The Earth fully rotates in 23 hours and 56 minutes. Where do those extra four minutes go??
I know the answer is supposedly leap day, but I still don’t understand it from a daily time perspective.
I have to be up early for my job, which right now sucks because it’s dark out that early. So every day I’ve been checking my weather app to see when the sun is going to rise, and every day its a minute or two earlier because we’re coming out of winter. But how the heck does that work if there’s a missing four minutes every night?? Shouldn’t the sun be rising even earlier, or later? And how does it not add up to the point where noon is nighttime??
It hurts my head so much please help me understand.
In: Earth Science
The 4 minutes is because of the earth’s orbit around the sun. A day is an average time between two solar noon. Solar noon it the point in time when the sun is highest in the sku
If Earth was not rotating the sun would move around it once per orbit. so the orbit creates a day that is a year long. That means the sun will be in the same place in the sky 24*60/365=3.9 minutes later.
So earth rotation + earth orbital moment around the sun result that the average time between two solar noons is 24 hours.
This is the average length because earth orbit is elliptical. The shortest say is 21 seconds less than 24 hours and the longer 30s longer. This will change the time of solar noon by +-17 minutes during a year.
So if we based the clock on earth rotation noon would move around and it could be at any time during a year. But because we base our day on the solar noon is around the same time every day. The position of stars in the sky move around during the year because of this.
This is not why days in the winter is short and long in the summer. It could not be because the southern hemisphere has summer when the northern have winter.
The length of days and the season is because the earth’s axis is tilted relative to our orbit around the sun. During the summer the hemisphere you are on point towards the sun and the days are longer and in the winter it points away from the sun.
Leap days exist because a tropical year is 365.24219 days. To have a calendar that follows the season you need to have years with different lengths. 1 extra day every 4 years is a close match 365.24219*4-365*4-1=0.031 days. So we need special rules for years divisible with 100 and 400.
A topical year according to Wikipedia is
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>A tropical year (also known as a solar year) is the time that the Sun takes to return to the same position in the cycle of seasons, as seen from Earth; for example, the time from vernal equinox to vernal equinox, or from summer solstice to summer solstice. This differs from the time it takes Earth to complete one full orbit around the Sun as measured with respect to the fixed stars (the sidereal year) by about 20 minutes because of the precession of the equinoxes.
The 20 minuted difference from the obit around the sun is because the earth axis slowly changes direction. The difference is why the day of the zodiac do not match today and when the common variant was made around 2000 years ago.
20 minutes per year after 2000 years is 20*2000/60/24=27.7 days. So small difference per year adds up.
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