Download Distances to Stars Scales of Size and Time

Distances to Stars
Physics 113 Goderya
Chapter(s): 1
Learning Outcomes:
Scales of Size and Time
Astronomy deals with objects on a vast
range of size scales and time scales.
Most of these size and time scales are way
beyond our every-day experience.
Humans, the Earth, and even the solar
system are tiny and unimportant on cosmic
scales.
A Campus Scene
16 x 16 m
1
A City View
1 mile x 1 mile
The Landscape of Pennsylvania
100 miles x 100 miles
The Earth
Diameter of the Earth: 12,756 km
2
Earth and Moon
Distance Earth – Moon: 384,000 km
Earth Orbiting Around the Sun
Distance Sun – Earth = 150,000,000 km
Earth Orbiting Around the Sun (2)
In order to avoid large numbers beyond our
imagination, we introduce new units:
1 Astronomical Unit (AU)
= Distance Sun – Earth =
150 million km
3
The Solar System
Approx. 100 AU
Example
• Venus orbits 0.7 AU from the sun.
What is that distance in Kilometers?
Answer: 1.05x108km
(Almost) Empty Space Around Our
Solar System
Approx. 10,000 AU
4
The Solar Neighborhood
Approx. 17 light years
The Solar Neighborhood (2)
New distance scale:
1 light year (ly) =
Distance traveled by light
in 1 year
= 63,000 AU = 1013 km
= 10,000,000,000,000 km
(= 1 + 13 zeros)
= 10 trillion km
Approx. 17 light years
Nearest star to the Sun:
Proxima Centauri, at a
distance of 4.2 light years
The Extended Solar Neighborhood
Approx. 1,700 light years
5
The Milky Way Galaxy
Diameter of the Milky Way: ~ 75,000 ly
Example
• How long does it take light to cross
the diameter of our Milky Way
Galaxy?
Answer: 75000 yrs
yrs.
The Local Group of Galaxies
Distance to the nearest large galaxies:
several million light years
6
The Universe on Very Large Scales
Clusters of galaxies are grouped into superclusters.
Superclusters form filaments and walls around voids.
7