December 2015: The Immensity of the Cosmos

This month, Astronomy takes you on a guided tour through the cosmic distance scale from Earth’s neighbors in the solar system, past the Milky Way and its galactic cousins in the Local Group, through the Virgo Supercluster, and out to the limits of the cosmos.
By | Published: October 26, 2015 | Last updated on May 18, 2023
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WAUKESHA, Wis. — It takes an unusual perspective to understand the immense distances introduced by even a cursory study of space. December’s special issue of Astronomy magazine offers this special perspective by conducting a guided tour through the cosmic distance scale from Earth’s neighbors in the solar system, past the Milky Way and its galactic cousins in the Local Group, through the Virgo Supercluster, and out to the limits of the cosmos. The distances at every step are so large they defy human comprehension, but at each level, Astronomy offers insight into the planets, galaxies, clusters, and superclusters that mark off distances in the otherwise black emptiness of space.

Physically, at least, astronomy and cosmology have been able to home in on the answer to one of humanity’s great questions: What is our place in the universe? We’ve come a long way since the Copernican revolution that displaced Earth from the center of all things, but astronomers are still puzzling out how we fit into our sprawling corner of the cosmos known as Laniakea, a massive collection of galaxy superclusters, or how the universe’s scaffold of dark matter supports the cosmic web that encompasses all the galaxy clusters that light up the overwhelming dark.

To highlight the colossal distances that come into play when exploring space, Astronomy’s editors have also added a scaled trip through the universe that runs throughout the magazine, guiding the reader from the Great Attractor “only” 100 million light-years distant to the oldest light in the universe, the faint glow of the Big Bang 13.82 billion light-years away. Read along and see where your favorite ultra-deep sky object falls on the space-timeline.

To better understand your place in the vast, ever expanding universe, pick up the December issue of Astronomy, on newsstands November 3.

“How immense is the universe?”
Editor David J. Eicher introduces the cosmic distance scale. From the measuring stick of the Sun-Earth distance known as an astronomical unit that astronomers use to map out the solar system to the expansion of the universe, astronomers have many different ways to ponder the immense scale of the cosmos.

“Our solar system: Realms of fire and ice”
Science writer Francis Reddy kicks off the tour of the universe by sharing some of the highlights from decades of close-up exploration of the planets, asteroids, and comets that make our home solar system, the only region in the cosmos humans can explore in situ.

“The Milky Way: Earth’s home galaxy”
Francis Reddy continues the space trek by exploring the Milky Way. Crammed with fantastic objects like the Crab Nebula (M1) and the glittering Pleiades star cluster, Earth’s home galaxy has taught astronomers most of what they know about how stars live and die. With distances of only hundreds or thousands of light-years, these “nearby” targets represent science’s best efforts to understand the greater cosmos.

“The Local Group: Our galactic neighborhood”
The Local Group of galaxies to which the Milky Way belongs also contains the magnificent Andromeda Galaxy and the Large and Small Magellanic Clouds. It also reveals the entourage of numerous tiny dwarf galaxies that ride the coattails of their more massive brethren. Katherine Kornei explains what these galactic neighbors have taught astronomers about how galaxies live and grow.

“The Virgo Supercluster: Our 100,000 closest galaxies”

Already massive groups of galaxies hang together in superclusters, and the Virgo Supercluster is the Milky Way’s home address. Sarah Scoles details how the gravitational push and pull of these titans of the cosmos shapes our local corner of the universe.

“Limits of the cosmos: The far reaches of space”
The universe is mostly empty space. Even the largest structures astronomers can observe, like the Laniakea collection of superclusters, cling to filaments that spiderweb across the cosmos, leaving gaping voids in between the glittering strands. Liz Kruesi lays out the universe’s organization on these most massive scales.

December sky events visible without optical aid

  • December 1 — Venus, Mars, and Jupiter shine bright in predawn skies.
  • December 5 — The Moon and Mars make a striking pair in the evening sky.
  • December 14 — The Geminid meteor shower peaks.

Also in the December 2015 Astronomy

The Sky this Month,” Snapshot, Astro News, Ask Astro, Bob Berman’s Strange Universe, Jeff Hester’s For Your Consideration, Stephen James O’Meara’s Secret Sky, Glenn Chaple’s Observing Basics, Adam Block’s Cosmic Imaging, Erika Rix’s Astro Sketching, New Products, Letters, Web Talk, Reader Gallery, and Breakthrough.

About Astronomy magazine:
Astronomy offers you the most exciting, visually stunning, thorough, and timely coverage of the heavens above. Each monthly issue includes expert science reporting, vivid color photography, complete sky-event coverage, spot-on observing tips, informative equipment reviews, and more. All of this comes in an easy-to-understand user-friendly style that’s perfect for astronomers at any level. Contact Astronomy, the world’s best-selling astronomy magazine, at 262.796.8776 or email