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Ephemeris: 09/25/2025 – Today is Equilux day

September 25, 2025 Comments off

This is Ephemeris for Thursday, September 25th. Today the Sun will be up for 12 hours to the minute, setting at 7:33, and it will rise tomorrow at 7:35. The Moon, halfway from new to first quarter, will set at 8:50 this evening.

Today is Equilux day it’s the day we have exactly 12 hours of sunshine, and 12 hours of night. But isn’t that what we had three days ago on the equinox? That’s what equinox means. But, it only works on the equinox if the Earth didn’t have an atmosphere, and we decided that sunrise and sunset was when the middle of the sun crosses the horizon. The actual definition of sunrise and sunset is when the top of the Sun hits the horizon. So it rises a little earlier and so it’s a little bit later than it does geometrically. Also, the Earth has an atmosphere which causes the Sun to be higher in the sky when it’s closer to the horizon, which prolongs daylight. Check the weather app on your smartphone for your own personal sunrise and sunset times.

The astronomical event times given in this blog are for the Traverse City/Interlochen area of Michigan (Lat 44.7° N, Long 85.7° W; EDT, UT – 4 hours) unless stated otherwise. Times will be different for other locations.

Addendum

Atmospheric Refraction
How the atmosphere bends the light of the Sun or Moon rising or setting to appear higher than it actually is. S is the actual position of the Sun, S’ is the apparent position of the Sun. The blue line is the observer O’s horizon. The gray line is the actual, though much exaggerated, light path bent or refracted by the Earth’s atmosphere. The black line is the apparent sight line to the Sun. Credit Francisco Javier Blanco González, 2017
Categories: Concepts, Ephemeris Program, Equinox