Download Measuring the Distance to the Stars

Measuring the Distance to the
Stars
What is a Light Year?
• A light year is the distance light travels in
one year.
• If the speed of light is 300,000 Km/sec.
then how many Km is a light year?
• 300,000Km/sec. x 60sec/min x 60min/hr x 24hr/day x 365 days/year
• One light year is 9,500,000,000,000 Km
• 9.5 trillion kilometers
How close is the nearest star?
•
•
•
•
•
•
Our sun is 8 light minutes away.
Proxima Centauri is 4.2 LY away.
4.2 x 9.5 x1012 = 40 trillion Km
In a scale model 1 cm = 1 light min.
Our sun would be 8 cm away.
Proxima Centauri would be 23 km away.
How do we find the distances to
stars?
Which star is closest to earth?
2
4
January
3
1
July
(6 months
Later)
2
1
5
4
3
6
5
2
4
January
1
6
3
6
5
How do we find the distances to
stars?
Parallax:
The closer an object is, the more it appears to
move against the background.
Parallax activity
• As the earth goes around the sun closer
stars seem to move a lot against the
background of stars.
A
B
Background Stars
C
D
E
F
G
Far Star
Near Star
Earth January
Sun
Earth July
• As the earth goes around the sun farther
stars do not seem to move much against
the background of stars.
A
B
Background Stars
C
D
E
F
G
Far Star
Near Star
Earth January
Sun
Earth July
•As the earth goes around the sun closer
stars seem to move more than far stars
against the background of stars.
A
B
Background Stars
C
D
E
F
G
Far Star
Near Star
Earth January
Sun
Earth July
Which star is closest to earth?
2
4
January
3
1
July
(6 months
Later)
2
1
5
4
3
6
5
2
4
January
1
6
3
6
5
Reading Stellar Parallax
• Pg. 467-468
• R&C 2,3 Pg. 470
• How do we find the distance to the distant stars?
• How do we find the distance to the distant stars?
• Unit of brightness
distance to star
• How do we find the distance to the distant stars?
• Unit of brightness
distance to star
1
1 unit
• How do we find the distance to the distant stars?
• Unit of brightness
distance to star
1
1 unit
1/4
2 units
• How do we find the distance to the distant stars?
• Unit of brightness
distance to star
1
1 unit
1/4
2 units
1/9
3 units
• How do we find the distance to the distant stars?
• Unit of brightness
distance to star
1
1 unit
1/4
2 units
1/9
3 units
1/X2
(inverse square)
X units
An example of how to use star brightness to find
the distance to stars.
• The center of the galaxy is about 100 times
dimmer than the stars we can see with our eyes.
• The stars we can see are about 3000 LY away.
So, how far is the center of the galaxy?
• The center of the galaxy is about 30,000 LY
away from earth.