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Can You Find the Comet?

apod.nasa.gov

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Re: Can You Find the Comet?

#71

Post by giancarlostoro »

AntiUSAbah wrote: post #65

We do not need Starlink! It only provides service to 9 Million! People We are a planet with 8 Billion People. Do i want cheap and reliable internet everywhere and perhaps work remote? Yes. Should someone like Musk destroy our look into space for just me and my use case? No.

I do wonder if in 100 or 200 years if we do become interplanetary as a species, and technology advances if many of these satellites will just disappear from the night sky and it would be long since forgotten or if remembered only as a steppingstone towards an interplanetary future.

In the meantime, Starlink is the only thing that gives my sister in Puerto Rico access to the internet when the grid gets completely nerfed by a hurriance so she can tell us she's alright, well, that and landlines if she gets a power generator, otherwise, we're left to wonder how my sister and nephews are doing.

Re: Can You Find the Comet?

#72

Post by AntiUSAbah »

giancarlostoro wrote: post #71
AntiUSAbah wrote: post #65

We do not need Starlink! It only provides service to 9 Million! People We are a planet with 8 Billion People. Do i want cheap and reliable internet everywhere and perhaps work remote? Yes. Should someone like Musk destroy our look into space for just me and my use case? No.

I do wonder if in 100 or 200 years if we do become interplanetary as a species, and technology advances if many of these satellites will just disappear from the night sky and it would be long since forgotten or if remembered only as a steppingstone towards an interplanetary future. In the meantime, Starlink is the only thing that gives my sister in Puerto Rico access to the internet when the grid gets completely nerf…

You don't need starlink to get a message out of Puerto Rico.

We also don't need starlink as a stepping stone.

What we need is food for the planet, resiliance infrastructure, proper health care, stable energy grids.

Re: Can You Find the Comet?

#73

Post by [deleted] »

giancarlostoro wrote: post #71
AntiUSAbah wrote: post #65

We do not need Starlink! It only provides service to 9 Million! People We are a planet with 8 Billion People. Do i want cheap and reliable internet everywhere and perhaps work remote? Yes. Should someone like Musk destroy our look into space for just me and my use case? No.

I do wonder if in 100 or 200 years if we do become interplanetary as a species, and technology advances if many of these satellites will just disappear from the night sky and it would be long since forgotten or if remembered only as a steppingstone towards an interplanetary future. In the meantime, Starlink is the only thing that gives my sister in Puerto Rico access to the internet when the grid gets completely nerf…

[deleted]

Re: Can You Find the Comet?

#74

Post by giancarlostoro »

AntiUSAbah wrote: post #72
giancarlostoro wrote: post #71

Earlier quoted context omitted.

I do wonder if in 100 or 200 years if we do become interplanetary as a species, and technology advances if many of these satellites will just disappear from the night sky and it would be long since forgotten or if remembered only as a steppingstone towards an interplanetary future. In the meantime, Starlink is the only thing that gives my sister in Puerto Rico access to the internet when the grid gets completely nerf…

You don't need starlink to get a message out of Puerto Rico. We also don't need starlink as a stepping stone. What we need is food for the planet, resiliance infrastructure, proper health care, stable energy grids.

I sure hope you never have to wonder if your relatives are safe and doing well after they have no way to communicate with you for weeks.

Re: Can You Find the Comet?

#75

Post by nayuki »

jlarocco wrote: post #70
nayuki wrote: post #62

Earlier quoted context omitted.

Pretty much every DSLR/DSLM camera out there has a "bulb" mode that keeps the shutter open as long as you hold down the shutter button. I think my personal record is a 20-minute exposure. As for actually holding down the button, you can either use an external wired shutter button that has a mechanical lock to hold it down, or you use a wired controller that has an electronic timer, or you use a software feature in th…

For anybody wondering, the reason not to do a single ultra-long exposures is noise. There's an equilibrium between exposure duration, aperture, and ISO that gives the best results for the conditions with a minimum amount of sensor noise, and getting close to the equilibrium and stacking the images typically gives better results than one massive exposure.

I believe your claim about noise and long exposures is false. To start, I posit that there are three sources of noise:

0) Photon shot noise from the object that you want to photograph. This is an inherent and unchangeable quantum-mechanical fact.

1) Sensor read noise per photo taken. This increases with the number of subexposures.

2) Dark current noise per time and per temperature.

#0 and #2 only depend on the total exposure time, not the number of subexposures. #1 actually gets worse with more subexposures, but what you gain are the ability to reject satellite trails, bad mount tracking, cosmic rays, wind gusts, rolling clouds, and other transient artifacts. Whereas if you took a single hour-long exposure, it's essentially guaranteed to be ruined by something.

The trade-off in how many / how long subexposures to take has been analyzed and discussed to death by astro imagers. To cite a few videos I enjoyed: https://www.youtube.com/results?search_query=astrophotograph... , https://www.youtube.com/watch?v=T_k9B01AeFM , https://www.youtube.com/playlist?list=PLaDi49CzWbrYhWEKxWiwB... , https://www.youtube.com/watch?v=mj5zn_Jz3dE , https://www.youtube.com/watch?v=n1RbyswFUqs

As for ISO, it is very commonly misunderstood. ISO amplifies photon noise and dark current noise, and changing the ISO doesn't make your images better or worse in these aspects. ISO in the form of analog gain can help boost the signal above the analog-to-digital converter noise, and that's what it's useful for. The MinutePhysics video explains excellently: https://www.youtube.com/watch?v=ZWSvHBG7X0w . More and more sensors these days approach "ISO invariance", where analog amplifier gain has about the same effect as digital gain (i.e. multiplying the measured numbers on a computer).

