# The sun, galaxy, universe.

1. Apr 1, 2005

### Prague

Orbits

What does our galaxy orbit?

more questions will follow once previous ones are answered

Last edited: Apr 1, 2005
2. Apr 1, 2005

### brightstar2005

The Great Attractor

3. Apr 1, 2005

### Prague

So whats the great attractor orbiting?

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New questions: answer if you'd like.

If one were to be placed 4.5 Billion years away, would they be able to see the creation of the solar system? If yes, which I believe you will say is true, to what extent would they be able to see it? Would they be able to see just the light emitted or would they be able to see details such as the planents? Hypothetically, lets say they had a telescope that could magnify their vision to be able to see an ant on the street (this is still 4.5 Billion light years away) would they be seing the present time? Or would they still be seeing the creation of earth because the light they see is arriving at that spot from creation? I will clarify this more if it sparks some interest, I think you'll get what I am getting at though.

4. Apr 1, 2005

### misskitty

The big goldfish in the pond the turtle that carries the earth swims in.

That's an awefully far way away. We could ask ourselves the same question about solar systems that are created fromt he remants of stars that are reforming into new galaxies.

5. Apr 1, 2005

### whozum

If he is 4.5 billion years away, im guessing you mean light years.
In this case, everything he sees will have occured 4.5 billion years in the past. If he has a telescope that can pick out any detail, then theres no reason he can't see the planets form.

Keep in mind the solar system didnt form overnight.

6. Apr 1, 2005

### misskitty

Stupid questions for 100: how is that possible?

7. Apr 1, 2005

### whozum

How is what possible?
Being 4.5 billion light years away? I guess its possible, but dont count on it happening any time soon.

The definition of a light year is the distance light travels in 1 year. If you are one lightyear away from object X, it will take light one year to get from object X to you. Lightyears are very very very very long distances.

It is sort of similar to how light from the sun is about 9 minutes old I believe. So if the sun was to explode, we wouldnt SEE an actual explosion until 9 minutes after.

8. Apr 1, 2005

### misskitty

Sorry, I should have been more specific.

I meant the how could he see everything form 4.5 billion light years away. I know light years is a very long was away; I'm not sure I understnad how he could see everything.

9. Apr 1, 2005

### whozum

The original assumption was he has a telescope strong enough to see these events.

10. Apr 1, 2005

### misskitty

Ah, my apologies, my mistake. He'd be needing a big bowl of popcorn for that show (assuming he would have some). How cool would that be to watch a solar system form?

11. Apr 1, 2005

### whozum

It would be very boring actually. It would take a couple million years. Tivo would be useful.

12. Apr 1, 2005

### misskitty

Yes it would. It would have some pretty awesome pictures though. Some of the pictures I have seen from the Hubble telescope have a lot of colour in them. Is that colour really there or is that just something that gets added to make the pictures look that much more intriguing?

13. Apr 1, 2005

### whozum

Nope the colors are there, color is an extremely helpful tool in learning about the chemical and physical properties of interstellar objects.

14. Apr 1, 2005

### misskitty

How do colours help people learn about the chemical and physical properties?

15. Apr 1, 2005

### whozum

Frequency and energy are related by:

$$E = h\nu$$
h is Planck's constant, $$6.626 x 10^{-34}$$, and the v looking thing, called nu, is the frequency f the wave.

The visible light spectrum is part of the electromagnetic spectrumm, which follows from light being an EM wave. So if each color is part of the light spectrum and the light spectrum is part of the EM spectrum, then each color is part of the EM spectrum and has a unique frequency. If you know frequency, you know the energy output of that planet per unit area.

Also, different atoms have different electron configurations, and a common occurance is the increase or decrease in energy of an electron by transferring from one electron shell to another. When this happens, a photon is emitted with energy proportional to the drop in energy levels of the electron, the higher the energy drop, the higher the energy of the wave. The higher the nergy of the wave, the higher the frequency. What this does in the macroscale is each of the elements gives off a different color when it changes energy states, so if we pick up the colors that are emitted by a planet, working backwards we can find its chemical composition.

Also, using effects such as doppler shift and redshift/blueshift we can find the speed, direction, and spin direction of said objects.

16. Apr 1, 2005

### misskitty

Huh, learn something new everyday. We hijiacked the thread, so in an attempt to get back on topic; what does our galaxy orbit? Other galaxies?

