From the February 2021 issue

The devil’s in the details

What should you really look for through the eyepiece?
By | Published: February 18, 2021
This 2004 image of Saturn shows clearly the Cassini division — the dark gap between the planet’s A and B rings. Spotting details like this is what keep us returning to the eyepiece.
NASA/JPL/Space Science Institute
You’ve heard the cliché about details. But it’s celestially inaccurate, because details are where we usually discover the sublime — or, at least, they’re what lure our attention. So, what is it that we crave to see, time and time again?

For the sake of newbies who are just starting on this epic adventure of exploring the universe, let’s help whittle down the long process of deciding where to look. Our theme this month is the exquisite detail that, I guarantee, you’ll keep trying to observe.

For example, everyone enjoys watching Jupiter’s four big moons form a straight line with military band precision. As giant Ganymede circles back to its starting point once a week, Europa goes around exactly twice — to the second! And in that same interval, Io completes four revolutions, again with one-second accuracy. They’re bright, easy to see, and unique. And no other planet with satellites shares Jupiter’s lack of axial tilt. Jove’s poles angle a negligible 3° from vertical. And since its satellites orbit its equator, they must line up no matter where in their orbit they happen to be.

M51 (on the right) is a face-on spiral galaxy with prominent arms that attentive amateurs can glimpse through the eyepiece.
Stephen Rahn
Very cool, but not a fine-detail challenge, since observing them requires no more than a $5 toy telescope. Sharp-eyed observers have even claimed to see them unaided. So if you did invest more than $5 and want to “open ’er up” to see what the 440-horsepower engine under your telescope’s hood will accomplish, you’ll want more of a challenge.

But first, a reminder that whatever cosmic wonder you’re after, optics alone aren’t enough. If someone gave you the keys to the two 6.5-meter Magellan Telescopes (along with the instruction booklet explaining how to detach all 30 cables from the echelle spectrograph and instead insert a nice 30mm visual eyepiece), you’d still need a night of good seeing, or atmospheric stillness. Fine detail always requires good seeing. Where I live, excellent seeing conditions arrive as often as magnetic pole reversals. But when they do come — heralded when stars are not twinkling in the least — we excitedly look for cool details.

NGC 7000, also known as the North America Nebula, floats in the upper left corner of this image. Can you see the faint outline of the continent for which it is named?
Dennis Harper
On Jupiter, that starts with the Great Red Spot, the comically understated name for the universe’s largest hurricane. (Official celestial names rarely serve as worthy observing suggestions.) Jupiter’s coolest features may be the unnamed cloud details: Between its main dark belts, on the equator, diagonal white clouds contain breaks where one can peer deeply down and see actual blue sky, no joke. Some of us routinely seek out those amazing unnamed cobalt sky patches.

On Saturn, most observers seeking fine detail first try for the Cassini division. This inky gap between its A and B rings highlights the yawning breach separating the rings’ unique, epic beauty and their names, lazily derived from the alphabet. We often give things letters, like the six stars in M42’s stunning Trapezium and lunar craters around larger ones (Copernicus A, B, C, etc.). It’s not a bad idea, except where exceptional beauty cries out, unanswered, to try to stir a poet on the International Astronomical Union’s naming committee. As for that Cassini break, its impossibly narrow, half-arcsecond width somehow materializes whenever the air is steady. In the entire universe, no other thin dark line is more observed, sought after, or treasured.

You get the gist of my criteria. So, I’ll skip any further literary flourishes and simply list 10 examples of details telescopists try for when observing various celestial objects:

But what about you? Is there some marvelous detail you glimpsed long ago and have sought out ever since? Some enchanting feature the rest of us should hunt for? Share it! That’s the point of this column.

Let’s make it a contest — the winner gets to replace the names of Saturn’s A and B rings with more inspirational letters.