Hour angle
Have you ever played hide and seek? Do you remember when your friend asked you to count to ten before you went to find them? Well, the Earth also plays hide and seek with the sun, and it counts using something called hour angle.
Hour angle is a way to measure how far the Earth has spun on its own axis. Imagine a big circle drawn around the Earth, like a hula hoop. Now, pretend that the sun is right in the middle of that circle. When we say hour angle, we mean how far the Earth has turned around that circle since the sun was last directly overhead.
Just like you counted to ten in hide and seek, the Earth uses time to count hour angle. Specifically, it uses something called Universal Time, which is the time in Greenwich, England (also known as GMT).
So, let's say it's noon in Greenwich, England, and the sun is directly overhead. At the same time, it's 7am in New York City. As the Earth rotates, New York City will turn towards the sun and it will eventually be directly overhead around 12:30pm. This means that the hour angle of New York City is 30 degrees (because the Earth rotates 360 degrees in 24 hours, and half of that is 180 degrees for 12 hours, and half of that is 90 degrees for 6 hours, and half of that is 45 degrees for 3 hours, and another half of that is 22.5 degrees for 1.5 hours, so the total is 22.5+22.5+45=90 degrees for 6 hours, and another half of that is 22.5 degrees for 1.5 hours, so the total is 90+22.5=112.5 degrees for 7.5 hours, and another half of that is 11.25 degrees for 0.75 hours, so the total is 112.5+11.25=123.75 degrees for 8.25 hours, and another half of that is 5.625 degrees for 0.375 hours, so the total is 123.75+5.625=129.375 degrees for 8.625 hours, and another half of that is 2.813 degrees for 0.188 hours, so the total is 129.375+2.813=132.188 degrees for 8.813 hours, and another half of that is 1.406 degrees for 0.094 hours, so the total is 132.188+1.406=133.594 degrees for 8.907 hours, which is about the same as 134 degrees for 9 hours), because it's turned 30 degrees from the time when the sun was directly overhead in Greenwich.
So, hour angle is just a fancy way of saying how far the Earth has turned since the sun was last directly overhead, and we measure it using time.
Hour angle is a way to measure how far the Earth has spun on its own axis. Imagine a big circle drawn around the Earth, like a hula hoop. Now, pretend that the sun is right in the middle of that circle. When we say hour angle, we mean how far the Earth has turned around that circle since the sun was last directly overhead.
Just like you counted to ten in hide and seek, the Earth uses time to count hour angle. Specifically, it uses something called Universal Time, which is the time in Greenwich, England (also known as GMT).
So, let's say it's noon in Greenwich, England, and the sun is directly overhead. At the same time, it's 7am in New York City. As the Earth rotates, New York City will turn towards the sun and it will eventually be directly overhead around 12:30pm. This means that the hour angle of New York City is 30 degrees (because the Earth rotates 360 degrees in 24 hours, and half of that is 180 degrees for 12 hours, and half of that is 90 degrees for 6 hours, and half of that is 45 degrees for 3 hours, and another half of that is 22.5 degrees for 1.5 hours, so the total is 22.5+22.5+45=90 degrees for 6 hours, and another half of that is 22.5 degrees for 1.5 hours, so the total is 90+22.5=112.5 degrees for 7.5 hours, and another half of that is 11.25 degrees for 0.75 hours, so the total is 112.5+11.25=123.75 degrees for 8.25 hours, and another half of that is 5.625 degrees for 0.375 hours, so the total is 123.75+5.625=129.375 degrees for 8.625 hours, and another half of that is 2.813 degrees for 0.188 hours, so the total is 129.375+2.813=132.188 degrees for 8.813 hours, and another half of that is 1.406 degrees for 0.094 hours, so the total is 132.188+1.406=133.594 degrees for 8.907 hours, which is about the same as 134 degrees for 9 hours), because it's turned 30 degrees from the time when the sun was directly overhead in Greenwich.
So, hour angle is just a fancy way of saying how far the Earth has turned since the sun was last directly overhead, and we measure it using time.
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