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Questions tagged [optics]

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

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What are the reference signal(s) for a closed-loop space-based adaptive optical system?

Closed-loop control systems in general have the following form: Here the controller seeks to eliminate or minimize the difference between a given signal (this can be either a constant signal of the ...
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Do all photons coming out of the Sun go out radially?

I am trying to understand why we can assume that all light rays from the Sun are in parallel.
Curious Cat's user avatar
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Vera C. Rubin's LSST's ginormous camera's shutter; why does it open/close 1000 times a night & is this typical for large-format survey telescopes?

CNET's April 23, 2024 World's Largest Camera, the 3.2-Gigapixel LSST, Is Complete says after about 02:19 That shutter is actually so big it had to be broken down into two pieces just to fit inside ...
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Is gravitational lensing "additive" in a line of sight?

As usually depicted, gravitational lensing implies, at least, three objects: a distant source, an observer, and a "massive enough" object in the middle, where enough is the mass needed to ...
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Can telescopes under $200 help you see saturn clearly by eye without editing the image on a computer?

I had a telescope that only cost 50 dollars for viewing the moon and it was good for that but the planet's were always badly out of focus. I am thinking of getting a better telescope for up to $200 ...
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4 votes
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Formation of spacecraft instrumentation [closed]

List of spacecraft instruments are selected to meet a mission's science goals. Let's take New Horizons as an example and study the composition of Pluto's atmosphere, the shape and geological ...
ayr's user avatar
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How accurate is the Sudarsky Scale today?

How accurate is the Sudarsky scale of gas-giant classification today? Do the different classes still exist, and look roughly the same?
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Did this satellite streak past the Hubble Space Telescope so close that it was out of focus? If so, how close was it?

The new Nature Astronomy paper The impact of satellite trails on Hubble Space Telescope observations (Kruk et al. 2023) describes an AI-based object classification method used to find satellite trails ...
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Ritchey–Chrétien telescope with a short back focus

I have an observing project that requires a 30 -- 40 cm (12 -- 16 inch) diameter primary and no refractive/transmissive elements (i.e. lenses). Telescopes like this Ritchey–Chrétien has a back focus ...
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Why does one object (star?) in this JWST image have two sets of six+plus+two diffraction spikes but another, similar object nearby have only one?

CNN's February 24, 2023 Astrophysicist says 'there is nothing wrong with not knowing' is basically an opportunity for Neil deGrasse Tyson to give us a pep talk and reminder about the exciting process ...
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How would the "Fluidic Telescope (FLUTE)" next generation telescope make and control a smooth, correct concave optical surface figure in microgravity?

The January 10, 2023 NASA Ames Research Center news item Fluidic Telescope (FLUTE): Enabling the Next Generation of Large Space Observatories discusses a proposed project to study the feasibility of a ...
uhoh's user avatar
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What are optical artifacts in source images?

In Stellarium, there are two green squares in the constellation Sextans (close to the star Alpha Sextantis). The app doesn't provide any information as to what these are. I was curious and so I ...
William's user avatar
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For lenses, what is the practical difference between plano- and bi-?

I don't know if this is a trivially obvious question for astronomers. If so please forgive my ignorance. I've looked around at a lot of diagrams of lenses in telescopes. The plano-convex and bi-convex ...
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How do astronomical spectrometers measure spectra from single stars separately, without contamination from all of the nearby stars?

I am currently looking into light spectrometers, and I noticed that the ones I found had a similar problem; when the light reaches the spectrometer, it mixes giving a broad range of light wavelengths. ...
Aakarsh Tathachar's user avatar
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Would it be possible to create a telescope from a hanging reflective cloth?

A chain suspended on two points hanging under gravity forms a curve called a Catenary, which can look pretty similar to a parabola. I'm not sure if this generalizes to the two dimensional case where ...
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Angular resolution of naked eye at night; type of vision used

It appears that most sources quote the angular resolution of the eye as 1', regardless of day and night. For instance, Naked eye Seconds of Arc and the Unaided Eye However, the following websites give ...
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Astrometry and Geometric Distortions

CCD's are widely used for astrometry. Since a spherical surface (the celestial sphere) is projected onto a rectangular surface, the plate scale or pixel scale (approximated with 1/focal length etc) is ...
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What is the spectral reflection curve of cold white dwarfs and neutron stars?

Suppose that I got a white dwarf and a neutron star and after some trillions of years their temperature are down to just a few °K so cold that they don't emit any appreciable black body radiation. Now,...
Victor Stafusa's user avatar
4 votes
2 answers
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Is it possible to block the surrounding light in a solar eclipse if we made the moon bigger or closer to the earth?

