Earth/solar position vs spiral arms

In summary, a PDF on global warming includes a figure showing the Earth's solar position over the past 200 million years as our sun moves in and out of the spiral arms of the Milky Way. This is because the spiral arms are density waves, not a permanent structure that rotates with the stars. The variation in speeds of stars in our current local group may have caused the need for "dark matter." Compression waves are responsible for moving stars within the galaxy, and it is possible to determine the position of our sun in a given spiral arm at a specific time in the past.
  • #1
ray b
181
0
in a post on global warming linking to a PDF http://www.spacecenter.dk/research/...blications/svensmark_2007cosmoClimatology.pdf
there is a figure #9 showing the earth+ solar position over the last 200 million years
as our sun moves in and out of the spiral arms of the Milkyway

WHY does this happen
as if the other stars moved at a near speed
would not the solar position stay with in a given spiral arm
or the whole arm no long be in place as the stars move out
is our sun at a special orbit or speed
or what is going on?
 
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  • #2
Spiral arms are 'density waves' rather than a permanent structure that rotates with the stars. This means that stars are sometimes in and sometimes out of the spiral arm.
 
  • #3
The spiral arms are not due to star movement around the center of the galaxy. They are compression waves moving through the galaxy.
 
  • #4
how much variation in speeds is there in our current local group of stars

I thought the whole need for "DARK MATTER" was to limit the speed of the outer
stars as they move at nearly the same speed in orbits around the galaxy

so how do compression waves move a star or group of stars
and how can someone say our sun was in a give arm at a given date 100 or 300 million years ago?
 

1. What determines the position of Earth within the spiral arms of the Milky Way galaxy?

The position of Earth within the spiral arms of the Milky Way galaxy is determined by its distance from the center of the galaxy and its location within the galactic disk. Earth is currently located about 26,000 light years from the center of the galaxy and is situated within the Orion Arm, one of the Milky Way's four main spiral arms.

2. How often does Earth pass through different spiral arms of the Milky Way galaxy?

Earth passes through different spiral arms of the Milky Way galaxy approximately every 150 million years. This is due to the fact that the Milky Way galaxy rotates, causing the spiral arms to move and change position over time.

3. What effect do the spiral arms of the Milky Way galaxy have on Earth's orbit?

The spiral arms of the Milky Way galaxy do not have a significant effect on Earth's orbit. Earth's orbit around the Sun is primarily influenced by the Sun's gravity, and the gravitational pull of other planets in our solar system.

4. How do scientists study the position of Earth within the spiral arms of the Milky Way galaxy?

Scientists study the position of Earth within the spiral arms of the Milky Way galaxy through a variety of methods, including studying the distribution of stars and gas in the galaxy, measuring the Doppler shift of light from distant stars, and using computer simulations to model the movement of the galaxy.

5. Are the spiral arms of the Milky Way galaxy permanent structures?

The spiral arms of the Milky Way galaxy are not permanent structures. They are constantly changing and evolving due to the gravitational interactions between stars and other galactic forces. Some spiral arms may merge or dissipate over time, while new ones may form in different locations within the galaxy.

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