Does the Sun Look a Little Smaller to You? Earth at Aphelion


Ok, so the Sun shouldn’t look any smaller, but it is slightly farther away than usual.

The Earth reaches aphelion on Monday, July 4th, 2011. At this time the Earth will be at its farthest distance from the Sun for the year. If this sounds a little odd, that the Earth is farther away from the Sun in the middle of summer, remember that when the northern hemisphere is experiencing summer, the southern hemisphere is in the midst of winter.

Seasons on the Earth are caused by the tilt of the Earth’s axis relative to Earth’s orbit around the Sun. Please review last week’s blog entry about the summer solstice for more information on the seasonal changes.

Like all planets, Earth orbits the Sun in an elliptical orbit, not a circular one.

Earth at aphelion, July 4th, 2011

Earth at aphelion, July 4th, 2011

So, at some point during the year Earth and Sun will be closest together, and at some point they will be farthest apart. Earth reaches perihelion (closest approach to the Sun) around January 4th each year, and aphelion around July 4th each year. This distance change has an insignificant effect on the seasonal changes. Even though Earth’s orbit is an ellipse, the distance between the two focal points is very, very small. The difference between Earth’s closest approach to the Sun and its farthest distance from the Sun is only about 5 million km. This may sound like a great distance, but we need to realize that the average distance between Sun and Earth is about 150 million km.

On another note, totally unrelated to aphelion, the Moon is at New Moon on Friday, July 1st, and there is a partial solar eclipse associated with New Moon this July. Unfortunately, you have to be on a boat between South Africa and Antarctica to see it.

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