AstroKids › Everything in the sky › The Sagittarius Dwarf Galaxy and Stream
dwarf galaxy · satellite galaxy being torn apart by the Milky Way

The Sagittarius Dwarf Galaxy and Stream

A small galaxy is being pulled apart by ours right now, and its stars are being stretched into a long stream wrapped around the Milky Way — our galaxy grew big by eating little ones like this!

🚀 Travel there
The Sagittarius Dwarf Galaxy and Stream — Drawn, not photographed.

What it is

Small satellite galaxy being gravitationally shredded by the Milky Way, leaving a stellar stream wrapped around our galaxy.

Dwarf galaxy: A small galaxy, often orbiting a bigger one. Every kind of thing there is →

Can you see it?

No. No telescope on Earth will show you this one; it is here to be understood, not seen. It is here because it is worth knowing about — and because leaving it out would make the sky look emptier than it is.

Worth knowing about the Sagittarius Dwarf Galaxy and Stream

On the 100-meter-track scale model of the Milky Way, this satellite galaxy's core would be about 65 meters from the Sun — already more than half the length of the whole track. Light takes 65 thousand years to get here from the Sagittarius Dwarf Galaxy and Stream, so what you are looking at is the Sagittarius Dwarf Galaxy and Stream as it was 65 thousand years ago.

What it is made of
A small satellite galaxy being torn apart by the Milky Way's gravity, leaving a long ribbon of stars (the Sagittarius Stream) wrapped around the galaxy.
How we know: Wide-sky surveys mapped positions, distances, and motions of millions of stars and found a distinct population with matching ages/chemistry/orbits.
What makes it worth knowing
Some stray stars from this doomed galaxy have been found passing through our own solar neighborhood.
The numbers
Distance from uscore ~65,000 light-years away, stream loops much farther

How anyone knows this

Nobody flew a tape measure out there. Every number on this page was worked out from the ground:

Next to it

The Milky Wayspiral galaxyNaked eyeProxima CentauristarWith effortAlpha Centauri A & Bbinary star systemNaked eyeSiriusstarNaked eyeVegastarNaked eyeArcturusstarNaked eye
📖 How the Milky Way fits together

Then go outside

Not this one. But the sky over your head is full of ones you can see, and the Planetarium knows which.

🌙 Plan an evening outside🌌 Everything else in the sky