Questions tagged [telescope]

Questions related to the physical instruments for astronomical observations.

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1answer
106 views

Does anybody recognize this kind of prism?

Supplemental to this answer to Did Edmund Scientific 4¼ inch Newtonians have 90° prisms as secondary mirrors in the 1970's? I was poking around a bit further and ran across this "1960's Edmund ...
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2answers
127 views

Did Edmund Scientific 4¼ inch Newtonians have 90° prisms as secondary mirrors in the 1970's?

I mentioned my old telescope's secondary mirror in this answer (stiffness) but I'm not certain I am remembering correctly. My first telescope was a Edmund Scientific 4¼ inch Newtonian reflector. This ...
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4answers
488 views

Why not use only one support vane for the secondary mirror, to avoid multiple diffraction spikes?

Each vane holding the secondary mirror in front of the primary causes a diffraction spike. Couldn't the secondary mirror be held with only one vane? If stability is the issue, couldn't it be ...
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1answer
130 views

Telescope focal point and inversion

When looking at a diagram of the optical path through a newtonian reflector, the lines always cross before the eyepiece. I understand that the eyepiece is used to focus this diverging light cone so ...
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1answer
27 views

Comparing info for WISE and GALEX

I'm trying to compile a table showing the wavelengths and flux at m=0 for WISE, Spitzer and GALEX, but I can't find the right data for GALEX. Here's what I have so far: ...
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2answers
221 views

Why does this Lowell Observatory telescope have so many knobs? What do they all do?

The Fox News article Arizona city played critical role in moon exploration history covers several interesting activities that took place in Arizona in preparation for the Apollo Moon landings. It ...
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2answers
90 views

Which Lowell Observatory telescope is this? (used to draw Moon maps for the Apollo program)

The Fox News article Arizona city played critical role in moon exploration history covers several interesting activities that took place in Arizona in preparation for the Apollo Moon landings. It ...
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3answers
2k views

Why different specifications for telescopes and binoculars?

Sorry for the noob question but I don't seem to be able to find the answer on the internet. I've been looking through some telescopes and binoculars and noticed that shops typically give different ...
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1answer
195 views

Old Telescopes versus New

I am having trouble finding the quality of old telescopes. My question is how does a decent modern telescope that cost about a couple hundred USD compare to the top-notch telescopes in the nineteenth ...
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1answer
307 views

Unable to locate Big Dipper through Polar Axis Finder

I have recently purchased a CG-4 Polar Axis Finder for my CG-4 mount. This PAF has markings on the lens for aligning with Big Dipper or Cassiopeia, which looks like this: I have aligned the PAF to ...
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0answers
120 views

Telescope was working and now it's not

We have a Celestron 70AZ 70mm f/10 refractor that has been working perfectly. Our children knocked it over the other day, and now when we try to view the moon, it ...
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1answer
138 views

How to find the source of the light? [closed]

There are millions of galaxies out there in the entire universe. When a telescope is set to a direction to to identify the stellar objects, it can capture all lights from all the objects. How do we ...
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8answers
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Determine the moons of Jupiter through a telescope

I was doing my own "space exploration" last night with a telescope. Being a space noob I can't visually determine stars or planets (I know the moon, though), but I focused on one particularly bright ...
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1answer
899 views

Recording Spectral Lines at Home

I was wondering if it would be possible to record the emission/absorption spectra of stars without expensive spectroscopy equipment. Would it be possible to somehow utilize diffraction grating? I own ...
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1answer
100 views

Custom telescope

I am currently trying to make a Keplerian telescope from "scratch" with plano-convex lenses bought online. I have found my objective and eyepiece lenses. I'm just not sure if they will suffice to ...
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2answers
770 views

How to locate nebulas visible through AstroMaster 114 telescope without device assistance?

I will be going to the desert this month and it's my understanding that the night sky will be very dark there. I've got some practice locating the planets but I'd really like to get a look at a nebula ...
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0answers
82 views

Why look at an infrared telescopes's mirror with ultraviolet light? (Herschel Space Observatory)

While link-clicking for Where did Herschel Space Telescope go in 2013? I ran across the 2009 Time Magazine article Two Telescopes to Measure the Big Bang which shows the file photo below with the ...
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1answer
74 views

Long tube for eyepiece

I have two short telescopes. The tubes that the eyepieces fit in are different; one is short and one is long, such as the tubes on the Celestron first scope and the Jason Comet chaser. Why is this so ...
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0answers
114 views

How was the astrometry of the famous 1919 solar eclipse confirmation of General Relativity calibrated and verified?

