# Coordinate Systems - How to standardise the locations of objects! - Altitude and Azimuth - Very observer focused - Altitude - How high in the sky - Azimuth - which way from north - Doesn't work well with collaboration - Right ascension (RA) and declination - Standardised azimuth/altitude  - Right ascension (east and west) might be measured in time, declination is how far north and south it is in the sky - Basically longitude and latitude - 360 degrees in 24hrs - 1 hour is 15 degrees. - Earth orbits the Sun, so things being directly overhead is a specific time of year - Some stars you can only observe in Summer, winter etc. - Sky is advanced in RA by 2 hours every month - This is changing due to precession (every 26,000 years) - Use something defined for 2000 (J2000) - Ecliptic coordinates - Earth is tilted relative to the plane of the solar system (gives us seasons) - These two coordinates are tilted relative to each other by 23 degrees - Looks at how things moving in the same plane - Other planets in solar system have ecliptic latitude near 0, ecliptic longtitude that changes in the year - You can translate from ecliptic to RA and Dec and vice versa - Python - astropy - Celestial to ecliptical - Learn Python for astronomy! - Galactic Coordinates - Galactic longitude: angle between us and the centre of the galaxy (0-260 degrees) - Galactic latitude: how in or out of the plane of the galaxy you are (-90 to 90 degrees) - Earth centred ## Time standardisation - Doesn't matter if you tell people where to look if you can't say when to! - Supernovae can change over weeks - Binary Stars change over minutes - Time standards are problematic because Earth is moving - We move by 2 Au in half a year - Earth is 8 light minutes from the sun - Looking at an object in space from one side of the sun, you might be 16 minutes earlier/later just because light has to physically travel further to get to you - Clocks on Earth might have 8 minutes of lag. - Need a Barycentric correction to clocks (centre of gravity of the solar system which all planets and sun revolve around - not quite in the centre of the sun since Jupiter and Saturn tug it extra hard when they're lined up and all the other planets to a lesser degree) - This is just a function of time (we know our locations very precisely - then you know what time in a frame-agnostic sense you are measuring) - Seasons - things aren't always in the sky (only when opposite the sun) # References 1. https://youtu.be/ufpW5vEbECE # Footnotes