Cool astronomy photos

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Anaxagoras
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Re: Cool astronomy photos

Post by Anaxagoras »




It's pretty cool. I'm not sure there's a purpose to it other than to do something that's never been done before, but it's cool nonetheless.
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Rob Lister
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Re: Cool astronomy photos

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It is admittedly very cool. I wonder what specific battery technology their using. I doubt it's just standard Li-Ion.
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Re: Cool astronomy photos

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Why?


Is there something better?
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ceptimus
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Re: Cool astronomy photos

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It's probably some form of Lithium Ion, but I guess with a heater of some sort built in because Lithium batteries don't perform that well at normal Mars temperatures.

Some of the rovers on Mars, despite being powered by solar cells, still have radioactive decay heaters bolted inside to keep them warm during Mars night time and winters. Other rovers are actually powered by radioisotope generators (aka 'atomic batteries'). For deep space probes venturing beyond Saturn, radioisotope generators are always used, because the sunlight out there is too feeble to make solar panels effective.

Even if the Mars helicopter has a radioisotope generator (which I doubt) then that won't power the flight directly - it will be used to recharge Lithium batteries while on the ground, and then those batteries would be fairly quickly discharged during the flights. Solar cells could also recharge the flight batteries when standing on the ground, though it would most likely take longer recharge periods between flights for solar cells small enough to be practical on a helicopter.

A small radioisotope generator can provide low-to-medium power output for many years, but is not suited to provide brief periods of high power: radioisotope batteries have very high energy density, but fairly low power density - in contrast Lithium batteries have very high power density, but (relatively) low energy density.
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Rob Lister
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Re: Cool astronomy photos

Post by Rob Lister »

robinson wrote: Mon Aug 03, 2020 6:09 pm Why?


Is there something better?
'better suited'? Yea. There are battery technologies that are probably better suited (better energy density), Li-air, for one but there are many. Most are either too expensive to produce, have poor charge/discharge cycles, or are impossibly (thus far) to mass produce. None of those matter much for this application.
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Witness
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Re: Cool astronomy photos

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Image

The rings appear brighter at opposition.
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ceptimus
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Re: Cool astronomy photos

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It's a similar effect that makes the (sunlit parts of) the moon all appear almost equally bright. If you put a giant golf ball or apple in place of the moon, it would look darker around the edges - think how you're taught in art class how to paint such objects so that people can tell where the light is coming from.

The grains of dust on the moon's surface tend to scatter light in an unusual way, so that the edges of the full moon's limb, that are only being illuminated at a shallow angle by the sun, appear, from earth, just as bright as the centre which is being lit by the sun perpendicularly.

The moon's surface is actually not very reflective. It appears bright to us, but remember that it's being lit by a very bright sun! It's about as reflective as a lump of coal - if it were more like a golf ball it would be dazzling to look at, and we'd need sunglasses (moon glasses?) to view it comfortably.

In the case of Saturn's rings, the lumps of ice that make up the rings tend to reflect the incoming sunlight straight back towards the sun. So at opposition, when the earth is directly in the line from the sun to the planet, the bright reflected light is also reflected straight at us.
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Re: Cool astronomy photos

Post by Witness »

Hmmm… I had hypothesized that when the sun is exactly behind the earth (as seen from Saturn) we can't see the shadows thrown by the various lumps in the ring (on other lumps), and so the material seems brighter because we only see the lit parts.

I'll google it later, think it over a bit more.
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Re: Cool astronomy photos

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Witness wrote: Mon Aug 03, 2020 10:41 pm Image

The rings appear brighter at opposition.
Works with bathtub rings too.
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Re: Cool astronomy photos

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Image
The Jezero crater delta, where the Perseverance rover and Mars Helicopter Ingenuity, will land; clays are visible as green in this false colour CRISM / CTX image.
From the Mars 2020 Wikipedia page.

