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Table of Contents Enchanted Learning
All About Astronomy
Site Index
Our Solar System Stars Glossary Printables, Worksheets, and Activities
The Sun The Planets The Moon Asteroids Kuiper Belt Comets Meteors Astronomers

Astronomy Dictionary
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

Click on an underlined word for more information on that subject.

X



X-RAYS

X-rays are a type of electromagnetic radiation (between ultraviolet light and gamma rays in wavelength, frequency, and energy) - basically, it's light that is way past the blue-violet end of the visible spectrum - we cannot see it. They have short wavelength (and high frequency) as compared to visible light. Each photon of X-ray radiation has a lot of energy. X-rays can go through most solid objects. X-ray images of celestial objects are one way of learning about their high-energy properties. For example, the sun's corona emits X-rays, especially over sunspots. The Einstein X-ray satellite was launched in 1978 to survey celestial X-ray sources.

X-RAY ASTRONOMY

X-ray astronomy studies celestial objects by looking at the x-rays that they give off.

X-RAY BINARY STAR

X-ray binary stars are a special type of binary star in which one of the stars is a collapsed object such as a white dwarf, neutron star, or black hole. As matter is stripped from the normal star, it falls into the collapsed star, producing X-rays.

X-RAY BURSTER

An X-ray burster is an object that emits bursts of X-rays.

Y

Planet YEAR
Mercury 87.96 Earth days
Venus 224.68 Earth days
Earth 365.26 Earth days
Mars 686.98 Earth days
Jupiter 11.862 Earth years
Saturn 29.456 Earth years
Uranus 84.07 Earth years
Neptune 164.81 Earth years
Pluto 247.7 Earth years
YEAR
A planetary year is the length of time it takes that planet to revolve around the sun.


YELLOW DWARF

Yellow dwarfs are small, main sequence stars. The Sun is a yellow dwarf.


YERKES OBSERVATORY

University of Chicago's Yerkes Observatory is an astronomical observatory located at Williams Bay, Wisconsin, USA. It has a 40 inch (102 cm) refracting telescope; this is the largest refractor in the world. The Observatory was named for Charles Tyson Yerkes (1837-1905), a Chicago transportation tycoon who financed it. The observatory was designed by George E. Hale in 1892.


YLEM

Ylem (or Yelm) is the name given to the hypothetical primordial matter from which all the elements have formed. George Gamow proposed the existence of ylem.

Z

zenith

ZENITH

An observer's zenith is the point directly overhead.


ZETA ORIONIS

Zeta Orionis (Alnitak) is a star at the eastern end of Orion's belt (in the constellation Orion). Alnitak means belt. Alnitak is spectral Type O9.7Ib. It is also known as Alnitah.

ZODIAC

The zodiac is a band of 12 constellations along the ecliptic. The constellations in the zodiac include: Capricorn (the goat), Aquarius (the water bearer), Pisces (the fish), Aries (the ram), Taurus (the bull), Gemini (the twins), Cancer (the crab), Leo (the lion), Virgo (the virgin), Libra (the balance), Scorpio (the scorpion), and Sagittarius (the archer).


ZODIACAL LIGHT

Zodiacal light is a slight glow in the sky that is near the horizon and has a roughly triangular shape. It is caused by light from the Sun that is reflected by tiny dust particles located in space (this dust is part of our Solar System and is orbiting the Sun).

Astronomy Dictionary
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

Click on an underlined word for more information on that subject.
If the astronomy term you are looking for is not in the dictionary, please e-mail us.




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