Download Astronomy Rough Notes

Astronomy Rough Notes - Scaling
DISCLAIMER: These notes do NOT cover everything you need to know. You will often need to look up
some item or concept online or in a text. Test questions are not exact copies of the OBJECTIVES but if
you know the OBJECTIVES thoroughly, you should do well on the exams.
HANDOUTS:
Ranking Exercise
SI (metric) system prefixes
SI system sizes homework
Data for scale model (in notes below)
Scaling the Earth-Moon tutorial
NOT HANDED OUT BUT USEFUL
Practice problems for powers of ten and scientific notation (work these but do not hand in)
EARTH-SUN SCALE MODEL PHOTO (hand in)
OBJECTIVES:
Picture/rank the size of the following objects: our Moon, Earth, Sun (or a star), our solar system, the
Milky Way galaxy (our galaxy), the universe.
Picture/rank the distances to the following objects: our Moon, Earth, Sun (or a star), our solar system, the
Milky Way galaxy (our galaxy), the Andromeda Galaxy (nearest big neighbor galaxy to the Milky Way.
Define Astronomical Unit. Know its abbreviation.
Define light-year. Know its abbreviation.
Identify objects that are about a m in size, a cm in size, a mm in size.
Estimate sizes of various objects using the appropriate metric unit (m, cm, or mm).
Measure in m, cm, mm.
Learn the name, meaning, and symbol for SI system prefixes giga, mega, kilo, centi, milli, micro, nano.
Given a number in scientific notation, write it in standard form.
Given approximate sizes and the scale, build a scale model of the Earth-Moon system and the Sun-Earth
system.
Given approximate sizes and the scale, build scale models of other objects or systems in the universe.
HOW CAN I IMAGINE THE SIZE OF THE UNIVERSE?
I. Take virtual trips.
II. Use big numbers like 2.2 X 1018 m or small numbers like 3.8 X 10-8 kg
III. Use large units like a light year or small units like a nanosecond
IV. Use scale models
I. VIRTUAL TRIPS
1. Zoom out from Earth to edge of visible universe (excellent, uses real data)
http://antwrp.gsfc.nasa.gov/apod/ap100120.html
2. Steps through powers of ten using photos/drawings (good)
http://micro.magnet.fsu.edu/primer/java/scienceopticsu/powersof10/index.html
3. Animated steps through powers of ten (excellent)
http://htwins.net/scale2/
4. “Cosmic Voyage” video (in my office) – excellent, ~50 minutes
5. “Powers of Ten” video (in my office) – excellent although dated ~10 minutes
Also on you tube at http://www.youtube.com/watch?v=0fKBhvDjuy0
6. Here’s one just on the scale of the solar system
http://joshworth.com/dev/pixelspace/pixelspace_solarsystem.html
7. "The Scale of the Universe 2" http://htwins.net/scale2/
Ranking Exercise (Done in class)
II. LARGE NUMBERS - SCIENTIFIC NOTATION (Expressing big numbers)
102 means 10 X 10 = 100
And
1
1
1
104  4 

 0.0001
10 10 10 10 10 10000
108 is 100 000 000
10-8 is 0.000 000 01
(Use spaces not commas)
(Use a 0 in front of the decimal)
6.3 X 102 means 6.3 X 100 which is 630.
For a short cut, start with 6.3 and move the decimal two places right giving 630.
Convert 2.81 X 104 to a standard number.
Start with 2.81
Move the decimal four places right.
28 100.
4.903 X 10-3 means 4.903 X 0.001 which is 0.004903.
For a short cut, start with 4.903 and move the decimal three places left, ie, 0.004903
Convert 8.2 X 10-5 to a standard number.
Start with 8.2
Move the decimal five places to the left.
0.000 082
Practice problems for powers of ten and scientific notation (Work but do not hand in.)
Check the web for more practice. Here are two of many sites:
http://janus.astro.umd.edu/astro/scinote/
or at
http://www.khanacademy.org/video/scientific-notation?playlist=ck12.org%20Algebra%201%20Examples
III. USE LARGE OR SMALL UNITS
Unit = Any standard of measurement or exchange.
