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Size and Scale of the Earth and Moon

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Size and Scale of the Earth and Moon
It’s one thing to see a picture of the relative size of the Earth and Moon, but it’s more memorable to feel it, and measure it! For this activity you need a fairly large room or a hallway where the workshop participants can stand during the second step.
Break the group into pairs. Have each pair of students select 2 different balls that they think represent the relative size of the Earth and the Moon. Ask each pair to hold their models in the air so all can compare. Reveal that the moon is actually about ¼ the diameter of the Earth. Ask students to choose new balls in the correct ratio of sizes. About 4 of the small Moon balls will be able to fit across the larger Earth balls.

Now, ask the pairs to stand where they think the Moon and the Earth are relative to their sizes. Once every group has made a prediction, reveal that the Earth is actually 30 Earth distances away from the Moon! Measure the diameter of each student’s Earth and multiply that by 30. Use the tape measure to indicate where each student should actually stand.

Size and Scale of the Universe Interactive
This video starts at the Dudley Library in Roxbury and zooms out through the universe, stopping at certain points along the way. Whenever you see a question mark in the video, it can be fun to pause and have participants guess what they think the number should be. When everyone has made a prediction, press play and see who was closest!



Length of the Dudley Library from front to back

150 feet

Distance Across Roxbury

Number of Libraries across:

2 miles (10,560 feet)


Diameter of Earth

Number of Massachusetts across:

7,930 miles


Distance from the Earth to the Moon

Number of Earths the can fit between them:

238,900 miles


Distance from the Sun to Neptune

Number of Earths between Sun and Neptune

2 billion miles


Distance across the Milky Way Galaxy

Number of Solar Systems across:

600 quadrillion miles

200 million

Vocabulary Game: Jump Up!
Give the same vocabulary cards to students on 2 teams. The first student with the correct card to jump up and say the vocabulary word gets a point. Here is a vocabulary card template.







Exposure Time






Our Solar System



Milky Way





False Color Table




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Image Show and Tell plus Astronomy Information
Use this information to talk to participants about images they’ve requested and processed!

What's Out There?

Notes, Description

Where in the Universe?

Size Range

Note: 1 light year = 10 trillion (10^12) kilometers

Notes about telescope observing

The "Bit Players"





These objects (including our own Earth) are the left-overs from star formation… they orbit their parent star. They don't glow with their own visible light, but reflect the light of their star.

There are eight planets, some dwarf planets and oodles of comets and asteroids in our own solar system, here on the outskirts of the Milky Way Galaxy.

Using special telescopes and instruments, astronomers have discovered nearly 200 other stars with "Bit Players" -- planets -- circling them as well. The big question: are any of them a host for living organisms?

Bit Players can range from fist and house-size (asteroids) to Jupiter-size (around 10 times Earth's diameter, or 70,000 km). Much bigger and they no longer qualify as "bits" -- If Jupiter were much larger, it's gravity might cause it to start glowing on it's own to become a star!

As they orbit our Sun, solar system objects move around with respect to the far-away background stars, so you'll need to use the pull-down pointing menu, or, for comets and asteroids, look up the coordinates for the exact time you want to observe.

Because they are relatively close and reflect the Sun’s bright light, exposure times for the moon and planets will be short.

The Stars


Double stars

Clusters of Stars

These are the main source of visible light in the universe! Sunlight is starlight.

The inward force of a star's great gravity causes nuclear fusion at its core--the source of a star's light & energy. Optical telescopes like Micro-Observatory are starlight recorders.

All the stars you see in the night sky, and all the stars you will observe with your on-line telescopes, are located outside our Solar System but inside our Milky Way Galaxy. The closest stars you will observe will be several light-years away; the farthest star clusters will be halfway across our Galaxy tens of thousands of light years away.

Active stars (nuclear fusion in cores) range in size from a few hundred thousand km (our Sun is 700,000km) to a few million km. But even the largest stars are so far away that their apparent diameter is too tiny to resolve in most telescopes. Star clusters, however, range from a few light years across to hundreds of light years across.

