The apparent magnitude of a celestial object is a number that is a measure of its brightness as seen by an observer on Earth.
A constellation is a group of stars that are considered to form imaginary outlines or meaningful patterns on the celestial sphere, typically representing animals, mythological people or gods, mythological creatures, or manufactured devices.
In astronomy, an epoch is a moment in time used as a reference point for some time-varying astronomical quantity, such as the celestial coordinates or elliptical orbital elements of a celestial body, because these are subject to perturbations and vary with time.
Hydra is the largest of the 88 modern constellations, measuring 1303 square degrees.
A star is type of astronomical object consisting of a luminous spheroid of plasma held together by its own gravity.