Astronomy and Space

Posted: Thu Jul 22, 2021 6:21 pm
by Gfamily
Hubble fun fact: the Wide Field Camera has a field of view about the same as what one goalkeeper sees if the other goalkeeper was holding up a postcard, with each standing on their respective goal line.

Re: Astronomy and Space

Posted: Fri Jul 30, 2021 6:01 am
by shpalman

Re: Astronomy and Space

Posted: Fri Jul 30, 2021 8:14 am
by Grumble
Seems like they just about got away with that :shock: