Weather Whys: Why don't we have exactly 12 hours of daylight on the spring equinox?

Weather Whys: Why don’t we have exactly 12 hours of daylight on the spring equinox?

As we approach the start of spring many assume that our daylight will equal 12 hours of daylight and 12 hours of nighttime, but that's not necessarily true. We investigate in Weather Whys.

The term "equinox" translates to equal night, but there are a couple of factors as to why we don't have exactly 12 hours of daylight and 12 hours of nighttime on the spring equinox exactly. Latitude has a lot to do with it. Locations near the Equator have about 12 hours of day and night all year long. Milwaukee sits at a latitude of 43° North which means our day of equal day and night would be later than our friends to the south and earlier than our friends to the north. 

We also measure the sunrise and sunset times by the top of the sun as it crosses the horizon. If we measured it from the middle of the sun our daylight would be closer to 12 hours during the equinox. Another factor is that Earth reflects sunlight allowing our sunrise and sunset times to happen earlier than they truly are. 

On Monday the sun rose at 7:01 a.m. and set at 7:00 p.m. with a daylight time of 11 hours 58 minutes 53 seconds. We are averaging a gain of about 3 minutes of daylight each day right now and on Tuesday the daylight will surpass 12 hours at a time of 12 hours 1 minute 50 seconds. 

Weather Whys is a segment by Meteorologist Justin Thompson-Gee that airs during the CBS 58 News on WMLW - The M from 7 a.m. to 8 a.m. The segment answers viewer weather questions, explains weather phenomena and reveals interesting weather stats. To submit your question reach out to Justin on Facebook, Twitter or by emailing him at [email protected].

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