The new New York Times article The Eclipse That Made Einstein Famous describes several events and discussions on the hundred year anniversary of the the 1919 solar eclipse and verification of the ...
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1answer
63 views

How to check what telescopes were looking at a certain portion of sky at a particular time?

I have some data that I collected from observations at a specific RA, DEC and I am trying to figure out what telescope surveys were looking at that portion of the sky at that particular time? I am ...
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2answers
6k views

What detail can Hubble see on Mars?

I'm researching a scene for a sci-fi novel in which the near-future protagonists observe earth through a station-mounted telescope in Mars orbit. My goal is to understand how much detail they ...
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1answer
45 views

What determines the surface material of the ALMA and Spitzer telescope?

The transition between metal dish and mirror happens around hundreds of microns. For example, the shortest wavelength the ALMA(metal dish) can detect is about 0.3mm, while the longest wavelength the ...
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1answer
254 views

Why did the Event Horizon Telescope take so long to take a photo of a black hole?

The Event Horizon Telescope is in the news now because they are about to release the first ever picture of a black hole. They have been working on this since 2006. Why did it take 13 years to produce ...
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1answer
167 views

Event Horizon Telescope Data Cleanup

I was wondering how the researchers were able to minimize or neutralize confirmation bias regarding the data collected? As I understand it, the algorithm pruned much of the data, which would make ...
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54 views

What description of the image can we expect from the image of first black hole? [closed]

The EHT has published the first image of a black hole. I was wondering what could be the size of the original image of the first black hole and the format of the image captured?
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2answers
64 views

What to observe with a remote telescope close to sunrise time?

I have an access to a remote telescope at 05.15-05.45 am at Hawaii time. The sun rises at 06.15 am. I will use this telescope for educational purposes for high school students. I wonder 30 mins is ...
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0answers
52 views

Within a given image of a multiple-image producing gravitational lens, does Fermat's principle apply?

The question Does gravitational lensing provide time evolution information? is excellent! When we see multiple images of the same object because of the phenomenon of gravitational lensing, do all the ...
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2answers
1k views

What should I expect to see with my telescope with what EP's?

Recently got a Celestron 130 SLT (first "real" scope) and have a question. I have the following: 130mm F/5 newtonian, 650mm focal length scope 9 and 25mm factory EP's (more on that later) Svbony 2x ...
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3answers
407 views

Why does the Moon appear to be flat?

There's no way around it: when I look at the full moon at night it looks like a mostly flat disc, with at most a bit convexity in the middle. Phases of moon look like a full moon seen through a cut-...
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1answer
271 views

Angular diameter of the Sun's reflection from the ocean, seen from Sun-Earth L1?

I'm trying to understand how smooth the reflecting ocean surface would need to be to produce such a small bright spot as seen from the DSCOVR satellite at Sun-Earth L1. It appears to be only about 8E-...
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2answers
16k views

Which planets, nebula, and other objects can be seen using Celestron Astromaster 130EQ

I have got a Celestron Astromaster 130EQ telescope, which lens should I use to see the various planets and nebula? When I tried to see Mars it was only a small red dot on scope. As per the ...
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1answer
179 views

What I can observe with a 80/900 refractor telescope? What can I study?

Recently I bought a telescope after a very good conversation with an astronomer friend of mine. The main goal is to see planets. However, Mars is so difficult and is far to find it in opposition. I ...
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1answer
120 views

How can a galaxy in-between our view and the galaxy behind it have a 'lensing effect'?

In this article, the author writes: This galaxy is so distant that it would have been invisible without the gravitational lensing effects of a large galaxy cluster called Abell 1689, located nearly ...
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1answer
963 views

How does making a refracting telescope very long reduce the chromatic aberration of an uncorrected lens?

