Lab1_The_Scale_and_Overview_Universe-2
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University of Southern California *
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Course
343M
Subject
Astronomy
Date
Dec 6, 2023
Type
docx
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6
Uploaded by AmbassadorCrane3712
Name
: Eric Chung
Lab N
o
: 1_______
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Date 2/4/23
THE SCALE OF THE UNIVERSE
Activity 1: Some Research
These essential facts and concepts will be used throughout the semester, and all
students should familiarize with them.
For our purposes, approximate answers are
much better than precise answers.
For example, the radius of the Earth should be
remembered as 6000 km, rather than 6,378 km.
The unit "LY" refers to light years.
Astronomers used different units from our everyday units (e.g. km instead of miles), and
they tend to make things simpler to express and relate distances of objects in the
universe and to carry out various astronomical calculations.
1-
Baltimore is about 2,217,600 inches from DC. Is this numerical distance
meaningful to you, i.e. do you have a “feel” for how far away this is? Why?
No, because it is in inches, however, we can use it and convert it into miles to have a
feel for how far away it is.
2-
Let use another unit:
mile.
Find out how many miles are between DC and
Baltimore?
35 miles
3-
Do you have more of a “feel” for the DC-Baltimore distance, now that it’s
expressed in a larger, more appropriate unit?
Yes, since it is in a more appropriate unit. Now it is easier to feel the distance.
Describing distances efficiently requires us to use appropriate units. In this lab we will
attempt to use units and scaling to get a “feel” for distances within the solar system and
galaxy.
4-
The first exercise is to do some research on the internet to complete this
worksheet with your partner. You should supply the requested quantities
in round
numbers.
Notation:
1
Km = Kilometer
AU = Astronomical Unit
LY = Light Years
Quantity
Given Value
Approximate Value
Earth's Radius (km)
6,378 km
6,000 km
Earth-Moon Distance (km)
384,399 km
385,000 km
Astronomical Unit (km)
1.496e+8
150,000,000
Moon’s Radius (km)
1,737 km
2,000 km
Sun's Radius (km)
695,700 km
696,000 km
Solar System Radius (AU)
960.78 AU
970 AU
Speed of Light (km s
-1
)
299,792 km
s
-1
300,000 km
s
-1
Length of Light Year (km)
9.46 trillion km
10 trillion km
Milky Way's Radius (LY)
52,850 LY
53,000 LY
Distance to Galactic Center (LY)
25,800 LY
26,000 LY
Local Group Radius (LY)
5,000,000 LY
5,000,000 LY
Virgo Supercluster Radius (LY)
55,000,000 LY
55,000,000 LY
Radius of the Visible Universe (LY)
46.508 billion LY
47 billion LY
5-
What is a light year?
Distance light travels in a year.
6-
What is the definition of one astronomical unit or AU?
Distance between Earth and the sun.
Please give the value of 1 AU in miles.
1 AU =
93 million
miles
Activity 2:
Scaling Relationships
1-
What is the ratio between the Earth’s diameter (radius) and the Moon’s diameter
(radius)?
Ratio =
Earth Radius
Moon Radius
=
3:1
2
2-
What is the ratio between the Sun’s diameter (radius) and the Earth’s diameter
(radius)?
Ratio =
Sun Radius
Earth Radius
=
116:1
3-
What is the ratio between the Sun and the Earth (1AU) and the diameter of the
Sun?
Ratio =
1
AU
(
km
∨
miles
)
Sun Diameter
(
km
∨
miles
)
=
107:1 km
4-
Describing distances in the solar system in miles, while accurate, does not give
us a “feel” for these vast distances.
