▪absolute magnitude- The actual brightness of an object if it were at a standard ten parsec distance. We can know the absolute magnitude of a star if its physical characteristics are known. The difference between absolute and apparent magnitude can be used to calculate the distance to an object.▪albedo - The reflectivity of a solid object, on a scale of 0 to 1. Snow has an albedo of essentially 1.0 whereas coal would have an albedo near 0.▪annular - referring to a type of solar eclipse. When the Moon is too far away in its elliptical orbit to completely cover the Sun, we see an annular eclipse where a ring of light from the photosphere remains. The sky does not darken dramatically and all of the other fun things about a total solar eclipse do not occur.▪aphelion - For a body orbiting the Sun, aphelion is that point where it is farthest from the Sun. All objects orbit in paths that are ellipses, not circles.▪apogee - the point at which an object is farthest from the Earth as it orbits in an ellipse around our planet. ▪apparent magnitude - The brightness of a celestial body as seen by an observer on Earth. The magnitude system used by astronomers is a ranking system, so smaller numbers mean brighter objects.▪asterism - A small group of stars that forms a simple geometrical pattern. The Big Dipper is a well-known asterism that is formed by the seven brightest stars of the constellation of Ursa Major.▪astronomical unit- The average distance between the Sun and the Earth. It is our unit of distance for orbits in our solar system. One A.U. is about 147 million kilometers.