# Tag Info

## Hot answers tagged telescopes

25

Money and willpower. With any program (scientific, military, public works, etc.) it all depends on the amount of money someone is willing to put to it, and how much backing and protection that program has from getting money re-prioritized to other projects. You are making a false dichotomy of attempting to present our past actions as a justification for ...

20

Mauna Loa is an active volcano. The last eruption was in 1984.

19

It looks like as if there was a race between our point running away from those galaxies (with the expansion of universe and space) and the light that was emitted at that time. And only now that light has reached and overtaken us. That's correct. A photon from a distant source has to overcome the expansion of the universe in order to reach us. I'll ...

19

It's spherical because the main dish cannot be steered; steering is done by moving the receiver (the big thing hanging over the center of the reflector). A parabolic reflector would produce varying errors when aimed in different directions; a spherical reflector has the same error for all directions. Presumably the receiver is designed to compensate for ...

15

If you want to start, you may skip scopes for a while and focus on binoculars. This will allow you to get to see a little more than with naked eye, and learn your way around the sky.

15

Telescopes (and binoculars) are, primarily, light-concentrating devices. I get the impression that most people unfamiliar with telescopes think of a telescope as a "microscope pointing upwards". It is no such thing; a microscope's purpose is to magnify the image of a small object, and it uses a "strong" backlight for illuminating the object under the ...

15

I think the first sentence from the Wikipedia article on Ritchey–Chrétien telescopes is one of the major compelling reasons: A Ritchey–Chrétien telescope (or RCT) is a specialized Cassegrain telescope designed to eliminate coma, thus providing a large field of view compared to a more conventional configuration. Elimination of optical ...

15

I think what you are looking for is the aperture magnitude relationship. Your current reflector has an aperture of 6". The more aperture you have the fainter the objects you will be able to see. Fainter objects in the sky have a higher magnitude. Celestron has table on their website (reproduced below) along with a full explanation of the math used to get ...

15

Actually reaction wheels or control moment gyros are only part of the answer. To maintain the the accuracy and precision on the order of what Hubble demands requires a fully integrated Feedback Control System of actuators and sensors. For microradian pointing, reaction wheels provide only the first stage of isolating disturbances in a multi-stage pointing ...

12

A very high energy gamma ray spontaneously pair-produces a particle and anti-particle, the idea being that the gamma ray has enough energy that a decay into matter is feasible. The particle and anti-particle which are created are still very high energy - they have velocities near the speed of light in a vacuum. Whenever a particle flies through a substance ...

11

They use reaction wheels, which are a type of flywheel to stabilize many spacecraft. For missions that need to be extremely stable (i.e., any mission with telescopes like Hubble), they try to avoid using the thrusters as these cause small vibrations to "ring" throughout the spacecraft. The vibrations can last for relatively long periods of time on some ...

11

The optical equivalent of radio telescope arrays has been done. The Wikipedia article on optical interferometry gives a good summary. The problem is that although interferometry gives improved angular resolution it doesn't necessarily give you any improvements in the ability to collect light. In many (most?) applications of optical telescopes the limiting ...

10

In most cases you are right, stars are pointlike. They are spread over multiple pixels not because of charge overflow (this can be overcome with shorter exposures and/or better equipment; there really should never be overflow in the image) but because the point spread function (PSF) of the telescope is larger than a single pixel (which is a good thing; you ...

10

First let's quantify what kind of resolution we have of Earth from the moon? This can be calculated. The distance (range) from the Earth to the moon is is $R_\text{EM} \approx384,400,000$ meters. The angular resolution of the human eye is $\theta_\text{eye}\approx.07^o \approx .0012 \text{ radians}$. The spatial resolution of the earth viewed by the ...

10

Given that HST already exists, it's been true for a long time that there is more scientific "bang for the buck" in building instruments whose strengths correspond to HSTs limitations, rather than trying to build an instrument that has the same strengths, but better. There are many telescopes and instruments that see different wavelengths, have wider ...

10

According to this website, you may actually have a big enough refractor to see them, but only on a "good viewing" night, and when Mars is close (opposition): 4-6" reflectors or 3" refractors: polar caps, large surface features 3"=76mm This website also says that 80mm to 90mm will let you see the Martian polar caps: Martian polar caps and major ...

10

(Assuming you're in the US) It's hard to compete with the Chinese "econo-dobs" on price. A 150 ... 200 mm (6" ... 8") GSO-made dob (sold rebranded by the various companies here) is \$300 ... 350. Could you build a dob for less than that? Umm... mmmmaybe?... But you'll have to be pretty persistent in hunting down the best deals for materials and stuff. Even ...

9

First make sure all your screws are tight, and that there isn't any shaking because of slack in any areas where things connect to each other. Another thing you can do is buy vibration dampening pads to put your tripod on. Finally, you can add counter weights and pendulum weights to the tripod to give it more mass to withstand the wind and touches.

9

Interferometry is dependent upon preserving the phase data from signals from widely separated locations. This can be done physically by relaying the actual EM radiation along waveguides or optical paths, or it can be done synthetically by precisely recording enough phase data from the signals to simulate the same process in a computer. This requires ...

9

A telescope can never increase the surface brightness (brightness per unit of apparent area) of an extended object like a planet or nebula (as opposed to a point-object, like a star). This can easily be demonstrated using the theorems of optics. So, if you look through a telescope at any object that is larger than a mere dot - let's say the Moon, or any of ...

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