Telescope Definition and 517 Threads

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. mathisrad

    I Right ascension and Declination calculations

    I've been doing astronomy for Science Olympiad for a few years now and know all the basics about DSOs, HR diagrams, etc. However, I've only recently acquired a telescope since I thought it would be nice to locate some DSOs independently. I understand how RA and D are calculated, but I am not...
  2. J

    Sell Amateur Telescope Making - Ingalls

    Pages are in excellent condition, lettering on cover is faded, name and date purchased written inside front cover (20 Aug 1974). These books convinced me that I could make a telescope, but that it was a larger task than I really wanted to tackle. Make an offer, preferably enough to at least...
  3. PhysicsEnjoyer31415

    Stargazing My photo of Jupiter (I think)

  4. felizgu

    How Far Can A Person See?

    The tallest building in the world is Burj Khalifa in Dubai, United Arab Emirates, at 2717 feet and 160 floors.The observation deck is 1450 feet above ground level. How far can a person standing on the observation deck see (with the aid of a telescope)? Use 3960 miles for the radius of Earth...
  5. xchen2004

    Keplerian Telescope and real image

    I know that the Keplerian Telescope produces an inverted virtual image. What modification should I make to generate real images? Will switching the first lens with the second lens change the telescope into a microscope? Thank you!
  6. Filip Larsen

    B First light from the Euclid telescope

    https://www.esa.int/Science_Exploration/Space_Science/Euclid/Euclid_s_first_images_the_dazzling_edge_of_darkness
  7. Mukhtar

    I Is it possible to build a Telescope the Size of Half the Solar System size using all Lagrange Points?

    If all the Lagrange Points(L1, L2, L3 and L4) are utilized to depart telescopes like JWST, Luvoir and Habex then is it possible to have a Telescope aperture with a half size of Solar System?
  8. Skaiserollz89

    I Tilted plane wave through a 2 lens system

    I have 2 lenses. L1 and L2 with focal lengths f1=910mm and f2=40mm, respectively. They are separated by a distance d=f1+f2. The magnification of the system is M1=-f2/f1=.044. If I have a normally incident, collimated beam pass through my system I will have a beam, parallel to the optic axis exit...
  9. G

    Image distance of a Keplerian telescope

    I found a problem where the question is asking for image distance. The focal lengths of the objective and eyepiece convex lenses are in the ratio 8:1 for aparticular telescope. The telescope is pointed at a building that is 10 km from thetelescope and is 100 m tall. What is the distance to the...
  10. mihaivzr

    Optical What would an amateur need to make accurate astronomical measurements?

    Planning to manually rediscover or confirm our exact place in the Solar System, Galaxy and Universe. I've noticed that even 50 mm high quality amateur telescopes are likely well better than what Galileo Galilei era scientists had for the first half century. The theodolite looks like an inspiring...
  11. pinball1970

    B Circumgalactic Black hole imaged by the Hubble Space Telescope

    From NASA: https://www.nasa.gov/feature/goddard/2023/hubble-sees-possible-runaway-black-hole-creating-a-trail-of-stars "We think we're seeing a wake behind the black hole where the gas cools and is able to form stars. So, we're looking at star formation trailing the black hole," said Pieter...
  12. Q

    I Phase Contrast Telescope - Part II

    Over a year ago I started a post on a theoretical proposal for a phase contrast telescope (link here https://www.physicsforums.com/threads/why-no-phase-contrast-telescopes.1010127 ). However, the post was based on real experiences that were so different from anything I’ve ever experienced in my...
  13. A

    I What does the output of a radio telescope look like?

    What does the output of a radio telescope look like? I suppose it is not an image like that of a telescope observing visible light
  14. collinsmark

    Stargazing Fixing declination runaway on a Meade LX200 telescope

    Part I: Introduction to the problem. I made this thread to document and discuss the repairs I made to my 10" LX2000-ACF telescope to fix a declination runaway problem. It involves replacing an optical encoder attached to the declination/altitude motor. I expect this documentation will be broken...
  15. Erwinux

    I Calculating the thermal coefficient between the insulated interior of a telescope instrument package and the cold ambient air outside

    I've built an insulated chamber to protect a sensitive instrument at freeze temperatures in the winter. The instrument is mounted on a telescope, so the heat inside the chamber will slowly dissipate in the ambient. A digital PID thermostat is used to keep the temperature at a safeguard level...
  16. Orodruin

    B Event Horizon Telescope, Milky Way supermassive black hole stream

    Streaming now:
  17. B

    B Why is the Webb Space Telescope placed at L2?

    Why is the Webb placed at L2 (Lagrange point 2)? I read some articles that said it would be perpetually shaded being on the opposite side of the sun and moon, but that makes no sense when the Webb orbit is so huge? So why is it at L2?
  18. S

    Is the animation/graphics for NASA's Webb telescope in error?

