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Questions tagged [telescopes]

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What is a simple model of telescope sensitivity?

I am looking for a simple model of how sensitive a telescope is to low numbers of incoming photons. A train of individual photons hit one pixel of a detector, and I want to know what the numeric ...
causative's user avatar
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1 answer
40 views

Assessing the quality of wavefront correction in adaptive optics systems: the case of single and multiple radiation sources

Generalized diagram of an adaptive optical system is as follows: Wavefront from the observation object passes through the atmosphere and is distorted. It is then reflected from the deformable mirror ...
ayr's user avatar
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General questions on the "big picture" of scalar diffraction theory

When studying diffraction, my courses at university stopped with frauenhofer diffraction, which - as far as I understand it - describes the diffracted far field for diffraction of a more or less ...
Pidrittel's user avatar
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1 answer
84 views

Keplerian telescope with parabolic mirrors

Is it possible to arrange two off axis parabolic mirrors (OPAs) to transform the emitted rays of a point source into a collimated beam, as in the figure below? That is, similar to a Keplerian ...
tush's user avatar
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2 votes
1 answer
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Advantage of a single large telescope over many small ones for optical/infrared spectroscopy?

In a thought experiment where we would like to do optical/infrared spectroscopy on distant galaxies, and in which we would like to increase as much as possible the resolution of the spectroscopy (...
Vincent's user avatar
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How to calculate losses due to diffraction?

Assume a transmitter with a laser source generating gaussian beams and is transmitted using a telescope with radius of aperture $a_T$. The light is collected at the reciever end using a telescope of ...
Dotman's user avatar
  • 161
2 votes
2 answers
94 views

How to collapse telescope image cone into an optical fiber?

I have an application where a telescope will be receiving light from a laser source. I would like to couple the output of the telescope, which is the image cone, into an optical fiber. Does anyone ...
Anthony Knighton's user avatar
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1 answer
41 views

What could a year long journey look like, while traveling near the speed of light, through the lens of that telescope?

Hypothetically speaking if you had a satellite going near the speed of light in a straight line towards an exoplanet light years away and that satellite had a telescope pointed at the surface of an ...
Matthew Harwood's user avatar
6 votes
8 answers
516 views

Why specifically is looking through a telescope at the sun more dangerous than the naked eye?

At first this seems like a stupid question: "Have you never used a magnifying glass on a sunny day?!" But any lens will only ever make the focused image as intense as the target or weaker. ...
Leon Frickenschmidt's user avatar
1 vote
1 answer
70 views

In the future, can advanced telescopes be used to observe different laws of physics at the time of the big bang?

I've heard that because light takes time to travel from one place to another, we see objects in distant galaxies as they were when they released the light. new and advanced telescopes are able to see ...
Hannah's user avatar
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Equivalent focal length of two mirrors

I have two concave mirrors of the same size, both with $f=1.5\ \text{m}$. I would like to build a setup to increase the focal length, i.e. have a setup with a focal length of around 6 m. How do I ...
soki74's user avatar
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Focal Length of a Rotating Liquid Mirror [closed]

I saw this video on YouTube about using rotating liquid metal as parabolic mirrors to make reflecting telescopes. In the video apart from the standard equation of the curve the liquid makes, the focal ...
Pupz's user avatar
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18 votes
5 answers
4k views

How do telescopes see many billion light years distant object in our universe?

How do telescopes see many billion light years distant object in our universe? As an individual with limited expertise in the field of astronomy, my current understanding suggests that the observation ...
Sazzad Hissain Khan's user avatar
0 votes
1 answer
60 views

Could an optical waveguide improve the angular resolution of a telescope?

I have recently learned about the diffraction limit of telescopes that limit their angular resolution. This YouTube video, "Resolving Power of a Telescope" also provides some good background....
ericnutsch's user avatar
6 votes
2 answers
2k views

Does the light that gets reflected off of us, during our existence, travel through space forever?

Photons do not disintegrate when there is no interaction with other particles, and will continue to carry their initial momentum and information to travel through space forever. Telescopes captures ...
Bhanu Goyal's user avatar
2 votes
0 answers
81 views

Keck versus Webb: discrepancies in the redshift measurements of the galaxy GN-z11 (the most distant galaxy discovered with the Hubble Space Telescope)

Two years ago Nature Astronomy published a paper based on measurements from the Keck Telescope stating that the redshift of the galaxy GN-z11 (discovered by Hubble) is: $$ z=10.957 \pm 0.001 $$ Source:...
Albert's user avatar
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1 vote
2 answers
134 views

Quantum mechanical description of a photon arriving at a telescope from extremely far away

Typically, telescopes are explained in terms of bouncing light paths around. For example, this image from wikipedia shows "photon tracks" being redirected: I realize this is a very ...
Craig Gidney's user avatar
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How do you know what focal lengths to use in a 3 lens terrestrial/Galilean telescope?