17. Apr 1, 2005

### Grogs

Well, I think one common misconception is that one thing orbits another. If one object is much, much smaller than another (the Earth vs. the Sun for example), you can say this and it will be pretty accurate. In reality though, both the Earth and Sun are rotating about their common center of mass. So our galaxy and all the other galaxies in our local cluster are rotating around the common center of mass of the local cluster.

18. Apr 1, 2005

### Prague

This is very interesting, bare with me I do not know if I will be able to successfully express my thoughts.

Ok, so we have a guy 4.5 billion light years away looking at the earth through a high (very high) powered telescope. Now, earth (present) will be point A, the man Point B. The earth at present time is C and the light of the Earth which is 4.5 billion years away from earth is D.
Questions:
If B is at the same position as D why would he need a high powered telescope to view earth? (I have some sort of answer, I suppose that the light is just a continuous image, so it shows the earth still 4.5 billion light years away so you would need to magnify it, correct?)

If he was able to magnify it so he could see say a volcano on earth how is this possible? After all it's light that is moving not the volcano. Does this means that everything is simply a form of light? At this moment a snapshot of me is being sent out into space at 186,000 miles a second?

(this next one is just an absolute sci-fi question, I am not sure why I am even bother asking it.)

If this light emits the image of everything, would it be possible to travel within the light? This is how I view all the questions I am asking, a snapshot of a second is taken and it then begins traveling through space at the speed of light, if you view this "light image" you see what was happening at that present time. Now could you ever go in that "light image?" I suppose if you could, time travel, atleast to the past would be possible, although we could never catch up with earth's "light images" we would have to be traveling the speed of light and even at that speed the image of a second before us will always remain a second before us. (odd, now i understand the twin paradox and the time dilation, glad i asked this odd question now. so, time stops when you travel the speed of light?)

19. Apr 1, 2005

### whozum

C and D arent analogous quantities, I dont understand what your getting at.

Thats the thing, it takes 4.5 billion years for the light to get from A to B. They are both existing at the same time, but B wont know what happens at A until 4.5billion years pass.

The same reason you can see the volcano. Just because light is travelling alot farther doesnt change anything about what information its conveying. No, not everything is a form of light. Lets simplify a volcano to a green sheet of paper. Green paper absorbs all colors of light and emits green light. So when light strikes the paper and goes towards your eyes, it has the frequency corresponding to the color green. What you will see is the a region in space that is emitting green light, from there its up to your brain to determine other things such as texture, depth, etc. Now if you are standing 10m away or 10000000000000000000000000000000000m away, green is green. That light is green, and it will be green until it reflects off of something else. Hopefully thats easier to see.

Its interesting but your conception of light is incorrect. Light travels in a spherical shape, so the green paper for example (lets assume its a spherical paper for now) emits green light in all directions. Whether YOU see it or not, doesnt affect whether it was emitted. However, this light is just a reflection of what was there over time, in a certain sense, yes it is a photograph, and this is linked very closely to how the basics of photography work.

Just try to picture someone standing next to you waving at you, what your eyes get is a stream of photons each at a different frequency depending on the color of light emitted from a certain region infront of you. Their hand is brown lets say, since the hand is moving you'll see brown light coming from different regions inthe space infront of you. Your brain will identify this as an 'object' and focus it. However thats not all you see, you get alot of ambient light from things around you like the sky, buildings, everything. Now this light is transmitted in every direction from the source, not just straight at you. Light doesnt know you are there.

20. Apr 1, 2005

### cepheid

Staff Emeritus
Sometimes the images are false colour, they are not only true colour. The true colour Hubble images are taken through red, green, and blue filters separately, and later combined. From what I have heard, they represent pretty faithfully what we might see with our own eyes if they were sensistive enough. False colour images are not just coloured to make them look "intriguing", but also for scientific purposes. E.g. sometimes differnt colours indicate different temperatures, or wavelengths of light being emitted, or different elements present in a cloud of gas.

21. Apr 3, 2005

### Prague

Alright, I think I understand now, I did have a misconception. Just a few last questions that need some resolution.

So, light isn't a physical form? It just merely reflect a physical form.
The image that you see (when your 4.5 billion years away) is simply a reflection, in some sense it's not "real" and you could never interact with it?