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Astronomy 2e

Key Terms

Astronomy 2eKey Terms
exoplanet
a planet orbiting a star other than our Sun
giant molecular clouds
large, cold interstellar clouds with diameters of dozens of light-years and typical masses of 105 solar masses; found in the spiral arms of galaxies, these clouds are where stars form
Herbig-Haro (HH) object
luminous knots of gas in an area of star formation that are set to glow by jets of material from a protostar
mini-Neptune
a planet that is intermediate between the largest terrestrial planet in our solar system (Earth) and the smallest jovian planet (Neptune); generally, mini-Neptunes have sizes between 2.8 and 4 times Earth’s size
protostar
a very young star still in the process of formation, before nuclear fusion begins
stellar wind
the outflow of gas, sometimes at speeds as high as hundreds of kilometers per second, from a star
super-Earth
a planet larger than Earth, generally between 1.4 and 2.8 times the size of our planet
transit
when one astronomical object moves in front of another
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