# Tag Info

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Because of variable atmospheric haze from day to day, especially in the lowest 15 degrees from the horizon, the correct theory answer above is probably not applicable. You can try testing by presuming that a uv indicator card happens to change in response to the same uv ranges as your skin will (afro-caribbeans, that won't apply to everyone), and test with ...

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I would guess that given that the book was designed to teach amateur astronomers that most of the book refers to measurements made with reference to earth. Now, you can measure the component of velocity along the distance line between the star and the earth by using the doppler effect and the adsorption lines for particular elements(measuring the adsorption ...

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It's pretty natural to think that a star can have velocity - there's no reason a star shouldn't be able to move. The first thing you need to know is "velocity relative to what?" Stars in our galaxy are all in some kind of orbit around the galaxy, so you can talk about velocity in galactic coordinates. Binary stars orbit each other, so you can talk about ...

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What we see from the Earth's surface with our eyes are just stars, any planets surrounding them - indeed, entire planetary systems are not visible by the naked eye. That does not mean that there aren't any planets around those stars, the exoplanets listed in this European based Exoplanet catalogue were detected using much more precise and sophisticated ...

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A top's precession is caused by torque from the point not being aligned with the center of gravity, this tends to try to get the top to rotate away from the stable axis. In the case of Earth, the oblateness interacts with the sun's, moon's, and Jupiter's gravity to try to align the axis of rotation perpendicular to orbital plane. This is a torque that tries ...

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Types of observations (at least): Lyman $\alpha$ forest at $z\approx 2.5-6.5$ Thomson Scattering Optical depth for Cosmic Microwave Background radiation Intergalactic Medium temperature at $z<\approx 6$ Lyman $\alpha$: One method: An absorption phenomenon seen in the spectra of background quasi-stellar objects. Based on the neutral hydrogen ...

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https://www.uwgb.edu/dutchs/planets/cratform.htm This has a nice explanation regarding this.

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You'll need to amplify the light coming in. There are two classes of devices which do this: cameras and telescopes. You can understand them by analogy to your eye. A telescope works by having a very wide "pupil", letting more light in, but then using lenses to focus this light onto a smaller "retina" (which is in fact your pupil). A camera is slightly ...

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I've built several CD based spectrometers myself. The best resolution is obtained with a CD-RW because the data lines are much closer together than on a ordinary CD. But evaluating the light from stars is seriously difficult because so very little light reaches the spectrometer because stars are so far away. At the very least you'll need a good quality ...

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Ram Pressure produces a large amount of atmospheric drag force, by the compression of the air located ahead of the meteor. It's equation is: P = $\rho$v $^2$ P is the pressure, $\rho$ is the fluid density and v is the velocity of the meteor. The remainder of your answer might be found here, Drag and Heat, so rather than duplicate that, I will ask you ...

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Actually, any planet $X$ can be see to transit the sun from any other planet $Y$ with a larger orbit. That being said, the frequency for which the a particular transit happens tends to decrease as the planets you choose are further away from the Sun. For example, here on Earth, the angular diameter of the Sun is about 32 arcminutes, or just slightly more ...

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The Extended Hipparcos compilation (Anderson+, 2012) provides distances for stars in the Hipparcos catalogue, together with the apparent magnitude in Johnson V (which approximates to how bright a star appears to be to the human eye). The distance calculation is Dist = 1000/Plx * (1+1.2*(e_Plx/Plx)^2). Applying the search criteria Vmag<6 & Dist>0 ...

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In the 1800's the AU was connected to: the time average of 1 divided by the Earth-Sun, and that is the reason Gauss's constant occurred (until 2012) in the calculation of the AU. The reciprocal of the distance was used because it has less of a linear tread and also because it is not as dependent on the eccentricity (which has a large ~linear trend over the ...

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Just to add up on the previous answers, you can indeed see a few stars in the images but they are faint By adjusting the levels of the raw image, I obtain the following image where you can spot a few

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Neither database is "more reliable" because both draw from a plethora of sources. You can use either to get a rough idea of an object, but beyond that you have to look at what the source of the measurement is (both databases list the publication or other source that reported each measurement). In your particular example I'd be wary of the luminosity of 6.27 ...

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The $\alpha$ refers to "alpha process elements" which are the result of a class of fusion processes involving helium. The $\alpha$ elements are roughly speaking a bunch of helium nuclei ("$\alpha$ particles") stuck together, so they have an integer multiple of 4 nucleons. The $\alpha$ elements are Ne, Mg, Si, S, Ar, Ca and Ti. A measurement of any one of ...

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I asked my local SDSS experts, and the answer is that the fourth and fifth arrays are both bitmasks. Some background: the spectra are often generated with separate exposures that are combined into one dataset. Each exposure comes with its own set of flags. When combining datasets, the question naturally arises "Do we set a flag if it appears in any of the ...

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