    I am looking at the webpage for the status, and it seems to me that there is a big error in the graphics: https://webb.nasa.gov/content/webbLaunch/whereIsWebb.html?units=metric It shows the Earth such that it appears that the axis of rotation is going from the bottom-right to the lop-left...
  19. V

    The James Webb Space Telescope

    Maybe this is more general discussion, but I am excited / nervous about the upcoming launch of the JWST. https://jwst.nasa.gov/content/webbLaunch/countdown.html I can't wait to see the observations this endeavor will bring!
  20. anorlunda

    Lucy spacecraft and James Webb space telescope

    Apparently, one of the solar arrays on the Lucy spacecraft failed to fully deploy. https://scitechdaily.com/nasas-lucy-stable-in-cruise-mode-problematic-solar-array-is-75-to-95-deployed/ The fault may not be fatal. They may have enough solar power to complete the mission. At the same time...
  21. Buzz Bloom

    B Question re Webb telescope at L2

    The diagram in the article seems to say that the Webb will orbit around the unstable L2 point. At any distance near L2 but not exactly at L2 the Webb will tend to move further from L2, unless Webb has an engine and fuel to maintain it in the special orbit. I was not able to find any description...
  22. R

    Stargazing Calculating the Resolving power of a Telescope

    Lets assume I have a telescope with an aperture of 200 mm, if we also assume λ has a wavelength of 500 nm According to; http://labman.phys.utk.edu/phys222core/modules/m9/resolving_power.htm θ = 1.22 λ/d, where θmin is the angular separation that can be resolved. 1.22 * 500 nm / 200 mm = 3.05...
  23. russ_watters

    Stargazing Is the Hubble Space Telescope Dead?

    I first saw note of this about a week ago and I don't think it has gotten enough attention: https://www.cnn.com/2021/06/30/opinions/hubble-telescope-glitch-opinion-lincoln/index.html While I don't want to eulogize too soon, I'm wondering where the HST ranks in the annals of the most...
  24. GhostLoveScore

    Calculating flux density of radio telescope

    Hello I've made a small program that does FFT, Fast Fourier Transform on a signal from radio receiver (RTL SDR), and parabolic antenna. Of course, the output is amplitude depending on frequency. I want to use it to detect and measure 1420MHz radiation from space. But I'm not sure on what's the...
  25. A

    I Coude Spectrograph vs Cassegrain?

    What is Flux Throughput? Explain how there can be a flux throughput advantage in using a coude spectrograph compared to a Cassegrain spectrograph? I'm confused on what this actually means when comparing the two. Is it asking what are the seeing advantages in terms of resolving powers of a...
  26. K

    I Can Einstein-Chwolson rings be observed from a telescope on Earth?

    There may be too much absorption and distortion by the atmosphere of the faint images when viewed from Earth.
  27. M

    What kind of telescope can see planets in other galaxies?

    I was recently looking at a comic reprinting of Retro Sci Fi Tales # 9, and the synopsis on the site spoke about a story of the "Exposition Universelle", where at a fictitious worlds fair in Paris in 1878, they unveil a "grand inter-galactic telescope so powerful that it can view the surfaces of...
  28. gmax137

    Arecibo Observatory: The 57-Year Telescope Set to Be Decommissioned

    https://www.theverge.com/2020/11/19/21575025/arecibo-observatory-puerto-rico-decommission-structural-collapse-cable-breakThe world-famous Arecibo Observatory in Puerto Rico, known for helping scientists peer into deep space and listen for distant radio waves, is set to be decommissioned and...
  29. M

    B Nervous about James Webb Space Telescope?

    The Hubble Telescope helped us to see how enormous the universe really is. We now know from data built up from that that the universe likely has 2 trillion galaxies in it. Now when James Webb gets out their and starts taking better pictures; I’m afraid the count of galaxies will jump to 10 or...
  30. hutchphd

    B Snapped Cable Damages Arecibo Observatory Radio Telescope

    Anyone have more information...here is Scott Manley report...not good!
  31. Spinnor

    B The Hubble Telescope Images a Magnificent Galaxy With “Flocculent” Spiral Arms

    Had to Google Flocculent, adjective having or resembling tufts of wool. "the first snows of winter lay thick and flocculent" having a loosely clumped texture. "a brown flocculent precipitate"...
  32. TimeDoctor

    Whom to contact about my improvement on telescope optics?

    Hey guys. If you have a prototype of a new telescope, whom do you contact? This telescope uses the same lenses that we have but enhances their power in a n^4 So, if you have a lense that is supposed to magnify things twice, it'll magnify them 8 times. I just don't know whom to contact or where...
  33. lomidrevo

    B Lunar Crater Radio Telescope (LCRT)

    https://www.sciencealert.com/check-out-this-amazing-plan-to-turn-a-crater-on-the-far-side-of-the-moon-into-a-radio-telescope Original article from NASA: https://www.nasa.gov/directorates/spacetech/niac/2020_Phase_I_Phase_II/lunar_crater_radio_telescope/
  34. A

    How did Galileo manufacture his telescope?

