Hot answers tagged

61

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 ...


51

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 ...


31

Telescope mirrors and other mirrors used by scientists telescopes regularly do use a silver coating. See for instance here. However, aluminum coating are the norm (certainly for the large primary mirrors deployed in telescopes) because of durability reasons. I quote from the text linked to above: The challenge with using silver as a coating material is ...


30

The highest resolution 3d printers I know of are around 1600dpi, which is a resolution of about 15$\mu m$. Telescope mirrors have to be smooth to fractions of a wavelength of light, so the resolution of current printers is nowhere near good enough. Whether 3D printers could one day be good enough is a different question, but given that the improvement in ...


29

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 ...


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 ...


21

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 ...


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 ...


21

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


20

Johannes makes a good point about durability. As a footnote, I'll add that aluminum has another nice property over silver, at least as far as your plot shows: constant reflectance over the visible spectrum. Look at the slopes of the lines from $400\ \mathrm{nm}$ to $700\ \mathrm{nm}$ - silver varies from $80\%$ to $95\%$ reflectance, while aluminum stays ...


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 ...


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

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

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

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 ...


12

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

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 ...


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 ...


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 ...


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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