Our Milky Way galaxy of stars is so huge that even at the speed of light it would take 100,000 years to travel across it!
The further a star, the fainter it looks. Astronomers use this clue to figure out the distance to very distant stars. But there’s a big challenge to this method: You need to know the star’s "wattage"- how bright it really is - to begin with.
1908. Henrietta Leavitt discovers a way to tell the "wattage" of certain pulsating stars by observing how long it takes them to brighten and dim. The method opens the way to measuring distances all the way across the Milky Way galaxy.
ABOVE: This view toward the center of our galaxy shows the Milky Way as an immense city of stars. Our Sun and all the stars in the night sky are its residents.