In geometry, a solid angle (symbol: Ω) is the two-dimensional angle in three-dimensional space that an object subtends at a point. It is a measure of how large the object appears to an observer looking from that point. In the International System of Units (SI), a solid angle is a dimensionless unit of measurement called a steradian (symbol: sr).
A small object nearby may subtend the same solid angle as a larger object farther away. For example, although the Moon is much smaller than the Sun, it is also much closer to Earth. Therefore, as viewed from any point on Earth, both objects have approximately the same solid angle as well as apparent size. This is most easily observed during a solar eclipse.
Read more about Solid Angle: Definition and Properties, Practical Applications, Solid Angles in Arbitrary Dimensions
Famous quotes containing the words solid and/or angle:
“Every winter the liquid and trembling surface of the pond, which was so sensitive to every breath, and reflected every light and shadow, becomes solid to the depth of a foot or a foot and a half, so that it will support the heaviest teams, and perchance the snow covers it to an equal depth, and it is not to be distinguished from any level field. Like the marmots in the surrounding hills, it closes its eyelids and becomes dormant for three months or more.”
—Henry David Thoreau (1817–1862)
“It is a mistake, to think the same thing affects both sight and touch. If the same angle or square, which is the object of touch, be also the object of vision, what should hinder the blind man, at first sight, from knowing it?”
—George Berkeley (1685–1753)