Questions tagged [telescope]

Questions related to the physical instruments for astronomical observations.

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7
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2answers
2k views

Jupiter with a mobile phone and Celestron Astro FI 102mm Maksutov

My name is John, I am new here and now that I am retired I decided to get myself my first ever telescope, why I never got one before I have no idea...probably too busy. So I thought I would try and ...
7
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2answers
265 views

Ninth planet - what else could it be?

So recently it was announced that there might be a ninth planet out there. Some people (from NASA) say the odds are 50% that it is a real planet, since it hasn't been discovered by telescopes yet. ...
6
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1answer
947 views

Telescope collimation issue

Recently, I purchased a Chinese 8 inch reflector telescope from local store. When I observing stars and planets I've been having trouble getting really sharp image from this telescope. I observe Venus ...
6
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1answer
313 views

If we had the right technology could we see a distant star in detail?

If, for instance, Hubble's camera was a $10^{300}$ times better, could it see a distant star in details, or is there a limit to the amount of light that reaches the Earth's orbit or perhaps does the ...
6
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3answers
2k views

Could someone explain what is wrong with my telescope, and what should I be able to see with it?

In January of 2016, I received my first telescope, through Astronomers Without Borders. It was and is my first telescope: an AWB 130 Newtonian tabletop telescope with a 650mm focal length and a 130mm ...
6
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2answers
18k 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 ...
6
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1answer
322 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-...
6
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2answers
213 views

Do we know at which angle the Event Horizon Telescope will look at the accretion disk of Sagittarius A*?

Do we know at which angle the Event Horizon Telescope will look at the accretion disk of Sagittarius A*? Additionally, would it matter if we are exactly in the plane with the accretion disk, i.e. ...
6
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1answer
642 views

Do primary mirrors in large observatories undergo regular removal and re-coating of the aluminum? Why?

Performance of astronomical mirrors that are exposed to the environment for long periods of time can experience a slow degradation of performance. They usually need to receive some kind of regular ...
6
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1answer
2k views

How do telescopes "zoom" and change angle of view?

Images from the Hubble Space Telescope have widely different angles of view. Is this only the result of composing multiple images, or can the telescope itself change its "zooming" optically, ...
5
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1answer
503 views

Was the use of silver on 'optical' telescope mirrors more common in the past? Why?

In the past, weren't many astronomical telescope mirrors periodically removed and 'resilvered', and wasn't this actually done using silver? I'm guessing that this is much less common now - new ...
5
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1answer
123 views

lousy mirror corrected by software

Would it be possible to get a terribly shaped mirror, like a large sheet of something reflective, give it a general shape like a telescope mirror, but not anywhere near as precisely shaped as in a ...
5
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1answer
432 views

Surface brightness of deep-sky objects and telescope specs

I'm new to amateur astronomy, and I recently acquired my first small telescope. I've just learned a bit about surface brightness after an unsuccessful night of trying to locate a few nebulae that were ...
5
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1answer
1k views

How does a Bahtinov mask work?

For focusing the image of a telescope, one can use a Bahtinov mask. How does this mask work, and how did Mr Bahtinov get the idea to cut such a peculiar shape? Is it possible for me to design my own ...
5
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1answer
728 views

Why when we look through a telescope in space, do the billions of stars not block our view from seeing further?

I know that we are able to "see back into time" by looking very far away through telescopes such as the Hubble telescope, but my question is, wouldn't you run into at least a couple of stars that were ...
5
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2answers
28k 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, ...
5
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1answer
109 views

Is Cosmic Ray Astronomy a thing?

Historically astronomy has been the regime of visible light, looking at distant objects in the visible spectrum and later taking photographs in the visible spectrum. In the past century radio ...
5
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1answer
200 views

How to choose portable, yet powerful telescope

Due to the nature of my job, I have to spend log periods of time (4 - 6 months each), at different countries across Europe, Middle East and Far East. I have a 12 Inch Dobsonian at home, but I rarely ...
4
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2answers
278 views

Will I be able to see both Jupiter and Saturn at the same time in my Astromaster 114?

