Transits and Other Close Encounters

Venus, Mercury, and Jupiter align low in the Western sky this weekend. If your skies and horizon are clear, you can check a solar system triangle that shifts evening to evening.

This conjunction got me thinking … how close do the planets get as viewed from Earth? I’m looking for real excitement–not just some first magnitude “temp” constellation.

I have one event marked on my calendar. Just before Christmas in seven-point five years, Jupiter and Saturn will sit within six minutes of arc in the night sky. This won’t be some fleeting glimpse above my neighbor’s trees. I’ll get to see this one a good chunk of the night. Better yet, I’ll be able to see both Jupiter and Saturn and their brightest moons in the view of my small telescope.

Here’s what to expect on 21 December 2020, as depicted by the NASA/JPL solar system simulator:

This encounter is pretty darn close. At this moment simulated above the two largest planets in the solar system will appear as far apart in Earth’s skies as the moon’s Mare Imbrium is wide. That’s the right eye of the “man in the moon.”

Do planets ever occult (cover up) or transit across the face of another planet? Indeed they do. It hasn’t been seen much through telescopes, however. The last time it happened was the third of January, 1818 when, in the early morning sky, Venus passed in front of Jupiter, as seen from the Earth. Since the disk of Venus appears smaller than the king of planets, this simulation, left, is called a transit. Like last summer when Venus transited the sun for only the 2nd time since 1882.

Venus will transit Jupiter again in 2065. That’s the next such planet on planet encounter as seen from the Earth. Our grandchildren and great-grandchildren will then have the opportunity for four more encounters before the century is out–all involving Mercury and another planet.

Do transits (smaller body in front), occultations (smaller body behind) or eclipses (bodies about the same size) have any scientific value? Not much, really. In the pseudo-scientific tradition of astrology, I’m sure two planets appearing line-on from the Earth has super significance. But I’m just looking out for the eye candy.

Talking beyond our solar system, there is great significance for serious science. Transits are one method for detecting planets in orbit around other stars. That is very useful to scientists–it helps astronomers determine the relative size of a planet by the slight dip in stellar light (and radiation) that reaches our most sensitive instruments. The Kepler Space Telescope is one such tool. Go here to learn more about its discoveries.

Meanwhile, keep an eye on those planets. And if you stick around long enough, you might see something cool.

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About catholicsensibility

Todd and his family live in Ames, Iowa. He serves a Catholic parish of both Iowa State students and town residents.
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