![]() ![]() When the rotational axis is tilted away from the sun, the energy gain per square meter is lower. With the rays being closer to vertical, the energy gain per square meter of area is higher. Here’s the counter-intuitive part: Earth is closest to the sun in early January and most distant in early July! Turns out seasonal heating and cooling isn’t caused by how close we are to the sun, but instead is affected by the Earth's axis tiling toward or away from the sun. When the rotational axis is tilted toward the sun, the sun’s energy strikes that part of the planet at a steeper angle. These are the two extremes of annual solar illumination: longest days in the summer and shortest days in the winter. The winter Earth is tilted away from the sun the north pole deep in darkness around December 21. The summer Earth shows the north pole tilted towards the sun, bathed in sunlight, around June 20. To understand how the tilt causes seasons, look first at the summer and winter Earths. The table shows approximate dates for when day and night are of similar lengths for some latitudes.This image is waaaaay out of scale in almost every dimension shown (that’s another whole subject by itself!) but it does illustrate how the Earth’s daily spin axle is tilted away from vertical. This day is known as the equilux, and its date depends on a location’s latitude and can occur several days to weeks before or after an equinox. Latitude Determines Day LengthĮven if day and night aren’t exactly equal on the day of the equinox, there are days when sunlight hours and nighttime hours are both very close to 12 hours. ![]() Our calculations in the Sunrise and Sunset Calculator assume the standard atmospheric pressure of 101.325 kPa and temperature of 15° C or 59° F. The extent of refraction depends on atmospheric pressure and temperature. This causes every day on Earth, including the days of the equinoxes, to be at least 6 minutes longer than it would have been without this refraction. The same thing happens at sunset when you can see the Sun for several minutes after it has dipped under the horizon. This refraction, or bending of the light, causes the Sun’s upper edge to be visible from Earth several minutes before the edge actually reaches the horizon. ![]() date of "Equal Day & Night" LatitudeĪnother reason for why the day is longer than 12 hours on an equinox is because the Earth's atmosphere refracts sunlight. The time it takes for the Sun to fully set, which can be several minutes, makes the day just a bit longer than the night on the equinoxes. Sunrise and Sunset are defined as the exact moment the upper edge of the Sun’s disk touches the eastern and the western horizon, respectively. If sunrise and sunset were defined as the moment the geometric center of the Sun passes the horizon, then the day and night would be exactly 12 hours long. One of the reasons why most locations on Earth do not enjoy exactly 12 hours of daytime and 12 hours of nighttime on the equinoxes is how sunrise and sunset are defined. On the equinox, the tilt of Earth’s axis is perpendicular to the Sun’s rays as in the illustration. On the equator, the day is always a little longer than 12 hours all year round. Perfect opportunity to see the Midnight Sun! On the South Pole, the Sun will be up 24 hours. Johannesburg inhabitants will also enjoy a similar number of daylight hours. Moving southwards, Melbourne in Australia will see a 12 hours and 8 minutes long day. Even in Longyearbyen, one of the world's northernmost cities, the day will last for 12 hours and 37 minutes. Those in Amsterdam will get 2 more minutes of daylight with a 12 hours and 12 minutes long day. On this day, New York City residents will enjoy a 12 hour and 10 minutes long day. The next equinox is at 03:06 UTC on 20 March 2024. How long is the day where you are? More Than 12 Hours of Sun In fact, most locations on Earth tend to enjoy more daylight hours than nighttime hours on these two days of the year, thanks to the Earth's atmosphere and our definition of sunrise and sunset.Įquilux: when day and night are (actually) equal The day and night are only nearly equal on the September equinox and the March equinox. The day is just a bit longer than the night on an equinox. Business Date to Date (exclude holidays). ![]()
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