- Why is the Moon sometimes red during a total lunar eclipse?
- This red color, often called a 'Blood Moon,' is caused by Rayleigh scattering of sunlight in Earth's atmosphere. As sunlight passes through our atmosphere, shorter blue wavelengths are scattered away, while longer red wavelengths are bent (refracted) into Earth's umbral shadow, softly illuminating the Moon. This simulator uses schematic colors for clarity but does not model this atmospheric scattering effect.
- If the Sun is so much bigger than Earth, how can Earth cast such a large, dark shadow?
- Earth's shadow appears large because it is a long, tapering cone. While the Sun is enormous, it is also very far away. This geometry creates a shadow cone that is narrow at Earth but extends over a great distance. At the Moon's distance, the umbra's cross-section is still about three times the Moon's width, allowing it to be fully enveloped.
- Why don't we see a lunar eclipse every full moon?
- The Moon's orbit is tilted by about 5 degrees relative to Earth's orbital plane (the ecliptic). Most full moons occur when the Moon is above or below this plane, so it passes north or south of Earth's shadow. Eclipses only happen during a 'syzygy'—when the Sun, Earth, and Moon align nearly perfectly in a straight line, which typically occurs 2-4 times per year.
- What is the difference between a penumbral eclipse and a partial eclipse?
- In a partial eclipse, part of the Moon enters Earth's dark central umbra, creating a distinct, sharp 'bite' out of the lunar disk. In a penumbral eclipse, the Moon only passes through Earth's faint outer penumbra. The dimming is very subtle and often difficult to notice with the naked eye, as the Moon is still illuminated by part of the Sun's disk.