S8-GU1L1-HOL - Distance In The Universe

Distances In The Universe

S8-GU1L1-HOL

Multiple Choice

The diameter of Jupiter is about ten times Earth’s diameter. How many Jupiters would it take to cross the sun?

• 10

• 9

• 8

• 20

It would take about ten Jupiters to cross the sun’s diameter.

• The diameter is the distance from one point on the surface of Earth, through the center, and to the other side.

• Earth is actually wider at the equator (12,756 kilometers) than from pole to pole (12,715 kilometers). 

What are some other units of length for very small distances?

• There are a thousand micrometers to a millimeter, and a million nanometers in a millimeter.

• When measuring something that is about the size of an atom, many scientists prefer to use the ångström, which is equal to 0.1 nanometer.

What are some other units of length for very large distances?

• The astronomical unit, or AU, is the average distance between Earth and the sun.

• A light year is the distance that light travels in one year, about 10 trillion kilometers. 

About how far is Earth from the sun in astronomical units?

While the distance between Earth and sun varies throughout the year, the average distance of Earth to the sun is one astronomical unit (AU). That is the definition of an astronomical unit. 

About how far is Earth from the sun in light years?

• It takes light 8.3 minutes to travel the distance between the sun and Earth, so you could say that Earth is 8.3 light minutes from the Sun.

With each change in view, the image zooms out to show a larger view of space. What does that do to the scale? 

• The scale of each image changes. The more of space we see, the larger the scale.

When you have a scale model of a car, what does that mean?

• Usually scale is written as a ratio.

• Something that is full scale is referred to as one to one, or 1:1.

• This means that one unit on the object equals one unit on the model.

• A 1:64 scale model car means that one millimeter on the model equals 64 millimeters of the real car.

Make A Prediction

Open Ended

How will you compare sizes and distances in space, from the size of the earth to the distance between galaxies? How will you determine why different units are used to measure these distances?

Did you set a goal and include these steps?

• Observe different views of space, from earth to the nearest galaxy.

• For each view use the distance measurement tool to measure the size of the object or the distance between two objects in space.

• record the distance and the unit of measurement in the table.

Why might you want to know how far Mars was from Earth?

• If you want to know how long it takes for a space probe to get from Earth to Mars, and you know how fast the space probe can travel, you need to know how far Mars is from Earth to figure out how long it will take.

• Once the space probe is there you would also want to know how much time it will take to send instructions and to receive data.

• Even though radio travels at close to the speed of light, it takes over ten minutes to receive a message, and another ten minutes to send a response. 

Learning Alert

Is the moon slowly getting closer to Earth because of Earth's gravity?

• Actually, because Earth spins so much faster than the moon, its gravity transfers some energy to the moon, so it moves into a higher orbit, and Earth slows down.

• The moon's distance from Earth increases about 38 millimeters per year, and during the same period of time Earth's day gets about 15 microseconds longer. 

What different units of measure will you use in space? 

• Kilometers are useful for objects relatively close to each other, like the distance between the moon and Earth, or between planets.

• Astronomical units are helpful to visualize longer distances in the solar system.  

• Light-years are best when discussing the distance between stars and galaxies.

What is a parsec?

• A parsec is an astronomical unit that equals about 3.6 light-years.

• It is based on the difference in the angle between two measurements of the position of a star in the sky.

• Most astronomers prefer to use light years instead of parsecs.

What might you want to measure in space?

• It would be interesting to know how far the space station is from Earth, or the distance to the nearest start, or how long it takes light to travel from another galaxy. 

Learning Alert

Why isn't Pluto included in this investigation of the distances between planets in the solar system? 

• In 2006 the International Astronomical Union (IAU) reclassified Pluto as a dwarf planet, which is defined as "a celestial body orbiting the sun that is massive enough to be rounded by its own gravity but has not cleared its neighboring region of planetesimals and is not a satellite."

• They took this decision because many objects outside the orbit of Neptune resembled Pluto in structure — and one, named Eris, was even the same size. 

Experimental Assumption

The distance you are measuring between each planet and the Sun is actually the average distance between the two. In fact, this distance can vary by many kilometers as planets move in their orbits. How can you explain this difference?

• The planets' orbits appear circular in this model, but they are actually elliptical.

• The shape of this ellipse varies among the planets, but most are slight enough that they appear circular in a model this small.

• Note that the planets' orbits do appear elliptical in the model showing Eris, the farthest dwarf planet.

• That's because Eris orbits the sun on a different plane than the eight planets. This model shows the view directly above Eris' orbit.

• To see this view, the orbits of the inner and outer planets appear at an angle, rather than from above. 

Open Ended

How does the size of earth and the sun compare to distances in the solar system, between stars, and between galaxies? Why are different unit of measurement used to describe these distances?

Answer:

• The size of Earth and sun is tiny compared to distances in the solar system.

• The solar system is tiny compared to distances between stars and galaxies. As you move out into space, distances increase dramatically.

• We measure the size of stars and planets in kilometers, distances in the solar system in AU and greater distances in light-years.

• In kilometers, these numbers would be incredibly large and hard to compare.

End of presentation

to be continued