How do astronomers use standard candles (what are those?) and surface brightness fluctuations (what are those?) to find distance between Earth and celestial bodies?
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A standard candle is an astronomical object which has a known brightness. If we know how bright something really is, we can work out how far away it is because it dims with distance.
A type 1 supernova always explodes at the same mass, and therefore brightness. We can tell it isn’t a type 2 supernova by the amount of hydrogen in the resulting cloud: type 1s have hydrogen, type 2s don’t.
A Cepheid variable is a star which “pulses” in brightness, and the longer the pauses between the pulses, the brighter the star.
Surface brightness fluctuations … well, get a microscope and zoom into IDK a piece of wood. You’ll see all kinds of variations of size, colour, brightness etc. Zoom out and the variations decrease.
The closer we are to a galaxy, the more individual stars, nebulas, black holes etc we can see. Further away, it just looks “smooth”.
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