I'm trying to make a telescope with three converging lenses but can't figure out what my middle, erecting, lens' focal length should be. Right now I'm using a 200mm objective lens and a 25mm eyepiece ...
Beans's user avatar
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0 answers
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What's the formula of SNR (Signal to Noise Ratio) to dipole antenna array (eg, LOFAR) look like?

It was wellknown that the SNR of single dish telescope reads $$s/n=\frac{P_s}{P_n}=\frac{P_{s}}{T_n}\sqrt{\frac{t}{B}},$$ where $P_s$ is the collected power, $T_n$ the noise temperature, $t$ the ...
Hunter's user avatar
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1 vote
1 answer
96 views

How do you actually use an astronomical interferometer to measure small distances?

The question in the title might be too broad, so for definiteness we can focus on the Michelson stellar interferometer which, as I understand it, is more or less just two telescopes some distance ...
Javier's user avatar
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3 votes
2 answers
77 views

How deep can a 'deep field' image be?

Hubble's famous deep field image was created by pointing the telescope at the same spot for 10 days continously. This aggregates photons and creates a coherent image - If I understand what's going on ...
vineeth venugopal's user avatar
1 vote
1 answer
359 views

Optics proof: Beam expander telescope

Beam expanders are afocal optical devices that widen/narrow the diameter of an incoming laser beam $D' = D / M$. Telescopes are afocal optical devices that multiply angle of incidence of each light-...
BrainOverflow's user avatar
0 votes
0 answers
64 views

Is a tilted, no lens telescope, can work?

I got a crazy idea to build a no-lense telescope with an optical zoom of 100,000. Please tell me where it will fail :) Go into a dark room Make a 0.1-millimeter hole in the ceiling Take a 10-meter ...
Ilya Gazman's user avatar
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0 votes
2 answers
309 views

Can we see our solar system in the past from earth?

Since our solar system is moving through the milky way galaxy, if we point our telescope to a certain point where we determine that the solar system was a certain time ago, will we see our solar ...
Sahil Sharma's user avatar
3 votes
1 answer
126 views

Diffraction pattern and grating using mesh and Telescope

I recently attended a demonstration at an observatory when a undergraduate Astronomy student showed me something neat. A telescope was pointed at a star. The student then waived a window covering with ...
Omid's user avatar
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0 votes
1 answer
25 views

How does the DKIST filter out photosphere light?

How does DKIST filter out light from the sun's photosphere while capturing light from the chromosphere? I'd like to know the physical or mathematical mechanics that accomplish this. If the naive ...
Joshua Honig's user avatar
7 votes
1 answer
879 views

Could the solar shield on the James Webb telescope have been pitch black or does it need to be highly reflective?

When I look at pictures of the sun shield on the James Webb Space telescope (JWST), I see something that looks highly reflective (and hence must have a very low emissivity). My intuition tells me that ...
SalahTheGoat's user avatar
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0 answers
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Is there a naturally occurring siderostat (fixed orientation, absolutely nonrotating object as if locked to the distant galaxies or the universe)?

Often, a telescope is attached to an equatorial mount with a motor that counteracts the earth's rotation so that the telescope has no net rotation. It may be designed to counteract the known rotation ...
Matthew Christopher Bartsh's user avatar
4 votes
1 answer
155 views

What are the farthest distances JWST can see?

I was just wondering a simple question: what is the farthest distance (equivalently the least time after the Big Bang) that the JWST could theorically see? Can it be estimated somehow WITH SOME ...
riemannium's user avatar
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2 votes
1 answer
71 views

Would a telescope travelling at close to the speed of light be able to make better images because the object would be nearer (Lorentz contraction)?

The Lorentz contraction means that when you fly toward (or away from) a distant object, that object becomes less distant in your frame of reference. So if a telescope were flying towards a distant ...
Matthew Christopher Bartsh's user avatar
3 votes
1 answer
148 views

In what sense is the JWST image of Jupiter an improvement over prior telescopes?

JWST photographed Jupiter: The data includes images of Jupiter and images and spectra of several asteroids... The data demonstrates Webb’s to track solar system targets and produce images and spectra ...
spraff's user avatar
  • 5,148
3 votes
0 answers
29 views

How do astronomical spectrometers select a single object from the field of view?

The JWST is said to have a capability to observe the spectrum of the light from individual stars and exoplanets. The field of view of JWST is usually filled with hundreds or thousands of objects. How ...
paki eng's user avatar
  • 139
62 votes
7 answers
9k views

Why do some lights captured by the Webb telescope have rays and others don't?

On the images captured by Webb telescope one can see some lights with 6 rays, but most others don't have any. One would expect the optics to transform all light sources at infinity in the same manner. ...
Michael's user avatar
  • 1,951
17 votes
1 answer
2k views

Questions about first JWST image

Why do the circled galaxies seem to form long circular arcs that surround the white point at the center? And why do most of the galaxies in this image seem to be facing that same point? What is in ...
bloop's user avatar
  • 297
3 votes
1 answer
350 views

Why space telescopes images show diffraction spikes around stars, but not galaxies?

