| Term | Definition | Contributor | Modified |
|---|---|---|---|
| Hoosier (Nickname) | No definition provided | Christopher Rauch | 2023.12.01 |
| Hopeite | No definition provided | Ryan McGranaghan | 2023.04.16 |
| Hope (Privateer) | No definition provided | Christopher Rauch | 2023.12.01 |
| Hop flea-beetle | No definition provided | Christopher Rauch | 2023.12.01 |
| Hopi Indians | No definition provided | Christopher Rauch | 2023.12.01 |
| Hopi Indians--Art | No definition provided | Christopher Rauch | 2023.12.01 |
| Hopi language | No definition provided | Christopher Rauch | 2023.12.01 |
| Hop industry and trade | No definition provided | Christopher Rauch | 2023.12.01 |
| Hops | No definition provided | Christopher Rauch | 2023.12.01 |
| Hops--Diseases and pests | No definition provided | Christopher Rauch | 2023.12.01 |
| Hops--Pests | No definition provided | Christopher Rauch | 2023.12.01 |
| Horae (Books of hours) | No definition provided | Christopher Rauch | 2023.12.01 |
| horizon | No definition provided | Ryan McGranaghan | 2023.04.16 |
| HorizonCoordinateSystem | altazimuth coordinate system or horizon coordinate system, astronomical coordinate system in which the position of a body on the celestial sphere is described relative to an observer's celestial horiz on and zenith . The coordinates of a body in this system are its altitude and azimuth . Altitude is measured from the celestial horizon along the vertical circle through the body and the zenith of the observer. Azimuth is measured along the celestial horizon from the observer's south point (the point on the horizon directly south of him) to the point where the body's vertical circle intersects the horizon. Because the earth rotates on its axis, the altitude and azimuth of a celestial body are constantly changing. | Ryan McGranaghan | 2023.04.16 |
| Horizon, Dip of | No definition provided | Christopher Rauch | 2023.12.01 |
| horizontal | The fault is horizontal | Ryan McGranaghan | 2023.04.16 |
| Horizontal | Parallel to or in the plane of the horizon ora base line. | Ryan McGranaghan | 2023.04.16 |
| Horizontal bar | No definition provided | Christopher Rauch | 2023.12.01 |
| Horizontal branch | A set of roughly horizontal points in the Hertzsprung-Russell diagram of a typical globular cluster. It displays a stage of stellar evolution which immediately follows the red giant branch (RGB) in st ars with an initial mass < 1.2 M_sun. When the star's ascent of the RGB is terminated by the helium flash, it moves down to the Horizontal Branch (HB). The star's effective temperature on the HB is higher than it was on the RGB, but the luminosity is considerably less than at the helium flash. Usually HB stars have two energy sources: in addition to the helium burning in their cores, they experience hydrogen fusion in a surrounding shell. The thickness of the shell determines the color of the HB stars. A thin shell, involving low opacity, makes the star look blue. The HB domain encompasses a very large effective temperature range with several members: extreme HB, blue HB, RR Lyrae, red HB, and red clump stars. The locations depend on many parameters, including stellar mass, metallicity, age, helium abundance, and rotation. | Ryan McGranaghan | 2023.04.16 |
| Horizontal branch stars | A star lying on the horizontal branch. | Ryan McGranaghan | 2023.04.16 |