A partial solar eclipse happens when the Moon passes between Earth and the Sun, but they do not line up perfectly, so the Moon covers only part of the Sun’s bright disk instead of blocking it completely. From the ground, the Sun looks like a bright circle with a dark “bite” taken out of it or like a glowing crescent, depending on how much of the Sun is covered.

What a partial solar eclipse is

  • A partial solar eclipse is a type of solar eclipse where the Moon obscures only a portion of the Sun as seen from Earth.
  • The Sun never goes fully dark in a partial eclipse; daylight just dims somewhat, so the event is less dramatic than a total eclipse.

How it actually occurs

  • Solar eclipses can only happen at New Moon, when the Moon is between Earth and the Sun, but a partial eclipse occurs when that alignment is off-center rather than perfectly straight.
  • Because the Moon’s orbit is tilted about 5 degrees relative to Earth’s orbit, most New Moons miss the Sun; a partial eclipse occurs when the New Moon passes near, but not exactly on, the line of perfect alignment.

Shadows: penumbra vs umbra

  • The Moon’s umbra is its dark inner shadow, where the Sun is completely blocked; people inside this region see a total solar eclipse.
  • A partial solar eclipse is seen from the broader penumbra , where the Moon blocks only part of the Sun, so the Sun looks partly covered rather than fully hidden.

What you see from different places

  • People directly under the umbra’s path (if it reaches Earth) may see a total eclipse, while those to the side in the penumbra see only a partial eclipse at the same time.
  • Some eclipses are “only partial” for everyone on Earth, when the umbra passes above or below the planet and never touches the surface, so the entire visible event is partial.

Simple step-by-step picture

  1. The Moon reaches its New Moon phase and moves between Earth and the Sun.
  1. The alignment is imperfect, so the center of the Moon’s disk does not cross the center of the Sun’s disk.
  1. The Moon’s penumbra falls on part of Earth, and observers inside that zone see the Moon take a “bite” out of the Sun.
  1. As the Moon continues along its orbit, the covered portion of the Sun grows to a maximum and then shrinks until the Sun looks normal again.

Information gathered from public forums or data available on the internet and portrayed here.