Download Distances in Space

Distances in Space
This Mini Lesson Will Cover:
What units do astronomers use to
measure vast distances in space?
Day 1: Units of Measure in Space
 “Are we there yet”
 Go to the following link and check out how
vast space really is. Plug in the typical speed
of a car (70 mph) or NASA’s fastest space
probe, Voyager I, (39,000 mph) and see how
long it would take to get to some objects in
deep.
http://janus.astro.umd.edu/astro/distance/
Day 1: continued
 Obviously, distances in space are large. The
Sun is 93 million miles from earth and the
nearest star after that is 23 trillion miles and it
only gets worse.
 What units do astronomers use to measure
vast distances in space besides miles and
kilometers?
Day Uno:
1)
Astronomical Unit (AU) = the average distance from
the Earth to the Sun.
a)
b)
c)
2)
About 93 million miles or 150 million kilometers
Used for measurements in our Solar System.
The Earth is one AU from the Sun.
Light Year (ly) = the distance that light travels in a vacuum in
one year. (HUGE)
a)
About 9.5 trillion km or 5.7 trillion miles
b)
Used to measure the distance between stars and galaxies.
c)
Proxima Centauri, the next closest star after the Sun, is 4.2
ly away. It takes light 4.2 years to travel that distance.
d)
** Remember, Light-year is a distance, not a unit of time.
Day 1: How are distance measured in
space.
 1) Giant Meter Sticks (Just Kidding)
 2) Parallax – shifting of the apparent position
of a nearby star as Earth orbits the Sun.



What’s that. Hold up a finger in front of you.
Close one eye and then the other. See the
shift.
Astronomers can determine the distance to
nearby stars by measuring that shift.
Doesn’t work for far away objects.
Day 1: cont…
 3) Cepheid Variables are stars that get
brighter and fainter in a regular pattern. They
are used to determine longer distances. (this
is all you need to know.)


The longer the period between two bright
maximums the greater the stars absolute
magnitude.
The apparent magnitude can then be
calculated which will give you the distance.
Day 2: Problems

Use what you learned yesterday to answer the
following questions.
You want to record the distance to the Andromeda
Galaxy. What unit of measure should you use?
2. Pluto is 39 times farther from the Sun than the
Earth. How many astronomical units is Pluto from
the Sun?
3. Earth is 149.6 million km from the Sun. If Saturn is
1,434 million km from the Sun. How many
astronomical units is Saturn from the Sun?
4. Sunlight reaches Earth in 8.33 min. How long, in
minutes, would it take sunlight to reach Pluto?
1.
Day Dos: Answers
 1. light-year
 2. 39 AU
 3. 1,434 million km / 149.6 million km = 9.5 AU
 4. (39 AU x 8.33 min) / 60 min = 5.4 hours
Day 3: Problems
 1) The distance between Polaris and Earth is
431 ly. If light travels at 3.0 x 108 m/s in
space how far is Polaris from the Earth in
km?
 3) What are two methods of determining
stellar distances.
 2) Explain why looking at distance objects in
space is like looking back in time?
Day 3: Answers
 1. 431 ly(3.0 x 108 m/s) / (3.16 x 107 s /year) =


4.1 x 1018 m
* Don’t to forget to figure out how many seconds are in a
year.
 2. Parallax and Cepheid Variable periods
 3. Answers can vary. Light takes time to travel through space.
The light that hits your eye may have travelled for thousand,
millions or billions of years. Therefore you are witnessing
events that have already happened. Astronomers try to appear
farther into the universe because they can see events that
happened when the universe was first forming.