Exactly what I'm refuting:

> exposure duration

In astronomy, more is better. Get as much total exposure time as you can afford (e.g. time being at a suitable location, time spent monitoring the equipment, time under clear skies).

> aperture

In astronomy, more is better. Buy the biggest aperture you can afford - obviously, subject to constraints such as cost, weight, mountability, focal length. Also, telescopes don't have adjustable aperture blades, unlike general photographic lenses. You could put a disc cut-out in front of the telescope to close down the aperture, but that's just a waste of light.

> minimum amount of sensor noise

You get the least amount of sensor noise by reducing the exposure time and reducing the temperature (dedicated astro cameras have Peltier cooling). Note that although noise increases with time, signal increases with time faster, so the signal-to-noise ratio is proportional to the square root of time. So 100× more exposure time gives you a 10× better SNR.

> stacking the images typically gives better results than one massive exposure

This is the main falsehood that I wanted to address. Taking multiple images actually gives more noise overall, even if it's a tiny bit. But multiple images gives you much more processing flexibility and the ability to selectively reject things.

Re: Can You Find the Comet?

#76

Post by adolph »

mark-r wrote: post #28
albert_e wrote: post #15

Why are satellite trails not continuous lines Is the camera exposure taking a few seconds of break between takes that get stacked later with some "missing" moments in between?

I'm not aware of a digital camera that can take a 10 minute continuous exposure, but maybe there are special astronomy cameras that can?

How is a 10 minute continuous exposure functionally different from 10 minutes of video with every frame stacked? In the former, each photodiode acts as a compositor for each pixel instead of whatever algorithm is chosen to combine frames in the latter?

Re: Can You Find the Comet?

#77

Post by nayuki »

adolph wrote: post #76
mark-r wrote: post #28

Earlier quoted context omitted.

I'm not aware of a digital camera that can take a 10 minute continuous exposure, but maybe there are special astronomy cameras that can?

How is a 10 minute continuous exposure functionally different from 10 minutes of video with every frame stacked? In the former, each photodiode acts as a compositor for each pixel instead of whatever algorithm is chosen to combine frames in the latter?

You pay the read noise every time you read out the sensor and digitize the values. Also, you lose a tiny bit of time between exposures as the sensor resets itself. And you might have a bottleneck in moving the data off the sensor and saving the image. Furthermore, if you perform lossy compression on the video, then your digitally stacked image will differ significantly from analog stacking on the silicon sensor.

Re: Can You Find the Comet?

#78

Post by adolph »

adrian_b wrote: post #16
ultratalk wrote: post #12

Earlier quoted context omitted.

Opinion: We need to move our astronomical observation equipment off of Earth and onto other bodies, especially radio astronomy, which, unlike telescopes that operate in other wavelengths, is still affected by Earth's emissions in LEO/near-Earth space. We should put a radio telescope on the far side of the moon [0] to benefit from the thousands of kilometers of lunar material separating Earth's emissions from telescop…

Unfortunately, that seems to be the only solution. However, it has serious disadvantages. It will exclude the poorer from astronomical research, except within the limits enabled by whatever cooperation the richer will be willing to do with them. For the richer, that will make astronomical research much more expensive. When even USA, who claims to be the richest country, cuts a lot of the scientific funding, this make…

> It will exclude the poorer from astronomical research, except within the limits enabled by whatever cooperation the richer will be willing to do with them.

Isn't it the case that most astronomical research uses source data from large telescopes and sky surveys? An example is the Rubin Science Platform [0] which makes available images and metadata from the Rubin Observatory along with compute and APIs?

https://data.lsst.cloud/

Re: Can You Find the Comet?

#79

Post by NegativeLatency »

ultratalk wrote: post #12
adev_ wrote: post #11

Earlier quoted context omitted.

And this is just the visible spectrum. The situation is one order of magnitude worst in radio-astronomy. It is fair to state that satellite constellations will certainly be the main obstacle to multiple major scientific discoveries in the next decade.

Opinion: We need to move our astronomical observation equipment off of Earth and onto other bodies, especially radio astronomy, which, unlike telescopes that operate in other wavelengths, is still affected by Earth's emissions in LEO/near-Earth space. We should put a radio telescope on the far side of the moon [0] to benefit from the thousands of kilometers of lunar material separating Earth's emissions from telescop…

Or even out past the heliosphere/heliopause

Re: Can You Find the Comet?

#80

Post by silon42 »

christophilus wrote: post #13
ultratalk wrote: post #12

Earlier quoted context omitted.

Opinion: We need to move our astronomical observation equipment off of Earth and onto other bodies, especially radio astronomy, which, unlike telescopes that operate in other wavelengths, is still affected by Earth's emissions in LEO/near-Earth space. We should put a radio telescope on the far side of the moon [0] to benefit from the thousands of kilometers of lunar material separating Earth's emissions from telescop…

Agreed. It’s the only solution short of a ban on constellations.

IMO, everyone that launches/operates a constellation should pay for launch of large telescope every 5-10 years (assuming science organizations can fund/build them).
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