What is an eclipse?
An eclipse happens when one space object gets in the way and its shadow blocks light from reaching another object. Because light travels in straight lines, a shadow forms behind whatever blocks the light. The Sun, Moon and Earth must line up in a straight row for an eclipse to happen.
Key idea
A solar eclipse is Sun–Moon–Earth. A lunar eclipse is Sun–Earth–Moon.
Solar and lunar eclipses
In a solar eclipse, the Moon moves between the Sun and Earth. The Moon's shadow falls on Earth, and the sky can go dark in the daytime. Never look straight at the Sun with bare eyes.
In a lunar eclipse, the Earth moves between the Sun and the Moon. The Earth's shadow falls on the full Moon, so the Moon looks dark. This can only happen at night during a full moon. A lunar eclipse is safe to watch with your eyes because you are only looking at the dim Moon, not the bright Sun.
Eclipses do not happen every month because the Moon's path is a little tilted, so the three objects only line up perfectly now and then. That is why an eclipse is a special event to watch.
Remember
- Eclipses happen because light travels in straight lines.
- A solar eclipse is safe to watch only with proper eye protection.