35
votes
Accepted
Why do satellites appear as streaks in telescope images?
Satellites are moving. They are in orbit around the Earth. Satellites in low Earth orbit are moving at about 7000 m/s relative to the ground.
You can work out the orbital speed by $$v=\sqrt{\frac{GM}{...
- 115k
29
votes
Why do satellites appear as streaks in telescope images?
Can you explain me in simple words why the satellite in this telescope image appears as a streak? The exposure time is 1 second.
This drawing should explain it:
(Note: It could be the other way ...
- 2,506
26
votes
Accepted
Is there enough data in light coming from distant exoplanets for Earth-orbiting telescopes to take a high-resolution photo of it?
No, not with the current or any projected "next-generation" of telescopes.
The problem isn't dust, it is distance. To put it in context, you can consider a scale model of the universe. ...
- 115k
20
votes
Is there enough data in light coming from distant exoplanets for Earth-orbiting telescopes to take a high-resolution photo of it?
There is a fundamental limit to resolution called the "diffraction limit" that depends on three things:
The angular size of the feature you're trying to resolve,
The wavelength of light you'...
- 758
18
votes
Accepted
Which are stars and which are noise in this comet photo?
Is that right?
Yes.
Is the fuzzy one an extended object?
That would certainly be my guess (probably a distant galaxy).
What causes so many isolated pixels to be so much brighter ...
- 16.4k
15
votes
Is there enough data in light coming from distant exoplanets for Earth-orbiting telescopes to take a high-resolution photo of it?
The only real problem is lack of angular resolution at optical and near infrared wavelengths. Lack of photons is not an issue.
Suppose there were something the size of Jupiter orbiting Alpha Cen A. At ...
- 146k
10
votes
Accepted
What is the "lost light" in this unusual Hubble Deep Sky image?
Let me see if I can explain the main aim and accomplishment of this work.
First off: the picture you're puzzling over is a "luminance RGB" image, in which the bright regions are represented by color (...
- 16.4k
8
votes
What is the "lost light" in this unusual Hubble Deep Sky image?
When you plug the lead researcher's name into Arxiv, the first search result is The missing light of the Hubble Ultra Deep Field.
3 main steps:
Creation of sky flat fields for the four filters....
- 3,024
8
votes
Accepted
What does "additive fringing from the (multiplicative) twilights" mean?
The fringing pattern is caused by thin-film interference within the CCD. The signal received in a pixel will be proportional to the light falling on it, multiplied by a sensitivity, but then some ...
- 146k
8
votes
Accepted
Why does the background noise in this image of 2020 QG look like corduroy?
I agree that it’s noise in a fixed pattern, but I think it’s unlikely to be related to ADC sensitivity. Typically if you have multiple ADCs, they read out blocks of the sensor (e.g. one on each ...
- 4,864
7
votes
Why do satellites appear as streaks in telescope images?
A relatively simply way to remove the streak is to take two-or-more photos, with a short pause between them. The stars won't move much in that time, but the satellite will have drawn a short dash on ...
- 183
7
votes
Will the first Event Horizon Telescope image of the Milky Way's black hole Sgr A* just be another lumpy orange donut?
Yes. See today's press release from the Event Horizon Telescope. The image is remarkably similar to M87, but note that this a time-averaged composite over about 10 hours, because the emission from the ...
- 146k
7
votes
Accepted
Why are photos from telescope stretched at their edges?
It's a general property of optics. In what way an image is distorted depends on the exact optical setup and will need careful calibration. Usually the best imaging quality is found in the center of an ...
- 17.5k
7
votes
Accepted
If I can't unscramble an egg, how do Astronomers unscramble views gravitationally lensed by complex mass distributions?
I work in gravitational lensing, so maybe I can give you an idea.
In those JWST you have a massive galaxy cluster that is bending the light behind and acting as a true lens. If you have a temptative ...
7
votes
Accepted
Where can i find dark frames in the ESO archive?
