Why are there more than 12 hours of daylight on the Equinoxes?

 

#Toronto enjoyed 12h 01m of daylight today, March 17, 2025. So, why wasn't today the #Equinox?

 

The Equinox is not until March 20th when Toronto will have 12h 10m of daylight – not exactly “equal day, equal night” - however, on the Equinoxes there are about 12 hours between the times at which the centre of the actual sun’s disk aligns with the horizons (i.e. at 0° altitude).

Now, there are two reasons why we actually have more than 12 hours of daylight on the Equinox…

 

1) the official times of #sunrise and #sunset are when the top edge (not the centre) of the sun’s disc appears on the horizon, and

 

2) the refraction of the sun's rays through the atmosphere – yes, light bends around the earth.

 

See diagram below.

 

When we first see the sun at sunrise, or when we last see it slip below the horizon at sunset, the sun is actually below the horizon. The following explains…

 

The semi-diameter of the sun is about 16 minutes of arc and average refraction accounts for about 34 minutes of arc. So, since the true sun’s centre is about 50 minutes of arc (i.e. about 1.5 sun diameters) below the horizon when we see a sunrise or sunset, the overall length of daylight increases.

 

 

How much more daylight can you expect in March?

If you live in southern Ontario, the number of daylight hours will increase in March by about an hour and a half. Great news for those tired of the long winter we've had. Further north, the increase will be even greater. To the south, however, the increase becomes less - to essentially zero at the Equator where day and night are each 12 hours long all year.

 

To give you an idea of how the increase in daylight hours in March varies with latitude, the following is a summary in 5° latitude intervals. The cities listed serve as an approximate guide.  

• 60°N - 2h 44m      - Seward AK, north limit of BC, AB, SK and MB, mid-Hudson Bay
  
• 55°N - 2h 15m      - Ketchikan AK, north end of James Bay, Schefferville QC
• 50°N - 1h 52m      - Kelowna BC, Medicine Hat AB, Winnipeg MB, Sept-Iles QC
• 45°N - 1h 34m      - Yellowstone Park WY, Minneapolis MN, Bracebridge ON, Bangor ME
• 40°N - 1h 19m      - Boulder CO, Columbus OH, Philadelphia PA
• 35°N - 1h 06m      - Edwards AFB CA, Albuquerque NM, Memphis TN, Charlotte NC
• 30°N - 0h 54m      - Houston TX, New Orleans LA, Jacksonville FL
• 25°N - 0h 44m      - Key Largo FL

It does not matter where you are east-west; longitude is not a factor. Enjoy

Cheers, Ralph

Torontohenge 2025

 

Torontohenge is the name given for the phenomenon that occurs four times per year when the sun rises or sets in line with Toronto's major east-west streets downtown.  The event, twice per year at sunrise, and twice at sunset, gives photographers great opportunities to capture the sun as its top edge grazes the horizon between the canyon walls of buildings on either side of the street. 

Photo courtesy of Rudy Limeback @rudydotca

Although Torontohenge technically falls on the dates given below, great photos can be taken for about a week before the August and October dates and a week after the February and April dates as the rising/setting sun passes over the street.  Not great for driving, but quite a sight just the same.

The Torontohenge dates for 2025 are:

February 15  Sunset - 5:48 PM EST

April 19  Sunrise - 6:28 AM EDT

August 23  Sunrise - 6:31 AM EDT

October 25 Sunset - 6:18 PM EDT

See monthly Toronto sunrise and sunset times here...

Warning for Drivers and Pedestrians
Despite the opportunities for photographers, conditions for motorists and pedestrians may be difficult for a week or more after the February and April dates and before the August and October dates.

NOTE:  The first and last hours of daylight are typically the worst.  Be prepared, and be extra careful.

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Cheers, Ralph