Behaviour and properties of light, and its interaction with matter, particularly in detection of light.

learn more… | top users | synonyms

15
votes
1answer
200 views

Why does a mirror bent 'like a potato chip' allow space telescopes to be smaller and have a wider field of view?

I was browsing NASA featured items and came across this - Out With the Old, In With the New: Telescope Mirrors Get New Shape Called freeform optics, this emerging mirror technology, brought about ...
7
votes
1answer
215 views

Theoretically, what is the biggest optical telescope that may exist?

Recently, I read yet another news about E-ELT. It will have 39.3-metre-diameter segmented primary mirror. And I was interested in the next question: Theoretically, what size of the primary mirror (...
7
votes
2answers
144 views

Why aren't secondary mirrors offset to get rid of diffraction spikes due to the support vanes?

Some kind of ellipsoidal shape mirror could reflect to a secondary mirror which is not in the way of the infalling light. Two advantages are immediately obvious. The primary mirror would not be partly ...
5
votes
2answers
324 views

Why does e.g. Hubble's secondary mirror not block part of the picture?

The SOHO observatory has an opaque object in the light path that blocks the direct light from the sun making it possible to observe the corona. Hubble and many other telescopes have a big primary ...
4
votes
1answer
115 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, ...
4
votes
1answer
154 views

Is it possible to steer the sight of a Liquid Mirror Telescope using a plain mirror scheme? If yes, why hasn't it been done?

I have read about Liquid Mirror Telescopes in a number of places, and according to these sources, a major disadvantage of these telescopes is that they can only "see" straight up. In a nutshell, the ...
4
votes
1answer
346 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 ...
4
votes
1answer
70 views

Could spy satellites use laser guide stars (for adaptive optics)?

Are sodium lasers useful for Earth observing space telescopes/spy satellites?
3
votes
1answer
71 views

Is it practical to hand grind a convex parabolic or hyperbolic mirror?

I know it's practical to hand grind a convex spherical mirror and that it's practical to make a concave parabolic mirror from a spherical one. But as I understand it, the procedure for doing so depend ...
2
votes
1answer
181 views

Why can't the surfaces of stars be observed?

If I'm correctly informed, only three stars: Sol, Betelgeuse and Altair have surfaces which have been resolved by telescopes. All other stars are only point sources of light, even in the greatest of ...
2
votes
2answers
56 views

Astronomical telescope making

I am thinking about making a telescope. I have a 100cm focal length lens which I can use as objective lens in my telescope. So which is the best focal length I can use as eyepiece in my astronomical ...
2
votes
4answers
565 views

Enhanced Star-Gazing with Special Glasses

I watched a video yesterday on how telescopes not only magnify images but also increase the amount of light entering into your eye, allowing you to see things not normally visible with naked eye. ...
2
votes
1answer
40 views

Adaptive Optics?

I get the general idea of adaptive optics. The light from an object distorted by differences in the earth's atmosphere, and a telescope with AO tries to compensate for this distortion by various ...
1
vote
2answers
55 views

What is the longest observable wavelength of light using an optical telescope?

How far outside the visible spectrum could an optical telescope feasibly operate?
1
vote
2answers
183 views

Dish antenna as parabolic mirror for OPTICAL telescope?

Can i use a chrome painted dish tv antenna as a parabolic reflector for my Optical telescope ? Given that glass mirrors are quite expensive, i am thinking of using a Dish TV antenna and coating its ...
1
vote
1answer
63 views

Magnification of a telescope

I took an image of Jupiter through my 8" Dobsonian Telescope, attaching a DSLR and a 1.25" Barlow Lens where the eyepiece goes, as shown in this video: https://www.youtube.com/watch?v=reFxoF3XoaU ...
1
vote
2answers
147 views

How to make a telescope for viewing planets, moon and DSOs using a convex lens of aperture 100 mm and focal length 200 mm and other lenses at home?

I wanted to make a telescope with DIY things lying around in home. I read up that the aperture was a very important aspect and thus bought a convex lens with 100mm aperture and 200mm focal length, to ...
1
vote
1answer
250 views

Can the Sun be used as a point source of light to achive better focus?

There's a limit to how well sunlight can be focused by a parabolic reflector or a lens because the Sun is not a point source. I wonder if the sunlight could be engineered to work as if it was (much ...
1
vote
0answers
54 views

What would be the maximum theoretically possible angular resolution?

I have studied some basic astronomy, but I have difficulty conceptualizing the physics of luminosity and optics. We use electromagnetic spectra to detect existence and properties of distant planets, ...
1
vote
0answers
10 views

What makes small interferometers useful? Like NIRISS on JWST

NIRISS is an instrument on the James Webb Space Telescope. It has a "non-redundant aperture mask" which obviously covers most of the area of the sensor. It seems to be advantageous for high contrast ...