Daniel ast103_03: Discovering the Universe for Yourself: Supplement

  1. See IAL 3: The Moon: Orbit, Phases, Eclipses, and More.
  2. lunar month = 29.530588861 days (J2000) ≅ 29.53059 days (mean J2000 to 7 digits) ≅ 29.5 days, but see also sidereal month (27.321661554 days: J2000).
  3. The astronomical phase angle subtended at Earth between Moon Sun determine the lunar phases as seen from the Earth and then diurnal rotation of the Earth determines moonrise and moonset. However, one can say moonrise/moonset determine the lunar phases in the same way that an index entry for a thing determines the page of the thing. See Wikipedia: Moonrise and moonset: Time.
  4. Since the Moon 90° west of the Sun, the lunar phase is 3rd quarter moon. All lunar phase questions can be answered by the figure below (local link / general link: moon_phases_calculator.html).

  5. The Moon tidally locked to the Earth.
  6. The eclipse season midpoint every 173.31 days.
  7. Saros cycle (period 6,585.321347 days, J2000) and triple Saros cycle (AKA exeligmos, period 19755.9639 days ≅ 54 years + 33 days, J2000). For solar eclipse paths for the 2001--2040 period illustrated in the two images in the figure below (local link / general link: solar_eclipse_2021_2040.html).

  8. The planets move relative to the stars in regular way. So they are different from stars. Note inferior planets stay close to the Sun in astronomical phase angle, but superior planets can have any in astronomical phase angle from the Sun. This should have been a clue. apparent retrograde motion was another clue.
  9. The lack of observed stellar parallax was an argument against a moving Earth, but this only an argument among the ancient Greek astronomers and NOT their main argument. But the main argument as that the Earth seems to be at rest and rest and motion were thought of absolutely different NOT relative states. You knew when you were moving and when at rest---or so it seemed the ancient Greek astronomers and everyone else way back.
  10. For Aristarchos of Samos (c. 310--c. 230 BCE), see the figure below (local link / general link: aristarchos.html).

    It's reasonable to guess, that Aristarchos was led to heliocentrism by the same reasons that led Copernicus.

    We'll discuss those reasons below in the section Nicolaus Copernicus (1473--1543) and Heliocentrism.