What is Telescopes: Definition and 89 Discussions

A telescope is an optical instrument using lenses, curved mirrors, or a combination of both to observe distant objects, or various devices used to observe distant objects by their emission, absorption, or reflection of electromagnetic radiation. The first known practical telescopes were refracting telescopes invented in the Netherlands at the beginning of the 17th century, by using glass lenses. They were used for both terrestrial applications and astronomy.
The reflecting telescope, which uses mirrors to collect and focus light, was invented within a few decades of the first refracting telescope. In the 20th century, many new types of telescopes were invented, including radio telescopes in the 1930s and infrared telescopes in the 1960s. The word telescope now refers to a wide range of instruments capable of detecting different regions of the electromagnetic spectrum, and in some cases other types of detectors.

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  1. collinsmark

    Diffraction Effects and Artifacts in Telescopes like the JWST

    [Mentor Note -- Discussion spun off from the main JWST thread] Yes, the apparent hexagonal shape of that star is due to the diffraction within the telescope optics (optical filter characteristics may also have played a role). For clarity, we're talking about this star: They are (images...
  2. QuarkDecay

    Fourier transformation for circular apertures

    My notes say that the Resolution of the Aperture(in the Electric field of the wave) is the Fourier transformation of the aperture. Then gives us the equation of the aperture: and says that for the circular aperture in particular also: My attempt at solving this: We know that the Fourier...
  3. A

    I Portable telescopes inside the International space station (ISS)

    I would like to know what will be the visibility from the portable telescope aboard the International Space Station. What could they potentially view, and what are (at least some of) the things they are known to have looked at? Presumably they use it *inside* the ISS and not outside, and are...
  4. yucheng

    Astronomy Technical, physical text on (astro)photography & telescopes?

    It appears that many texts on astrophotography and telescopes for amateurs tend to avoid mathematical formulas, as such, they are of little use to do some practical calculations. What I am interested in is: Magnification Image scale Focal length Focal plane and sensor plane! (CCDs!) Focal-ratio...
  5. L

    I Resolution of observation telescopes?

    I was wondering how the resolution is of a observatory station and compare that to its field of view? Higher rez with larger field or higher rez with more narrow field but much more scanning across the sky to create full images?
  6. G

    Stargazing Could Elon Musk's Starlink orbitals piggyback telescopes?

    Elon Musk's Starlink orbital internet communication system is presently seen as a detriment for observing the cosmos by ground observers, but have astronomers thought asking Elon Musk if he would consider mounting compact low-energy telescopes on the back of his orbitals, facing away from Earth...
  7. S

    Correct statement about telescopes

    My answer would be (e) but is it just the same as (b)? So there are 2 correct answers? Thanks
  8. S

    B Are the telescopes at Mauna Kea available for anyone to use?

    This article seems to say so. https://www.accuweather.com/en/travel/the-best-stargazing-sites-in-the-us/632888
  9. P

    I Observing colour through telescopes

    Excluding planets and given normal dark skies, what minimum aperture size of a (non-refractor) telescope is required to just start getting hints of colour in deep sky objects like nebulae and galaxies? I mean in real time, unaided eye, no photography.
  10. wolram

    Stargazing Efficient Follow-Up of Exoplanet Transits Using Small Telescopes

    1903.11078.pdf Would it not be cool to find an exoplanet from your back lawn. This paper is to introduce an online tool1 for the prediction of exoplanet transit light curves. Small telescopes can readily capture exoplanet transits under good weather conditions when the combination of a bright...
  11. N

    Stargazing Is there any material I can use for an aperture solar filter?

    I live in a small town and would like to make some observations today. However i don't have a solar aperture filter, i only have an eyepiece filter of which i do not trust. So is there any household items, materials i could use safely to save me from from ordering on the net and waiting...
  12. L

    Stargazing Best Telescopes for $1K: Mars, Planets & Night Sky Views

    I'm hoping this is ok to post here as I imagine some of you will know the answer. I like to read the insights on this forum, but generally don't believe my command of the subject matter lends itself to the discussion. That said, I enjoy the night sky and am looking to get a portable telescope...
  13. P

    Stargazing How is noise removed in radio telescopes?

    For an optical telescope, light pollution is a problem and that's why put ground-based telescopes in remote places where there isn't much light. However, aren't we bombarded by radio waves from satellites for our phones and TVs? How do radio telescopes remove those?
  14. OmCheeto

    Stargazing The League of Extraordinarily BIG Telescopes

    I just finished up some hypothetical maths, as I saw yesterday that someone else on the internets repeated my repeated assertion that a really big telescope lens would collapse into a black hole. I don't think that's correct. Now, the original author of the claim, claims to be an...
  15. R

    I Detecting Asteroid Collisions: 'Oumuamua & Radio Telescopes

    A reasonably read and educated laymen, would response to a claim that science and technology still have no means to detect a big asteroid collision with earth, by saying that according to what he read and saw in communication channels reliable enough, an object of that size on course to hit...
  16. esha

