Without a doubt, it’s the most common question I’m asked at Camp Arrowhead. On Monday evenings in the summer--clouds permitting--I shuffle the 10” Meade LX200 out on to the deck of the Carmine Environmental Center. The center’s director, Suzanne Thurman, greets a group or two of the campers who have signed-up for the weekly astronomy program.

I still fumble over the answer though. After all, it isn’t so much “how far?” but “how faint?” Right? That explains why amateurs avoid the Moon and schedule star parties on new-moon weekends. And why amateurs and the pros alike are concerned about light pollution, travelling far away from city lights for observing. Larger and larger telescopes are built for collecting photons from distant objects for pictures and spectra. Observatories now boast of telescopes with mirrors 40 times the size, 1600 times the light-collecting ability of the Camp’s telescope.

A better answer would be: “Two billion light-years.”  This isn’t as arbitrary as it sounds. In Virgo, some two billion light years distant is the brightest quasar 3C 273 (arrowed at right). It is also quite probably the most distant thing visible with the eye through this telescope under even the best viewing conditions. Impressive at a gee-whiz level, but hardly a knock-your-socks-off sight, appearing as an ordinary 13th magnitude star. Interestingly, this answer is phrased both in terms of time and distance. The telescope is a look-back time-machine of a sorts: something two billion light years away appears as it did two billions years ago. Surely something to think about, but hard for a 3rd grader to get a handle on.

Another possibility is: “Thirty-six times farther than with your eyes alone.” The calculation is as follows: doubling the distance, quarters the light, but an aperture with four times the area, twice in diameter, collects the same quantity of light. Given: 10" = 250 mm, and youngster's pupils can dilate to 7 mm across. Thus,  250 mm / 7 mm = 36. So the universe expands 36 cubed in volume, “You can see almost 50,000 times more stuff.” It’s not a very good result though: while the math is fine, it ignores one of the most important astrophysical results of the last century: the universe is lumpy. Galaxies, each of billions of stars, are separated by millions of light years of empty space. Nonetheless, it sure sounds impressive.

Bigger scopes of course let you collect more light and see farther. But down here--at sea level--the view is up through the “swimming pool” of the atmosphere. Photon collecting outruns resolving power at just about 10” more or less. More magnification just makes dimmer an already turbulence-blurred image. And from mountaintops, astronomers are approaching the edge of the light and time around 15 billion light years away and ago.

But on Mondays at Camp Arrowhead, we don’t get nearly that far away or that faint. Nor do we try. The Moon, high in the sky around First Quarter, is everyone’s favorite. It’s bright, big and familiar. Smudges of light called galaxies, light buckets for photons and snapshots of the Orion Nebula drive the hobby of amateur astronomy. But the Moon lights-up the kids. More often than not, a crisp view of the Moon prompts the second most asked question: “Can you see the American flag?”

During the daylight, the LX200 is used for viewing the osprey nests along Reboboth Bay, located a mere light - microsecond away. Moondark is written by Doug Miller and published on the web, in the Delmarva Star Gazers'Star Gazer News and in the Delaware Astronomical Society's FOCUS. Please address comments and suggestions to dmiller@udel.edu. This document was last revised on 25 July 1999. All text and images copyright © 1999 Douglas C. Miller, All Rights Reserved. This material may not be reproduced in any form without prior permission.