Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: Shabnam J on 06/05/2010 10:30:03
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Shabnam asked the Naked Scientists:
Dear naked scientists, I got a question regarding space.
If we are a part of the milky way galaxy, considering the size of it how can we see it as a line in the sky as opposed to being surrounded by it?
I appreciate your response and your program. Keep up the good work (http://www.thenakedscientists.com/HTML/podcasts/).
Shabnam
What do you think?
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I am not certain but I think what we see as the milky way is actually an arm of the entire spiral, the milky way is a 100,000 light years across so I think we would not be able to see the other side with the naked eye.
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This photo is a 360° panorama so the image is distorted: the milky way appears as an arc when it is actually straight
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http://antwrp.gsfc.nasa.gov/apod/ap070508.html
The part of the galaxy directly opposite the bright galactic centre is just visible in the photo close to the horizon on the left,
i.e. the galaxy can be seen to surround Earth (from areas where there is no light pollution).
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The reason that the Milky Way appears as a 'line' in the night sky is because our galaxy appears to be shaped like a thin 'disk', reckoned to be about 100,000 light years in diameter but only about 1,000 light years thick. When we look across the diameter of the disk then, we see a lot more stars than when we look up and out through the 'top' or 'bottom' of the disk and it is these stars that we see when looking across the diameter of the disk that show up as the Milky Way.
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It is just so hard to imagine. 1000 LY is still allot compared to the dimesions of our planet. I even wonder how is it possible to see something outside of our galaxy in our night sky. Aren't there any obstacles between us and what we see in the sky. our eyes can see only 120 degrees or something like that. It is hard to understand how I can see even a tiny part of our universe outside our galaxy. this might not sound so scientific but to me it is like being really close to a picture you wouldn't be able to recognize what it is until you step further away to see it. Now I am limited to seeing with my eyes and stuck on earth. Is it possibly because the distance between each two object is soooo large? by the way thanx for your response.
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Yup... "Space is big. Really big. Now you may thing that it's a long way down the road to the chemist's, but that's just peanuts to space..."
(From the Hitch Hiker's guide to the Galaxy)
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Is it so big and sparsely populated that we can just see the next galaxy without any obstacles or are all the pictures available are modified by computer? Is there any material with mass filling this empty space?
Thanx
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Is there any material with mass filling this empty space?
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Dark regions within the band [marked in yellow], such as the Great Rift and the Coalsack,
correspond to areas where light from distant stars is blocked by dark nebulae (http://en.wikipedia.org/wiki/Dark_nebulae).
http://en.wikipedia.org/wiki/Milky_Way#Appearance_from_Earth
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Is it so big and sparsely populated that we can just see the next galaxy without any obstacles or are all the pictures available are modified by computer? Is there any material with mass filling this empty space?
Thanx
Nope, there's no need to modify the pictures: there's hardly any matter between galaxies. You might find one or two molecules of gas per cubic km of space and perhaps one or two specks of microscopic dust per cubic 1,000,000km, but other than that intergalactic space is pretty much empty.
The most distant object that can be seen with the naked eye is the Andromeda galaxy, which is our nearest 'big' galaxy. It's pretty dim to the naked eye (mag 3.4), so you'll only see it with the naked eye when there is very little light pollution, but when you can see it, it's pretty impressive. Through a large telescope it's about six times the width of the full Moon but with the naked eye you'll only see the brighter inner parts, but even then it'll be about the width of the full Moon.
The average distance between the Earth and the Sun is about 93,000,000 miles, which is known as an Astronomical Unit (AU), but the Andromeda galaxy is about 158,000,000,000 times further away, being about 2.5 million light years distant.
This means that when we see the Andromeda galaxy we're seeing it as it was 2.5 million years ago, but the most distant stuff that's been observed is actually about 13+ billion light years away i.e. more than 5,000 times further away than Andromeda is from our Milky Way galaxy.
So yup, space is big, really big...
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Lee
I will have to look out for Andromeda galaxy next time I am out of London - I love looking at stars from an aesthetic point of view rather than a scientific. For any real city resident like me the stars on a clear night without light pollution are a revelation - some of the smaller greek islands turn off all power for a few hours in the early morning and the sky appears to be more light than dark. I have made a note to find out how to find Andromeda before I next head out of the city . Thanks, Matthew
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I have always been an astronomy fan but I never tried to look at it closely. Now that you reminded me of how big it is, my brain have reached its boiling point.
That picture that you marked is amazing, so simple laws of physics still apply and that is something that I can digest and makes me feel a little less intimidated by all this.
The number 13 billion LY, is that the magic number for the birth of universe?
Is that how they figured it out?I hope you are not getting a head ache with my questions yet [:I]
Thanks allot [:)]
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I have made a note to find out how to find Andromeda before I next head out of the city
Where I am, at about 51° North, Andromeda is pretty low on the horizon during summer and is best seen in the winter months, when it gets higher in the sky. Even the simplest of astronomical sky viewers/planetarium programs will be able to help you find where it's located in the sky, once you've entered your latitude and longitude.
If you don't already have an astronomical sky viewer you could try the open source Stellarium program, which is available for Linux, Windows and MAC OSX at:
http://www.stellarium.org/ (http://www.stellarium.org/)
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The number 13 billion LY, is that the magic number for the birth of universe?
Pretty much yes, although the universe is slightly older than this. We can't see right back to the very beginning because the universe is believed to have been opaque to EM radiation in the earliest stages, so light couldn't travel through it.
Is that how they figured it out? I hope you are not getting a head ache with my questions yet [:I]
Not quite, how old the universe is, and how far back in time we can see are related and are really two sides of the same coin. Have a read of:
http://en.wikipedia.org/wiki/Age_of_the_universe (http://en.wikipedia.org/wiki/Age_of_the_universe)
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Thanks Lee