I've seen this tweet recently: https://twitter.com/ThePlanetaryGuy/status/1544801752893067265 Additionally to the image, where it's pretty clear, the post says: Stars are six-pointed; everything else ...
Jeffrey's user avatar
  • 1,003
6 votes
1 answer
684 views

Why are radio telescopes in orbit radio telescopes?

We use radio telescopes on Earth because of the atmosphere, right? It blocks the more energetic wavelengths but not radio waves and microwaves. So, since radiation like x-ray and gamma radiation are ...
CosmeticMichu's user avatar
1 vote
0 answers
35 views

The Event Horizon Telescope collaboration will announce groundbreaking observations of our galaxy at 12 May 2022, what this announcement could be? [closed]

"Live webcasting for the ESO-hosted EHT 2022 event On 12 May 2022 at 15:00 CEST, the European Southern Observatory (ESO) will host a press conference on groundbreaking new Milky Way results from ...
Markoul11's user avatar
  • 4,170
0 votes
0 answers
20 views

Calculating magnification of a put together telescope

My objective lens has focal length of 50 cm and I am using a 10x eyepiece (I don't have anymore info). I am not sure how to calcuate the focal length of eyepiece. How do I find the total magnification ...
Rocket Hack's user avatar
2 votes
0 answers
122 views

How does the James Webb Space Telescope avoid stick/slip and creep problems when positioning its mirrors?

The JWST is now positioning its mirrors so they form a single image. How James Webb's Mirrors MUST Work To do this, each mirror must be positioned in 8 nanometer steps in 6 degrees of freedom. Here is ...
mmesser314's user avatar
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0 votes
1 answer
63 views

Are there Wolter telescope lenses for consumer cameras?

Wolter telescopes are used for x-ray astronomy. However, I see no reason why they couldn't be used for visible light as well. How would a visible image look when taken through a Wolter telescope? Are ...
SarahJuliet1510's user avatar
1 vote
1 answer
65 views

How many pixels could an image of Proxima b taken by James Webb have?

I know it's very difficult for the James Webb to image Proxima b without a coronograph (I have been told by NASA scientists that they don't know yet whether they will be able to do so), but I wonder ...
James's user avatar
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0 votes
1 answer
38 views

Doubt regarding the positioning of starshade in new world's mission of Nasa

The new worlds mission of NASA has an occulter with the telescope, Why did they place the occulter at a distance instead of attaching it to the telescope such that there is a hole as big as the size ...
25 Simran Tiwari's user avatar
1 vote
1 answer
91 views

Why do we see dark black spots in night sky with the naked eye if those same spots are filled with stars when looked at with a telescope?

When looking in the sky with the naked eye, we often see dark regions with no stars. However, when we look at those same spots with a telescope, it is full of stars or clouds of dust. Why is that?
Tom Moore's user avatar
2 votes
1 answer
285 views

Has Rindler horizon already been tested experimentally?

For an accelerated frame, there is a Rindler horizon at a distance of $$X = \frac{c^2}{a}$$ where $a$ is the proper acceleration. For $a = g$ it is about 1 light year. If one of that spacial ...
Claudio Saspinski's user avatar
2 votes
2 answers
117 views

Will the spacing between the mirror segments of the Webb space telescope degrade the sharpness of its images?

I've noticed that the existing spacing between the 18 mirror segments of the Webb space telescope are many times the operational infrared spectrum wavelengths (i.e. 0.6-28μm) of the telescope meaning ...
Markoul11's user avatar
  • 4,170
0 votes
2 answers
142 views

Why is the JWST orbit only taking 30 days?

Presumably the Ariane 5 rocket launched the James Webb Space Telescope into an elliptical orbit with its apogee at the L2 point. Such an orbit’s period is about 70 days, i.e. the journey to L2 should ...
adlibber's user avatar
  • 425
1 vote
1 answer
244 views

How can the limited to infrared James Webb space telescope do spectroscopy of the exoplanets' atmosphere without seeing in the visible spectrum?

image source: https://www.youtube.com/watch?v=bI-JIAmiL7A JWST will look for the composition of exoplanets' atmosphere using the spectroscopy method. However as far as I know for elements of the ...
Markoul11's user avatar
  • 4,170
17 votes
4 answers
3k views

Why do we need very large stationary telescopes in addition to the orbital telescopes?

Most of the existing telescopes are located on Earth since it is easier and cheaper to construct, build and operate on Earth. Space launches are very expensive, and, moreover, if there is some problem ...
spiridon_the_sun_rotator's user avatar
2 votes
2 answers
83 views

Is it the term "telescope" the same as a "detector"?

For example, in this reference, MITO: muon telescope they use the term telescope but clearly the "telescope" is a muon detection system. And they also talk about angular resolution, angular ...
Las Des's user avatar
  • 123
1 vote
0 answers
392 views

Galilean telescope magnification coefficient?

So I've seen the magnification coefficient of the compound concave telescope to be $\frac{f_0}{f_e}$, but what is the magnification coefficient in the case of the convex galilean telescope? This may ...
HakemHa's user avatar
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