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25

There are several clues. The Milky Way is a flat disk The first one, and the simplest one, is that we live in a disk. As you can see on images like the ones from the 2MASS survey in the infrared range: We clearly see that we are inside a disk, since what we see when we look around us is a disk seen edge-on. It does not look like an ellipsoid or any other ...


19

We are situated inside the galactic disk. The first image below, showing our approximate location, is a fabrication rather than a photograph. Such a photo would require a space probe to be tens of thousands of light years above the plane of the disk, which is patently infeasible with current technology. We don't even know exactly how many spiral arms our ...


18

The Milky Way Galaxy is a large spiral galaxy with some characteristic features worth mentioning: 1) The bulge - This refers to the collection of tightly packed stars located in the central region of the galaxy. 2) The spiral arms or the disk - This region extends from the inner region of the galaxy (where it meets the bulge) to outskirts of the galaxy, ...


17

Here's a rough sketch of the Milky Way and the Andromeda galaxy,* showing their approximate sizes and distance from each other to scale:   What the picture (hopefully) illustrates is the incredibly vast gap of empty space — around 2.5 million light years, to be exact — between the galaxies, each of which has a diameter of only(!) around ...


15

4 billion years is the same timeframe of the life remaining to our Sun. So if we have not yet invented interstellar voyages, we're screwed, with or without Andromeda. Besides, stars do not interact directly with each other in a galactic collision. What we will notice from the several stars we are on is that star orbits around the galactic centre will be ...


14

What will happen to life on earth or human beings on earth? Assuming that human beings, or life, still exists on Earth at that time, they will have survived so much due to the ongoing death of the sun, that the gravitational pertubations due to the galactic collision will be nothing. Keep in mind that in about 1-2 billion years, the sun will be so hot ...


13

The main reason we don't see the bright center of our galaxy, which is composed of millions of stars, is dust. Visible light is absorbed and scattered by interstellar dust, but that doesn't mean we can't see it on other waves of the spectrum, for example, infrared light doesn't suffer as much because of the dust. Notice on this image how bright the galaxy ...


12

Photos of the galactic center aren't too bright because of all the gas and dust between us and it. For example (in infrared): I'm guessing, though, that you're talking about other galaxies, because there are no views of the galactic center of the Milky Way face-on. Although the galactic center is pretty luminous, just not in the wavelengths we're used to. ...


11

Not really, for the same reason that you cannot travel west by jumping up in the air and let Earth rotate underneath you, such that you land a little farther to the west. The reason is that standing on Earth's surface, you already have a velocity toward the east which matches exactly the speed of the surface. Thus, in the reference frame of Earth, you ...


10

There are several different lines of evidence which together form a coherent picture: that of a barred galaxy. Moreover, as most disc galaxies are barred, we should expect the same from the Milky Way. The various evidences are: The observed light distribution (2MASS) shows a left-right assymmetry in brightness and the vertical height. This is explained by ...


10

First, note that by the time Andromeda is close enough for collisions with wandering stars to become a concern, Earth's average temperature will have changed significantly, and the planet will be unrecognizable. When Sol is 8.5 billion years old, it will still have hydrogen available for fusion, but as it fuses it contracts and expands differentially. The ...


9

This is actually a really, really tough question. Look at this diagram: Purple: Norma Arm and Outer Arm. Green: Scutum-Centaurus Arm Pink: Carina-Sagittarius Arm Cyan: 3 kpc Arm and Perseus Arm So we can slightly modify this picture by saying that there are four arms, and calling them by the following names: Norma-Outer Arm This arm has one end at ...


8

Well, because the axis of the rotation of the Earth is not the same as the axis of rotation of the disk of the Milky Way (and also because we're transforming a 2-dimensional spherical map into a 2-dimensional cartesian map), the path of the disk of the Milky Way galaxy looks something like this: So, there is actually a wide range in declination that the ...


8

In addition to @MBR's answer; there are other (less confusing) ways to represent the data. This paper describes the method used; basically they plot the position and motion of the stars, or of hydrogen clouds. The hydrogen distribution of our galaxy looks like this: Now there's a lot of noise in these measurements, but generally you can see that the ...