Most stars and star clusters will require an exposure time of 10 to 20 seconds.

Stars come in different colors, which you can investigate by taking images through different colored filters.

What's Out There?

Notes, Description

Where in the Universe?

Size Range

Note: 1 light year = 10 trillion (10^12) kilometers

Notes about telescope observing


Clouds of gas and dust

Star birthplaces (e.g. Orion Nebula)

Stellar graveyards (e.g. Crab Nebula)

Nebulae are the great chemical recycling centers of the universe. Huge clouds of dust particles and gas molecules collapse under gravity to form new stars. Meanwhile, dying stars spew out their newly formed chemical elements in gentle puffs (e.g., the Ring Nebula) or in violent explosions (supernovae). The atoms of carbon and calcium that make up your skin and bones were once in a great interstellar cloud at the beginning of the Solar System.

Nebulae, like the stars, are distributed around our Milky Way galaxy, beyond our own Solar System. Most nebulae seen through your on-line telescopes will range from hundreds to thousands of light years away.

These clouds of gas and dust can range from a light year across to tens of light years. Typically star-forming clouds are bigger than the star-death remnants of supernovae or "planetary" nebulae.

Unlike stars, nebulae don't glow as a result of nuclear fusion. Rather they shine in one of 2 ways: they either scatter or reflect the light of nearby stars; or they absorb ultra-violet light from the nearby stars and "fluoresce" like a glowing neon gas lamp.

Because nebulae are mostly made of Hydrogen, and hydrogen glows with a red color, you'll find that nebulae are often brighter through the red filter than through the blue. Use long exposure times to gather the faint light from these diffuse cloudy objects.





Galaxy clusters

These cosmic cast members could also be called the "Hollywoods of the Heavens" — they are huge cities of hundreds of billions of stars.

Everywhere! Our own Milky Way Galaxy (which we cannot see from the outside since we are inside) is but one of billions of galaxies that appear to populate the cosmos all the way out to the very limits of the observable universe!

While galaxies had been observed since the invention of the telescope, it was only in the 1920s that we realized they were huge islands of stars outside our own galaxy.

Galaxies are VERY big, averaging about 100,000 light years across (that's 10^17 kilometers).

Because galaxies are very far away (millions to billions of light years) -- they are dim, so you'll need long exposure times.

When you see an image of a galaxy, you're seeing the combined light of billions of stars, but our telescopes can not resolve individual stars. In fact, at the scale of a typical galaxy image (say 2 inches across or 100 pixels), a single star would be much smaller than an atom!

Exotic stuff

Black holes, Quasars, Pulsars

These weird members of the cosmic stage are often special cases of stars or galaxies….

Found in our own galaxy as well as others

Stellar sizes to galactic sizes

Hard to observe with online telescopes.

Kinesthetic Life-cycle of Stars




Star-forming Nebula
[Gravity rules.]

A cloud of gas and dust forms many stars. A single star is created when clumps of this material (mostly hydrogen gas) are pulled together by the force of gravity.

Students, scattered randomly throughout the room, point in the direction where “the most other clumps” are, and slowly make their way to that point.

Birth of the Star (Protostar)
[Gravity rules. Fusion begins.]

As a region of the cloud collapses, gravity pulls the clumps of gas together. The gas in the center becomes hot enough and dense enough to begin fusion. Hydrogen atoms inside the clumps smash into each other, combining to create helium and releasing light and heat. The star begins to shine.

Students clump together, forming a large ball. Those on the outside (“envelope”) continue to move toward the center. When students on the inside (“core”) start bumping into each other, they face outward.

Life of the Star (Main Sequence)
[Gravity and fusion in balance.]

Fusion in the core generates an outward force to balance the inward gravitational force from the outer layers.

Core students and envelope students gently push against each other, palm-to-palm, elbows bent, balancing. There should be one or two envelope students per core student.

Red Giant
[Fusion overtakes gravity.]

As the core nears the end of its fuel supply, the outer layers continue to push inward, increasing the temperature in the core. This produces a new series of fusion reactions that produce enough outward force to overpower the inward gravitational force and expand the star.

