What are secondary standard candles?

Secondary standard candles are tools scientists use to measure how far away things are in space, just like a known distance on Earth helps us find out how big something is.

Imagine you have a flashlight that you know is always as bright as a new bulb. If it gets dimmer, you can tell it’s farther away. Scientists use this idea with stars, they call them standard candles, because just like your flashlight, they give off a known amount of light.

Sometimes, scientists don’t know the exact brightness of a star at first. But if they see that same kind of star somewhere else where they do know how far away it is, they can use that to figure out how bright it really is, and then tell how far away other stars like it are.

Think of it like this: If you have a known-size balloon and you see another balloon from afar, you can guess how big it is based on how close or far the known one looks. Scientists do something similar with stars to understand the universe around them.