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4
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5answers
900 views

Are telescopes with a concave lens useful for astronomy?

Are telescopes with a concave lens (instead of convex ones) ever useful for astronomy? And if so, where are they used? Do they ever affect resolving power?
2
votes
2answers
43 views

WHY is a Refracting telescope image distance $S'=-\infty$?

In the above slide, it says that "Eyepiece '2' makes the image distance $S'$ approach $-\infty$." However, What I don't understand is that if I place my eye right at the Eyepiece 2, then I would see ...
4
votes
1answer
32 views

Absorption lines in the context of identifying elements in far away celestial objects

I understand that absorption lines are used to identify elements but how are individual absorption spectrums identified in the light that is received by a telescope?
0
votes
2answers
61 views

Can I use one convex lens to create a telescope?

Is it possible to create a telescope with only one convex lens? Specifically, is the image I drew below possible? (This was supposed to be rotated 90 degrees counterclockwise.) In this picture, ...
0
votes
1answer
53 views

Does sign convention in geometric optics fail to explain the cases of image formation by virtual objects?

Here is an example of Cassegrain telescope: Parallel rays from a distant object get reflected by the concave mirror forming an image at its focus behind the convex mirror. This image acts as a virtual ...
1
vote
0answers
37 views

Any cheap (less than 100 euro) telescope for observing Jupiter? [closed]

The moon is not challenging. I would like to observe the big planets and their rings.
5
votes
2answers
483 views

Are there any astronomical objects at night that are dangerous to look at (through a telescope)?

Are there any astronomical bodies that would be dangerous to my vision to view through a telescope? Obviously the sun is dangerous, but are there other bodies at night I should avoid?
4
votes
1answer
228 views

Future space-based telescope array

Radio-telescopes (e.g. the Very Large Array (VLA)) can simulate one gigantic dish by using separate smaller dishes. Q: Could such an array of optical telescopes potentially see an exoplanet at say 20 ...
5
votes
1answer
59 views

What do the latest FERMI results say about dark matter?

There was an announcement at a recent UCLA symposium on dark matter by the FERMI collaboration which hints at some evidence of dark matter. The results aren't yet published, but the symposium news ...
2
votes
3answers
4k views

How to ‘correct’ reflected image on my telescope?

When viewed using my reflector telescope, the image, for example the moon, is flipped over and upside down (reflected). Therefore I need to do the ‘opposite’ movements when I want to align something. ...
2
votes
2answers
77 views

How to calculate error of parallax and sextant based navigation?

First of all, why wasn't the sextant ever used for land navigation? The horizon is easier to see at sea, but land based sextants could be used in conjunction with artificial horizons (as at sea when ...
0
votes
1answer
61 views

CCD's and the photoelectric effect

Do charge coupled devices as found in telescopes use the photoelectric effect if not what eles librates the electons. Also what is charge intergration in reation to CCD's.
2
votes
0answers
42 views

need data-point: count rate of APD (avalanche photo-diode) for specific aperture and stellar magnitude

I hope lab / experimental physics is fair game for this web-site. If not, sorry! I'm designing a sensor system to perform specialized [astronomy and space-sciences] experiments, and need a "reality ...
19
votes
2answers
638 views

Optimal telescope size?

Consider a diffraction-limited telescope with unobstructed aperture $D$. Such a scope is capable of yielding an angular resolution $\alpha$ that scales as $\lambda/D$, with $\lambda$ denoting the ...
4
votes
3answers
56 views

Are our telescopes capable of taking actual images of brown dwarfs?

One nice result from NASA's WISE infrared survey of the sky is the discovery of particularly cool (as in 'not very warm') stars, now called 'Y dwarfs'. This was reported, for example, in NASA's ...
2
votes
3answers
1k views

How could I translate a field of view value into a magnification value?

When I zoom in with Stellarium, it indicates a field of view (FOV) value in degrees, but most binoculars and telescopes are advertised with value like "nX magnification power." How could I translate ...
1
vote
1answer
42 views

Is it possible to build an optical system that increases the perceived surface brightness?

