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As spring begins, consider the seasons on other planets

Other planets have equinoxes, solstices (when the Sun reaches the highest or lowest point in the sky) and therefore seasons. But the length of those seasons varies significantly from those on Earth.

Posted Updated
Mars rover Curiosity
By
Tony Rice
, WRAL contributor/NASA Ambassador
While Wednesday’s forecast might not look very spring-like, spring arrived Tuesday at 12:15 p.m., astronomically speaking. The equinox occurs when the sun is directly above the equator.

This occurs twice yearly, either on March 19, 20 or 21 and again marking the beginning of autumn on September 22, 23 or 24. On other days, the 23.4 degree tilt of the Earth’s axis causes one hemisphere to more directly face the sun, giving us the seasons.

Eccentricity is the measurement of how round a circle is. A circle is 0, anything between 0 and 1 is an ellipse. Earth has an orbital eccentricity of 0.02, pretty circular but not quite. The length of the seasons vary slightly for this reason. This spring lasts 92 days and just under 18 hours. Summer is 93 days 16 hours, autumn 89 days, 20 hours, and winter just under 89 days for those of us in the northern hemisphere.

Other planets have equinoxes, solstices (when the Sun reaches the highest or lowest point in the sky) and therefore seasons. But the length of those seasons varies significantly from those on Earth.

Mars has a very Earth-like 24 degree axial tilt, but it is in an orbit further from the Sun, making for a year that is 687 Earth days long. Its more highly elliptical orbit (eccentricity 0.09) makes its seasons not only longer but even more differing. Summer began in Mars’ northern hemisphere on Nov. 20, 2017, autumn arrives May 22. Spring lasts 199 (Earth) days, summer 183, autumn 105 and winter 158 days.

Varying seasonal temperatures would be the least of your concerns if you were standing on Mars. Due to the thin atmosphere – about 100 times thinner than Earth’s – the temperature from your head to your feet will vary by about 20 degrees Fahrenheit. That thin atmosphere also makes it hard to hold onto any of that heat. The last daily low temperature reported by the Mars rover Curiosity was -103 F, the high was 21 F.

Seasons are barely noticeable on Venus due to its 3 degree axial tilt. Each season lasts a more regular 55 to 58 days due to the planet’s nearly circular orbit (eccentricity 0.01). Not much sunlight makes it to the surface of Venus, however, due to thick clouds of carbon dioxide and sulfuric acid. Seasons also occur in the outer solar system where planets have even more highly elliptical orbits. Each season lasts about 3 years at Jupiter, 7 years at Saturn, about 20 years at Uranus, and more than 40 years at Neptune. The amount of sunlight varies a lot on Saturn and Neptune due to their tilt of about 27 degrees.

Uranus is the oddball of the solar system, rotating backwards when compared to Earth and other planets. It is essentially on its side at 81 degrees axial tilt.

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