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Earth and Space 6-8 / Week 04 / Sky Night
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Week 04 · Seasons

Sky Night

Sky Night: Sunset check
// A tilted axis that always points the same way
⏱ about 20 min

Sky Night: Sunset Check

Saturday evening, the crew gathers at the Sky Deck spot a few minutes before sunset, exactly where they stood in week 1.

Rocket holds up the week 1 horizon drawing. "The glow was right by the fence post. Where is it now?"

Raven watches the horizon, never the Sun. "Past the post. What do you notice about the direction it moved?"

"Along the fence toward the shed," Rocket says. "Four weeks, about a fence panel."

Nova hovers low. "That is the tilt at work," she says. "Keep marking. By the solstice it will stop and turn back."

The glow fades. No Moon shows above the roof.

"Waning gibbous last Saturday," Rocket says. "Now a waning crescent. It rises before sunrise."

Raven writes "not up" and the date in the Moon log. Nova hums. "Two patterns, one night."

  1. Earth's axis is tilted about 23.5 degrees and points the same direction all year.
  2. When your hemisphere leans toward the Sun, sunlight hits more directly and the Sun stays up longer. That is summer.
  3. The two hemispheres have opposite seasons. Distance is not the cause: Earth is closest to the Sun in January.
  4. A flashlight straight down lights fewer squares brightly. At a slant it lights more squares dimly. That is summer and winter light.
  5. The sunset point moves along the horizon through the year, north of west in June and south of west in December.
◇ FAMILY SUNSET CHECK AND MOON LOG
Stand together at the exact week 1 spot a few minutes before sunset. Bring the week 1 horizon drawing.
Without looking at the Sun, watch where the glow meets the horizon. Mark it on a new drawing beside the old mark.
Agree as a family which direction the sunset has moved and about how far. Write the date beside the mark.
After dark, look for the Moon. If it is up, everyone sketches it and names the phase. If not, write "not up" and the date in the Moon log.
Cloudy night backup: indoors, redo the grid-paper flashlight test and let each person count the squares.
For a grown-up
The Sun is never looked at directly, even low on the horizon, with or without sunglasses, a camera or a phone.
Evening observing happens only with you, from the yard, a porch or a window. Use a known spot and a flashlight for the path.
The recap facts come from OpenStax Astronomy at openstax.org, NASA at science.nasa.gov and the Naval Observatory at aa.usno.navy.mil.
Safety first
Never look at the Sun. Read its position from the glow on the horizon and from the shadows.
Stay in your known spot with a grown-up. Never cross a road or climb anything for a better view.
The flashlight is for the path only, never shone into anyone's eyes.
THINK IT THROUGH
  • Read the question.
  • Tap your answer.
Your sunset mark has moved along the horizon since week 1. What is the cause?
A friend in the Southern Hemisphere says it is summer there. What season is it in the north?
Sky Night checkTrue or false?
The sunset point stays in exactly the same place all year.?
It is safe to look at the setting Sun because it is low.?
The tilt of Earth's axis causes both the seasons and the moving sunset point.?
WHY THIS EXERCISEFour weeks of Sky Log marks have become evidence for the tilt.
Draw tonight's horizon with both sunset marks, week 1 and tonight, and an arrow between them. Add tonight's Moon with its phase name, or write not up.
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