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16 june 2018

Jupiter is probably the easiest object to identify in the night sky, aside from the Moon. Is it really, really bright? Is it far from the Sun? Then it's almost certainly Jupiter. Actually these days I always check an app on my phone to see what's what, but before tech assistance was available, you could be fairly safe when guessing you were looking at Jupiter.

William Sheehan and Thomas Hockey, in a new book for the Reaktion Kosmos series, explain all kinds of cool things about the largest and most unusual planet. One of their key themes is how much of our knowledge of this giant neighbor is due to amateur backyard stargazers, even to this day. Jupiter is always changing. It whirls faster than Earth does, despite its dimensions, and as a result its clouds are always churning kaleidoscopically. With its enormous gravity well, Jupiter persuades smaller objects to crash into it all the time. Meanwhile, contrary to popular belief, professional research astronomers rarely sit up all night in hopes that something strange will happen on the gas giant. There are only so many professionals to go around, and grant funding to stare at a well-documented object is thin on the ground. As a result, avocational enthusiasts are the likeliest people to see the newest storm, asteroid impact, or other lightshow on the big planet.

Significant information can still be gained just by sketching what you can see of Jupiter through a home telescope. Sheehan & Hockey include a template shaped like the planet – because of the speed of its revolution, it looks like a somewhat deflated basketball – and invite the reader to draw the planet from life. Jupiter is lavishly illustrated, and the authors' favorite images are the greatest hits of planet-sketching, going all the way back to Galileo.

Sheehan & Hockey begin with a brief prologue on some cultural invocations of Jupiter. Jupiter fit into various ancient cosmologies; Wordsworth mentioned it, as did Whitman; Donato Creti painted an enigmatic image of Jupiter; but the planet doesn't figure much in high or popular culture. Bart Howard (unmentioned in Jupiter) wrote the lines that got the orb its most airplay:

Fly me to the moon
And let me play among the stars.
Let me see what spring is like
On Jupiter and Mars.
In other words … hold my hand.
In other words, baby, kiss me.
I dunno about Mars, but spring on Jupiter is apparently a wild ride. "On a planet where winds howl at half the speed of sound," the authors remark, "the general appearance … is one of seething and roiling chaos" (56). Some honeymoon tour.

Sheehan & Hockey are fascinated by the moons of Jupiter (like Tolstoy's unhappy families, each moonlike in its own way). They also provide images and narratives of the various craft that Earthlings have shot past Jupiter on their way to interstellar space. Jupiter is not only hard to avoid, but it also provides a much-needed gravity boost to propel our longest- and farthest-thinking artifacts into the great beyond; and these spacecraft have provided memorable photographs of the giant planet on their way out. I would get Jupiter for the artwork alone.

Sheehan, William, and Thomas Hockey. Jupiter. London: Reaktion, 2018.