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- Habitable
- a place that is suitable for life to exist.
- Habitable Zone
- the region of space in a solar system that scientists believe would be suitable for life.
- Hack
- in computer science, hacking means to take advantage of a weakness in a computer system to bypass its normal operations. Sometimes hacking can be beneficial by making the system do more than it was designed to or it can be harmful if it stops the system from doing what it was meant to do.
- Hadron
- baryons and mesons together are categorized as hadrons. These are particles made of quarks.
- Hard X-rays
- the highest energy X-rays are commonly referred to as “hard” X-rays; the energy of these X-rays is typically above 10 keV.
- Helium-3
- He-3, which is used in nuclear fusion research, is rare on Earth. He-3 has 2 protons and 1 neutron. Some scientists have speculated that it could be used as a source of fuel for future spaceships.
- Helium-4
- the most common form of helium, making up 9,999 of every 10,000 helium atoms; it has two protons and two neutrons in its nucleus. A bare He-4 nucleus (stripped of its two electrons) is sometimes called an alpha-particle
- Higgs Boson
- according to the Standard Model of Particle Physics (the most complete and accurate model we have of elementary particles), the Higgs boson is responsible for giving the other particles mass. The Higgs was detected in 2012 and verified a few years later.
- Homogeneous
- looks the same from every location.
- Hydroponics
- growing plants with their roots suspended in a nutrient rich solution rather than soil.
- Hydrostatic Equilibrium
- hydrostatic equilibrium in stars is the state in which the inward force of gravity is balanced by the outward force of the pressure inside the star, thus making the star stable against collapse or expansion. The pressure is due to the hot gas and the radiation, and each contributes different amounts to the total pressure depending on both the type of star and on what region of the star is being considered.
- Hypergiant
- these are the biggest stars in the Universe, more than 100 times the mass of our Sun and with up to millions of times its brightness. These stars are so bright that they burn through their fuel quickly, causing them to have short lifespans of only a million years or so. In comparison, our Sun’s lifespan is about 10 billion years.
- Hypernova
- the explosion of an extremely massive star at the end of its lifetime. The explosion is triggered when the star exhausts the nuclear fuel in its core and can no longer support itself against gravity. Hyperrnovae can liberate hundreds of times the energy of a supernova.
- Hypernova Remnant
- the expanding cloud of material ejected by the star during a hypernova explosion.
- Hypothesis
- a testable prediction about how something works based on the observations you have initially made.
