# Tag Info

53

I've made this into an answer because it's too long for a comment, and I really want to show the pictures. It is tempting to think of visible light as "close enough" to (near by wavelengths) and to conclude that "yes, actually, the yellow does affect it. I want a mirror without an obvious tint" However you are wrong, Physics will slap you down. Exhibit A ...

46

If you look at the reflectivity of gold (vs silver or aluminum) you can see a plateau at wavelengths below 500 nm source: If blue wavelengths are not reflected as well as other colors, the resulting image will look "more yellow" - which is what you see. At longer wavelengths, gold is a very good reflector (better than the other two above 600 nm). It also ...

27

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 ...

25

Sort of. As Space.com writes, The raw Hubble images, as beamed down from the telescope itself, are black and white. But each image is captured using three different filters: red, green and blue. The Hubble imaging team combines those three images into one, in a Technicolor process pioneered in the 1930s. (The same process occurs in digital SLRs, except ...

21

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

21

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 ...

20

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 ...

16

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 ...

16

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

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

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 ...

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.

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

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 ...

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 ...

11

Any reasonably flat piece of sort-of reflective metal will function perfectly well as a heat collector, but would not be terribly suited to do astronomical observations with. In principle, you could probably pull it off. But it would require a lot more accurately shaped mirrors, with a lot better quality reflective surface. Also, there's good reasons ...

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

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

The classic color mapping for Hubble is described in Flase-color astrophotography explained. What you have is (in the Hubble palette): Line Freq True False Ha (656.3 nm) Red -- Green S-II (672.4 nm) Red -- Red O-III (500.7 nm) Green -- Blue An example of this for true color from John Nassr at Stardust Observatory at Coming to Life ...

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 ...

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