Every month the Moon is new, and every month it is full. Eclipses are rarer than that. The Moon’s path is tilted about 5° to the plane of Earth’s path around the Sun, so the Moon usually passes above or below the lineup. Slide away from a node — the crossing — and the shadow misses. Pair with the Moon phase dial and with seasons, which is a different tilt: Earth’s axis, not the Moon’s orbit.
Educational schematic — not an eclipse prediction and not a map of who stands in the shadow. The Sun, Earth, and Moon are enlarged, the gaps are compressed, and the 5° tilt is drawn steeper so the miss is readable on a phone. Umbra and penumbra are a cartoon. No dates for upcoming eclipses live on this page.
Interactive · Side view
Sunlight from the left · slide the offset · 0° is a node
Umbra · inner shadow
Penumbra · outer shadow
Node · the crossing
0°
Literacy · words for the shadow
Umbra
The dark inner shadow, where the light source is completely blocked. In a solar eclipse, people in the Moon’s umbra see a total eclipse. In a lunar eclipse, the Moon in Earth’s umbra is a total lunar eclipse — often reddish, because sunlight bends through Earth’s air. NASA describes both.
Penumbra
The lighter outer shadow, where the light source is only partly blocked. On Earth that is a partial solar eclipse. If the Moon only crosses Earth’s penumbra, the eclipse is penumbral: a slight dimming, easy to miss. The diagram labels that pale band when the Moon is in it.
Node
One of the two places the Moon’s tilted orbit crosses the plane of Earth’s orbit. Eclipses happen near a node. Everywhere else, new Moon and full Moon still occur, and the shadow misses. The slider’s 0° mark is that crossing.
Eclipse season
A stretch of weeks, about twice a year, when the Sun is near a node and a new or full Moon can line up. NASA names these eclipse seasons. They are not the same thing as a synodic month.
Solar eclipse
New Moon, near a node: the Moon’s shadow falls on Earth. The umbra is total; the penumbra is partial. NASA’s types page also describes annular and hybrid eclipses, which depend on the Moon’s distance and Earth’s curve. This slider holds distance fixed, so it does not draw the ring of Sun.
Lunar eclipse
Full Moon, near a node: the Moon passes through Earth’s shadow. Deep in the umbra is total, a bite of the umbra is partial, and the penumbra alone is penumbral. NASA notes the lineup happens anywhere from four to seven times a year — not twelve.
Sources · public NASA education
Cited, not invented
NASA Science — Why do eclipses happen? — solar eclipses at new Moon; umbra (Sun completely blocked) and penumbra (partly blocked); the Moon’s orbit is tilted by about five degrees, so the shadow usually misses Earth; eclipse seasons are the two times a year when a new Moon can cross the Earth–Sun plane.
NASA Science — Eclipses and the Moon — the tilt is why eclipses are occasional instead of monthly; lunar umbra, partial umbra, and penumbra; the Moon’s shadow on Earth is only about 300 miles (480 km) wide; anywhere from four to seven eclipses a year.
NASA Science — Types of solar eclipses — total, annular (Moon near its farthest, a ring of Sun), partial, and hybrid; eclipse seasons twice a year; lunar eclipses at full Moon, sometimes turning the Moon red. Safe viewing: except for the brief totality of a total solar eclipse, use eclipse glasses or a pinhole projector.
Fred Espenak, NASA GSFC — Periodicity of lunar eclipses — orbit inclined about 5.1°; nodes; a full Moon within about 17° of a node can bring a lunar eclipse; synodic month 29.53 days; eclipse-season midpoints 173.3 days apart; nodes regress westward by 19.3° per year.
The slider is a classroom picture of “on the node” versus “about 5° off,” with the tilt exaggerated on screen. It is not Espenak’s 17° window, and it does not predict a date, a magnitude, or a city. Kilometer and mile figures are the ones NASA publishes on the pages above. Earthrise preview: NASA / Bill Anders (public domain).