8

A galaxy group is a set of galaxies that are close together and gravitationally bound, i.e. barring outside influences they will stay together indefinitely. That means a galaxy that is in the space occupied by the group but "passing through" it at a high velocity would not be considered part of the group. The upper limit for calling it a group is roughly ...


8

Direct collisions between stars and planets is highly unlikely, due to the relatively low density of objects in the Milky Way and Andromeda. For instance, the stellar density in the solar neighborhood is only 0.004 stars per cubic light year. The problem is that gravitational interactions between objects is not low. Stars that eventually pass too close to ...


8

The objects in a galaxy orbit it's center as a planet does with it's star, they keep the same distance. They look like a spiral for something that is called density waves that make some parts of the galaxy (the arms) more dense. You have to imagine a star system like ours orbiting the galaxy in your picture following those radial lines, so sometime the ...


8

Density waves cause the build up of galactic material in to spiral arms. An object does not have to stay in a spiral arm; it can join or leave it as the density wave passes through the galaxy. However, the likelihood of an object being in a spiral arm is greater. The shape of the arms does not relate to matter falling in; this is an illusion. Objects ...


6

The farther away, the faster the galaxies move away from us. But that's only the overall expansion of the universe. Locally velocities can differ and are to be added to the overall expansion. The Andromeda Galaxy is close enough to Milky Way to be able overcome the overall expansion of space. The Andromeda Galaxy and the Milky Way attract each other by ...


5

Normally when two galaxies collide, it is the gas that interacts with each other. The odds of stars impacting each other are nearly zero due to the huge distances between the stars. The same goes for planets hitting each other. The timescales on this happening are so large that it is difficult for our mind to understand these distances (and the timescales ...


5

One additional source of evidence comes from other spiral galaxies. We can see what they look like, how they are composed and we can see that the evidence we have from observations of our own galaxy fits with those galaxies. It's not as strong as the observational evidence shown elsewhere in the answers here, but it does support them.


5

In short, the escape velocity from the region we find ourselves in the milky way is 544 Km/s +- 10%. This number, and an extensive explanation of how it was calculated can be found on a paper called The RAVE Survey: Constraining the Local Galactic Escape Speed Also important to consider is the fact that we already are at aproximately 220 Km/s because of ...


5

If we look at Newtonian physics, and how galaxies will interact, a central black hole should just be considered as a massive, dense object. The Milky Way does not fall into its own central black hole, it orbits it - as physics tells us it should. When we get closer to Andromeda, the gravitational influence of Andromeda will act more strongly on us, and ...


5

Update for clarity: For the visible part of a standalone galaxy, the stars can all be measured to orbit that galaxy's core. So if you wanted to measure the furthest extent at this simplified level, it would be very easy. The problem is that there is a lot of mass which is not stars, and which is dark matter. Some of it is so far out, it may be impossible to ...


5

The Kepler space telescope had a field of view along the so called Orion arm, or spur, of the galaxy. The same structure which we ourselves are inside. It basically looks along a line where the star density is the greatest within the distance that it could detect transiting planets. Less than 3% of the galactic diameter, I think. Note that the illustration ...


5

There are a few nearby galaxies that can be seen with the naked eye, but clear & dark skies are essential. Most notable for northern-hemisphere viewers is the Andromeda Galaxy also known as M31, best viewed in late summer and fall; from the southern hemisphere the Magellanic Clouds, irregular satellites of our own Galaxy, are famous landmarks. These all ...


5

This page, from June 2012, contains a fairly detailed summary of three papers that considered the tangential velocity and collision problem. I'll quote a few choice bits from that page: Andromeda (M31) and the Milky Way are the two largest galaxies in the small group of galaxies called the Local Group. At the moment, M31 is about 770 kpc away from our ...


4

I think the image you posted is not quite reallistic. On it, objects are just inverted from some radius on, while what you can expect from a real black hole seen from near enough is a combination of these: a) an accretion disc b) a companion being sucked c) Hawking's radiation d) X-Ray burst from the poles (really starting out of the event horizon) You ...


4

The paper "Frequency of nearby supernovae and climatic and biological catastrophes" by Clark, McCrea, and Stephenson published in Nature estimates (at 50% probability) that the Solar System passes within 10 parsecs of a supernova every 100 million years. This supernova would be part of a 20-parsec strip in which an estimated 50 supernovae occur. They do ...



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