- Heliocentric - “Referring to the sun. A heliocentric orbit is one based on the sun as one of the two foci of the (elliptical) orbit (or as the center of a circular orbit); a heliocentric magnitude is the brightness of an object as would be seen from a heliocentric distance of 1 AU (which means a distance of 1 AU from the sun).”
- Heliopause - “The point in space at which the solar wind meets the interstellar medium or solar wind from other stars.”
- Heliosphere - “The space within the boundary of the heliopause containing the Sun and the Solar System.”
- Homogeneous - “The same at all locations. Homogenized milk is not separated into cream and milk.”
- Hot Big Bang - “A model of the Universe beginning at very high density and temperature, which expands and cools to become like the Universe we observe now.”
- Hot Dark Matter - “A type of dark matter that was moving at close to the speed of light 10,000 years after the Big Bang.”
- Horizon - “The edge of the visible Universe, but not the edge of the Universe since the Universe has no edge.”
- Hydrogen - “An element consisting of one electron and one proton. Hydrogen is the lightest of the elements and is the building block of the universe. Stars form from massive clouds of hydrogen gas.”
- Hubble Constant - “or Ho, the ratio of velocity to distance in the expansion of the Universe, so v = HD. The “o” [pronounced “naught”] on Ho means the current value, since the Hubble “constant” changes with time (but it is the same everywhere in the Universe at a given time). The measured value of Ho has also changed dramatically since even before Hubble’s work, as shown in Huchra’s Ho history.”
- Hubble’s Law - “The law of physics that states that the farther a galaxy is from us, the faster it is moving away from us.”
- Hydrostatic equilibrium - “A state that occurs when compression due to gravity is balanced by a pressure gradient which creates a pressure gradient force in the opposite direction. Hydrostatic equillibrium is responsible for keeping stars from imploding and for giving planets their spherical shape.”
- Hypergalaxy - “A system consisting of a spiral galaxy surrounded by several dwarf white galaxies, often ellipticals. Our galaxy and the Andromeda galaxy are examples of hypergalaxies.”
Posted on Tuesday, August 7, 2012 | 114 notes
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