Most of those of us in the right-side-up half of the earth look forward to the first day of spring, the vernal equinox, when the sun crosses the equator and becomes ours again. For as long as I can remember, this has been touted as the day we start to get more day than night, but the charts generated by this site seem to indicate that is not the case. At my location, about 47.6N, sunrise on St. Patrick’s Day ends the first 12 hour night. If I look at, say, Brownsville Texas, the Ides mark the return of longer days, while Nome has to wait a day later than us for it. Why is this? Does it have to do with the earth’s eccentric orbit as we move outbound?
Start with this - Analemma - Wikipedia
The biggest difference is in how “sunrise” and “sunset” are defined. If you define them in terms of when the center of the Sun is above the horizon, then you find that it’s the equinoces, as you’d expect. More often, though, they’re defined according to when you can see any little sliver at all of the Sun, which buys you a few extra minutes at both ends.
The site says
Sunrise and sunset conventionally refer to the times when the upper edge of the disk of the Sun is on the horizon. Atmospheric conditions are assumed to be average, and the location is in a level region on the Earth’s surface.
So I guess that kind of explains it. Since the sun is still visible after it has passed completely below the horizon due to atmospheric lensing, if they are using physical, ground-based-type observations instead if sidereal math, I could see how the numbers would be early.
To elaborate on this, because the sun is not a point source of light, but rather a disc (with an angular diameter of about 32 minutes of arc), sunrise begins when the upper limb of the sun (that is, the top of the disc) first peeks over the horizon. This occurs before the center of the sun does so. Likewise sunset occurs when the upper limb has finally dropped below the horizon, which occurs after the center of the sun has done so. The effect of this is to length the duration of daylight.
Atmospheric refraction also causes the sun to appear above the horizon when, on an atmosphere-less planet, it would appear to be below the horizon. Again, this lengthens the duration of daylight.
At sea level, the times sunrise and sunset can be approximated by calculating when the center of the sun has an altitude of -51 minutes of arc (i.e., -0.85 degrees).
At great elevations, the curvature of the earth will also extend the visible horizon, which will again lengthen the duration of visible daylight.
The equinoxes are the moments when the declination of the sun is at the celestial equator. The name “equinox” is unfortunate, because the relative equality of day and night is more of an artifact of this definition, rather than being an element of the definition.
The days on which there is an equal amount of daylight and twilight+nighttime are known as the equiluxes, they are about 7-10 days off from the equinoxes, in the direction of the winter solstice (i.e., the spring equilux is earlier than the spring equinox and the autumnal equilux is later than the corresponding equinox).
But you should still be able to stand an egg on end, or something like that. Snopes says it’s bull but everybody knows that they’re in bed with the people who make those little wire stands for coloring easter eggs.
See, there was this West Wing episode, except, I think that egg fell over because it was hard-boiled, you need a raw egg.
If you are married, though, make sure you clear your browser history afterwards. 