    The validity of ray optics in telescopes

    the largest telescope in the world has an aperture of 10 m. According to the fresnel distance this makes ray optics valid for it, for a wavelength of lightsay 500 nm, uptil a distance of 2 * 10^7 m. I have read that after the fresnel distance, diffraction tends to dominate. But telescopes tend...
  17. N

    Height of the image of Jupiter created by the objective lens

    Homework Statement I have the following variables: f = .93 m f(e) (eyepiece) = .0082 m distance toJupiter pj = 588 E^9 diameter of Jupiter dj = 139822 E^3 Find the height of the image of Jupiter created by the objective lens of a telescope. Homework Equations M = -q/p q = f Where M is the...
  18. O

    Stargazing Different Simultaneity for telescopes in space and earth?

    I was just wondering. According to Lorentz transformations, if two events are simultaneous in one reference frame, they will generally not be simultaneous in another. The time difference that I get between the two events in the other reference frame is \Delta t^{`} = \gamma\beta\Delta x...
  19. G

    Stargazing What telescopes are good for seeing planets and galaxies?

    Hello, I am currently considering on buying a telescope to do some of my own research and for sight seeing. Any recommendations? I would prefer to have a telescope that requires me to use code or at least a computer so I can familiarize myself with the mechanics.
  20. P

    Stargazing How can the telescopes take photos of distant galaxies?

    So how can the photos of distant galaxies have no nearer stars in front of them? Or photos of nebulae? I feel like there are so many stars.that it would be impossible to take a photo of a distant object without a star in front of the photo blocking the way. Or is it luck that there are no stars...
  21. C

    Stargazing Want to purchase new telescope

    Hello all, First of all thanks for taking the time to look at my post, and thanks ahead of time to those willing to answer my question. I've always loved Astronomy and have done quite a bit of self-study over the years. I have a pair of binoculars but want to get a telescope. I'll start by...
  22. sophiecentaur

    Stargazing Artificial Stars for testing telescopes: the final answer?

    I feel the need to make sure my Dobsonian scope is working at its best. I was considering a conventional (?) red LED collimator but I suddenly begin to see these Artificial Stars on sale. Would that be a better way to go? Anyone have experience of them? Looking at real stars tells me that the...
  23. J

    What is the role of focal lengths in ray diagrams for telescopes?

    When you look up a ray diagram for a telescope you get the following: From reading my book it seems clear that the objective lens forms and image on the focal plane. This then serves as an image for the eyepiece. Since the focal length of the eyepiece at the focal length of the objective lens...
  24. S

    Astronomy Telescope Books: Guide to Different Types & Physical Approach

    I need a book on telescopes which has got a physical approach to different types of it.if anyone knows a good book on it please suggest.
  25. U

    Stargazing Compute In-Band Irradiance with an Infrared Telescope

    I'm trying to remember back to my undergrad physics days. Can anyone point me to a good textbook to compute the following? Given an infrared telescope with given specifications, such as the Infrared Astronomical Satellite and a star of defined intensity in the field of view at a specific point...
  26. pioneerboy

    Quit undergrad physics -- Wishes and options? Advice please

    Hello everyone, I am brand new here in the PhysicsForum and this is my very first message. So it's apleasure to meet likeminded people sharing the same interest and probably also profession. The latter is also the reason why I finally registered in this forum and I sincerely hopethat I am given...
  27. BWV

    Stargazing What are the upper physical resolution limits on telescopes?

    So if we become a Kardashev type II civilization, able to harvest all the energy and matter in the solar system what could we see through the massive telescopes that would be possible to construct? (say with a lens the size of Saturn). Could you get surface detail on extrasolar planets, for...
  28. kelvin490

    Why an array of telescopes is used?

    To increase the resolution of an instrument, smaller wavelength and larger aperture is desirable. It is mentioned in some textbooks that the "effective" diameter of a telescope can be increased by using arrays of smaller telescopes. I just wonder why it is possible because every telescope is...
  29. S

    Studying Top Telescope Books for Exploring the Universe: A Comprehensive Guide

    Can anyone suggest a good book on telescopes
  30. S

    Stargazing What is the difference between linear and angular magnitude in telescopes?

    what is the difference between linear magnitude and angular magnitude
  31. G

    Stargazing Why no telescopes on the moon?

    We are placing everyday more telescopes in satellites in orbit. Would't it be convenient to have some permanent telescopes placed on the moon's surface? I guess if we don't do that it's because that would be much more expensive than launching satellites? Are there no plans to place telescopes on...
  32. 2

    Stargazing Understanding reflecting telescopes?

    I have been looking at these diagrams: From the following link http://www.astronomynotes.com/telescop/s3.htm And I just can't seem to figure out why the first telescope design doesn't show a shadow and in the second why the presence of the secondary mirror, and the hole, do not affect the...
  33. Kelson Adams

    Stargazing Astrophotography -- Best Telescopes?

