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The velocity of the Earth going around the Sun changes such that the sign changes every six months. Therefore, the part of the aberration due solely to the Earth's motion about the Sun also changes sign. In fact, the aberration from the Earth's orbit makes the positions of stars go into ellipses that take 1 year to complete. The motion of the Sun about ...


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Like the above: they can be significantly separated by space. One way to visualize this is to turn on constellations in Celestia then travel to a different star. The constellation outlines can shift significantly. Celestia is an open source visualization thing, it is available at: http://www.shatters.net/celestia/


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Only very rare instances would get close to such stars being on a plane, if any can be found. A nice graphic image showing how the Big Dipper stars appear on an imaginary plane as viewed from Earth combined with a side-view showing approximate distances can be seen at this earthsky.org page.


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Constellations and asterisms are generally not proximate in space, but rather happen to be nearby only when viewed from Earth. From Wikipedia's article on asterisms: Like constellations, asterisms are in most cases composed of stars which, while they are visible in the same general direction, are not physically related, often being at significantly ...


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The stars are not in the same plane and move in different directions. See this youtube video.


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The Hertzsprung-Russell diagram is an observational tool. The axes are things that can be observed, or at least estimated reasonably well, for most stars (well, those with known distance anyway). We cannot in general measure the masses of stars - only those in some binary systems. The schematic that you show, with an arrow indicating that mass increases ...


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There really isn't anything as comprehensive as you want. And, we don't have accurate information for all of these variables for a large number of stars. The two main problems are masses and radii. Really the only set of stars that have both measured masses and radii are those in eclipsing binary systems. If these binary stars also have distances, measured ...


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I did something similar with the HRD about a week ago. I found that VizieR has a very large database with observations. You can download the tables in different formats (like csv or plain text), but you should first check if the Temperature (mostly log.Tegg) and luminosity (logL) are available. A very detailed one is table V/19. It has those values for 68 ...


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Micro black holes are believed to exist, coming into existence for a very brief period of time following high energy particle collisions. Some theorists believe that this may occur naturally in Earth's atmosphere due to cosmic rays. I read a statistic somewhere which said that at any given time there would be three black holes in our atmosphere due to this ...


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Here is the very study you are looking for by Bailer-Jones (2014). Using the re-reduction of the Hipparcos astrometry, he has integrated orbits for 50,000 stars to look for objects that might come or might have come close to the Sun. The K-dwarf Hip 85605 is the winner on that timescale, with a "90% probability of coming between 0.04 and 0.20pc between ...


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There have of course been extensive observations of clusters of stars. To all intents and purposes, to the limits of experimental accuracy, it looks like stars that are born in the same open cluster or star-forming region are all born with the same composition. e.g. http://adsabs.harvard.edu/abs/2014A%26A...567A..55S , ...


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Most stars are of a solar-mass or below. The average number of companions that each stars has (in the sense of being part of binary or higher multiple systems) systems ranges from 0.75 for stars of a solar mass to approximately 0.35 (not a well-established number) for the more numerous M-dwarfs. Let's take a compromise value, say 0.5. The separation ...


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What is far apart? In the universe there are zillions upon zillions of stars, some of them small that live fast and die young.In lamens terms so to speak,they burn all of their fuel at a very fast rate. While large stars burn much slower there are many different ways in which they react to each other, some stars are in binary form. They become dependent upon ...


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Binary stars are not very far apart. Which begs the question, how did they get so close together, if most star systems are quite far apart.


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Here's how parallax works. You measure the position of a star in a field of stars that are (presumably) much further way. You do this twice, separated by 6 months. You then calculate the angle that the star has moved against its background stars. This angle forms part of a large triangle, with a base that is equal to the diameter of the Earth's orbit around ...


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The actual answer has nothing at all to do with the temperature. Even low-mass stars would form black holes if they ran out of nuclear fuel to burn, and simply cooled whilst being supported by "standard" gas pressure in their centres. That is because that gas pressure would be proportional to the temperature, but the star is able to cool so it would need ...


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Most of the universe is pretty empty in terms of the density you're used to in daily life. It's perhaps not that stars are far apart, but that they are pretty compact. This is because baryonic matter (as opposed to dark matter) can lose energy via electromagnetic radiation and hence condense to smaller and denser objects. This is only opposed by angular ...


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The Stars are far apart because the Universe has been expanding for billions of years at a fast rate of speed. So since the Stars have been moving away from one another for so long it is only natural that the Stars are so far apart.


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The dwarf planet Haumea two equatorial diameters, it is triaxial. The longest equatorial diameter is about twice the length of the polar diameter. According to Google and Wikipedia, the most oblate star is Achernar which has an equatorial diameter 56% larger than the polar diameter due to it rapid spin. The discussion at ...


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If you're only interested in objects devoid of non-microscopic empty spaces, then we're pretty much into the realm of stars, planets, and asteroids. Objects of this type larger than $\sim100$km are all nearly spherical, simply because of the effect of their own gravity (the spherical shape minimises the gravitational energy). However, small asteroids can ...


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For me, the best and most reliable source of absolute magnitudes and spectral types is the book Allen's astrophysical quantities. Chapter 15, called Normal Stars, contains spectral types, absolute magnitudes, colors and effective temperatures for main sequence, giant and supergiant stars. The references are at the end of the chapter. HTH, Germán.


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Saturn is the most oblate planet in the solar system. If the equatorial diameter is $a$ and the polar diameter is $b$ then its oblateness, $(a-b)/a = 0.1$. We do not know the oblateness values for more than one or two exoplanets and even these are somewhat uncertain, but are thought to be lower than Saturn's value. For example ...


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I think it is going to depend on the type of object being examined. Planetary objects tend to be more spherical than stars, which in turn tend to be more spherical than galaxies. My vote goes toward the Heliospheric current sheet, which is thought to extend 10-20 astronomical units (about 1.5x10^9km to 3x10^10km) from the Sun, and is thought to be about ...


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The spectra of a red giant and a red dwarf are completely different, so there isn't really too much to say about this. For example, alkali lines are almost non-existent in red giants, but strong in red dwarfs. The theory as to why this happens is the stuff of a standard graduate/undergraduate course on stellar atmospheres, not an SE answer. The fact is that ...


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just check what 'median' means. the median stellar mass is such that half of all stars have lower and the other half hihger mass. it has nothing to do with the logarithm. I havn't seen the term (median stellar mass) in the scientific literature. Looking at the paper you're referring to, they never use the expression "median stellar mass". Moreover, this ...



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