By Lori Lambertson

Have you noticed how the days are getting longer, or where and when the Sun is rising or setting?

Observing these changes and looking for patterns in them is a human endeavor, and has been practiced by cultures around the world for millennia. The Sun and the sky are available to us all!

Friday, March 20, 2026 is the March Equinox.
Equinox, from Latin meaning "equal night," is when all parts of the Earth experience close to 12 hours of daylight and 12 hours of darkness. The exact moment of this equinox will be Friday, March 20 at 7:46 AM PDT. This is the moment when the Sun will be directly above the equator, and each day it will be higher in our sky, due to the Earth's tilt and our orbit around the Sun, until the June Solstice. The days are changing in length now by minutes!

On the day of the equinox, daytime and nighttime are of approximately equal duration all over the planet. They are not exactly equal, however, due to several factors. Most locations on Earth have more daylight than nighttime on the equinoxes, due to how we define sunrise and sunset, and due to atmospheric refraction of the sun’s light. In San Francisco, the day length on the March Equinox will be 12 hours, 8 minutes, 49 seconds. 

The day when the length of night and day is nearly equal is known as equilux and will occur on March 17, 2026.

Here are some science activities related to the equinox (the first two from the Exploratorium’s collection of Science Snacks):

• Self-Centered Globe Science Snack models the patterns of daylight and nighttime on the globe in real time. 
• Height Sight Science Snack can be used to measure the Sun's altitude on the equinox at solar noon (1:17 pm PDT in San Francisco on the equinox). Look up solar noon times for your location here. Check out the Going Further section for how to measure the Sun’s altitude safely - never look at the Sun! How high is the sun at solar noon on the March Equinox? Do you think the Sun’s altitude will be the same, higher, or lower on the June Solstice at solar noon? Can you design an experiment to find out? Happy and safe sky viewing!
• Solar Motion Demonstrator

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