Midday is almost never 12:00
So, check this out: here in Melbourne the exact middle of the day (aka midday) is almost never 12:00 local time. From what I can see it’s actually never 12:00 here, but I’m still checking.
What defines the middle of the day? The symmetry of the Sun’s path in the sky does (1).
Firstly, look at today’s key values for the Sun:
It rises at 6:41 am and sets at 6:01 pm. And crosses the Meridian at 12:21.
The Meridian is literally the straight line from North to South in the sky. It splits the dome of the sky into two, right down the middle and right over your head. It’s actually your local Meridian. If you think about it – in terms of the Sun and stars etc – it would be different for someone in Adelaide, or Darwin and so on. But that’s not of real interest here.
The Sun is at its highest point above the horizon, when it crosses your local Meridian.
Have a closer look at those times. For today, 5 hours and 40 minutes after rising, the Sun crosses the Meridian. 5 hours and 40 minutes later, the Sun sets. That is a beautiful symmetry.
So, the day (aka the daytime) is symmetrical around the Sun crossing the Meridian. It follows that the middle of the day (mid-day) is…the time when the Sun crosses your Meridian. Today that is 12:21 pm.
Let’s jump forward. On November 9th 2020 it will be:
Daylight savings is active here (+ 1 hour). But you can see the day is still symmetrical around mid-day, which is 1:03 pm – with 7 hours either side. The numbers are rounded off, so one shows as 6:59.
I picked this date on purpose. The Sun is at its highest at 12:03 ‘sun time’ (no daylight savings) for a few days around this date. About the closest to local 12:00 it gets.
There’s a lot to explore here, so we’ll leave this for now and return with another post or two.
Notes:
(1) Yes, yes, the Sun isn’t ‘really’ moving, but 2020 is the year I ignore all pedantry 🙂 Besides it’s perfectly valid to consider the view from Earth ; we’ll be doing that more and more in these Astronomy posts.
