# Tag Info

24

With a binocular, all its optical components are fixed - the user can't change them. What's important for the user to know is the size of the front lens, which determines the brightness (and in theory sharpness) of the image, the magnification, and the field of view. These are all useful things to know. A telescope has an interchangable component, namely ...

11

It's complicated. Until late-20th century, we've tried to make bigger and bigger monolithic telescopes. That worked pretty well up to the 5 meter parabolic mirror on Mount Palomar in California in the 1940s. It kind of worked, but just barely, for the 6 meter mirror on Caucasus in Russia in the 1970s. It did work, but that was a major achievement, for the ...

11

Binoculars tend to be mostly used for daytime observing (of birds, ships etc) Telescopes are mostly used for astronomical observing. The users of the two types of equipment want different information. You may find large, mounted, astronomical binoculars described more like a telescope. Similarly, small "mononcular" may be described in the same terms as ...

10

It is an optical illusion. We perceive nearby objects in 3d because we have two eyes. As we see objects from two different viewpoints, our brain can put the images together to make a 3d image. Objects that are more distant perceived as 3d if they are moving fast enough for us to see them change appearance. Again it is not in the eyes but in the brain that ...

9

Freeform optics are a response to the specific challenge of cramming a telescope in a very limited space. A traditional instrument would have all optics symmetrical and aligned on the same axis. It would waste a lot of space within the cubesat. Also, traditional designs tend to be much longer than they are wider; they don't fit well in a cube; it is very ...

9

The first question anyone asks about a telescope is "what is the magnification?" It is almost always not the most important thing. Any telescope can magnify a million times, given a short enough eyepiece - the problem is, how good the image is. For observing planets, the main thing is resolving power - the ability of the telescope to discern tiny details. ...

9

Telescopes tend to have a fixed focal length. What changes is the size of the sensor in the instrument used. If a small sensor is used, then a smaller section of the field of view is exposed, resulting in a narrower field of view being imaged than the equipment is capable of. If a larger sensor is used, more of the field of view of the telescope is utilised. ...

9

There are many different ways to get spatial information about the surface of a star besides direct imaging. Direct imaging is difficult because the angular resolution available goes as $\lambda/D$. For a 8-m telescope and light at 500 nm, one can resolve $6\times10^{-8}$ radians (assuming the blurring of the atmosphere can be overcome by adaptive optics or ...

9

Absolutely. You are looking for a binocular eyepiece, or a binocular viewer. Most of them require you to insert two matching ocular eyepieces, so it can be fairly expensive. Most major telescope eyepiece manufacturers sell them. I'm not sure what the rules are for mentioning brand names, but a quick google for 'telescope binocular viewer' will turn up ...

8

I'm not sure it counts as "simple" but there is the ice cube neutrino observatory whose detector consists of a cubic kilometer of very clear ice a mile or so down in the antarctic icecap.

8

You can not check if a dimensional constant has changed because you can always reverse that change by a smart change of coordinates (system of units). Despite that, since the current Physics assumes the immutability of certain constants, you can verify this assumption by testing the change of an adimensional constant. One of the most common adimensional ...

7

Designs where the curved primary mirror is fixed, and steering is achieved via a moving flat mirror (siderostat) in front of it (or a set of flats) have been done before. One example is the Pfund telescope. The main design constraint that led to the invention of the Pfund telescope was the need to have a focal point which is fixed in space and easily ...

7

You're close! What you built is a back-to-back set of Galilean telescopes (with an overall magnification of 1:1). The reason you're getting a smaller circle, but with a life-size image, is that the light bundles in the middle are diverging faster, and so you lose the edges if the Galilean assemblies are too far apart. Military perisopes use optical relays ...

7

Very likely not. If it's a gravitational process like galaxy lensing, then a "mirror" would require a very large deviation. That's extremely unlikely with this process. With other processes, e.g. classic reflection, it seems even more unlikely. We don't know any natural processes that could craft mirrors at cosmic scale.

7

The diffraction pattern at the focal plane created by a circular aperture is called an Airy Disk or Airy Pattern. Both the outer opening and the inner hole plus secondary contribute to the exact function. This is usually not easily observed with ground based telescopes because the seeing fluctuations due to air turbulence smears it out. These images use ...

7

The actual math is a bit complicated, but there's a simple intuitive explanation. Longitudinal chromatic aberration happens because, when you cut a convergent lens in two, and you look at the cross-section, the edge of the lens looks a bit like a prism, doesn't it? (look at the diagram that you've posted above, the top of the lens) And it does exactly what ...

