The umbra is the innermost and darkest part of a shadow, where light is completely blocked by an object. In the context of astronomy, the umbra is often observed during a solar eclipse, when the Moon's shadow is cast on the Earth.
Detailed Definition:
The Umbra is the innermost and darkest part of a shadow. It is the area where light is completely blocked by an object, such as a planet or moon. When a celestial body, passes between a star and another celestial body, it can cast a shadow on that body. The umbra is the part of the shadow that is directly behind the blocking body. The lighter part of the shadow - penumbra, is the area where only part of the light is blocked. The umbra and penumbra can be observed during a solar eclipse, when the Moon's shadow is cast on the Earth.
Etymology:
Umbra (Latin) - shadow
Sample Sentence(s):
"Terms "umbra" and "penumbra" are not limited to celestial bodies, they occur in shadows of everyday objects."
"During solar eclipse, when an observer stands in umbra, dusk seems to set from all directions on the horizon at once."