Ex. - In 3 feet, the units are feet. In 5.5 seconds, the units are seconds. In $5, the units are
dollars.
In science, use SI system (meters, kilograms, seconds)
m, cm, mm
Size of each (meter stick)
Homework: SI system sizes homework
Other prefixes:
centi, milli
nano, micro, milli, centi, kilo, mega, giga
See list of prefixes and examples: SI (metric) system prefixes
See the web for more help. For example, http://physics.nist.gov/cuu/Units/index.html
Two larger units
1. Astronomical Unit (AU) – Average distance from Earth to Sun
Ex - Earth to Sun distance is 1 AU
Ex - Sun to Pluto ~40 AU
2. Light year (ly)
Speed of light
= 186 000 mi/s
= 300 000 km/s
= 7 ½ times around Earth in one second!!
=FAST
Light-second
Distance light travels in one second
(Speed of light = 186 000 mi/s)
So 1 light-second = 186 000 mi
Example –
Earth to Moon ~ 1.3 light-seconds
Traveling at the speed of light takes 1.3 seconds to reach the Moon
(~10 hours by rocket at 25 000 mi/h)
Light-year (symbol ly)
Distance light travels in one year
Example –
Sun to next nearest star, Proxima Centauri ~ 4.3 ly
Light from the Sun takes ~4.3 years to reach the NEXT nearest star
IV. USE SCALE MODELS
Models help us visualize and think about systems.
Example:
Scale the US to a scale of 1 mm = 10 mi (equivalently 1 cm = 100 mi and 1 m = 10 000 mi)
Then choose some common objects to build your scale model.
Given data Twin Cities’ diameter is ~20 mi
Chicago’s diameter is ~50 mi
TC to Chicago is
~600 mi
TC to LA is
~2000 mi
TC to Moon is
~240 000 mi
The TC is about 20 mi in diameter so start with 1 mm = 10 mi. Then 20 mi is 2 mm.
(mathematically just divide the 20 mi by 10 mi)
Therefore, on the scaled drawing the TC is 2 mm in size.
Similarly, Chicago is 50 mi/10 mi or 5 mm in size.
The distance to Chicago from TC is 600 mi/10 mi or 60 mm.
You could also start with 1 cm = 100 mi so 600 mi/100mi gives 6 cm. Either result is fine.
Our scaled drawing now looks about like:
6 mm
2 mm
TC
6 cm
Chicago
2 mm is about the size of pin head. 6 mm is about the size of a tic-tac. 6 cm is about the width of a
calculator. So to build a scale model of the TC and Chicago, you could use a pin head and a tic-tac
separated by the width of a calculator.
To include the Moon in this scale model, start with 1 m = 10 000 mi. The Moon would be 240 000 mi/10
000 mi or 24 m away, about on Hennepin Av from the classroom.
Question: It is about 1 mi to the downtown library from here. If you wanted to represent that distance on
your scaled map, would you use a pencil point dot or the diameter of a dime to represent that distance?
Explain.
Answer: 1 mm = 10 mi so 1/10 mm = 10/10 mi or 0.1 mm = 1 mi
So 1 mi on the scale model is 0.1 mm which is the size of a pencil point dot
Tutorial Exercise: Scaling the Earth-Moon tutorial (begun in class)
HOMEWORK
Read the notes especially the OBJECTIVES.
Read a text, the web or other source.
Make flash cards for OBJECTIVES.
Bring at least two flashcards to the next class answering at least two objectives.
Work the practice problems for powers of ten and scientific notation exercises and check your
answers. Do not turn this in.
Work the SI system sizes homework and hand it in.
Finish the Scaling the Earth-Moon tutorial if you did not finish it in class. Do not hand it in.
Produce the EARTH-SUN SCALE MODEL PHOTO and follow its directions. Hand it in.
Revised 2 January 2016