Altitude of the Sun and Moon
July 17th, 2005
- Change the latitude to see the effect of moving into the arctic circle
- Change the date to see the effect of slipping towards Winter – note how the mid-day Sun gets lower in the sky
- The thick blue horizontal line represents the horizon, so estimate the times of Sunrise and Moonrise and set
- The vertical gridlines are 6 degrees of altitude apart and -6 degrees of altitude is taken as ‘civil twilight’
- The detail above is set to BST so the Sun is highest in the sky just after 1300 (corresponding to minutes after Noon UT)
- Find a day when the Sun is setting as the Moon is rising – this will always be near full Moon.
- The Full Moon reaches the highest in the sky during winter, when the Sun is lowest
I find an OHP and a globe plus this spreadsheet help liven up an introduction to angles and geometry. Many people have experience of holidays within the Tropics but have forgotten or never learned what the ‘Tropics’ mean. The Arctic circles become meaningful when you can show that the Sun never rises above the blue line in Winter. The detail above shows that full astronomical twilight is never quite reached in the Summer months in the UK.