Core students fully extend their arms, pushing the envelope students backwards, expanding the star.

Death of a Low-Mass Star (Planetary Nebula with White Dwarf)
[Fusion ends; gravity wins.]

As the core runs out of fuel for fusion, it emits one last push outward, ejecting the star’s outer layers, which drift away into space. The core then contracts under its own gravity, forming a white dwarf.

Core students push the envelope outward then move together into a tight blob at the center. The envelope students, in a ring-like shape, drift away from the core.

Death of a High-Mass Star (Supernova, with Neutron Star or Black Hole)
[Fusion ends; gravity wins.]

The massive core continues to fuse elements and expands the star so it is even larger. Once the core runs out of fuel, it collapses to form a neutron star. The outer layers then collapse as well. As material falls toward the star’s center, it bounces off the core and explodes outward through the star. This explosion is called a supernova. In the most massive stars, the collapsed core will become a black hole.

Core students extend their arms, expanding the star. Then, they stop pushing and scrunch together at the star’s center. Envelope students rush inward, and bounce off the packed- together students in the core, exploding outward dramatically, revealing the collapsed core.

To transition between the deaths of low- and high-mass stars, facilitators must rewind the clock, to the original star-forming nebula or to the main sequence stage. Recreating all stages of the activity up to the red giant phase, from students’ memory, is most effective because it highlights the parallel paths of the two stars and allows students to review and teach back what they have learned.

Jeopardy Game







An instrument that makes a far away object look nearer by collecting and focusing light. Allows us to see more details that we can see with our eyes only.

What is a Telescope?


A type of telescope that uses lenses to collect and focus light.

What is a refractor or refracting telescope?


A type of telescope that uses mirrors to collect and focus light.

What is a reflector or reflecting telescope?


The part of a reflecting telescope that reflects and focuses light.

What is a mirror?


The part of a telescope that opens and closes to let light shine through.

What is the shutter?

Our Solar System


Made of our one star the Sun, and all the planets and their moons which orbit the Sun.

What is our Solar System?


A chunk of material (usually rock) that travels in a circle around a planet.

What is a moon?


A chunk of material (can be rock or gas) that travels in a circle around a star.

What is a planet?


A massive ball of gas that shines brightly because of the huge amount of energy that is produced inside it.

What is a star?


A force that pulls all things together.

What is gravity?

The Universe


A huge explosion that releases gas and dust. One of the ways a massive star can end its life.

What is a supernova?


A giant cloud of gas and dust.

What is a nebula?


A collection of many billions of stars, gas and dust (including nebulae), all held together by the force of gravity.

What is a galaxy?


Earth and our solar system are part of this galaxy. All the stars visible in the night sky are part of our ‘home’ galaxy.

What is the Milky Way?


Made of billions of galaxies. All the galaxies you could see are part of it.

What is the Universe?



The opening in a telescope through which light enters.

What is the aperture?


The amount of light that was collected by the telescope from part of an object. Measured as “pixel value” from an image using MicroObservatory Image software.

What is brightness?


The range of brightness (pixel value) that we choose to display in an image. We don’t HAVE to display the WHOLE range of brightness in an image.

What is contrast?


The part of a telescope that collects the focused light and records it as an electronic image.

What is the detector?


The amount of time that the shutter stays open.

What is exposure time?

Image Processing


Short for “picture element.” The smallest square portion of an electronic image where light was collected by each part of the detector.

What is a pixel?


A tool that uses colors to represent the brightness of pixels in an image.

What is a false color table?


Extra brightness in an image that did not come from light from an object, usually from the detector electronics.

What is noise?


A tool that makes clearer the edges between nearby regions of high and low brightness.

What is sharpen?


A tool that takes away the parts of an image around a chosen area.

What is crop?

Materials: index cards cut into 1/3, pencils
Goal: Students will need to create captions for their exhibits, and it can sometimes be difficult to come up with descriptions for an image. Astro-Poetry is a good way to come up with a compelling caption, and practice observation and description.

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