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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
After a perfect launch, spectators try to catch a last glimpse of Space Shuttle Columbia, barely visible at the top end of the twisted column of smoke.
7 Accidents and Disasters in Spaceflight History
VAN, TURKEY - OCTOBER 25: A building and car ruined during the earthquake of Van-Ercis on October 25, 2011 in Van, Turkey. It is 604 killed and 4152 injured in Van-Ercis Earthquake.
What Is an Aftershock?
Black widow spider
9 of the World’s Deadliest Spiders
Albert Einstein in Washington, D.C. c. 1921-1923. Physicist
The Solar Eclipse That Made Albert Einstein a Science Celebrity
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?
solar eclipse, sun, moon, astronomy, space
How Do You Tell the Difference Between Total, Annular, Solar, and Lunar Eclipses?
African Americans demonstrating for voting rights in front of the White House as police and others watch, March 12, 1965. One sign reads, "We demand the right to vote everywhere." Voting Rights Act, civil rights.
Timeline of the American Civil Rights Movement

The first reliable measurement of the size of the Galaxy was made in 1917 by American astronomer Harlow Shapley. He arrived at his size determination by establishing the spatial distribution of globular clusters. Shapley found that, instead of a relatively small system with the Sun near its centre, as had previously been thought, the Galaxy is immense, with the Sun nearer the edge than the centre. Assuming that the globular clusters outlined the Galaxy, he determined that it has a diameter of about 100,000 light-years and that the Sun lies about 30,000 light-years from the centre. (A light-year is the ...(100 of 13945 words)

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