I have a Celestron Astromaster 114 Newtonian reflector telescope. The specs: aperture: 114mm focal length: 1000mm focal ratio: f/8.77 I also have a t-ring so I can connect a Nikon camera to it. Will ...
4
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2answers
93 views

New to Astrophotography

I just had a quick question on my telescope I recently purchased. I have a Canon Rebel XTi and I paired that with the William Optics Guide Star 61 Guidescope. The Specs on the Scope are: Guide Scope ...
4
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2answers
365 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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4answers
5k views

Mars looks like a blur

I took my telescope out tonight (I am new, just got the telescope a few days ago, it's my first one) and I was observing Mars, however all I see is just an bright orange circle, with no surface detail,...
4
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1answer
2k views

Why does any planet look like a (not so) big white ball through my telescope?

I have a 130mm (5") diameter Newtonian reflector with a 650mm focal length (f/5). I have collimated my telescope already but when I'm looking at Mars or Jupiter (not a star I'm sure), all I see is a ...
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1answer
3k views

Challenges when trying to build a telescope using two lenses

I have some lenses - a 10 cm and 7 cm convex lense and a 4 cm and 1 cm concave lenses. I am trying to make a telescope by combining one of convex and concave lenses, but I am struggeling to do so. The ...
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2answers
724 views

Will these simple 2 convex lens arrangement telescope see the moon clearly?

Hi readers, I am planning to build my telescope. Does this very simple 2 convex lens arrangement even possible to observe the moon clearly with high magnification? I am planning to buy 5 cm diameter ...
3
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2answers
101 views

Can we measure comets in a similar way to exoplanets?

A 2km comet at 40AU's can dim a sun sized star at 100 light years by 3%, and a 10km comet can cause an eclipse (is that right?) So would 2,3,10 km objects be easy to measure via star dimming if we had ...
3
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1answer
419 views

Telescope choice

Which one is better? Features: 1)Magnification: 18x - 90x Eyepiece Diameter: 5mm (18x), 10mm (60x) Objective Diameter: 50mm Focal Length: 36cm Tripod Height: 38cm Main tube Color: Silver Net ...
3
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2answers
535 views

Struggling to use my new telescope

I recently got my first telescope, a Bushnell reflector telescope. I spent a good while setting up my alignment. And I can see the moon perfectly! I went to look at another, Mars. I got it aligned in ...
3
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1answer
798 views

Celestron Astromaster 114eq Star pointer finder scope help required

Just got a Celestron Astromaster 114eq as a christmas present and I have tried setting up the Star Pointer in the daylight. I did not use the red dot method as in the instruction manual, instead, I ...
3
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1answer
328 views

How does this telescope work, and what is it for?

Procrastinating, I clicked on a suggested video (How Large Can a Telescope Be?) and after about 01:20 I saw a clip of a telescope shown below. I was confused as I ...
3
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1answer
123 views

What are criteria to compare and evaluate different 12 inch truss Dobsonian telescopes?

What are criteria to compare and evaluate different 12 inch truss Dobsonian telescopes? I'm primarily interested in comparing mirror quality and weight (price I can do myself of course). Two examples ...
3
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2answers
149 views

How can I obtain raw observation data of stars surrounding Sgr A*?

Are there any publicly available telescope that offers the sensitivity to observe the stars surrounding Sgr A*? If not, is there any raw data available that I could download?
3
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2answers
1k views

Is the angular resolution of a telescope irrespective of used eye-piece?

Suppose a telescope has aperture $D = 20$ cm. The angular resolution of such telescope, according to the Rayleigh criterion (if I have understood it correctly), is given by $$\theta = 1.22\cdot\frac{...
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0answers
56 views

Is it possible to build a ground-based telescope that can directly image Earth-like planets orbiting in the habitable zone of sunlike stars?