Is it possible to block the surrounding light in a solar eclipse if we made the moon bigger or closer to the earth? In an eclipse, you always see a ring of light surrounding the moon, but I am ...
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How far can the best telescope see in outer space from Earth?

I was wondering what is the farthest the best optical telescope can see into outer space from Earth. What causes them to see so far?
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What conditions are necessary for the sun to look [as described below]

First of all sorry for the weird title. I have no idea how to describe it in a succinct way because I've never heard of something similar happening and I've only witnessed it once. The only way for me ...
Tony's user avatar
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General process of calculating what a telescope's diffraction spikes would look like?

I was reading this question about the JWST's diffraction spikes, and I was rather surprised by the magnitude of the 4 sets of diffraction spikes. The large hexagonal spike pattern I believe is formed ...
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How are the aberrations seen in early JWST images corrected?

I found this image on space.com and it can also be found in NASA's JWST blog. This is one step in the process of aligning the 18 mirrors on JWST. A single relatively-isolated star has been selected. ...
Roger Wood's user avatar
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11 votes
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How exactly did JWST take a "selfie" of its own primary mirror, and what is the real purpose of this capability?

CNN's Webb telescope's first test images include an unexpected 'selfie' says only: The mirror selfie was captured by a special lens inside NIRCam that can image the primary mirror rather than what ...
uhoh's user avatar
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6 votes
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Does a star shaped mirror present problems either optically, or in signal processing over a more nearly circular mirror?

Pure speculation about a future replacement for the JWST that I almost certainly won't live to see. The JWST's mirror (and then some) would fit unfolded and flat into the Starship's 8m diameter ...
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Why is the Nancy Grace Roman Space Telescope's field of view shaped like a PacMan "ghost"?

The Curious Droid YouTube video NASA's Mega Hubble - The Roman Space Telescope illustrates the shape of the telescope's field of view and the outline has a smile or frown shape. For whatever reason it ...
uhoh's user avatar
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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 ...
uhoh's user avatar
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How exactly does NEOSTEL's fly's eye telescope's secondary mirror array split the primary beam among sixteen cameras?

Wikipedia's NEOSTEL says: The Near Earth Object Survey TELescope (NEOSTEL - also known as "Flyeye") is an astronomical survey and early-warning system for detecting near-Earth objects sized ...
uhoh's user avatar
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Tracking deep sky objects

I have a Celestron Astromaster 130Eq. I saw all the planets in our solar system and quite satisfied. Now I am in the hunt for DSOs, but living in a city is a disaster for tracking some good-for-...
Kavin Ishwaran's user avatar
1 vote
1 answer
267 views

Schmidt corrector plate on a Newtonian = Schmidt Cassegrain?

Went on with a wide range of telescopes and its mechanics. To my understanding, the only change in the optical function in Schmidt Cassegrain telescope is a Schmidt's corrector plate in front of an ...
Kavin Ishwaran's user avatar
3 votes
1 answer
380 views

Not getting quality images in telescope

I have a Newtonian telescope (Celestron 130 eq) with 5.2 inch (~132 mm) aperture with 650 mm focal length, Spherical mirror. And having 4mm, 10mm, 12.5mm, 20mm,20mm (erecting eyepiece), a 3x and 1.5x ...
Kavin Ishwaran's user avatar
10 votes
0 answers
211 views

How well conserved is etendue in extreme gravitational lensing scenarios?

This excellent answer to Could dark matter exist in the Universe in the form of sufficiently dense objects? includes the following image and description: Light from the background galaxy circles a ...
uhoh's user avatar
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6 votes
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190 views

What are the pros and cons of different types of echelle spectrograph cross-dispersers?

Echelle spectrographs, operating at high resolving power, typically consist of an echelle grating with a low numbers of lines/mm, used with high diffraction orders (often $n=$50-100). To separate the ...
ProfRob's user avatar
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4 votes
1 answer
166 views

Why does X-shooter use double passes through prisms for Echelle cross-dispersion instead of gratings?

