Now for something lighter. It was overshadowed by the Supreme Court events, but we passed the autumnal equinox at 9:53 PM, Saturday, September 22.
If you pass a plane through the Earth and the Sun, the Earth is tilted on its axis relative to the plane. The result of this is that for half the year, the North Pole is pointed toward the Sun and the other half, the South Pole is pointed toward the Sun. We see day and night because the Earth spins on its axis.
The word equinox means "equal night" so most places on Earth will get 12 hrs of daylight and 12 hours of night on an equinox.
But not every place will experience the exact same amount of daylight. For instance, on Saturday, Fairbanks, Alaska, will see 12 hours and 16 minutes of daylight. Key West, Florida,will see 12 hours and seven minutes. The differences are due to how the sunlight gets refracted (bent) as it enters Earth’s atmosphere at different latitudes.*
You might also notice that both of these locations have daylight times longer than 12 hours. Aren’t day and night supposed to be equal? Daylight time is slightly longer than nighttime on the equinox because of how we measure the length of a day: from the first hint of the sun peeking over the horizon in the morning to the very last glimpse of it before it falls below the horizon in the evening. Because the sun takes some time to rise and set, it adds some extra daylight minutes.*
Incidentally, all planets have equinoxes. Mercury's tilt is only 2.11 degrees. Earth's tilt is 23.5 degrees, similar to most planets, but Uranus is tilted 98 degrees. The planet Venus is weird in that its tilt is 177.4 degrees (i.e. its North axis is below the plane), and it also rotates in a retrograde direction opposite to the Earth.*** https://www.vox.com/science-and-health/2018/9/20/17873846/fall-equinox-2018-autumnal
** https://simple.wikipedia.org/wiki/Axial_tilt
No comments:
Post a Comment