Equinox and Solstice on Periscope

We can watch the effects of the changing seasons by carefully observing the world map found on Periscope.  The part of the Earth that is in sunlight dramatically changes through the seasons, and we can see that by way of this social media.

map Equinox Western HemisphereTake a closer look at the map to the left.  This is the same map that accompanies the title of this blog post.  You can see North and South America center and left, with Africa and Europe on the right edge.  I grabbed this image on Periscope at 6:31 am (ET) on March 20, the March Equinox.

Upon closer inspection of the map you may see that the left side is shaded slightly darker than the right side.  The terminator, in this case the dawn terminator, is the line that separates night time from day time.

On the March Equinox  the terminator ran directly north and south through eastern Canada and western Argentina.  There’s another one on the other side of the world running north and south through Asia and the Eastern Indian Ocean.

The dawn terminator moves from east to west, circling the world once every 24 hours.  At the time of the map above, people in California were still in the dark and the folks in Great Britain were in the light,  Many Californians would probably still be in bed, while our cousins across the pond are already about their day.

If on the March Equinox the terminator ran directly north-south, will it be the same on the June Solstice?  In other words, will the terminator be straight up and down on the map June 21?  And if not, what will be the orientation of the terminator then? Will the northern part tip counter-clockwise, toward California, (Choice #1 below) or tip clockwise, toward Great Britain (Choice #2)?  Or will the terminator go completely horizontal and run right on top of the equator (Choice #3)?

Choice 1                              Choice 2                       Choice 3


Which map did you pick?  Write your answer here: ___________

Some of my viewers on Periscope took this quiz.  (I did not offer Choice #3 to them.)  76% picked Choice #1, and 24% picked Choice #2.

Here are the images from the morning of the June Solstice, 2017.  The red dots indicate live broadcasts happening at the time.  Notice which way the terminator leans.


You can see that Choice #1 was the best answer.  The Northern Hemisphere part of the terminator does lean toward California.  But also notice at what angle the terminator leans and what happens to it as it approaches the North and South Poles. What conversation could you have with a novice amateur astronomer to explain what’s happening?

Now consider September at the Equinox.  What would you predict about the orientation of the terminator then?  How about on December 21. the Solstice?

Write your answers here:____________________________

There will be a test.


Periscope is a social media that allows user to broadcast live to the world.  There are more than 10 million subscribers to Periscope.  You can also watch other broadcasts from around the world.  For the App in iTunes click here.  For more information about Periscope, click here.

I currently broadcast a show called “Let’s talk Astronomy” twice a week on Periscope.  I have about 22,000 followers who get invited each time I begin a broadcast.  Viewership numbers are usually near a thousand per broadcast, but I have had almost 20,000 viewers for one show.

4 thoughts on “Equinox and Solstice on Periscope

  1. Hey – I wasn’t completely sure where to write something. Funny story, so I use Periscope to chat with a few Agnostics/Atheists around the world in my free time and one of them randomly shared your scope with me. He never shares much, but I really enjoy banter with this guy, so I thought I would check it out… And behold- It was my ELPSA teacher. What’s the damn probability? Well… glad you seem to be doing well. I’ll check out your religious scopes sometime 😉


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