The mission launched on July 30th and is expected to arrive on the surface of the Red Planet on 18 February 2021.
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Witness
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Re: Cool astronomy photos

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ceptimus wrote: Mon Aug 03, 2020 11:18 pm In the case of Saturn's rings, the lumps of ice that make up the rings tend to reflect the incoming sunlight straight back towards the sun. So at opposition, when the earth is directly in the line from the sun to the planet, the bright reflected light is also reflected straight at us.
Wikipedia seems to side with my shadow theory:
In the case of planetary rings (such as Saturn's), an opposition surge is due to the uncovering of shadows on the ring particles. This explanation was first proposed by Hugo von Seeliger in 1887.
Even for the moon:
In the case of the Moon, B. J. Buratti et al. have suggested that its brightness increases by some 40% between a phase angle of 4° and one of 0°, and that this increase is greater for the rougher-surfaced highland areas than for the relatively smooth maria. As for the principal mechanism of the phenomenon, measurements indicate that the opposition effect exhibits only a small wavelength dependence: the surge is 3-4% larger at 0.41 μm than at 1.00 μm. This result suggests that the principal cause of the lunar opposition surge is shadow-hiding rather than coherent backscatter.
https://en.wikipedia.org/wiki/Opposition_surge

Illustrated with this picture:

Image

But in fact you get the same "halo" effect if you take a picture of, say, grass or small-leaved plants with the shadow of your head (+ camera) in the field of view.
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ceptimus
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Re: Cool astronomy photos

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Witness wrote: Tue Aug 04, 2020 8:19 pm But in fact you get the same "halo" effect if you take a picture of, say, grass or small-leaved plants with the shadow of your head (+ camera) in the field of view.
Thanks. I only said the 'lumps of ice tend to reflect (more of) the sunlight straight back at the sun' I didn't say why they do that! :P
I hadn't thought of the shadow explanation - I was thinking it was some sort of reflective/refractive effect of light reflecting from and maybe partially passing through the ice - but the shadow explanation makes much more sense.

Not only can we not see the shadows of some lumps on other lumps at opposition, but we also see all the lit-up parts. When we're viewing at an angle, our view of many of the lit-up parts of the lumps is partially blocked by other lumps that happen to be in front of them.

You get the same sort of halo effect around your shadow with the Brocken Spectre - and because the shadow is falling on water droplets, you sometimes see a rainbow effect in the halo - which is called a 'glory'.

See images at https://www.atoptics.co.uk
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Re: Cool astronomy photos

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Image
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Re: Cool astronomy photos

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Re: Cool astronomy photos

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Not sure which topic ....
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Re: Cool astronomy photos

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Perseid meteor shower:

Image

Technical details: https://old.reddit.com/r/SonyAlpha/comm ... i_24mm_gm/
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Re: Cool astronomy photos

Post by Abdul Alhazred »

Titan. Linky poo only because best viewed full screen, :)

https://apod.nasa.gov/apod/ap200820.html
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Re: Cool astronomy photos

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Re: Cool astronomy photos

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The Heart nebula (IC 1805) with stars removed:

Image

Technical details: https://www.galactic-hunter.com/post/ic ... art-nebula.
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Re: Cool astronomy photos

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Image
Shell Galaxies in Pisces

This intergalactic skyscape features a peculiar system of galaxies cataloged as Arp 227 some 100 million light-years distant. Swimming within the boundaries of the constellation Pisces, Arp 227 consists of the two galaxies prominent right of center, the curious shell galaxy NGC 474 and its blue, spiral-armed neighbor NGC 470. The faint, wide arcs or shells of NGC 474 could have been formed by a gravitational encounter with neighbor NGC 470. Alternately the shells could be caused by a merger with a smaller galaxy producing an effect analogous to ripples across the surface of a pond. The large galaxy on the top lefthand side of the deep image, NGC 467, appears to be surrounded by faint shells too, evidence of another interacting galaxy system. Intriguing background galaxies are scattered around the field that also includes spiky foreground stars. Of course, those stars lie well within our own Milky Way Galaxy. The field of view spans 25 arc minutes or about 1/2 degree on the sky. [Roughly the angular size of the moon.]