# Astronomical Distances - nanometres - light (400 to 700e^-9) - 1e-9 - kilometres - things that are very close like the moon. - astronomical unit - au - pluto is 45au - For solar system - Alpha centauri - 200,000au away - parsec - more info in parallax (background isn't changing) - 360 degrees in the sky, 60 minutes per degree, 60 seconds in an arc minute ([celestial coordinates](celestial%20coordinates.md)) -  - Nearest stars are about one parsec away - We can get to micro arcseconds for 100 or 1000 parsecs away - for galaxy - 20,000 to 50,000 parsec across - Light year - distance light travels in 1 year - Not too different from a parsec (3-4 ly per parsec) - things aren't instantaneous These are the measurements to do with distance (can get back to m) - Things far away aren't moving towards us - Red shift - very far away - stretched far away - Doppler effect - Not necessarily proportional - Observable horizon - Cosmic Microwave Background It explodes into a bigger scale as you zoom out # References 1. https://youtu.be/wEHPCc5Hc6s?feature=shared # Footnotes