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Human color vision is based on three types of "cones" in the eye that respond differently to different wavelengths of light. Thus, not counting overall brightness, the human color space has two degrees of freedom. In contrast, the spectra of stars are very close to a black body, which depends only on effective temperature. As one varies the temperature, the ...

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The answer is: frequently. There are many amateur astronomers that make it their ambition to discover new supernovae or to observe and report on new variable stars. As an example, let me cite amateurs Robert Evans, who apparently holds the record for most supernovae found by visual observation, or Tom Boles, who holds the record for supernova discoveries by ...

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No, black holes are not the only cause of HVSs, although it is thought to be the most common mechanism. Hyper velocity stars are believed to be caused when binary stars come close enough to a supermassive black hole for one of the pair to be captured while the other star is ejected at high velocity. This appears to the main mechanism for HVSs. See for ...

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It's begining to look like there aren't as many brown dwarfs as was once thought: NASA's Wide-field Infrared Survey Explorer, or WISE, has been turning up a new crowd of stars close to home: ... Previous estimates had predicted as many brown dwarfs as typical stars, but the new initial tally from WISE shows just one brown dwarf for every ...

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The relative direction to an object depends mainly on two things: The location of the observer and the object The coordinate system you use to determine direction. So the first part of that concerns where we are compared with Polaris (and by extension of your question, where the other stars are as well). Yes the stars and other components of the galaxy ...

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This question is very broad - there are very many techniques for estimating temperatures, so I will stick to a few principles and examples. When we talk about measuring the temperature of a star, the only stars we can actually resolve and measure are in the local universe; they do not have appreciable redshifts and so this is rarely of any concern. Stars do ...

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I presume what you mean is how does the plane of the orbit compare to the equatorial rotation plane of the star? The answer is, you can sort of estimate this, by using something called the Rossiter-McLaughlin effect (see also Rossiter 1924; McLaughlin 1924). You can find plenty of information on the web - I'll add a couple of links when I have a moment - ...

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In the case of multiple images of a background, distant object, the answer is relatively simple. You take a spectrum of the multiple images or parts of an extended lensed image and you see whether the spectrum looks the same, and in particular whether the redshift of the multiple images are the same. Gravitational lensing affects light of all wavelengths ...

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It's pretty easy to put upper limits on how bright any nearer stars could be. As a rough guide, consider a survey like Hipparcos, which is complete to something like 9th magnitude. If there's another star closer than Alpha Centauri, the brightest possibility is if it's at the same distance. Wolfram|Alpha tells us that a magnitude 9 star at Alpha Centauri's ...

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A black hole (BH) never sucks anything in. 'Sucking' requires gas pressure, but a black hole only acts via its gravity. A non-rotating (=Schwarzschild) black hole attracts all massive objects, very much like the Sun attracts the planets. Yet, the planets are not falling into the Sun. This is because the planets move on near-circular orbits when the ...

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The Sun is of course in motion with respect to other stars in our Galaxy, but it does not move quickly compared with the vast distances involved. For instance it takes about 220 million years for our Sun to orbit the Galaxy once, travelling at around 200 km/s. The stars that are closest to the Sun tend to be orbiting in more-or-less the same direction and at ...

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In this answer you can find a calculation for how bright "Nemesis" would be at near-infrared wavelengths. This calculation assumed we were looking for a 20 Jupiter mass object with a similar age to the Sun at a distance of 1.4 light years (to fit in with the Nemesis hypothesis). The calculated magnitudes were H=14 and W2=8 (in the WISE infrared satellite ...

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The European Southern Observatory has catalogues with image data available from http://www.eso.org/qi/, you will have to register before you are able to access them. I'd suggest you look at other observatory's websites for their data. You will have to look past the pages targeted at the general public and find links for data or science, or user portal or ...

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Yes. If you have the Hipparcos data from ftp (http://vizier.u-strasbg.fr/viz-bin/VizieR?-source=I/239&-to=3), you will have several data files. In hip_main.dat you have a field MultFlag at position 347 that indicates whether the star is a double or multiple star: Note on MultFlag: indicates that further details are given in the Double and ...

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Basically you need to convert between luminosities (which you can add) and magnitudes using $$M-M_\odot=-2.5\log_{10}(L/L_\odot)$$ Let's call the total luminosity $L_0$ and magnitude $M_0$ and the individual luminosities and magnitudes $L_1$, $L_2$ and $L_3$ and $M_1$, $M_2$ and $M_3$. Then, you have the total luminosity of the system, directly ...

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Yes, and not only from space but from the Earth surface too. Stars emit in almost all wavelengths depending on their surface temperatures. The hotter the star is the shorter (higher energy) wavelengths it'll emit. You can try this simulator to check this: http://astro.unl.edu/naap/blackbody/animations/blackbody.html

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Stan has essentially answered this in his comment, which I will attempt to spell out a little more laboriously. The significant majority of our Sun's energy output comes from the proton-proton chain. This was advocated by Eddington back in the 1920's, but at that time your basic concern was a very real and major problem. Objects with like electrical ...

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You need to specify on what timescales and at what wavelengths to get a proper answer. Despite your question, the Sun does appear to be a very stable star indeed. The luminosity changes over the solar cycle are about 0.1% (or 0.001 magnitudes) and even the biggest sunspots modulate the light by a fraction of one percent. If you wanted to find stars more ...

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The chemical elements in our bodies are inherited from the Earth. The Earth was formed in a disc of gas and dust swirling around the protosun 4.5 billion years ago. The material that formed the Earth was a selection of the material from that protostellar nebula that was itself once part of a larger molecular cloud. So the atoms in our body were once part of ...

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Let's assume that what is falling onto the neutron star is "normal" material - i.e. a planet, an asteroid or something like that. As the material heads towards the neutron star it gains an enormous amount of kinetic energy. If we assume it starts from infinity, then the energy gained (and turned into kinetic energy) is approximately (ignoring GR)  ...

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