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Things unseen

by William J. Bechaver

EARTH — Last week the Earth was at aphelion on the Fourth of July. That is the day when the Earth was at its furthest distance from the sun in its orbit.

Many think that the Earth is closest to the sun in the summertime, but the seasons have nothing to do with our planet’s proximity to the sun.

The seasons are dictated by the tilt of the Earth’s axis, and which side of the planet more directly faces the sun. When we are furthest away from the sun, the north pole is tilted toward the sun, allowing sunlight to shine more directly on the northern hemisphere, creating longer days with more sunlight, and summer north of the equator. Likewise, it is winter in the southern hemisphere, when we happen to be farther from the sun.

Therefore, we are at our closest approach to the sun when it is winter in the northern hemisphere. Our distance from our controlling star has little to do with the surface temperature of the planet, or the cycle of the seasons.

We can’t really observe the distance to the sun increasing, though the difference in distance does alter the gravitational effects on Earth, affecting the tides slightly. But the major factor influencing the tides is the gravitational pull of the moon. Though much smaller than the sun, it’s nearness to Earth means it has a much greater gravitational effect than the sun.

Our daylight hours are also longer due to the tilt of the Earth. As Earth has the north pole tilted toward the sun, a smaller part of the northern hemisphere is left in the dark, so the night is shorter during the summer.

All planets have seasons. Some are more dramatic than others, and some are very similar to ours. Amazingly, we have discovered that other bodies in the solar system also experience tidal flows due to gravitational shifts, some creating gaseous eruptions on moons of Jupiter and Saturn, and some affecting liquid water under the bodies’ surfaces much in the same way it affects our suface water here on Earth.

Even way out on tiny Pluto, we have discovered the effects of gravitation and seasons have in the far reaches of the solar system. With Pluto’s temperature change, it develops a more substantial atmosphere at times during its orbit. We have made boundless discoveries about Pluto in the past year, and we’ll explore some of the more amazing aspects of what we’ve discovered next week, and look at the future of the New Horizon’s spacecraft as it delves even deeper into the far reaches of our outer solar system.

Thanks for the positive feedback about our columns, and your continued interest in astronomy. If you have any questions or article requests, contact us at, or follow us on Twitter @ColoSpacEScapE for updates and viewing opportunities. We are SPACE, Spanish Peaks Amateur Cosmos Enthusiasts, the premier Astronomical Society for Southern Colorado and Northern New Mexico.

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