Eclipses
Run the real Sun and Moon from 2000 to 2050. Most new and full moons miss: find the ones that line up, and see each shadow to scale.
Total solar eclipse. Greatest at 17:46 UTC.
Total solar eclipse now.
What students walk away with
- 1A solar eclipse is the Moon's shadow on Earth, at new moon. A lunar eclipse is the Moon in Earth's shadow, at full moon.
- 2The Moon's orbit is tilted about 5 degrees, so most new and full moons pass above or below the shadow. Eclipses come in two seasons a year, when the line-up falls near a node.
- 3The Moon's shadow is small and darkens only part of Earth; Earth's shadow is wide, so all of the night side sees a lunar eclipse.
Standards
- MS-ESS1-1 Patterns of the Earth, Sun, and Moon
Sim. Grades 6 to 12. Question sets for middle school, high school, and upper high school.
How the model works
The sim runs on real dates from 2000 to 2050 and opens on today. The Sun and the Moon come from Jean Meeus's Astronomical Algorithms (the full lunar series of chapter 47). Every eclipse it lists from 2017 to 2035 matches NASA's catalog in date and type, and its times of greatest eclipse agree with NASA's to within a couple of minutes. Times are in UTC.
The Space view is not to scale. The Moon is really about 30 Earth diameters away; here it is drawn about 3. The Moon's orbit is tilted about 5 degrees to Earth's orbit; it is drawn at about 20 so students can see it. The view turns with the Sun, which stays on the left all year, so the line through the nodes is seen swinging slowly round. It lines up with the Sun twice an eclipse year (about 346.6 days), which is why eclipse seasons come about 19 days earlier each year. Shadow cones are not drawn there, since at that scale they would cover the Moon at the wrong times; instead the Moon turns copper, and Earth darkens, exactly when the model says the shadow is on them.
The Shadow view is to scale. For a solar eclipse it looks from the Sun along the Moon's shadow: the dashed circle is the penumbra (a partial eclipse anywhere inside it), the black dot the umbra (total) or antumbra (annular), and the dark band the path of the umbra or antumbra on the ground. For a lunar eclipse it looks from Earth at Earth's shadow, enlarged slightly for the atmosphere as most almanacs do (Danjon's rule).
Left out: the Moon's mountains at its edge, local sunrise and sunset limits on who sees a partial eclipse, and the slow change in Earth's turning (it shifts times by about a minute). Dates outside 2000 to 2050 are not offered.
Run it with a class
Pick the questions, get a class code, and watch answers arrive live. Students need only a first name.
Set up an assignment