Space: STARS

[kingwinner]

I have just started the space unit in school and have 3 questions. I hope someone can answer and explain. I would appreciate! B)

 

1) "If you look into the night sky, you will see a cloudlike band of stars that stretches across the sky. Because of its milky appearance, this part of the sky is called the "Milky Way". The "Milky Way" is the disk of the "Milky Way Galaxy".

 

I don't get this part! Are "Milky Way" and "Milky Way Galaxy" the same thing or are they different? What is a "disk" and what does it mean by "The 'Milky Way' is the disk of the 'Milky Way Galaxy'."?

 

For example, in the following picture, which part is the disk?

 

2) As you observe the night sky, why do stars apear to move westward across the sky?

 

I would say earth's rotation causes stars to appear moving westward around a central point (Polaris). And earth's revolution causes them to shift slightly to the west each night, over a period of a year. Am I right?

 

3) "The earth is 4.6 billion years old. How many revolutions around the center of galaxy has it travelled? The sun is located in one of the spiral arms and completes one revolution in about 200 million years."

 

For the sun, I can calculate that it has completed 460000000/200000000=23 revolutions around the center of the galaxy? When the sun completes one revolution around the center of the galaxy, does the earth completes one revolution around this center, too?

[Jay-qu]

1. they are the same thing. We are in the plane of the disk so that when we see the milky way we only see a band of gas clouds, dust and stars.

 

2. Stars dont actually move westward its the movement of the Earth that makes them appear to be moving.

 

3. The Earth is in orbit around the sun so it will have completed the same amount of orbits minus the time taken for the earth to form after the sun did.

[TheFaithfulStone]

I don't get this part! Are "Milky Way" and "Milky Way Galaxy" the same thing or are they different? What is a "disk" and what does it mean by "The 'Milky Way' is the disk of the 'Milky Way Galaxy'."?

 

A donut is round right? Look at the edge of a donut, and now it's kinda pill shaped. Same thing only we're INSIDE the donut, so when we look at it from it's side, donut all around.

 

tfs

[kingwinner]

1) Then, for example, in my picture, is the disk the whole thing shown there, including the spiral arms?

 

And I thought that everything we see with our unaided eyes is in the Milky Way Galaxy, then how come the quote says "this part (cloudlike band) of the sky is called the Milky Way", why it seems to only occuply a small section of the sky?

 

"The Milky Way is the disk of the Milky Way Galaxy"

This part of the quote is confusing me and it seems to me that they are 2 different things.........like the Milky Way is a part of the Milky Way Galaxy...If they are the same thing, whis is this statement trying to say?

 

2) So is it true that the stars APPEAR to move westward across the sky for 2 reasons??

(i) earth's rotation - apparent westward motion of stars around Polaris during a single night?

(ii) earth's revolution - apparent shifting motion of stars to the west from night to night?

[Turtle]

1) Then, for example, in my picture, is the disk the whole thing shown there, including the spiral arms?

Yes; what they don't show is the edge on view, which is like a plate with a bulbous center.

 

And I thought that everything we see with our unaided eyes is in the Milky Way Galaxy, then how come the quote says "this part (cloudlike band) of the sky is called the Milky Way", why it seems to only occuply a small section of the sky?

The view I describe above is the "cloudlike band" aspect. Our solar system is in an outer thin arm. Looking away from the "cloudlike band" , rather like "up" or "down" we see other galaxies. Our galaxy is the "Milky Way Galaxy", other like the "Andromeda Galaxy" have other names.

 

"The Milky Way is the disk of the Milky Way Galaxy"

This part of the quote is confusing me and it seems to me that they are 2 different things.........like the Milky Way is a part of the Milky Way Galaxy...If they are the same thing, whis is this statement trying to say?

Poor writing; see above.

 

2) So is it true that the stars APPEAR to move westward across the sky for 2 reasons??

(i) earth's rotation - apparent westward motion of stars around Polaris during a single night?

Yes; Earth's Eastward (counter-clockwise) rotation.

(ii) earth's revolution - apparent shifting motion of stars to the west from night to night?

It's a bit more complex than that.

 

See if we can't find an edge on view of our galaxy to help clarify things, shall we?B)

[Jay-qu]

See if we can't find an edge on view of our galaxy to help clarify things, shall we?

 

I have one!

 

[img=http://i3.photobucket.com/albums/y66/Jay-qu/milkywayband_gleason_big.jpg]http://i3.photobucket.com/albums/y66/Jay-qu/milkywayband_gleason_big.jpg[/img]