Changing Planet

Milky Way Punier Than We Thought

This wide-angle view looks toward the center of our own Milky Way galaxy. Courtesy David Talent/NOAO/AURA/NSF

Looks like our home galaxy, the Milky Way, has gone on the ultimate weight-loss program, according to astronomers.

According to a new supercomputer simulation, it turns out that the entire mass of our Milky Way galaxy is about half that of the great Andromeda galaxy, our nearest neighboring spiral galaxy some 2.6 million light-years away from us. Astronomers had long thought the galaxies were twins.

While the two galaxies have similar extents and structures, the difference in weight seems to involve the amount of so-called dark matter that is gravitationally bound to each galaxy. While dark matter remains unseen, astronomers can measure the weight of the stuff (thought to be masses of an exotic class of physics particle) by its gravitational effects on galaxies. 

The study, published in the Monthly Notices of the Royal Astronomical Society, suggests that Andromeda possesses twice as much dark matter as our home galaxy.

See for Yourself

Late July and early August tend to be some of the best times to glimpse the ghostly glows of the Milky Way in the late night sky. The best place to observe its faint band of light is from the dark countryside, far from the city lights.

With the moon currently in its new phase and out of our skies, this week will be a particularly good time to glimpse our own home galaxy. Look for the misty, white powder trail that is our Milky Way galaxy, stretching up from the northeastern horizon, arching high up the eastern sky, and then reaching down to the southern horizon.


Best seen in dark skies, the splash of Milky Way that we see in the summertime consists mostly of stars from one of its spiral arms and stars from its dense, bright core. The core hangs above the southern horizon when viewed from northern latitudes.

Sit back comfortably on a reclining lawn chair and cruise this entire swatch of glittering sky with binoculars, and you will notice that the galaxy’s hazy glow is actually a river of countless stars, all of them thousands of light-years distant.

Follow Andrew Fazekas, the Night Sky Guy, on Twitter and Facebook.


Andrew Fazekas, aka The Night Sky Guy, is a science writer, broadcaster, and lecturer who loves to share his passion for the wonders of the universe through all media. He is a regular contributor to National Geographic News and is the national cosmic correspondent for Canada’s Weather Network TV channel, space columnist for CBC Radio network, and a consultant for the Canadian Space Agency. As a member of the Royal Astronomical Society of Canada, Andrew has been observing the heavens from Montreal for over a quarter century and has never met a clear night sky he didn’t like.
  • Dwayne LaGrou

    That is simply because the Andromeda Galaxy has not found out about Jenny Craig yet!

  • Donald Hamilton

    Regretfully, this has been known for decades, at least done by de Vaucoleurs in the 70s I think.

  • James Kibler

    If the Republicans in The US House of Representatives get wind of this they will assuradely form a committee to blame President Obama for this disparity!

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