# Tag Info

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### 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}{...
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### 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 ...
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### 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 ...
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### 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 (...
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### 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....
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### 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 ...
• 120k
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### 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 ...
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### 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 ...
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### 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 ...
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### 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 ...
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### 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 ...
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### 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. ...
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### 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) ...
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### 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 ...
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### 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 ...
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### 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 ...
• 30.6k
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### 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 ...
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### 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 ...
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### 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 ...
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### 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 ...
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### Which are stars and which are noise in this comet photo?

This GIF is made (via giphy.com) from the new NAASA Goddard video Hubble's New Image of Interstellar Object. It shows the comet moving at quite a clip! This shouldn't be a surprise. From the link in ...
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### 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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### What was the first use of time-delay integration in Astronomy? Are there instances before GAIA?

This is usually referred to in astronomy as the "drift scan" technique, and has actually been used with ground-based telescopes since the early 1980s (e.g., McGraw, Angel, & Sargent 1980,...
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### 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 ...
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### Why do the Andromeda Galaxy images from NASA have some sort of color shifting in it

Oh! Okay I'm finally getting your question, sorry for being so slow. We'll wait for a card-carrying astronomer to answer but my guess is that you're seeing either the edge of a thin dust cloud which ...
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### 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 ...
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### Are there automatic methods to locate (stellar and supermassive) black holes?

There are roughly three methods to "discover" black holes: Find the x-ray signature of their accretion disk. Discover the gravitational wave signature of black hole mergers. Be clever and ...
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### Image sets for testing stacking algorithms?

It's pretty easy to create a dataset for yourself using remotely controlled telescopes. I've used iTelescope in the past and had a good experience. Their "starter" account costs \$20 and should be good ...
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### Computationally intensive technique to search for TNO's within the noise of historical photographic data?

Dark Energy Survey data have yielded several TNO discoveries. Bernardinelli et al. 2020 describe their method in detail. First they compute a trial orbit from images where a transient object was ...
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