A project of the Dark Energy Survey collaboration


As the sky turns: the fall and rise of the Milky Way


We are swept up in a cosmic merry-go-round.

Earth spins relative to the sky – about one revolution every 24 hours.

After twilight, our nearest star, the Sun removes its warm blanket of light, revealing the dancing lights overhead: collections of aeons-old galaxies and constellations of distant stars fill the night sky. For some precious hours, we have exquisite access to these pinpricks and smudges of light that have always swirled overhead – until we bask again in the Sun’s rays. During the day, all blinking tapestry is still above us, but the Sun washes out any hope of seeing it. Again, after dusk, familiar patterns fill the sky, as the dancers return like clockwork to their positions on the celestial stage.

Our entire solar system resides in a galaxy, the Milky Way. The Galaxy’s structure includes spiral arms and a disk of stars and gas: our pale blue dot, tethered to the Sun, is nestled in the suburbs, halfway to the edge of the Galactic disk. As we turn from day to night to day, the Galaxy itself also spins (over much longer periods than Earth’s day).

During the course of our daily/nightly sweep of the heavens, just as the stars and galaxies move across our sky, so does the disk of Milky Way. When we look up from the dark mountain tops of Cerro Pachon, we look into the plane of the Milky Way, into the heart of our Galaxy.

In the video above, the camera rotates from East to West through South – taking a picture every 30 seconds over the course of the night. Earth’s axis goes through the South pole, so we see the sky spin about that point: one side of the Milky Way sets, and by 1am on this October night, another side begins to rise.

Good night, and keep looking up,

Det. B. Nord




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