So is it possbile to build a system from lenses and mirrors that can make faint gas nebulas brighter or can be used as nightvision? If you increase the size of the aperture of a telescope it will ...
2
votes
1answer
76 views

Radio vs optical telescope imaging

As I understand, the visible light from an optical telescope is focused on a sensor which correlates light exposure to an electrical voltage, which is then converted to an image. A single antenna ...
2
votes
5answers
1k views

Recommended first accessories for starblast 4.5

My son got an orion starblast 4.5 for Christmas. It comes with orion explorer II 17mm and 6mm eyepieces. We are looking at some additional accessories and wondering what you would recommend as "first ...
1
vote
0answers
46 views

When viewed from a telescope, does an object get more magnified if its angular diameter is increased?

and if yes, how can the diameter be increased? Lets say I want to view saturn from a small telescope. Increasing the angular diameter will give a better magnification if the answer to the above ...
4
votes
2answers
153 views

Will a telescope show a more magnified image if the object is brighter?

I have a small telescope which shows me the moon's craters a little bit magnified. Consider a situation where the moon is very very brighter than its current brightness, so that the telescope's ...
1
vote
2answers
569 views

What is the highest useful magnification todays largest telescopes can offer?

I know that the maximum (useful) magnification is limited by the diffraction limit, but I was not able to find numbers for the highest useful magnification factors using modern large telescopes. How ...
11
votes
2answers
190 views

Could a mirror array used for thermal solar power plant double as a telescope at night?

I was looking at the Ivanpah Solar facility and it occurred to me that the large array of mirrors could double as some sort of telescope array at night. The climate in the desert would be ideal for ...
7
votes
1answer
200 views

Why aren't there any arrays of visible light telescope?

There have been many radio telescope arrays which are capable of resolving stars significantly fainter than can be resolved with a single "small" radio telescope. Why don't they do the same with ...
1
vote
2answers
84 views

Any projects to build a telescope in space?

Like in the title. With E-ELT we are pushing the limit of what we can build on the ground. With JWST we are pushing the limit of what can we launch into space. So instead, why don't we launch tools ...
5
votes
2answers
100 views

How many watts of light do instruments in modern telescopes need?

I just calculated that if the European extremely large telescope(978 m^2 area) would be pointed at the Andromeda galaxy once it is built, it will only get mere 1.2*10^-6 Watts of power from Andromeda. ...
5
votes
3answers
232 views

Is it possible to surpass the diffraction limit for telescopes?

Telescopes have angular diffraction limit depending on the observed wavelength and aperture diameter. I've read that it's possible to go beyond the limit for microscopes. But is it possible to do the ...
2
votes
1answer
118 views

How to measure the altitude of an object in the sky?

If I use a telescope to observe a plane in the sky, how can I find the altitude of the plane(altitude of the plane with respect to the ground)?
17
votes
5answers
324 views

Why don't we have a better telescope than the Hubble Space Telescope?

The Hubble Space Telescope (HST) was launched in 1990, more than 20 years ago, but I know that it was supposed to be launched in 1986, 24 years ago. Since it only took 66 years from the fist plane to ...
8
votes
1answer
389 views

Why are telescopes on top of Mauna Kea instead of Mauna Loa?

Many large and important telescopes are located on top of Mauna Kea on Hawaii. This is a great location for many reasons: it's tall enough to be above the weather, an inversion layer at night keeps ...
6
votes
1answer
333 views

How big of a telescope to view Gliese 581g in great detail?

I've always been interested in mega sized telescopes and how big they would have to be to see exoplanets in great detail. So, Gliese 581g is 22 light years away. Could we build a telescope in space ...
4
votes
3answers
346 views

Is it possible to take a picture of a star?

In this question I am not considering the sun, but only other stars. Stars are big, but they are also far away. https://en.wikipedia.org/wiki/Star The nearest star to the Earth, apart from the ...
16
votes
2answers
2k views

What is the theoretical limit for farthest we can see back in time and distance?

13.2 billion years ago the universe was rather small, having started only half a billion years ago. Today, with the help of Hubble Space Telescope, we are able to capture the light of galaxies emitted ...
15
votes
6answers
2k views

Lenses (refractor) or mirrors (reflector) telescope?