    What are the best telescopes for amateur astronomy? I realize that there are many differences between telescopes, but let's face it. If I'm going to invest in a great telescope, I want it to produce a high-resolution image and to survive for a significant amount of time. -- and I absolutely do...
  34. A

    Why don't compound microscopes use an erecting lens like terrestrial telescopes?

    I read that in terrestrial telescope there is an erecting lens whose function is to erect the inverted image formed by objective lens so that final image formed by eyepiece is also erect.there is no need of erecting lens in astronomical telescope because astronomical bodies are symmetrical in...
  35. Drakkith

    Stargazing Remote Telescopes for New or Old Astrophotographers

    Astrophotography is a challenging hobby whose unique challenges and high upfront cost can turn many would be astrophotographers away. Instead of worrying about spending thousands of dollars, finding a good spot to image from, and dealing with setting up and tearing down equipment, another option...
  36. R

    Stargazing ALMA vs James Webb: Which telescope will reveal more about the universe?

    What are the differences between these telescopes and which telescope will do more for our understanding of the universe? I know that ALMA is a series (66) radio telescopes, however, it also operates with optical telescopes. James Webb is an infrared telescope.
  37. S

    Why the discrepancy between telescopes and big bang?

    I am wondering why it is that we can look into Hubble's Deep Field and see galaxies 13.7 billion light years away, and 13.7 billion years ago, yet Big Bang theory tells us that 13.7 billion years ago all matter in the universe was very close together. Shouldn't we be seeing in HST that the...
  38. mishima

    Stargazing White paint of radio telescopes

    I was wondering what kind of paint is used for radio telescopes, generally. In the case of the Green Bank Telescope, the idea is to get white at visible wavelengths, black at mid-infrared, and transparent at radio wavelengths. Titanium dioxide based paint was one substance cited on the...
  39. E

    High energy neutrino telescopes

    Hello, I am opening this thread so as to discuss if possible what you believe is the science case of building a neutrino telescope. Being a fanatic in the field , I would like to hear opinions from whoever wants to say about whether it is important to build such a detector and why. Thank you!
  40. NATURE.M

    Stargazing Telescopes 101: Intro Guide For Beginners Under $500

    Hi, I am interested in purchasing a telescope, although I am not very familiar with the parts and overall structure. introductory feedback, and recommendations would be much appreciated, and also I don't want a budget of $500 (preferably price range $350-$450).
  41. J

    Where Should I Place My Telescope to Observe VY Canis Majoris?

    Homework Statement What type of location for a telescope would be needed in order to oserve the emissions of the dying VY Canis Majoris? The material is rich in dust and molecules that would vaporise around hotter stars and emits infrared radiation. Homework Equations N/A The...
  42. M

    What is the angular size of the moon as viewed from Earth's surface?

    Homework Statement a) what is the angular size of the moon as viewed from the Earth's surface? b) The objective and eyepiece of a refracting telescope have focal lenghts 80cm and 2.0cm. What is the angular size of the moon as viewed though this telescope? mean radius of the moon-...
  43. Vorde

    Stargazing Why are Radio Telescopes less detailed?

    In my experience pictures from radio antennae are far less accurate than pictures from other areas of the EMR spectrum, why is this?
  44. M

    Why virtual images in telescopes & microscopes?

    Why in telescopes and microscopes the ocular distance is such that it creates virtual images instead of real images?
  45. L

    Stargazing Muon Telescope: Unlocking the Universe's Secrets

    Ref: http://www.physorg.com/news/2011-05-cosmic-rays-southern-sky-physics.html After finishing the article, I wondered, can't this principle be used to understand the universe better? Could we not make a muon telescope and learn some interesting things about emissions in space?
  46. P

    If telescopes travels at 0.9999 c, we can seen things on andromeda almost realtime?

    hi, if i travels at 0.99999c, i will measure time between andromeda and I (events happens in andromeda) shrink to only 0.00447 x 2 millions yrs compared with a person in rest on earth? Is this right, from t' = t x (1-v^2/c^2)^0.5 So if i travels to 0.99999999999999999999...c, then i can see...
  47. Loren Booda

    Can Next Generation Telescopes See More than Just a Dime in San Francisco?

    What novel objects do you anticipate we will observe among the very first galaxies? Among the first stars?
  48. S

    Stargazing Ultra advance telescopes?

    will they ever make telescopes where the image is powerful enough to check out the surfaces of planets (real time) so we can see if there's life on them and also can see into other galaxys and maybe even pass through black holes and stuff? (not the actual telescope - i mean the image) we...
  49. B

    Stargazing Binoculars or Telescope: Which is the Better Choice for Amateur Astronomy?

    Binoculars vs Telescopes Which one would allow me to see farther into space: A 20x80 Astronomy Binocular or a 60x600 Telescope? Does an impression of depth with binoculars actually enhance the star-gazing experience? Sorry for the noob questions, but I'm about to buy my first...