Below are two cropped views of "Johannes Hevelius's 8 inch telescope with an open work wood and wire "tube" that had a focal length of 150 feet to limit chromatic aberration." from ...
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2answers
26k views

What can we expect to see with a telescope with a 70mm aperture and a 10mm eyepiece?

We purchased my young daughter a beginner telescope for Christmas and she's super excited to look at the large planets. Our telescope has a 70mm aperture and two eye pieces (10mm and 20mm) How much, ...
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2answers
4k views

Which eyepieces I can use it for best viewing experience using my existing telescope?

Telescope: Orion 09843 SpaceProbe 3,3 inch aperture(76mm), 700mm focal length, eyepieces - 25mm and 10mm focal lengths Hi, I am very happy and excited to see moon craters, Jupiter and Saturn. And ...
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0answers
67 views

What is the cost and benefit of building two identical telescopes?

I suppose that (especially space) telescope costs is dominated by design and development, not by material and manufacturing. So once a telescope has been developed and designed, how much extra would ...
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2answers
187 views

Source of mirror reflectivity data

I am trying to find a source of mirror reflectivity versus wavelength for the typical protected overcoat Aluminum mirrors used in astronomy. I need this to cover the whole visible range (300-1200nm) ...
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2answers
2k views

What's the useful magnification for a scope with 70mm objective lens?

Some of the spotting scopes which are e.g. 70mm claim to magnify terrestrial objects at 75x. But yet they cannot produce sharp and clear images at even 30x-35x. While 90mm scopes can do a better job ...
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4answers
463 views

Where exactly is the modification that first corrected the spherical aberration in Hubble's primary mirror?

The April 2015 CBS News article How NASA fixed Hubble's flawed vision - and reputation describes the modification taken to the Hubble Space Telescopes by the Space Shuttle that was used to correct for ...
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0answers
48 views

Combining lenses to make a telescope

Hi I have two Galileo 700mm x 60mm Astro/Terrestrial Refractor Telescopes. Can I take the lenses out and make one powerful telescope?
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2answers
298 views

VLT interferometry vs E-ELT?

If the VLT (very large telescope) can use interferomerty to act as a 200 meter mirror, then why are they trying to build the 39 meter E-ELT? What advantage does the E-ELT have, if the VLT can act as a ...
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5answers
22k views

Can an astronomical telescope view objects on Earth?

I am new to telescopes and I'm planning to buy an astronomical telescope like the "Celestron AstroMaster 114 EQ Reflector". Just curious to know whether it can be used to view objects on Earth (e.g. ...
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1answer
102 views

What are some formulas that are associated with the Schmidt corrector?

I want to fully understand how an SCT works. Thus, I figured out I can use some formulas that describe how an incident ray that is parallel with the axis would act after refracting off a Schmidt plate....
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1answer
852 views

76mm reflector vs 70mm refractor? Both are at sale at $200

I'm starting my astronomy hobby and looking for a beginner telescopes to start with. I've searched couple websites and found these 2 within my budget. I know for a fact that refractors gives you ...
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2answers
907 views

What are the aberrations of an SCT? And how can they be eliminated?

The Schmidt-Cassegrain telescope is amazing! It is compact, suitable for astrophotography ,and it requires little to no collimation. However, the SCT has some inherent optical issues. What are they? ...
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3answers
96 views

Seeking advice regarding buying a telescope

I'd like to buy a telescope with a focal length of 700mm and an aperture of 60mm. Would I be able to use a telescope of this power to study the closer planets (for example Mars and Venus) and ...
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1answer
151 views

Why aren't corrector plates aligned with the center of curvature in an SCT?

According to wikipedia, Schmidt corrector plates must be aligned with the center of curvature to eliminate the spherical aberration. However, in compact SCT designs by Celestron and Meade, that is ...
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3answers
879 views

Advice on first Telescope (refractor vs reflector), Barlow lens

I am planning on buying my first telescope. I am getting an 80mm refractor and a 114mm reflector for the same price range. Which would be a better option? Further, would a Barlow lens solve the ...
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1answer
93 views

Locate planets and stars for beginners

I am a beginner in astronomy. In fact, I just bought my first refractor telescope with 60 mm aperture and 600 focal lengths with 4mm, 12.5mm and 20 mm eyepiece and 3x barlow. Could I get info on ...

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