Suffering From Conjunction-itis | Almanac.com

Suffering From Conjunction-itis

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Let me prove how easy and fun astronomy can be.  And how dramatic.  All you need is a mostly clear sky this Tuesday evening, February 23. Anytime after around 8:30.

There’s the Moon—almost fully illuminated. And on the same night, a single brilliant star is almost touching it. That’s Jupiter—returning to our skies after a long absence.

It’s one of the most eye-catching of all celestial goodies—a bright conjunction.

That’s all you need to know. The Moon and Jupiter. Both together, brilliant, and begging for exploration.

  • The peak time for Jupiter’s conjunction with the Moon is 11 p.m. on Tuesday evening (the 23rd), as they come together in the southeastern sky.
  • To the unaided eye, neither the giant planet nor the Moon shows any detail.  Typical lunar craters are 60 miles wide.  But human 20/20 vision would only be able to discern something 200 miles across on the Moon’s surface.  Thus, not a single mountain range or crater could be glimpsed until that fateful January night in 1610 when Galileo pointed his crummy little telescope at the Moon. 
  • On Jupiter, all four of its major moons are easily visible in a straight line Tuesday night. Through any small telescope, you’ll see one on the top, and three below Jupiter. We call these the “Galilean” moons to honor discoverer Galileo.


Jupiter’s four major moons: Io, Europa, Ganymede, and Callisto. Image: Jan Sandberg/NASA.

  • The next evening, Wednesday, the Moon will have moved on but Jupiter is still there in the east at 9 PM, and now two of its moons are above the planet, with the other two below.

This conspicuous nightly change in the Jovian satellites blew Galileo’s mind.  It showed him that those moons were orbiting Jupiter at high speed, and instantly disproved the notion that had dated all the way back from Aristotle, that Earth is the center of all movement.  Can you imagine being in Galileo’s shoes 400 years ago?  Being the only one on Earth who knew the truth—that everything doesn’t revolve around us?

As for their distances,  if you could travel at light speed, you’d reach the Moon in less than two seconds. But it would take 40 minutes to reach Jupiter, far off in the distance.

It’s a wonderful yummy conjunction of Jupiter and the Moon, Tuesday night—in Leo the Lion.