Saturday, December 21, 2019

Happy Winter Solstice

Today is the day of the Winter Solstice - which is the moment the sun stands still at the southernmost point on its north/south cycle.  To be more specific, the moment the sun stands still is 11:19 PM EST according to the website Time and Date (dot com!)  From this day on, every sunrise will be a little farther north and a little earlier until June's summer solstice (ignoring DST).

How about a couple of solstice fun facts?

The motion of the sun in the sky traces out a curve called an analemma, and this is usually printed on globes.   You can photograph one of these yourself if you care to dedicate a camera to doing nothing else for a year as photographer István Mátis did using the view from a window in his apartment in Romania.

The trick is to start about now when the sun is as low on the analemma as it will get.  That sets the lower right end of the analemma.  Set up a camera on a tripod pointing out a window with a good view of the southeast and use a normal focal length lens.  You take a photo at the same time every few days (or once a week) - it doesn't have to be sunrise - and you'll get something like this, if you're good ... or lucky.  Once a week is a good, round number and you pretty much can't make the weekly exposures too short.  You expose very short exposures so it just captures the sun and one day out of the year that you think looks pretty enough, take a longer exposure to capture the sky.  This is probably a good use for a film camera that can do multiple exposures and an old roll of film that will only get the one picture on it.  

Mátis writes,
The discs of the Sun are taken between 11/6/2012 and 1/19/2014 at 7:00 UT, which is 9 o'clock in the morning local time during winter and 10 o'clock during daylight saving time. The background is made on 1/14/2014 at 7:55 local time, from the original location of the analemma.
More details here.  My guess is that the gaps in the pattern were caused by cloudy days.

The other fun fact is that while this is the shortest day of the year, it is neither the earliest sunset or latest sunrise.  The earliest sunset is generally during the first week of December and the latest sunrise is in the first week of January.  The converse is true for the summer solstice in June.  The earliest sunrise is at the start of June and the latest sunset is in early July.  I've never checked those times extensively for other locations, so yours may vary. 

1 comment:

  1. Also precisely sets his latitude. When we lived in Alaska the analemma was verrrrry different.