    Hi How can a single man without modern technology succeed in manufacturing such an engineering marvel? Galileo wasn't even an engineer he was a scientist. I'm interested to know that because I have always dreamt to invent and manufacture my own products just like Jimmy neutron but found out...
  35. mfb

    I Large Synoptic Survey Telescope -> Vera C. Rubin Observatory

    She might have been left out with the Nobel Prizes (she died in 2016), but now one of the next generation telescopes was named after her: The Vera C. Rubin Observatory will image all the available sky areas every few days with observations starting this year and full operation from 2022 on. It...
  36. W

    I Which instruments are used to determine the composition of dark matter?

    Hello, I have a general understanding of how we are aware of the presence of dark matter in the universe and the fact that we still don't know exactly what is that dark matter is made of. I would like to know which instruments are used to try and find an answer. For instance, from what I...
  37. D

    Worm Hole light years away and look at Earth through a giant telescope

    Summary: I'd like to know if anyone else thinks of these things <mentor moved to general discussion> What if one day we can "warp" x light years away from Earth, build an enormous telescope, and look back at the Earth x years ago with resolution that rivals the American flag on the moon? Do...
  38. T

    I Why are planets visible in a telescope in the daylight?

    Why are planets visible in telescope in daylight? As far as I understand both 1) total light flux from the planet 2) and that from the atmosphere receved by scope are proportional to the aperture area. So why then we can see the planets? And I have realted question. I am my city humidity and...
  39. Michael Price

    A Resolving power of a radio telescope array: Quantum or classical?

    My question is: is the resolving power of an array of radio telescopes a quantum or a classical effect? The increase in resolving power of a single telescope, as aperture size increases, is easy to explain in terms of Heisenberg's uncertainty principle. But when we go an array of telescopes are...
  40. mfb

    B Thirty Meter Telescope can resume construction

    Larger telescopes collect more light and, thanks to modern adaptive optics, achieve a better resolution. After several telescopes with ~10 m diameter three projects aim at much larger telescopes:Giant Magellan Telescope (GMT), Chile, 24.5 m diameter, 368 m2 area Thirty Meter Telescope (TMT)...
  41. B

    Astrophysics question: Wire mesh radio telescope antenna

    The answer says its 1 meter i don't understand how they arrived at this, The mark scheme suggests that the 50mm is the resolving power or Rayleigh criteria? https://downloads.umutech.net/Physics/Past_Papers/PA05/Astro/MS/physics_u5_astro_ms_jan_2003.pdf
  42. mfb

    Stargazing Event Horizon Telescope Results Released Yesterday (April 10, 2019)

    Media Advisory: Press Conference on First Result from the Event Horizon Telescope April 10, 15:00 CEST (13:00 UTC. In 8 days and 13 hours) Livestream links are on that website. The Event Horizon Telescope is a collection of radio telescopes all over the world which recorded data from the...
  43. M

    Numerical aperture of a Keplerian telescope

    Homework Statement [/B] Design an afocal Keplerian telescope to imagine an object of ##L = 5\, mm## with a resolution of ##R = 2\, \mu m## and a magnification of ##M=-2##; assume that the wavelength is ##\lambda = 500\, nm##. Don't use lenses faster than ##F/1##. Using the optical invariant...
  44. navneet9431

    Magnification of an Astronomical Telescope

    My teacher taught me a formula for magnification in case of Compound Microscope, Magnification=(Angle Made By Object On Aided Eye)/(Angle Made by Object on Un-aided Eye) Can I use this formula for calculating magnification of Astronomical Telescope? Thanks!
  45. V

    A Continuous Field Image: Hubble Deep Field & Exoplanets

    The Hubble deep field image was constructed by collecting photons from a specific region of space over a continuous duration of time; in this case ten days. As the number of collected photons increase, higher the resolution of the image. If this duration increases, how much more resolution do...
  46. Johnnyallen

    I Gaia Space Telescope and Lagrangian Point 2

    I'm confused (what else is new) about L2. While watching a video from PBS Digital Spacetime about the latest data drop from Gaia Space Telescope, Matt O'Dowd showed a CGI animation of the telescope leaving Earth then circling/orbiting L2 perpendicular to the Earth/sun plane. I thought that the...
  47. davenn

    Stargazing Australia's largest optical telescope

    Have been doing a bit of a road trip around the state of NSW, Australia, over this last week. Visited the Parkes 36m radio telescope. Then on to Coonabarabran and the home of the Siding Springs Observatory complex. One of the several scopes here is the 3.9m AAT (Anglo-Australian Telescope)The...
  48. P

    Stargazing What is the best Dobsonian telescope with a goto feature?

    My interests include; Large telescopes & Astrophotography Sub-atomic particles The Copenhagen Interpretation Black Holes Bubble universes and the Multiverse Many Worlds Theory The Holographic Proposal Quantum entanglement Causality, determinism and free will
  49. F

    Stargazing Telescope recommendations for watching a galaxy?

    I'm close to 60 years old now, and when I was a 12-14 years old kid my father had a small 50mm telescope -- I still remember how amazing the word "Tasco" looked back then! Back then I could watch the moon and Jupiter, although I was upset that Jupiter kept moving out of sight all the time. How I...
  50. turbo

    Insights Planning to buy a first telescope? - Comments

    Read the Insight guide here
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