It’s like describing the DC-Baltimore distance
in inches, as we discussed above. So, just like we replaced the inch with a larger
unit, the mile, to describe the DC-Baltimore distance better, now we’ll define
another unit, much larger than the mile, to help us understand solar system
distances. Let use another scale. One AU (93,000,000 miles) = 1 foot = 12
inches. Using this scale, complete the table below:
Planet
Distance from
the Sun (miles)
Scaled feet from
your location
Scaled inches
from your location
Mercury
36,187,500
.4 ft
4.7 in
Venus
67,230,00
.7 ft
8.7 in
Earth
93,000,000
1 ft
12 in
Mars
142,437,500
1.5 ft
18.4 in
Jupiter
486,437,500
5.2 ft
62.8 in
Saturn
888,200,000
9.6 ft
114.7 in
Uranus
1,786,400,000
19.2 ft
230.6 in
Neptune
2,798,800,000
30.1 ft
361.3 in
Pluto
3,666,200,000
39.4 ft
473.3 in
5-
Here’s yet another way to look at just how far apart things are in the Solar
System:
In 1905, Albert Einstein proposed that the speed of light (c) is the “cosmic speed limit,”
i.e. nothing can accelerate up to go faster than this. This has subsequently been
confirmed in many experiments. This is a natural barrier, not a technological one; that is,
3
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it’s not just a matter of building an engine powerful enough one day to accelerate this
fast—the very laws of nature forbid such an acceleration.
The speed of light is so phenomenally fast, a beam of light would circumnavigate the
Earth seven times in one second! Going even at this rate, light takes 8.3 minutes to
traverse 1 AU. That’s how big ONE AU is!
So that means, the light we are getting from
the sun here on Earth is literally 8.3 minutes old!
But let’s use Pluto as our example instead of Earth.
Using the data for Pluto from
column 3 of your table above, and knowing it takes light 8.3 minutes to go 1 AU, how
long would it take sunlight to get to Pluto?
Travel Time at Lightspeed to Pluto =
around 327
minutes
6-
Divide that number by 60 (as there are 60 minutes in an hour) to get the number
of hours it would take, even at lightspeed, to get to Pluto:
Travel Time at Lightspeed to Pluto =
around 5
hours
7-
The nearest star to us (other than the Sun) is called Proxima Centauri and is
about 300,000 AU away. How many miles would this be?
27.9 trillion miles
8-
If light travels 1 AU in 8.3 minutes, how many minutes would it take for light to go
the 300,000 AU to Proxima Centauri?
Travel Time at Lightspeed to Proxima Centauri =
2.49 million
minutes
9-
And since there are about 526,000 minutes in a year, how many years would it
take for light to travel to Proxima Centauri?
Travel Time at Lightspeed to Proxima Centauri =
around 4.734
years
The stars in the galaxy are so far apart that even the AU is of little use to us in
understanding the scale of this vast distance. The stars are so distant we have to use a
new unit, the light-year (LY), to describe how far away they are efficiently. The light-year
is the
distance
light travels in a year. (Note it is a distance unit, not a time unit!)
4
Thus, Proxima Centauri is over 4 LY away. Keep in mind that light goes so fast it would
go around the world seven times in the time it takes to snap your fingers, and yet it
would still take over 4 years to get to the closest star to the Sun. The other stars you
see at night are even further away. And the other galaxies are even further out.
Activity 3: Ranking
Alpha Centauri
Andromeda Galaxy
Antennae Galaxy
Eagle Nebula
Jupiter
Moon
Orion Nebula
Pleiades Star Cluster
Pluto
Ring Nebula
Sombrero Galaxy
Sun
Rank each of the above objects in order of increasing distance (note: some objects may
be similar in mass).
1.
Moon 385,000 km
2.
Sun 1 AU
3.
Jupiter 5.5 AU
4.
Pluto 35.6 AU
5.
Alpha Centauri 4.3 LY
6.
Pleiades Star Cluster 444 LY
7.
Orion Nebula 1344 LY
8.
Ring Nebula 2283 LY
9.
Eagle Nebula 7000 LY
10.
Andromeda Galaxy 2.5 million LY
5
11.
Sombrero Galaxy 29 million LY
12.
Antennae Galaxy 45 million LY
6
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