6

I would have added this as a comment (not enough rep yet, I'm afraid)... To elaborate on Andy's answer, the first reason is that the surface of the satellite dishes are too coarse to form any kind of image. Polished optical surfaces are smoothed to a polish (generally much smoother than one would achieve in polishing a car, though). Other problems come ...

6

As the question Instrument aperture sizes on Hubble Telescope shows, the focal plane area is large enough to focus on several instruments at the same time (but with each capturing a different area). If two objects of interest are separated by a certain angle (the instruments are fixed within the focal plane), the telescope can be rotated so that two ...

6

You can probably get most if not all of your questions answered by perusing the main DESI web site, which I encourage you to check out. There is, for example, a nice video describing the assembly of the main focal plane elements (the fibers and the associated robot positioners) here. But in simple terms: the circular focal plane is divided into ten wedges (...

6

So it looks something like this? https://cloud.planetmaker.de/index.php/s/RkmkBNfb8YyDHSE That sounds like the circum-horizontal ring (yes a name as simple as that). It (probably) is caused by hexagonal ice crystals floating horizontally. Where it touches the 22° halo you might see sun dogs which can be slightly colourful brighter patches. See also https://...

6

The movement of the diffraction spikes is similar to the phase detection autofocus that's been used in SLR cameras for decades. Before the days of autofocus, many SLR cameras had a split-image viewfinder that used the same principle as well1. To keep things simple, let's consider a mask with just two slits out at the very edge of the aperture. Now let's ...

6

My opinion (and I think there has to be a large element of that) is that the presence, and ultimately identification of the orbital period, of exomoons is going to come from very precise transit photometry. If a sufficiently large moon orbits a planet, then this will leave its signature in the transit light curve. A "Fourier-type analysis" of the ...

5

This is a term known at the limiting magnitude. This term refers simply to the faintest apparent magnitude your instrument can detect. Wikipedia has an article describing limiting magnitude. I pulled the info from there. The wiki article begins off explaining the basic way of finding limiting magnitude. $$5 \cdot \log_{10}\left(\frac{D_1}{D_0}\right)$$ ...

5

It's not possible I'm afraid. Optical wavelengths (light) are typically of a wavelength under a micron, and an optical surface needs to be accurate to this level or better to be useful. Radio wavelengths are typically 10-20cm or longer, and an adequate reflector can be made with surfaces accurate to a few centimetres (at a guess as I don't know the exact ...

5

I guess it depends what you mean by an optical telescope. However, if you just mean any telescope that can record images at visible light wavelengths, then it is possible to use these (with the appropriately cooled instruments) to make observation at so-called mid-infrared wavelengths of $\sim 20$ $\mu$m. See for example on the Gemini telescopes https://...

5

The ghost images in the video resemble the Sun and are separated by only 2 or 3 degrees (4-6 Sun widths), so we can rule out atmospheric phenomena. Sun dogs or parhelia have shapes different from the Sun and appear 22 degrees away from it. The effect is more likely due to looking through a double-paned window at an oblique angle. The bright image on the ...

5

You are not the only one whom sees a difference but remember that the statistics are skewed. Fewer people are awake early to see, or photograph, the sunrise while more people are awake to see the sunset. People and heating of the Earth are factors explaining the difference in the atmosphere through which the sunlight is filtered, that affects the appearance ...

5

Don't base the size of the Sun on what you see in that image because the Sun is over-exposed. The big spot in the center of the diffraction spikes are saturated pixels because they all appear to have the same value (the spot looks uniform) so you don't know what their real values are; you would need to take a shorter-exposure image (or put filters in front ...

5

Szymanek says he took some of his Flickr images with a GSO 10" Ritchey-Chrétien telescope. At least one third party offers these with Altair Astro branding and says the tube is made of carbon fiber. The Ritchey-Chrétien design is a Cassegrain with hyperbolic primary and secondary mirrors. It minimizes coma and spherical aberration at the expense of field ...

5

Supplemental to @PeterErwin's answer, some more details on the five thousand "robots". Each fiber has a circular "patrol area" with a diameter of 12 millimeters, and these are located on a hexagonal array with a pitch (nearest neighbor distance) of 10.3 millimeters. Motion is implemented with eccentric axis (Θ–Φ) kinematics. Instead of x-y or r-Θ which use ...

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