What differentiates, in terms of practical quality, not technical implementation, a refractor from a reflector telescope? Why would one prefer a refractor over a reflector, when reflectors come with ...
3
votes
1answer
1k views

Why do focal lengths affect magnification?

For compound lenses, the image formed by first lens acts as the imaginaryobject for the second lens. In telescopes, the objective lens projects an image on its focal point which works as the object ...
9
votes
2answers
243 views

Why does a blue sky at dusk appear nearly black through a telescope?

Earlier this evening I was looking at the Moon through my cheap toy telescope (x150 magnification) when I noticed a (rather mundane) optical effect I couldn't explain. The Sun had just dipped below ...
3
votes
1answer
1k views

Telescope size to view saturn

What is the properties (size, etc) of required lenses for minimal telescope to see the Saturn rings clearly?
8
votes
4answers
2k views

How can I stabilize an unstable telescope?

I have an 80 mm refractor telescope on a tripod, but it shakes on every touch. It's very hard to see via 6 mm (x120) ocular. Even a little wind causes the image to become too unsteady. How ...
10
votes
4answers
4k views

Is building your own reflector telescope worth it?

I have always fancied building my own reflector telescope. I am wondering - For a certain budget, can you get better results with a home made rig? Or is this a folly, and really it would be better to ...
3
votes
3answers
654 views

How to locate the Orion Nebula?

I was trying to see Orion Nebula for few days now and I simply can't spot it. I'm using Celestron PowerSeeker 127EQ ( 5" , Newtonian , 1000m ). I'm pretty sure I have the right spot as I saw many ...
3
votes
2answers
735 views

Hartmann mask based collimation

Is there a detailed description for a Hartmann mask based collimation process? I've been told by a friend that is possible to collimate an SCT by placing a three round holes Hartmann mask at the ...
3
votes
3answers
94 views

Quality loss when adding more components to a telescope?

I would think this would be inherently true, but I'm curious: (Assuming the highest quality amateur instruments are used.) Is quality lost when, say, adding a T-mount adapter, diagonal or any other ...
4
votes
1answer
63 views

Should I be concerned about spot corrosion on a telescope's primary mirror?

I am considering buying a telescope with a large primary mirror that is about seven years old - it has a small spot of corrosion on the mirror, that the owner says is stable. Should I be concerned ...
0
votes
2answers
528 views

Do I need to focus the telescope?

I purchased a 90x refractor telescope with below configuration. Objective: 50mm diameter with 360mm focal length 2 Eye pieces: 6mm, 20mm (10-1/ 8" scope) 1.5x erecting eye piece It measures 13- ...
3
votes
5answers
6k views

Having difficulties finding objects with Celestron Telescope

I have a Celestron Astromaster 114 EQ, which I saw was highly recommended as a great beginner scope. But I just can't seem to find anything in the sky with it. Yes, I've removed the lens cap, yes I've ...
3
votes
2answers
181 views

The Bahtinov focusing mask

I'm looking for a webpage or a book or reference that might give me a better (and hopefully more scientific) understanding of how the Bahtinov mask works (which I understand to be the same as ...
5
votes
5answers
58 views

Which current big Earth-based telescopes are equipped with adaptive optics?

I know only that the VLT is equipped with adaptive optics (AO) to bypass atmospheric distortion. Is it the only one, or have other telescopes been build with AO in the optical and infrared spectrum?
8
votes
5answers
100 views

Exoplanet detection via space-based parasol

I remember from watching Cosmos years ago, Carl Sagan suggested an interesting hypothetical method for directly seeing exoplanets. He proposed that in the 'future' we could launch a satellite designed ...
4
votes
3answers
97 views

How long would it take to scan the visible universe for unique signals?

The article Amazing rays as star succumbs to dark side talks about a very large black hole swallowing up a star. The report goes on to say that the only reason it was discovered was because it shot ...
9
votes
1answer
44 views

How do I use this 'Horizon Observatory'?

Just around the corner, we have one of these: It's at the Halde Hoheward (article in the German wikipedia), and it's called a 'Horizon Observatory' by the people who built it. How does it work ...