Calibration frames, including dark frames, for the ESO telescopes in general and the FORS2 instrument in this case, are taken by a general calibration program rather than the specific science program. ...
- 8,313
6
votes
Accepted
What is the size of the image sensor in the largest optical telescopes?
The current largest digital CCD camera is that of the Vera C. Rubin Observatory1 which has a whopping 3.2 gigapixels. The previous largest features on the Panoramic Survey Telescope & Rapid ...
- 286
6
votes
Why does the background noise in this image of 2020 QG look like corduroy?
That looks like a fixed-pattern noise to me.
Fixed pattern noise is a common sensor artefact for CCD sensors, One source for this is where you have less analog - digital converters (ADC) than pixels. ...
- 17.5k
5
votes
rms noise, confusion and dynamic range in radio images
RMS noise: Your understanding is mostly correct. RMS noise is the root mean square of fluctuations. Its square equals the sum of square of mean fluctuation and square of standard deviation of ...
5
votes
Is it possible to use Photolithography for telescope image sensor?
The pixel size is not a major constraint on the imaging capabilities of an astronomical telescope. The angular resolution of the image is limited by diffraction at the aperture of the telescope. For a ...
- 10.2k
5
votes
What does "additive fringing from the (multiplicative) twilights" mean?
The visual appearance of fringing is caused by the CCD (thickness) being comparable to the size of the wavelength (thin-film interference). An everyday example (same physics except with more colors) ...
- 1,111
4
votes
Why don't we see the gas behind the black hole?
The reason is that your animated gif shows a geometrically thin, optically thick accretion disk, whereas the disk around the M87 black hole is a geometrically thick, but optically thin disk.
The main ...
- 146k
4
votes
Accepted
Streaks on a stacked star field
Those are probably just "hot pixels" that don't move on the sensor like the real stars do, so that the stacking spread them out in an arc.
I don't think the software processes and treats ...
- 31.4k
4
votes
Accepted
Is it possible to use Photolithography for telescope image sensor?
Is it possible to use Photolithography for telescope image sensor?
Sure, in the sense that CCDs and similar devices are already made using photolithography, and have been for decades.
But since you ...
- 16.4k
4
votes
Converting an RGB image to fits (astropy)
I haven't done much astronomical image processing before, but as this question is unanswered I'll give it a shot - hopefully to some avail. If the problem is more specific, a code sample/image sample ...
- 41
4
votes
Accepted
Why do the Andromeda Galaxy images from NASA have some sort of color shifting in it
I think they are probably processing artefacts, because there are other artefacts there, and because the lines are parallel.
I sent it through RGB saturation and found other artefacts of linear star ...
- 4,188
4
votes
Why are diffraction spikes left in JWST public images?
Simple answer: false-color does not in any way "photoshop" the original image information. The term "cleanup" doesn't mean anything. Quite probably multiple images were ...
- 3,763
4
votes
Is there enough data in light coming from distant exoplanets for Earth-orbiting telescopes to take a high-resolution photo of it?
No, not with present telescopes. A very tiny blurred image is all that can be achieved with present telescopes
- 7,411
3
votes
What are some astrophotography editing options and strategies for taking photos of galaxies with a telescope and a cell phone?
For better astrophotography experience, here are some stratergies I usually if I were to shoot with a cell phone cam.
Capturing images
It starts with your smartphone itself, Your smartphone should be ...
- 2,610
3
votes
Hoping to do some viewing and astrophotography with a large-ish Dobsonian and a DLSR, is this scheme workable?
Yes it's workable, but it's not for everyone. I think that you, personally (given the knowledge and experience that you demonstrate on this site), with your expectations appropriately tempered, will ...
- 1,633
3
votes
Accepted
Why are the radio images of the jet of 3C 273 different?
The quick answer is yes, we indeed see real changes in the structure of the jet.
Longer answer; There are several factors that define how the jet of 3C 273 looks like: frequency of observation, ...
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