What is the glowing band across a really dark sky, and why can't a third of us see it?
Every star you can see belongs to the Milky Way, but only one hazy band of it gets the name, and city lights have hidden it from more than a third of humanity.
βΆ Start the storyThe glowing band is our own , seen from the inside. The Milky Way is the galaxy that includes the Solar System, and its name describes how it looks from Earth: a hazy band of light made of stars so far away that the naked eye cannot separate them. It arches across the sky as a hazy white band about 30 degrees wide.
Why a band and not a blanket of stars? The is structured as a plane, so when we look along that plane we look through a great number of stars, and we see the band. The stars outside the band are in the Milky Way too: all the individual naked-eye stars in the sky are part of it, and the name is only kept for the band. The Solar System sits about 27,000 light-years from the center, on the inner edge of the Orion Arm.
Step 1: A flat
The stars lie in a plane, like a disc
Step 2: We are inside
About 27,000 light-years from the center
Step 3: Look along the disc
A great number of stars lie in that direction
Step 4: A hazy band
Too distant to be seen one by one
The dark patches inside it are dust. blocks the light of distant stars, and peoples of the southern hemisphere, including the Inca and Australian Aboriginal peoples, saw those dark shapes as constellations of their own. The ancient Greeks saw milk: the name comes from the Latin via lactea, from the Greek for milky circle.
Today most of us never see any of this. The Milky Way has a low , so or moonlight can greatly reduce its visibility, and maps of artificial night sky brightness show that more than one-third of Earth's population cannot see it from their homes. To see it you need a dark sky, no Moon, and eyes that have had about half an hour to adapt to the dark.
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Recap
The band is the galaxy's flat disc seen edge-on from inside, and it takes a dark sky and dark-adapted eyes to see it.
π‘ A trick to remember it Β· You live inside a pancake of stars; look along it and the stars pile up into a pale road.
Surprising fact Β· More than a third of humanity cannot see it from home.
Connects to
- ποΈ What is the Bortle scale, and how much of the night sky have we lost to light pollution?
- β¨ Who decided there are 88 constellations, and is the Big Dipper one of them?
- π Why do the stars seem to turn around one star in the north?
- π Why does looking far into space mean looking back in time?
- Galaxy
Sources (1)
No source, no claim. Every fact in this lesson (15 claims) cites at least one of these.