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73 votes
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Why are we building larger land-based telescopes instead of launching larger ones into space?

It's cheaper. (1) With adaptive optics you can get 0.1 arc second resolution on the ground (admittedly only on a mountain top with particularly good air flow, but still!). This eliminates one of the ...
Mark Olson's user avatar
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67 votes

Why did it take so long to invent telescopes given glass was used 4000 years ago in Mesopotamia?

Ancient glass was opaque or at most translucent. It was also often full of bubbles. Glass was not even suitable for windows until the first century AD, and even then it was as a means of letting ...
James K's user avatar
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62 votes

Why is Starlink polluting the night sky a big concern if we have space telescopes?

It's a problem because there are still lots and lots and lots of ground-based telescopes. Ground-based telescopes are still (by far) the biggest optical telescopes, and the cost of space telescopes ...
James K's user avatar
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54 votes
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Is it possible to mount a telescope on a plane? Is it beneficial?

This has been done. SOFIA is an infrared observatory built into a Boeing 747 SP: SOFIA takes advantage of the fact that some infrared bands are visible at atltitude, these are attenuated by water in ...
Hobbes's user avatar
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49 votes
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How can telescopes see anything at all?

Yes, space is very empty. There is not nothing between us an the Eagle nebula, but little enough that we can still get a reasonable view of it. The pillars are ephemeral, they are evolving on ...
ProfRob's user avatar
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45 votes
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Why do small mirror imperfections matter with modern computers

correct for the distortion An imperfect mirror does not produce a distorted image - it produces a blurry image. With light-field sensors and phase imaging, one could possibly correct for the blur, ...
jpa's user avatar
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39 votes
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What would happen if someone had a telescope and watched Betelgeuse when it goes supernova?

No, it would not be a problem. Supernovae are not at all like flashbulbs – they brighten over a period of many days and dim again even more slowly. Here are a number of different light curves taken ...
Mark Olson's user avatar
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39 votes
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Why are almost all modern telescopes reflectors?

Several aspects of refractors limit their usefulness for large telescopes. First is chromatic aberration. Because refractors focus light with refraction, and refraction varies at different ...
antlersoft's user avatar
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38 votes

Please check my Mars photo

(Much of this echoes what antlersoft says in their answer) For a phone photo through the eyepiece that looks about right to me! The size... the brightness... both are as I expect. What you could try ...
Aaron F's user avatar
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38 votes

Could we detect the light of cities at night in other solar systems?

No. There are very few exoplanets that can even be imaged as "dots". There are none that can be resolved as discs and it would be well beyond current technology to see lights on the ...
James K's user avatar
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37 votes

Shouldn't this cause a fire?

It could start a fire if the screen is at the focal point of the optical system. That is how you light fires with a magnifying glass. Here, the blackboard is likely away from the focal point, so you ...
usernumber's user avatar
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35 votes
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Shouldn't this cause a fire?

For a magnifying lens or mirror to be able to ignite something with light from the Sun, its surface area must be large relative to the square of the focal length. Solar energy will be spread ...
supercat's user avatar
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35 votes
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What will succeed the Arecibo Observatory?

There's no simple answer. In the immediate future, different radio telescopes around the world will pick up the slack in various ways; how that happens will depend on the needs of individual observers ...
HDE 226868's user avatar
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35 votes
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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}{...
James K's user avatar
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35 votes
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Can a very powerful telescope show a person standing on the moon from the side rather than from directly overhead?

Yes. The person just has to be standing somewhere near the limb of the moon. That is near the edge of the apparent disc of the moon. We see everything near the limb of the moon from the side, at all ...
James K's user avatar
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34 votes
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What detail can Hubble see on Mars?

Forget about magnification. People who know telescopes don't think in terms of magnification. What matters is the angular resolution, or the resolving power: the angular size of the smallest details ...
Florin Andrei's user avatar
34 votes
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Is it possible to do planet observation during the day?

Jupiter can be seen during the day. This image is by Philip Crude. Philip is an experienced astro-photographer. On his webpage http://www.billionplanetsquest.com/p/planets.html he gives details of ...
James K's user avatar
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34 votes

What should I look for in a first telescope for a child?

A desire to see “the planets” is admirable but not realistic. An affordable back yard telescope will turn planets into shaky white blobs, not Hubble images. The resulting disappointment acts as an ...
Woody's user avatar
  • 1,040
33 votes

Could we detect the light of cities at night in other solar systems?

I did a few rough calculations. Let's assume a neighbor system (4 light years), and a population of 1 billion people each transmitting 1000W of light into the night sky. Then on Earth, a 100 square ...
Ralf Kleberhoff's user avatar
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 ...
Ilmari Karonen's user avatar
29 votes

Was Galileo expecting to see so many stars?

tl;dr: Probably yeah, Galileo was a smart guy and probably reasoned that if he could get a better view, he could see more stuff (like stars) Consider what a night sky looks like with absolutely no ...
Justin T's user avatar
  • 3,404
28 votes

Why can't we build a huge stationary optical telescope inside a depression similar to the FAST radio telescope?

The surfaces of telescopes need to be configured to a fraction of a wavelength. If one is working in the FAST wavelength range of 10 cm to metres, then that is a relatively straightforward engineering ...
ProfRob's user avatar
  • 152k
28 votes

Can a very powerful telescope show a person standing on the moon from the side rather than from directly overhead?

Yes, but only just. The best-case (called "diffraction-limited") angular resolution of a telescope (i.e. the smallest detail it can make out) is given by $$ \theta = 1.22 \frac{\lambda}{D} $$...
Steve R's user avatar
  • 389
28 votes

Could we detect the light of cities at night in other solar systems?

No, at least not with currently deployed telescopes. However, it is theoretically possible with current (or near future) technology. We could potentially image the lights of an exoplanet using a Solar ...
Brandon Harrison's user avatar
26 votes

Why do small mirror imperfections matter with modern computers

Also see answers to Could mirrors be replaced with CCDs? Is Digital Adaptive Optics Possible? The problem is that light imaging detectors convert amplitude to power during the detection process. ...
uhoh's user avatar
  • 30.8k
26 votes

Telescope on drones to escape light pollution?

Yes, but not in the exact way you think of. To avoid light pollution it is better to go sideways. If you are in a light-polluted city, there would still be light pollution at an altitude of 400ft (...
James K's user avatar
  • 122k
25 votes

What would happen if someone had a telescope and watched Betelgeuse when it goes supernova?

If you insist on observing the exploding Betelgeuse at peak brightness, you could potentially damage your eye. The complete answer enters the realm of physiology. Here I'll discuss the astronomical ...
pela's user avatar
  • 38.3k
25 votes

Which place in the world should be best for astronomy with an optical telescope?

High altitude, so there is less atmosphere to look through. Dry climate, so there is less water vapour, fewer clouds, less rain. Low latitude, so more of the sky is visible for at least part of the ...
James K's user avatar
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24 votes
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Could we parallax measure stars just based on the Earth's size?

In principle, it's not impossible. The Gaia spacecraft, designed primarily for measuring stellar positions, is able to measure parallaxes up to 10 kpc away with 20% uncertainty. Its baseline is 2 AU; ...
pela's user avatar
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24 votes
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Why different specifications for telescopes and binoculars?

With a binocular, all its optical components are fixed - the user can't change them. What's important for the user to know is the size of the front lens, which determines the brightness (and in ...
Dr Chuck's user avatar
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