This list brings together 17 astronomy words, running alphabetically from “Y Dwarf” to “Yutu”. They cover a wide mix of subjects, from cool brown dwarfs and giant stars to historic observatories and space missions. You’ll find them useful for building your vocabulary, exploring the night sky with more confidence, or simply satisfying your curiosity about how the universe works.
Astronomy words are the specialized terms scientists and stargazers use to describe stars, planets, spacecraft, and the physical forces that shape them. Many carry surprising stories, like “Yutu,” the Chinese rover named after the mythical Jade Rabbit that explored the Moon’s surface in 2013. Learning these words opens up a richer way of talking about space.
Below you’ll find the table with Word, Definition, and Description.
Word: the specific astronomy term, such as a star name, effect, or spacecraft, listed alphabetically for easy browsing.
Definition: a short, plain-language explanation that tells you what the word means in a single glance.
Description: extra context and detail that helps you understand why the word matters and how it’s used.
Astronomy words
Word
Definition
Y Dwarf
A class of extremely cool brown dwarf
Yarkovsky Effect
A force on rotating bodies from uneven thermal radiation
YORP Effect
A torque that alters the spin of small bodies
Yellow Dwarf
Common name for a G-type main-sequence star
Yellow Hypergiant
A rare, highly luminous evolved star
Year
The time a planet takes to orbit its star
Yerkes Classification
A stellar classification system based on luminosity
Yerkes Observatory
A historic astronomical research observatory
Ylem
A hypothetical primordial substance in early cosmology
Young Stellar Object
A star in the early stages of formation
Yed Prior
A star in the constellation Ophiuchus
Yed Posterior
A star in the constellation Ophiuchus
Yildun
A star in the constellation Ursa Minor
Y Canum Venaticorum
A deep-red carbon star, nicknamed La Superba
Yale Bright Star Catalogue
A widely used star catalog
Yohkoh
A Japanese solar observation satellite
Yutu
A Chinese lunar rover
Descriptions
Y Dwarf
The coolest known class of brown dwarfs, with atmospheric temperatures low enough to approach room temperature in the most extreme cases.
Yarkovsky Effect
A subtle push that gradually shifts the orbits of small asteroids as they absorb sunlight and re-radiate heat unevenly while spinning.
YORP Effect
Short for Yarkovsky-O’Keefe-Radzievskii-Paddack effect, it can speed up, slow down, or even tip over the rotation axis of small asteroids over time.
Yellow Dwarf
An informal term for stars like the Sun: mid-sized, moderately hot, and shining with a yellowish-white light for billions of years.
Yellow Hypergiant
An extremely rare and unstable class of supergiant that has swollen and cooled late in life, shedding huge amounts of mass into space.
Year
The period Earth needs to complete one full orbit of the Sun, roughly 365.25 days, and the basis for most calendars.
Yerkes Classification
Also called the MKK system, it sorts stars by luminosity class alongside temperature, distinguishing dwarfs, giants, and supergiants.
Yerkes Observatory
Located in Wisconsin, it houses the world’s largest refracting telescope and is often called the birthplace of modern astrophysics.
Ylem
A now-largely-historical term coined by physicist George Gamow for the dense, hot material thought to have filled the universe just after the Big Bang.
Young Stellar Object
A general term for a star still forming or newly formed, often wrapped in a disk of gas and dust that may later build planets.
Yed Prior
Officially Delta Ophiuchi, this red giant marks one of the shoulders of the Serpent Bearer constellation.
Yed Posterior
Officially Epsilon Ophiuchi, this orange giant sits near Yed Prior, and together they form a recognizable pair in the night sky.
Yildun
Officially Delta Ursae Minoris, a white star located in the tail of the Little Dipper, not far from Polaris.
Y Canum Venaticorum
Famous for its striking ruby color, this variable star is one of the reddest visible to skywatchers using binoculars.
Yale Bright Star Catalogue
A standard reference listing essentially every star visible to the naked eye, along with its position, brightness, and spectral type.
Yohkoh
Launched in 1991, this satellite studied solar flares and the Sun’s high-energy activity using X-ray and gamma-ray instruments.
Yutu
A robotic rover, whose name means Jade Rabbit, that landed on the Moon in 2013 as part of the Chang’e 3 mission to study lunar terrain.
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