Download Astronomical Distances

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Astronomical Distances
1. Imagine you are drawing a map of your exact position in the Milky Way Galaxy. You decide you are
going to start with the small scale of the classroom and then work your way out to where you are in the
Milky Way Galaxy. What units of measurement would you use to describe your positions at each level?
a. Classroom:
b. School: Meters, kilometers or yards
c. City:
d. State: Hundreds of miles
e. Country: Thousands of Miles
f. World:
g. Solar System:
h. Galaxy:
2. If you were measuring our Solar System, would miles or kilometers be the best unit of measurement?
Explain your answer.
Astronomical Units:
An Astronomical Unit was designed to measure the distance of celestial objects with respect to Earth’s
distance from the Sun. One Astronomical Unit is equal to the distance from Sun to the Earth, which is
149,598,770 km.
Using the table provided below, fill in the blanks to determine the distances to our fellow planets in the Solar
System using Astronomical Units. *Round to the nearest hundred thousand for your calculations.
Example: 3,098,000
3,100,000
Diameters & Distances from the Sun
Diameter (km)
SUN
MERCURY
VENUS
EARTH
MARS
JUPITER
SATURN
URANUS
NEPTUNE
PLUTO
Distance (km)
Astronomical Units
(AU)
1,391,400
0
0
4,878
57,900,000
0.39
12,104
108,209,000
12,756
149,598,770
6,794
227,900,000
142,984
778,200,000
120,536
1,429,200,000
51,118
2,875,000,000
49,528
4,504,400,000
2,302
5,915,800,000
1
Light years: How far does light travel per minute, per hour, per hour and per YEAR?
Did you know that light travels at 186,000 miles/second (300,000 km/second)!
The Earth is about 25,000 miles around. That means that light travels around the Earth 7.5 times in one
second!
25,000 miles
186,000 miles/second
= 0.134 seconds for
= 7.44 times
OR
light to travel around the
186,000 miles/second
25,000 miles
Earth
Per Minute
Per Hour
Per Day
miles/min 669,600,000 miles/hour
186,000 miles/sec
x 60
x
x
x
“Light minute”
“Light Year”
“Light Hour”
“Light Day”
Per Year
miles/day
365.25
3. Based on your calculations, what is the definition of one light-year?
Objects
Time for Light
to Travel
Sun to Earth
Earth to Moon
1.3 seconds
Earth to Saturn
1.2 hours
Earth to nearest star
(Alpha Centauri)
4.3 years
Earth to North Star
430 years
Earth to nearest
galaxy (Andromeda)
2 million years
Distance in
Light-units
8 “lightminutes”
1.3 “lightseconds”
“light-hours”
Distance in Miles
~241,800 miles
~803,520,000 miles
4. Why do astronomers use AU (Astronomical Units) instead of miles or kilometers?
5. Why would astronomers use light years instead of AU?
6. How many AU are there in one light year?
Challenge:
How many miles is it across the Milky Way Galaxy?
(Our Milky Way Galaxy is about 100,000
light years across)