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Transcript
STARS MOTION AND HOW IS IT SEEN FROM
EARTH?
By: Paul Jones & Antoine Henderson
PROPER MOTION & TRANSVERSE VELOCITY
•
Proper motion is equal to angular displacement (in arc seconds) divided by time. Ex:
300’’/50 yrs PM= 6 years of that star.
•
Transverse velocity is equal to the distance divided by the constant 3.2 x 10 7 th seconds.
Ex: TV= 4000000000km/ 3.2 x 10 7 th seconds therefore TV= 125 km/s
RADIAL VELOCITY & TRUE SPACE MOTION
•
Radial Velocity is equal to (apparent wavelength / true wavelength -1) (c).
•
Ex: RV=(399.85 / 400 -1) (300,000)
RV = (-.000375) (300,000)
RV= -112.5 km/s or 112.5 km/s
•
True Space Motion = sq. root of radial velocity sqrd. + transverse velocity sqrd.
•
Ex: TSM= sq root of (112.5 km/s)sqrd. + (125 km/s)sqrd.
TSM= sq root(28281.25)
TSM= 168.17 km/s
STELLAR PARALLAX
•
Astronomers use stellar parallax with stars through a series of steps such as follows.
1. First they look at the star from one part of Earth’s orbit make measurements and then
perform the same process on the other side of the orbit.
2. This is due to the great baseline needed to measure even the closest stars.
3. After having found the parallax and knowing the baseline to be 2 A.U. astronomers can
then determine the distance to the star.
•
This process however can only be used on a few of the closest stars due to the large
distances that make the parallax extremely small.
•
In fact they are so small that degrees aren't used, instead they use arc seconds which
when translated one arc second is one parsec and through determinations 1 parsec is
206,265 A.U.’s or 3.3 LY. That gives you an idea of how small the angles really are.
USING AN INVERSE SQUARE LAW WITH
LUMINOSITY AND APPARENT BRIGHTNESS
•
The inverse square law shown below represents the factor of squaring the are a certain
portion of light from a star has to fill. (2 times farther is 2 squared thereby making the
area the same amount of light having to cover 4, if it is 3 times farther it has to cover 9
times the area, so on and so forth). So by using this formula we can determine distance
based on luminosity and apparent brightness or energy flux. This also helps with
understanding of how bright a star really is. Ex: If two stars have the same apparent
brightness yet one star through calculations is substantially farther away therefore the
farther star must either be much hotter and brighter/bigger or both.
HOW DOES THIS SHOW MOVEMENT
•
By using these calculations and using them over time we can see small changes in how
stars move. Similarly when we watch a star spin we see red and blue shifts as it spins
away and at us while rotating. But by constantly watching and using Proper motion and
transverse velocity we can see movement with help from the previous ways of calculating
distance. By using these we can also determine if a parallax shifts as well as if the
distance changes thereby determining whether a star is moving or not.