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1

One way of thinking about this is to think of what, for instance, a digital sensor would see (does see!) when looking at a galaxy. Even if there is no dust to scatter light (which often there is), if there is, in most cases, one or more (generally 'more') stars in the bit of the image covered by a pixel in the sensor, then that pixel will be at least partly ...


2

You are mostly empty space. Every atom in your body is very tiny compared to the relatively vast spaces between it and its nearest neighbors. And the same goes for every "solid" object you ever saw. But when you look at yourself in a mirror, the number of atoms you see is so incredibly vast that you don't see the spaces between them but instead ...


0

Don't trust your eyes when they tell you something is solid. Please remember that the stars are suns. So, if our galaxy were really solid, you'd directly look into a star's surface in every spot of the Milky Way, and that would mean a band in the sky where every spot shines as brightly as the sun. Then the Milky Way would be 100 times brighter than our sun's ...


1

The actual transparency of something depends on whether a light ray will pass through the object or hit something, becoming absorbed or scattered. The total cross-sectional area of the stars of a galaxy is microscopic. This is why one can see the background galaxy through the foreground galaxy in NGC3314: However, dust can be actually opaque in this sense. ...


0

First, you are correct that galaxies are mostly empty space, at least in terms of stars. The Milky Way may have as many as 400 billion stars while Andromeda has roughly two and a half times that number. For the Milky Way that comes out to roughly one star every four light years, on average. Viewed from a distance, however, those stars are extremely bright ...


2

One thing you might try doing is to use the SkyServer Navigate interface to see if the object was imaged by SDSS. Enter the name in the "name" box in the upper left and then click on the "Resolve" button. If an image with the galaxy shows up, click on the "Object with spectra" checkbox in the "Drawing options" panel on ...


2

It's a little unclear what you're asking for, but... "Heliocentric velocity" means measured radial velocity of an object relative to the Sun. (Which basically means relative to us, except you take out the variations due to the Earth's motion around the Sun.) For galaxies more distant than, say, the Local Group, the heliocentric velocity is the ...


3

Stand on dune in a desert. Take a handfull of sand, all crushed from the same rock. Now close your eyes, Hold your hand up to the wind, let the wind blow all but one of the grains of sand, somewhere. Wait 2 years. Now go and find the other grains of sand that you dropped. It should be easy, right? They have identical composition as the sample you have. They ...


31

Here are the problems/issues: Most stars are born in clusters/associations but a cursory investigation of cluster demographics with age reveals that the vast majority of clusters do not survive to old age. The majority either are never gravitationally bound to begin with or become unbound in the first 10 Myr. The Sun was likely born in a cluster of $10^3-10^...


7

The two most general, publicly available packages for galaxy image fitting (other than GALFIT) are probably Imfit and ProFit. (Note that I am the developer of Imfit.) There is also Lenstronomy, which is specialized for fitting gravitational lenses; this might be more relevant to your particular needs, though I know very little about it.


3

There shouldn't be any correlation. The CMB light that we see is from a spherical region in the early universe. Its homogeneity strongly suggests that the interior of the sphere was just as homogeneous, but we can't actually see CMB light from the interior. The galaxies that we can see formed from matter inside the sphere, and quite far from the edge. ...


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