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Milky Way Galaxy
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Milky Way Galaxy Milky Way Galaxy Milky Way Galaxy globular cluster M80 open cluster NGC 290 Pleiades Orion Nebula (M42) Cat's Eye Nebula Crab Nebula Eagle Nebula
For Students
centre of the Milky Way Galaxy
Milky Way Galaxy summary
Quizzes
View of the Andromeda Galaxy (Messier 31, M31).
Astronomy and Space Quiz
The orbits of the planets and other elements of the solar system, including asteroids, Kuiper belt, Oort cloud, comet
Space Odyssey
Encyclopaedia Britannica thistle graphic to be used with a Mendel/Consumer quiz in place of a photograph.
27 True-or-False Questions from Britannica’s Most Difficult Science Quizzes
Related Questions
Read Next
Solar system illustration. (Sun; planets)
A Model of the Cosmos
Infinite space background with silhouette of telescope. This image elements furnished by NASA.
Telescopes: Seeing Stars
Galaxy clusters like Abell 2744 can act as a natural cosmic lens, magnifying light from more distant, background objects through gravity. NASA's James Webb Space Telescope may be able to detect light from the first stars in the universe if they are gravitationally lensed by such clusters. (astronomy, space exploration, galaxies)
How Fast Is the Universe Expanding?
Planet Jupiter with its moon Io at left, photographed by the Cassini orbiter during the Cassini-Huygens mission, 2000. spacecraft
7 Important Dates in Jupiter History
Colorful winter sunset
What's the Difference Between a Solstice and an Equinox?
Discover
Solar eclipse of the sun.
The Sun Was Eaten: 6 Ways Cultures Have Explained Eclipses
Albert Einstein in Washington, D.C. c. 1921-1923. Physicist
The Solar Eclipse That Made Albert Einstein a Science Celebrity
solar eclipse, sun, moon, astronomy, space
How Do You Tell the Difference Between Total, Annular, Solar, and Lunar Eclipses?
Vietnam War. U.S. President Lyndon B. Johnson awards the Distinguished Service Cross to First Lieutenant Marty A. Hammer, during a visit to military personnel, Cam Ranh Bay, South Vietnam, October 26, 1966. President Johnson
Vietnam War Timeline
Periodical Cicada, Adult, Magicicada spp. Requires 17 years to complete development. Nymph splits its skin, and transforms into an adult. Feeds on sap of tree roots. Northern Illinois Brood. This brood is the largest emergence of cicadas anywhere
Why Do Some Cicadas Appear Only Every 17 Years?
Pluto. The Changing Faces of Pluto. Most detailed view to date of the entire surface of the dwarf planet Pluto, as constructed from multiple NASA Hubble Space Telescope photographs taken from 2002 to 2003.
10 Important Dates in Pluto History
Stylish light blue jeans on wooden background, closeup of inset pocket
Why Do Jeans Have That Tiny Pocket?

The concept of different populations of stars has undergone considerable change over the last several decades. Before the 1940s, astronomers were aware of differences between stars and had largely accounted for most of them in terms of different masses, luminosities, and orbital characteristics around the Galaxy. Understanding of evolutionary differences, however, had not yet been achieved, and, although differences in the chemical abundances in the stars were known, their significance was not comprehended. At this juncture, chemical differences seemed exceptional and erratic and remained uncorrelated with other stellar properties. There was still no systematic division of stars even into different ...(100 of 13945 words)

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