Download Astronomical Distances

Astronomical Distances
Group
Class
One of the hardest concepts to get your head around in astronomy is just how big the things we talk about
really are. Walking from P.E. to the auto shop at NVHS is a long way, but is it a long way when we are talking
about traveling by car? In a car, going from Chicago to Champaign is a long way, but is it far when we are
talking about travel by plane? The distances in astronomy can almost be incomprehensible, but not if we
keep it in perspective.
When we talk about terrestrial (on Earth) distances we might use inches feet or miles, in science we might use
centimeters, meters, or kilometers. When we talk about objects in our universe these units are much too
small, it would be like calculating the distance between Naperville and London in millimeters. For example, the
distance is roughly 6,378,000,000 mm, this number is scientifically meaningful and accurate, but can you truly
understand what it means? For astronomy, we need to use units that are much larger than feet, meters, miles,
or kilometers. You will find that scientific notation will be very helpful here.
Distance
We are going to use two different units, the first is the Astronomical Unit which is equal to the average
distance between the Earth and the Sun which is 1.5 X 108 Km. The second is a light-year (ly) which is the
distance that light travels in one year which is about 9.46 X 1012 km (10 trillion miles…). Because we are using
the unit of light-year it may also be useful to calculate the amount of time it takes for light to get between
different places in our universe.
1. Write out the full numeric value for an AU ____________________ + ly ____________________
How many times larger is a light-year then an astronomical unit? ____________________
Times bigger a light year is than an astronomical unit = Km in a light year
Km in an astronomical unit
Velocity
Light travels at 186,000 miles per second or 3.0 X 105 km/second, that's pretty fast, but still it will take time
for light to get from place to place. A very useful equation for calculations in this lab will by v=d/t. That
means the velocity of the object is equal to the distance it travels, divided by the time it takes to travel that
distance. So it is also true (by rearranging the equation you can see this) that t=d/v.
As you proceed through the steps of this lab, take time to look at the data and understand what it is that it
means. Doing the calculations is a necessary part of this lab, but it is not the main purpose, although you
must provide sample calculations. The main purpose of this lab is for you to get an understanding of the
scale of the Universe. You may have a different perspective on the Universe when you finish this lab.
Sample conversion (10 days to seconds)
10 days 24 hours
1 day
60 minutes
1 hour
60 seconds
1 minute
= 864,000 seconds or 8.64 x 105seconds
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Procedure
Part A
Get a meter stick and place length wise on your lab table; this is going to represent the radius of our solar
system, or the distance between the Sun and the former planet Pluto. Here is a table to help you organize
these objects. Calculate the values (show all work) to fill in the following table. Then, mark off these objects
using small labeled pieces of masking tape on your desks. All of the conversions you need are found on page 1.
Object
Average Distance
from Sun (Km)
Number of
Astronomical
Units from
Sun(AU)
Light-years (ly)
Time it takes light
to go from the Sun
to the object (min)
Sun
0
0
0
0
Mercury
58,000,000
Venus
108,000,000
0.72
0.0000114
6
Earth
150,000,000
1
0.0000158 ly
Or
1.5 X 10-5 ly
Mars
229,000,000
500 seconds
or
8.3 min
12.72
Jupiter
777,000,000
5.18
0.0000821
43.17
Saturn
1,426,000,000
9.51
0.001507
79.2
Uranus
2,876,000,000
19.17
Neptune
4,490,000,000
0.000476
249
Pluto
5,914,000,000
0.0006183
At this scale:
1 meter = 5,914,000,000km, so 1cm = 59,140,000 km
1cm = 0.394 AU
1AU = 2.54 cm
2. Is a light-year a good unit of measurement for describing distances within our solar system?
3. Why?
4. Below make a very quick (but accurate) sketch of what you labeled string looks like.
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Part B
The Sun is just one of 70 million, million, million or 7.0 X 1019 stars in the known Universe. Now we are going
to look at distances within our Universe. The furthest observable object is about 10,000,000,000 light-years
away. Keep in mind that the current research suggests that our universe goes on for another 3,600,000,000
light-years past that or 13.6 billion light years.
Here is a table of a few notable objects in the heavens, most of which are observable with the naked eye.
Object
Significance
Time for light Light years
to reach earth from Earth
from object
(years)
Distance on
floor from
Earth in cm
The Sun
Closest star
0.000016
1.6 X 10-11
Pluto
Farthest
planetoid
from Earth
8.3 minutes
Or
3.0 x 10-7
5.42 hours
Or
6.19 X 10-4
Alpha
Centuri
Closest star
other than
Sun
4.27
4.27
4.27 X 10-6
Sirius
Brightest
star in sky
8.7
8.7
8.7 X 10-6
Pleiades
Cluster
Nearest star
cluster
400
400
Center of
Milky Way
Galaxy
Center of
our Galaxy
38,000
38,000
Andromed
a Galaxy
Closest
galaxy to
ours
2,200,000
2,200,0000
Half way
to the
edge of
the
Universe
No other
significance
6.800,000,000 6,800,000,
000
Unnamed
quasar
Farthest
known
object
10,000,000,00 10,000,000 10,000cm
0
,000
Distance from
Earth on floor in
meters (m)
Closest
classroom
0.0006183
0.0000000427
0.038
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5. Fill in the last column in table B
At this scale:
100 m = 10,000,000,000 light years,
1 m = 100,000,000 light-years
1cm = 1,000,000 light-years
In the hallway, 50m is marked off with pieces of tape on the floor. So 50m + 50m back = 100m this will
represent the universe instead of a string.. Use a meter stick to measure these smaller distances.
In the table above walk off the distances and write down the classroom that you are nearest for each object.
6. Which is a better unit of distance when discussing objects outside of our solar system, an astronomical
unit or light-year?
7. A person with perfect eyesight and with perfect conditions we can see about 3000 stars at once with the
unaided eye, the farthest star we can see with the unaided eye is about 4075 light years away. Stars in the
Universe are thought to be fairly evenly dispersed. That puts every star you can see with your eyes within
0.0004075 cm from the zero mark in the hall. Does that make you feel insignificant? If so, professional help
is available.
8. Did you have any idea that the Universe was so big?
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