Unit 10

Light years

and Theories

Warm Up

Test Review

Measuring Distance• Mph• Knots• Mach• Light Year• Warp

• What do theses terms measure?

• Turn to your should partner and discuss for 1 minute. BE PEPARED TO SHARE

Measuring Distance

• Mph: • miles traveled per hour

• Knots:• time it takes to travel one nautical mile per hour (A nautical

mile is longer than a land mile.)

• Mach: • an object's speed divided by the speed of sound

• Light Year: • distance traveled by light in one year

• Warp: • doesn’t exist, except on Star Trek-speed faster than the

speed of light

Measuring Distance• Mph: miles traveled per hour• Knots: time it takes to travel one nautical mile per hour (A

nautical mile is longer than a land mile.)• Mach: an object's speed divided by the speed of sound• Light Year: distance traveled by light in one year• Warp: doesn’t exist, except on Star Trek-speed faster than

the speed of light

• How are these terms similar? • Measurement is a commonality.

• In this unit, one way we measure great distances will be explored…light years.

MeasuringRuler(cm)

Meter Stick(m)

Pencil (pencils)

Yarn(yarn)

Entrance Door to pencil sharpener

Main water shut off to Xaiver’s cage

Trash can to filling cabinet

Lab Table 2 to Lab Table 7

Length of any desk in the room

Eye Wash to Goggle Cabinet

Open Measuring

Measuring• Which units are best to describe the

distances of objects to the door to the pencil sharpener?

• Which unit was not appropriate for describing the farthest distance? Why? • Pencil, difficult to use

• What measurement unit would be used to measure from the door to your home? • Kilometers

Measuring• What measurement could be used to

measure from the door to the next city? To the Moon? • Hundreds or thousands of kilometers

• What if we have to measure vast distances from Earth to another galaxy? Could we use centimeters, meters, kilometers, miles, and feet? • Yes, we could use those units, but it wouldn’t be

reasonable. The numbers would be extremely large.

• What type of measuring unit would we need for distances across space?

Warm Up

Notes

•Open Light Year Notes

• Copy what is in yellow

• What type of measuring unit would we need for distances across space?

• Light Year

• How far is far?

• How fast is fast?

What Is It?

A light year is the

DISTANCE that light

will travel, through a

vacuum, in one year.

Side Note:This is not a unit of time, but a unit of distance. A vacuum is simply empty space

Calculate Seconds •How many seconds are in a year? • 31,557,600 s/yr

60 s 60 min 24 hr 365.25 days

1 min 1 hr 1 day 1 yr ¿

What is the fastest speed we know?

The Speed

of Light

Speed of Light

•c = 299,792,458 meters per second or 186,000 miles per second

Speed of Light

• To get an idea of how fast this is. . . light can travel about seven times around Earth in one second!

Other Values

• One light year is approximately 5.880 trillion miles or 9.5 trillion km.

• The symbol for light year is “ly”.

Why “ly”?• Light years are used to measure the vast distances in space. •In the universe, the kilometer measure is too small to use.

In the universe, the kilometer measure is too small to use. For example, the distance to the next nearest big galaxy, the Andromeda Galaxy, is 21 quintillion km. That's 21,000,000,000,000,000,000 km. This is a number so large that it becomes hard to write, to relate to, and to use in calculations. Astronomers use other units of distance.

History Seen• Every time you look at objects in the night sky or the Sun, the light from that object is old. You are looking at history.

An Example• It takes eight light minutes for

light leaving the Sun to reach the Earth.

• To put this in perspective, if you

could drive from the surface of the Sun to the surface of the Earth, it would take you 180 years driving nonstop at 60 mph.

Example: Sirius• Sirius, in the constellation Canis Major, is the sky’s brightest star. It

is easy to find on winter and spring

evenings.

• When you look at Sirius, you are looking back in time to see how Sirius looked eight years ago. The light left the star eight years ago.

At some point, we may see the death or birth of a star long after the event occurred.

Clip• http://janus.astro.umd.edu/astro/distance/

Measuring

• Why is a light year a unit of distance rather than time? • It measures the distance light travels in a vacuum in one year - 9.5

trillion km or 5.880 trillion miles.

• Why do we need to use light years as a way of measuring cosmic distances? • If we used conventional measurements, the numbers would be huge

and difficult to calculate.

• What is the “speed of light”? • The rate at which light travels through empty space - 299,792,458

meters/second or 186,000 miles/second.

• How are light years used to measure distances in the universe? • If we know how fast light can travel from a particular distance, (the

Sun), we can apply this to other objects in our universe.

Videos• http://www.youtube.com/watch?v=ewGsiUPeBD4

• http://www.youtube.com/watch?v=yaX4iGw-b_Y

Light Year Model

•Light Year Model

Warm Up

Big Bang Theory

• What is a theory? •Theories are the most accepted explanation, based on information from research.

• What is the theory of the Big Bang? •This theory is based on the observation that other galaxies are moving away from our Milky Way galaxy at great speeds in all directions. 

Hubble Space Telescope• http://www.youtube.com/watch?v=tFC403WByiA

Big Bang Theory• Why do some scientists believe that the

universe is expanding? • It is based on the idea that galaxies are moving away

from us.

• Why do scientists revise theories? • Theories can change if the evidence supports the change.

Big Bang Theory• Big Bang Research Organizer

Big Bang Theory

• Theories are the most accepted explanation, based on information from research. Theories can change if the evidence supports the change.

• While the Big Bang theory is the most popular and widely accepted theory about the beginnings of the universe and supported by all the observational evidence, there are other theories that explain the evidence equally well. But, until further evidence supports a change, this theory is the currently accepted one.

• You will be researching one of 10 other theories. This handout models the information you will need to gather. You may summarize the information about the description of the theory and the evidence, but try to find all the types of information listed on the sample.

• Please do NOT plagiarize. Paraphrase information in your own words. 

Warm Up

• What is a theory? •Theories are the most accepted explanation, based on information from research.

• Why do scientists revise theories? •Theories can change if the evidence supports the change.

• NO WARM UP• You have until 2:00 to complete your research and

then we will share

Warm Up

• What is the theory of the Big Bang? •This theory is based on the observation that other galaxies are moving away from our Milky Way galaxy at great speeds in all directions. 

Warm Up• Study for your test for the next 5 minutes• Write “Test” on your Warm Up log• After the Test:• Finish your time line• Work QUIETLY