The Milky Way is on track to collide and merge with its nearest neighbor, the Andromeda galaxy, in about 4 billion years.
The galaxies will pass through each other, get snapped back together by gravity, and eventually merge cores.
NASA illustrations show what the arrival of an entire galaxy of stars will look like.
But while Andromeda's approach will make a bright and spectacular display in the night sky, life on Earth probably won't be around to see it. By then, the sun will have swollen past the orbit of Venus, charring Earth to a crisp.
The nearby galaxy Andromeda is speeding towards us at 250,000 mph. It has a long way to travel - about 2.5 million light-years - but it's likely to crash into the Milky Way in about 4 billion years.
When the galaxies do meet, it will make for a pretty sight. On approach, the Andromeda galaxy will warp the band of the Milky Way across our sky. Eventually, the galaxies' cores will merge.
Unfortunately, life as we know it won't exist on Earth as this spectacle plays out. By then, the sun will have started to run out of fuel, leading it to expand to the orbit of Venus. That will make Earth about as hot as Mercury is now.
However, NASA has created step-by-step illustrations depicting what those future night-sky views would look like as the Andromeda and Milky Way galaxies collide.
The Andromeda galaxy is our largest galactic neighbor. It's just 2.5 million light-years away. Andromeda and the Milky Way are creeping closer together every minute.
NASA's Hubble Space Telescope discovered in 2012 that Andromeda was on track to collide with the Milky Way in 3.9 billion years.
Measurements from the European Space Agency's Gaia space telescope suggest a different timeline, though. That data indicates the collision might just be a glancing blow 4.5 billion years from now.
Even if that is the case, the galaxies will merge over time, first in a chaotic mess of stars altering each others' orbits. Eventually, they will settle into one stable mega-galaxy. Here's what NASA expects that to look like from Earth.
Today the Milky Way looks like a band across the night sky. Andromeda is a mere light in the distance — the only other galaxy we can see without the help of a telescope.
In 2 billion years, Andromeda will loom much larger in the night sky.
In 3.75 billion years, Andromeda will fill the sky, and its tidal pull will begin to distort the Milky Way, according to Hubble's measurements.
About 3.9 billion years from now (by NASA's estimate), the galaxies will make their first close pass. Because galaxies are mostly empty space, they will pass through each other with very few collisions between stars, if any.
The close approach will, however, compress gas in that interstellar space. The sky will glow bright and colorful as the compressed gas and dust collapse to form new stars.
In 4 billion years, both galaxies will be stretched out and warped as they briefly drift apart again.
As gravity brings the galaxies back together 5.1 billion years from now, their cores — where ancient, swollen stars live — will be visible in the night sky. The period of rapid star formation will be over.
In about 7 billion years, the cores of the two spiral-shaped galaxies will merge, forming one oval-shaped galaxy. The night sky will be overwhelmed by light from the cluster of the two galaxies' largest, oldest stars.
But by the time Andromeda approaches, "our sun will have become a white dwarf and bye bye life on Earth," Didier Queloz, a physicist and Nobel laureate, said on Twitter.