Originally published 14 January 2003
On the evening of January 4 [2003], Saturn passed in front of the Crab Nebula.
This was a rare event, and amateur astronomers around the world squinted through their eyepieces hoping to catch a glimpse of the faint nebula as a backdrop for the ringed planet.
Saturn was ideally placed for the event — pretty much opposite the sun in the sky and about as close to the Earth as it ever gets — big and bright in the telescope. And its rings were tipped towards us, like the jaunty ringed planets we see in comic books.
The Crab Nebula is 50 million times farther away than Saturn, 6,000 light-years away. It is the shattered remnant of a star that blew up in the year 1054. Under clear, dark skies, it might be seen in a good amateur telescope as a barely perceptible smudge of light against the black of space.
On January 4, I was on a Caribbean island with dark skies. Unfortunately, I only had access to a small telescope of average quality, and my chances of seeing the nebula were slim. Nevertheless, I looked on the night of the conjunction, and on the nights immediately before and after. No luck. Saturn blazed away, but the ghostly Crab was not to be seen.
I won’t say I was disappointed. Amateur astronomy is as much a matter of imagination as actual seeing. The search is the thing, the tingle in the spine that comes from plastering one’s eye to a tiny circle of glass in the hope of seeing a distant star blowing itself to smithereens as a jaunty planet passes by.
My telescope wasn’t up to the job, but it was a marvel compared to the homemade instrument Galileo used to first observe the rings of Saturn in 1610. He was not able to discern that what he saw through his scope — a blob of light to either side of the planet — was rings, although his failure of interpretation may have been partly a matter of unprepared imagination. After all, what could be more improbable than Saturn’s rings?
Since Galileo turned his telescope heavenward, we have learned not to be surprised by anything we see in the sky. Year by year, the universe reveals itself as stranger than we imagined, ever more full of wonders. Who could have guessed, for example, that the night sky is full of objects like the Crab Nebula, stars that end their lives with shattering bangs.
Every time our telescopes get bigger and better, we have new surprises — spiral galaxies, quasars, pulsars, black holes, the expanding universe, the Big Bang. The best motive for building bigger and better telescopes is the possibility of seeing things that no one anticipated.
Which is why American and European astronomers — friendly rivals — have plans for ground-based instruments of a size that would have been unimaginable only a few decades ago.
The Americans want to build a so-called Extremely Large Telescope, with a light-gathering surface 30 meters in diameter, three times the diameter and nine times the light-gathering capacity of the largest telescopes in operation today, such as the 10-meter Keck Telescope on Mauna Kea peak in Hawaii.
The Europeans, not to be outdone, are talking about a telescope 100 meters in diameter — roughly two football fields side by side — dubbed the Overwhelmingly Large Telescope, or OWL. Such an instrument would have more light-gathering power than all the telescopes in the history of astronomy put together.
Such huge instruments would not be possible to construct, and certainly not affordable, without high-speed computers and some extraordinary advances in telescope design.
The days of grinding large telescope mirrors out of single pieces of glass are past. The behemoth mirrors of today are mosaics of many smaller hexagonal mirrors working together, something that wouldn’t be possible without computer control. Moreover, the shapes of the mirrors are continuously tweaked from behind by computers to compensate for atmospheric turbulence, a process called adaptive optics.
The European OWL would cost nearly $1 billion, plus another billion to operate over 10 years — not cheap. But if all goes as planned, these big new instruments will see objects too faint to be seen with present scopes, and see familiar objects with enhanced clarity.
Meanwhile, I squint through my 3.5‑inch scope at Saturn slipping past the Crab. I don’t see the Crab, but I know it’s there, and that’s what it’s all about. If any of us are going to appreciate the universe revealed by the next generation of giant telescopes, our imaginations must be prepared for the surprising, the unexpected, the mind-blowingly bizarre.
So I squint, and in my mind’s eye I see what my little telescope fails to reveal, a star that had a long and healthy life, and is now blowing itself and its planets — some of them perhaps with rings — to kingdom come.
