![]() ![]() By the way, this is true for every day of the year, not just on the equinox.Īs one approaches the Arctic at the time of the fall equinox, the Sun's angle of ascent becomes shallower and shallower. ![]() The result is a total of approximately 5 to 6 minutes of additional daylight. That adds another 2.5 to 3 minutes of sunshine at day's end. Similarly, sunset is the moment the trailing limb finally touches the western horizon. Since the solar disk is about ½° in diameter, its full disk takes between 2.5 and 3 minutes at mid-latitudes to clear the horizon. Instead, sunrise is defined as the moment when the Sun's upper edge breaches the horizon. If the Sun were simply a more brilliant version of Venus, all of it would rise in one pop. First, the Sun is a disk, not a point source. Venus, pictured here at dawn on September 14, 2023, is essentially a point source compared the Sun's disk.Įven on the equinox, daylight still edges out night for two reasons. There's more to daylight on the equinox than you might think. That's why we call it the equinox, which literally means "equal night." Right?ĭon't believe it. Day and night momentarily strike a balance, each of them 12 hours long on this day, so neither one of them has the upper hand. And no matter where you live except the poles it rises due east and sets due west.Īt both the spring and fall equinoxes, the Earth's axis tilts neither toward nor away from the Sun but sidelong. On the same day at the North and South Poles the Sun scrapes completely around the horizon. At local noon, when the Sun passes overhead, residents won't be able to avoid stepping on their shadows. On that special day, the Sun will pass directly overhead at noon for residents living along the equator, from Nairobi to Quito to Singapore. ![]() The celestial equator is a projection of Earth's equator on the sky. EDT, the Sun will cross the celestial equator going south and won't stop its descent until it bumps into the winter solstice on December 21st. That's what I'm thinking right now as we approach the first official day of fall (spring in the southern hemisphere), also known as the autumnal equinox. Both effects increase the amount of daylight we experience at the equinoxes.Īstronomical cycles acquaint us with the inevitable. Refraction also "lifts" the Sun into view at the horizon about 2 minutes before the real Sun arrives there. Denser air near the horizon acts like a lens and refracts (bends) the Sun's bottom half upward into the top, compressing the solar disk into a bean. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |