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Stars Indeed, the most readily apparent observables for stars are (1) their apparent luminosities, and (2) their spectra (or even just colors if you can only do photometry). The age has to be inferred, and this is where modelling comes into play. The Vogt-Russell "theorem" is the assumption that the initial mass and chemical composition of a star uniquely ...

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Cosmic rays at the highest energies are likely protons or iron nuclei or something in between (Auger and High-Res continue to disagree on this point), but as AMS-02 has pointed out, there are lots of electrons and positrons. Since the energy of the incoming cosmic rays is irrelevant we have to consider them at all energies, including very low energies, at ...

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According to E. V. Petjeva (2011), the measured rate of change of the Earth-Sun distance (astronomical unit) is (1.2 +/- 3.2) cm/yr, with the uncertainty value representing 3 standard deviations. In other words, any change is within the uncertainty of the measurement. She specifically addresses the Krasinsky and Brumberg value. E. M. Standish has also ...

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It would be more correct to say that distant galaxies appear than to say they disappear. Based upon the accepted big bang theory, there are galaxies that formed early in the universe from which light has not yet reached us, but that will reach us in the future. On the other hand, accelerating expansion of the universe could cause light emitted after a ...

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The density of a black hole is defined simply as the mass within the event horizon divided by the volume within the event horizon. This gives an average density, but doesn't imply that the density is uniform within the event horizon. So when you hear statements like the density of a supermassive black hole is the same as water don't take this too literally. ...

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In general a larger antenna gives a larger signal at the input of the receiver. Since the receiver is not noise-free the signal to noise ratio is increased, resulting in better reception. The antenna itself is not noise-free (unless strongly cooled down) but this is usually of minor importance. Actually amplitude modulation is not so much used, rather a ...

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Disclaimer: I updated my previous answer as I found a more accurate formula. The rotation angle $\theta$ is the angle between the vernal point and the meridian at Greenwich. This also corresponds with the Sidereal Time at Greenwich, converted to radians. For a given UTC time and a given date, the corresponding Greenwich (Mean) Sidereal Time (in hours and ...

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I will answer the question in the title: What happens to the electron companions of cosmic ray protons? They leave them behind in the plasma on which they originated. Have a look Plasma is the fourth state of matter, it is composed of ions and electrons, and is continually ejected by the sun. Any positive excess on the upper atmosphere will be ...

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You could not calculate the exact date of birth because the Moon is in the same constellation for up to 3 consecutive days, and the other bodies for much longer. The second problem is that constellations of Mercury and Venus are not independent of the constellation of the Sun. Mercury will usually be in the same constellation as the Sun (maximum ...

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