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Earth and Space 6-8 / Week 03 / Wednesday
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Week 03 · Eclipses

Wednesday

Sky Deck Lab: Shadows that hit and miss
// When the shadows line up
⏱ about 20 min

Wednesday: Sky Deck Lab: Shadows That Hit and Miss

Rocket sets the big ball on the table and holds the orange on its pencil in front of it. The lamp glows behind.

"Move the Moon between the Sun and Earth," Raven says. Rocket slides the orange in line. A small dark spot appears on the ball.

"Solar eclipse!" he says. "Only the spot sees it."

"Now swing it around behind," Raven says. Rocket does. The orange darkens in the ball's shadow. "Lunar eclipse."

Nova hovers above. "Now lift the Moon a little higher as it passes," she says.

Rocket lifts the orange a thumb's width. The shadow slides off into the air. Nothing is eclipsed.

"That is most months," Raven says. Nova hums. "A small tilt, a big difference."

Your mission

Today you use last week's model to make a solar eclipse, a lunar eclipse and then a month with no eclipse.

The lamp is the Sun, the big ball is Earth and the small ball or orange on a pencil is the Moon.

Eclipses are modeled indoors in this course. We never watch the real Sun, eclipse or not.

  • A lamp or flashlight on a table, turned on and left in one place
  • A big ball for Earth, set on a book or cup so it does not roll
  • A small ball, an orange or a rolled sock on a pencil for the Moon
  • A dim room, a sheet of paper to catch shadows, and your Sky Log
Safety first
Use a flashlight or an LED lamp. Never touch a lit bulb and keep paper away from it.
Never look straight into the lamp or shine a flashlight into anyone's eyes.
Never look at the real Sun, even during an eclipse, with or without glasses, a camera or a phone.
Clear the floor so nobody trips in the dim light. A grown-up handles any plug.
  1. Set the lamp at one end of the table and Earth about two long steps away. Dim the other lights.
  2. Hold the Moon between the lamp and Earth, in a straight line. Find its small dark shadow on Earth. This is a solar eclipse.
  3. Notice how small the shadow is. Only that spot on Earth sees the Sun covered.
  4. Swing the Moon around to the far side of Earth, in line again. Watch the Moon darken in Earth's shadow. This is a lunar eclipse.
  5. Notice the whole Moon darkens. Anyone on the night side of Earth could see it.
  6. Now orbit the Moon again, but lift it a thumb's width above the line. Watch both shadows miss. This is most months.
  7. Fill in the data table with what each position showed.
PREDICT BEFORE YOU TRY
  • Read the question.
  • Tap your answer.
Which shadow will be bigger: the Moon's on Earth, or Earth's on the Moon?
If you lift the Moon a little as it orbits, what happens?
Moon positionWhose shadow falls whereEclipse typeHow much of Earth could see it
Between lamp and Earth, in line
Behind Earth, in line
Between lamp and Earth, lifted
Behind Earth, lifted

Reading the model

The Moon's shadow on Earth was a small spot. OpenStax says a total solar eclipse is seen only inside a small area under the shadow's tip.

Earth's shadow swallowed the whole Moon. A lunar eclipse is visible to everyone who can see the Moon.

That is why a given place sees lunar eclipses far more often than solar eclipses, even though they happen about as often.

What the model gets wrong: the real Moon is about 30 Earth widths away. The real tilt is only about 5 degrees.

What the model showsTrue or false?
The Moon's shadow covered only a small spot on Earth.?
Earth's shadow could darken the whole Moon.?
Lifting the Moon a little made the eclipses bigger.?
The lunar eclipse happened with the Moon between the lamp and Earth.?
WHY THIS EXERCISEThe standard asks you to use the Earth, Sun and Moon model to explain eclipses.
Which eclipse could the whole night side of Earth see in your model? Type solar or lunar.
WHY THIS EXERCISEEarth's larger shadow is the reason lunar eclipses are seen from so much more of Earth.
Sketch the table from above twice: once with the Moon in line making a solar eclipse, once lifted so the shadow misses.

Both eclipses made and missed. Tomorrow you read a table of how often and how long real eclipses happen.

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