Cool astronomy photos

[shemp]

How come we can get pictures like that, but Bigfoot is always blurry?

[Witness]

How come we can get pictures like that, but Bigfoot is always blurry?

Because you're always drunk when you hang out with him, duh.

[Anaxagoras]

Bigfoot is a forest ninja.

[Witness]

Comet Neowise from the Brecon Beacons (Wales).

[Anaxagoras]

Link:

[Bruce]

Literally took all day.

[Witness]

↑ Great video!

There's something flying by between 15 and 16 s. Screenshot:

[Anaxagoras]

Another satellite perhaps? Or an airplane?

[robinson]

Literally took all day.

A day for the ISS is less than two hours

[robinson]

But it was a good joke

[Rob Lister]

Another satellite perhaps? Or an airplane?

It appears way too large to be an airplane flying a couple of hundred km below it. It's velocity is pretty close to that of the ISS (or we'd never see it) so if it is in orbit , it's a fairly near orbit. The video is speed up 4 times but I suppose it's possible to use the frame rate to work out the exact velocity and therefore the exact orbit and therefore the exact distance and therefore the exact size.

[Anaxagoras]

A UFO then. More proof!

[Bruce]

A UFO then. More proof!

No comment from Lord Kilik?

[Witness]

Neowise:



Technical details: https://old.reddit.com/r/Astronomy/comm ... _c2020_f3/

[Witness]

[ceptimus]

Curiosity after seven years on Mars:

In those Curiosity selfie photos, it's always difficult to see how Curiosity is holding its camera - no obvious signs of the "selfie stick" to me - neither in the photo nor the shadows.

[Witness]

In those Curiosity selfie photos, it's always difficult to see how Curiosity is holding its camera - no obvious signs of the "selfie stick" to me - neither in the photo nor the shadows.

The selfies are stitched-together panoramas. With ad hoc software you can choose which original image (or part of) to use for any part of the result, leaving the arm and its shadow invisible.
You can do that with Hugin, e. g. for getting rid of moving people in your panorama.

[Fid]

...You can do that with Hugin, e. g. for getting rid of moving people in your panorama.

"... intellects vast and cool and unsympathetic, regarded this Earth with envious eyes, and slowly and surely drew their plans against us. NASA they named it knowing the love Men hold for acronyms..."

[Witness]

The fault in our Mars



This image from NASA's Mars Reconnaissance Orbiter (MRO) of northern Meridiani Planum shows faults that have disrupted layered deposits. Some of the faults produced a clean break along the layers, displacing and offsetting individual beds.

Interestingly, the layers continue across the fault and appear stretched out. These observations suggest that some of the faulting occurred while the layered deposits were still soft and could undergo deformation, whereas other faults formed later when the layers must have been solidified and produced a clean break.

The map is projected here at a scale of 50 centimeters (19.7 inches) per pixel. [The original image scale is 54.6 centimeters (21.5 inches) per pixel (with 2 x 2 binning); objects on the order of 164 centimeters (64.6 inches) across are resolved.] North is up.

https://phys.org/news/2017-12-image-fau ... .html#nRlv

[robinson]

[Witness]

Mars launch: NASA sends Perseverance rover to space



The Perseverance rover and its Ingenuity helicopter are finally on the journey to Mars.
The spacecraft carrying the rover and helicopter successfully launched to Mars Thursday morning aboard a United Launch Alliance Atlas V 541 rocket from Cape Canaveral, Florida at 7:50 a.m. ET.
The team in the control center at NASA's Jet Propulsion Laboratory confirmed they received the spacecraft's signal shortly after 9 a.m. ET.
...
After traveling through space for about seven months, Perseverance is scheduled to land at Jezero Crater on Mars on February 18, 2021.

https://edition.cnn.com/2020/07/30/worl ... index.html

[Witness]

Dust devil taken by the Spirit rover.

[Witness]

NGC 1300, a barred spiral galaxy imaged by the Hubble Space Telescope

[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.

[Rob Lister]

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

[robinson]

Why?


Is there something better?

[ceptimus]

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.

[Rob Lister]

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.

[Witness]

The rings appear brighter at opposition.

[ceptimus]

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.

[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.

[shemp]

The rings appear brighter at opposition.

Works with bathtub rings too.

[Anaxagoras]

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.

[Witness]

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:



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.

[ceptimus]

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!
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

[Witness]

[robinson]

[robinson]

Not sure which topic ....

[Witness]

Perseid meteor shower:



Technical details: https://old.reddit.com/r/SonyAlpha/comm ... i_24mm_gm/

[Witness]

https://old.reddit.com/r/interestingasf ... midflight/