2021, July 5: Earth at Aphelion

July 5, 2021:  Our planet Earth reaches its farthest point in its yearly trek around the sun.  Our seasons are not related to Earth’s distance from the sun.  Coincidentally, the moon is at its farthest point from Earth today.

In this exaggerated diagram, the relative positions of perihelion, perigee, perigee, and apogee.
Chart Caption: In this exaggerated diagram, the relative positions of perihelion, aphelion, perigee, and apogee are displayed.(NOAA diagram)

by Jeffrey L. Hunt

Today (at 5:27 p.m. CDT) Earth reaches its farthest point from the sun in its yearly route.

Our planet’s orbital path is not a perfect circle, but it is slightly elliptical.  In the properties of shapes, the eccentricity of a circle is zero.  Earth’s orbital eccentricity is 0.017.  Only Venus and Neptune have orbital paths that are more circular than Earth.

In the solar system, we measure distances from the sun in Astronomical Units (AU), the earth’s average distance from the sun, 1.0 AU.  In round numbers, this is 93 million miles.

Earth’s distance from the sun varies throughout the year, although the difference is small.  In January, we reach our closest spot to the sun, known as perihelion.  This year that distance was 0.983 AU.

Today at aphelion, the distance is 1.017 AU.

Seasons are from Earth’s tilt.  During the warmer months in the northern hemisphere, the sun shines most directly at the northern half of Earth.  During the colder months, the sunlight is most directed south of the equator.

The moon has a similar close approach and farthest extreme during its monthly sojourn through its obit.  Coincidentally, the moon is at its farthest point today (apogee) at 9:47 a.m. CDT (251,846.9 miles).  It is closest (perigee) on July 21 at 5:25 a.m. CDT (226,526.9 miles).

Happy Earth Perihelion Day and Lunar Apogee Day!

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