In the following discussion I will refer to Earth-like exoplanets planets orbiting in the habitable zone of sunlike stars simply as “Earth-like exoplanets." NASA is currently developing or ...
3
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2answers
171 views

Telescope on polluted environment

this one bothering me,to buy a telescope. I live in a city,unfortunately with dust and polluted air, is there any affect in viewing a nice capture of our galaxy? Or i need to buy a special telescope?
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0answers
38 views

What is the difference between a Cassegrain telescope and a Gregorian one? Which one is better?

Of the three giant (or 'Extremely Large') new telescopes being built, the Thirty-Meter (TMT), the the Giant Magellan (GMT) and the Extremely Large Telescope (ELT), only the Magellan, from what I ...
2
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1answer
124 views

Fresnel lenses for a makeshift Galilei telescope?

For a kindergarden (pirate) party, friends of me want to build together with the 4 year old kids a functional pirate's telescope for each of the kids. On the web I found full constuction sets, e.g. ...
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0answers
50 views

Telescope optical tolerance from central axis

I sometimes encounter telescopes/binoculars with a decent objective diameter but are very difficult to use because they only work when the eye is looking down the central axis (i.e. in the centre of ...
2
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2answers
6k views

Why is the moon a fuzzy, white ball?

I currently own a telescope, I'm an amateur astronomer and currently just trying to view the moon. I own the Celestron PowerSeeker 70AZ. Link for information on the telescope: http://www.celestron....
2
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2answers
98 views

Using a refractor telescope 5" aperture, 900mm focal length for terrestrial viewing

Can I use a refractor telescope 5" aperture, 900mm focal length on an equatorial mount for terrestrial viewing.
2
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2answers
245 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) ...
2
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0answers
352 views

Which Barlow lens should I choose, 2x or 3x?

I recently bought a 6-inch reflector, 750 mm focal length and I want to get a Barlow lens to get better observations. I have 2 eyepieces, one 9mm and one 25mm. My question is: Should I go for a ...
2
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1answer
123 views

Number of actuators in adaptive optics

It is well known that diffraction resolution of a telescope depends on the exterior radius of aperture: One can, for instance, use just a narrow outer ring of a parabolic mirror and the resolution ...
2
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3answers
286 views

Does the size of the atom limit the focal length of telescopes?

Does the size of the atom place a theoretical limit on a telescope's focal length (and thus, resolution)? It seems to me that that the allowed margin of error for parabolic mirrors drops with an ...
2
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1answer
245 views

UTC to UT1 time corrections

Astronomic observations in geodesy. It is well understood that sun and star positions may be expressed in Greenwich hour angle and declination. Or Right Ascension Declination. And may be published ...
2
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1answer
100 views

How does eyepiece exit pupil diameter affect image clarity and viewing experience?

This answer to Not Able to View Objects with Barlow Lens includes a calculation of exit pupil diameter as a way to address the limits of useful magnification when observing planets with a small ...
2
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1answer
63 views

Limits of space telescope?

Watching this video describing the "next generation" space telescope, it seems like the biggest mirror will be ~6 meters in diameter. Theoretically, if a telescope was built in space instead ...
2
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1answer
629 views

Eyepiece recommendation for Orion XT8

I am looking for some eyepiece recommendations for my Orion XT8. There are so many kinds out there, and I am not quite sure what to get as recommendations vary wildly. Here are some Q&As that ...
2
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2answers
3k views

Mirror telescope: blocked sight

Today I try to watch Venus through a mirror telescope. I am no professional. No matter what lens I take, I see this image: What am I doing wrong? Edit: What happens when I refocus:Sorry for the bad ...
2
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1answer
117 views

Not Able to View Objects with Barlow Lens

I am new to using a telescope and am having a hard time using a Barlow lens. I was able to find Jupiter multiple times using a 6mm lens with a telescope that has a D = 60mm and FL = 700mm. I am very ...