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Saturn Opposition 2017 June 16, 2017

Posted by aquillam in Astronomy, MichiganAstro, Urban Observing.
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It’s summertime, and that means Saturn-time!

But why is that?

A year on Saturn is a bit more than 29 years on Earth, which means Saturn moves about 12º along the ecliptic each year. For comparison, the Moon moves about 15º per day, so in a whole year, Saturn’s position will change less than the the Moon changes in a single day! It fact it’s so little that it take Saturn an average of two years to move through each zodiac constellation. Last year Saturn crossed the boundary into Ophiuchus (between Scorpio and Sagittarius), and it won’t leave until December. That means Saturn will be visible in the evening at about the same time this year as it was last year.

Ophiuchus is often called the 13th zodiac because itt sits between Scorpio and Sagittarius

Saturn takes 29 years to make a complete circuit of the ecliptic

Of course 12º isn’t nothing. Each year opposition drifts just a little farther east along the ecliptic, so the date changes. And since there are 360º in a circle and 365 days in a year, the date corresponds to roughly a degree per day! This year, opposition was June 15th. In 2016, it was June 3, and in 2015, May 23. Next year, opposition will be June 27.

By the way, opposition is when something (like Saturn) is opposite something else (like the Sun) in the sky. So when Saturn is at opposition, it rises at sunset, then sets at sunrise. Each night it rises a little earlier, so the weeks following opposition are the best time for evening observers to get a look. Closest approach is always close to opposition too, so the planet will be bigger and brighter than usual.

elpOrbitsOpp

At opposition, the Sun, Earth, and outer planet are on a line with the Earth in between.

elpOrbitsClose

Because the orbits aren’t circles, the Earth may get closer to the outer planet a few days before or after opposition.

 

So enjoy summertime Saturn while you can. In about 4 more years, it’ll be fall when Saturn’s out.