The catchy title Down-the-barrel observations of a multiphase quasar outflow at high redshift: VLT/X-shooter spectroscopy of the proximate molecular absorber at z=2.631 towards SDSS J001514+184212 ...
uhoh's user avatar
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1 vote
1 answer
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Meade 4000 'LP' designation

I have a Meade 4000 super Plossl 26mm eyepiece in front of me with an 'LP' mark on it. I am a fan of the Meade 4000 series, but this is the first time I see this variant. It looks like it stands for '...
0xF2's user avatar
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2 votes
1 answer
237 views

Do point spread functions from large single telescopes using adaptive optics still look like Airy functions for narrow-band filters?

this answer to Claim that 30-m class telescopes will have resolution far superior to Hubble: true? mentions ...the possibility of attaining near diffraction-limited images using adaptive optics. The ...
uhoh's user avatar
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1 vote
1 answer
455 views

I am getting triple image of the moon from a 50mm telescope

I just bought a telescope and saw the moon but with the bright moon at the center there are two faint images of the moon above and below it. I figured out it was due to the periscope mirror. If I see ...
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6 votes
3 answers
413 views

How can there only be "11 phonons" in the mirrors of LIGO interferometers?

LIGO is an incredibly sensitive detector of small changes in space due to the passing of gravitational waves and uses some very high-level mathematics and physics and experimental techniques to drive ...
uhoh's user avatar
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0 votes
1 answer
283 views

What colors do other stars have when seen from space close to them?

The Sun looks yellow from Earth because we see it through the atmosphere; in space the Sun looks rather white. Do A-, B- and O-type stars look blue from both their planet's atmospheres and outer space?...
John's user avatar
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3 votes
1 answer
158 views

Do telescopes exist that reflect the incoming light more than three times along their length?

Refractors only use the length of the telescope once, reflectors twice, catadioptric telescopes like those of the Schmidt-Cassegrain design three times. Have telescopes been built that reflect the ...
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1 vote
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How did I flip some mirrors around in the dark at 3 AM and change the focal length of a 24 inch Boller and Chivens?

Current answer(s) to How do telescopes "zoom" and change angle of view? are "they don't", but traditional large genera-purpose observatory telescopes do sometimes (often?) have ...
uhoh's user avatar
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3 votes
1 answer
149 views

Are X-ray telescopes with glancing angle surfaces basically "funny-looking" Cassegrain telescopes mathematically?

In this answer I included the image below of a reflective X-ray telescope. It is made from two elements; the first is concentric shells of glancing (high incidence) angle paraboloidal surfaces, and ...
uhoh's user avatar
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3 votes
1 answer
169 views

What would "the next GAIA"-like instrument be like? Could it simply be a 3 to 5x scaled-up version of the same beautiful system?

This excellent, thorough and well-sourced answer to Has a gravitational microlensing event ever been predicted? If so, has it been observed? mentions several works where hundreds to thousands of ...
uhoh's user avatar
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1 vote
1 answer
96 views

Has lunar opposition surge ever been observed from Earth? From Earth orbit?

This thorough answer to How long does lunar opposition surge last? Are there measurements of the full Moon getting suddenly brighter? details observations of lunar opposition surge by the Clementine ...
uhoh's user avatar
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5 votes
1 answer
291 views

How long does lunar opposition surge last? Are there measurements of the full Moon getting suddenly brighter?

Wikipedia's opposition surge is a short article and forwards shadow hiding and coherent backscattering as proposed mechanisms, but it doesn't really explain how much the brightness of the Moon ...
uhoh's user avatar
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3 votes
1 answer
135 views

Telescope showing high chromatic aberration

Hi i have made a telescope with 1100 mm focal length objective lense and 21mm plano convex as eyepiece. Both these lenses are not achromatic. But when is looked through it , the images were completely ...
sanoj's user avatar
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2 votes
1 answer
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Benefits to adding a 32mm Pössl to my Celestron AstroMaster 130EQ's eyepieces?

I am getting a Celestron AstroMaster 130EQ soon. I have heard that its eyepieces aren't the best, so I am considering a 32mm Pössl. For such a choice, what would be the arguments for and against? How ...
Jacob Kurzawa's user avatar
2 votes
0 answers
133 views

What produces all of these small radial striations in this very overexposed image of a star by Hubble's WFC2? (the four big ones are from the vanes)

In a recent astrometry question in Space SE I needed to check Proxima Centauri's position and the article contained the image below. I've saturated the colors, cropped it, and added a "...
uhoh's user avatar
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2 votes
1 answer
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What does a narrow-band "point spread function" look like for long exposures from the VLT's large interferometric aperture?

In interferometric radio astronomy UV plots are the first step in understanding what a point spread function (PSF) will look like for a given location in the sky observed over a period of time. The ...
uhoh's user avatar
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8 votes
1 answer
181 views

How many photons does it take to determine the existence of a distant object?

This applies to any object, but I see the recent discovery of the oldest, most distant galaxy and it started me wondering what the limits are. Presumably you can do better with a bigger telescope and ...
Roger Wood's user avatar
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