It’s mid-summer, so where’s the Sun?

Someone was asking today why the sky is so bright at night at this time of year, so I had to have a think about where the Sun actually goes…

So we’re clear what I’m talking about, let’s say you’re standing outside around midsummer in the northern hemisphere, facing south.  Take a flask; you’re going to be there a while.  The sun rises behind your left shoulder to the north-east, travels across the sky until noon when it’s high, but to the south of you, and then drops back down over your right shoulder to the north-west, passing around “behind” the earth to the north before coming up again in the north-east.  Unless you’re in the tropics the sun never travels around the earth “under your feet”, just as it never goes directly above your head.

The Earth is currently inclined at about 23.5 degrees from the vertical, northern hemisphere towards the sun during the day.  After scribbling on a bit of paper I think I’m correct in saying that as the sun passes in front of you to the south then at its highest it will reach an altitude of ( 90 – latitude + 23.5 ), so 62.5 degrees above the horizon for me at 51N.  At night as it passes behind your head and the planet to the north it will be at most ( 90 – latitude – 23.5 ) below the horizon, so 15.5 degrees for me.  As “astronomical darkness” is defined as “when the sun is 18 degrees or more below the horizon” it’s not going to be that dark here.  And I’m fairly well south for the UK.  If you’re at 59N in the Orkneys the sun won’t drop more than seven degrees below the northern horizon and I imagine it’s pretty light all the time.

This entry was posted in Astronomy and tagged . Bookmark the permalink.

Leave a Reply

Your email address will not be published. Required fields are marked *