Moon Phases Quiz

Moon Phases

• The moon's orbit is tilted by 5 degrees, which is why lunar eclipses happen.
• A solar eclipse happens when the moon blocks the sun.
• A lunar eclipse happens when the earth blocks the sun, casting a shadow on the moon.
• New Moon: Unlit side faces the earth, rises with the sun, sets with the sun, not easily visible.
• Waxing Crescent: 3-4 days after the new moon, rises about 3 hours after the sun, sets 3 hours after the sun.
• Waxing Quarter: 1 week after the new moon, lit from the side, rises around 6 hours after the sun, sets around 6 hours after the sun.
• Waxing Gibbous: 10-11 days after the new moon, rises around 9 hours after the sun, sets around 9 hours after the sun.
• Full Moon: Two weeks after the new moon, only time when a lunar eclipse can occur, rises around 12 hours after the sun, sets around 12 hours after the sun, visible most of the night.
• Waning Gibbous: 10-11 days before the new moon, rises around 3 hours before the sun, sets around 3 hours after the sun.
• Waning Quarter: 1 week before the new moon, rises around 6 hours before the sun, sets around 6 hours after the sun.
• Waning Crescent: 2-4 days before the new moon, rises around 3 hours before the sun, sets around 3 hours after the sun.

Solar Eclipse

• Happens when the new moon crosses the ecliptic plane.
• Occurs rarely due to the moon's tilted orbit.
• Only casts a shadow on a small part of the earth.

Lunar Eclipse

• Happens when the full moon crosses the ecliptic plane.
• Can be seen from anywhere on earth.
• More common than a solar eclipse, since the earth has a larger shadow.

Limitations of Moon's Orbit Simulation

• Size of the sun and orbits are not to scale.
• The tilt of the moon's orbital plane is incorrect.
• The moon's rotation axis should be slightly tilted relative to its orbital axis.
• The orbit should be perturbed ellipses, not circles.
• The positions of the sun and earth should be affected by other objects in the solar system.
• Orbits should not be centered on the sun or earth.
• The orbital plane of the moon should precess around every 18 years.

Astronomy Before Copernicus

• Observations:
  • The sun, moon, and stars rise and set every day.
  • The earth feels fixed.
  • The stars seem to be unchanging.
  • Everything falls to the earth.
  • Planets experience retrograde motion.
• Conclusions:
  • The earth is the center of the universe.
  • Everything revolves around the earth in circles.
  • The planets move in circles within circles.
• Assumptions:
  • The heavens are perfect and incorruptible.
  • Circles are perfect.

The Geocentric Universe

• The earth is the center of the universe.
• All celestial objects revolve around the earth.

Nicolaus Copernicus

• Catholic/Canon scholar.
• Diplomat.
• Economist.
• Translator.
• Proposed a different idea:
  • The sun is the center of the universe.
  • Planets orbit the sun in circles.
  • The moon orbits the earth.

Apparent Retrograde Motion

• Earth orbits faster than Mars.
• As the earth passes Mars, the position of Mars on the sky, compared to background stars, changes.
• This explains retrograde motion.

Tycho Brahe

• Danish nobleman.
• Had his own island and observatory.
• Exiled for political reasons.
• Made extremely precise measurements of the motion of Mars.
• Observed a supernova.
• Used parallax to constrain the distance to objects.
• His data revealed problems with existing models.

Johannes Kepler

• Worked with Tycho Brahe's data.
• Concerned about the inaccuracy of models for theological reasons.
• Discovered a fix for Copernicus' model.
• Kepler's First Law: The orbit of each planet about the sun is an ellipse with the sun at one focus.
• Kepler's Second Law: A planet moves faster in the part of its orbit nearer the sun and slower further from the sun, sweeping out equal areas in equal times.
• Kepler's Third Law: More distant planets orbit the sun at slower average speeds, obeying a precise mathematical relationship.