Thursday, July 31, 2008

Something Old, Something New

This year, I began searching for something old and something new. No, I wasn’t outfitting myself for a traditional wedding. I was searching the sky for two celestial objects that fit squarely (or roundly, as the case may be) in the observing category I call “Things That Are Barely There.”

These two objects are really two manifestations of the same object: the Moon. New Moon is when the Moon’s too near the Sun in our sky to be visible. My quarry was an extremely young crescent Moon, less than twenty-four hours after New Moon, and an extremely old crescent Moon, less than twenty-four hours before New Moon. These are notoriously difficult to see. Imagine the thinnest slice of green cheese you can, and you’ve got the picture.

Something New

The very young waxing (growing) crescent Moon must be spied in the narrow window between sunset and moonset. On February 7, I realized I could snare a less-than-one-day-old Moon that evening. I made this determination by consulting the U.S. Naval Observatory’s Sun and Moon Data website. I find it to be an invaluable observing aid, and you’ll find a link to the site in most of my blog posts.

After entering my location and the date, I pulled up the relevant Sun/Moon data sheet. As you see in the image above, I had a 45-minute window between sunset and moonset. I knew that New Moon had just passed, and the data sheet confirmed it at 8:44 p.m. the previous evening. That meant at moonset (6:32 p.m.)--the last possible time to see the young crescent--it would be less than 22 hours old. It would also be a sliver. Note the data sheet says “waxing crescent with 0%…illuminated.” That meant the Moon’s face would be less than 1% illuminated and an elusive target.

Western horizon before sunset on 2-7-08
Chart created with
Your Sky

Armed with 10x50 binoculars and a more experienced observing partner, I drove to a location with a good view of the western sky. Because we knew the Moon follows approximately the same path across the sky as the Sun, we took note of the slanted path of the setting Sun (never look directly at the Sun!). We also noted precisely where the Sun set, relative to the land features. After the Sun was safely below the horizon, we began using the binoculars to scan for the meager Moon we knew was traveling in the Sun’s wake. We searched for 15 minutes, racing against the celestial clock, and then we spied it. It was breathtakingly slender, a curving piece of thread in a dusky sky. We tried, but weren’t able, to see it naked eye in the too-bright twilit sky. We took turns savoring it through the binoculars for the next 15 minutes. Then it disappeared behind the ridge to the west, sucked down like a strand of spaghetti.

Something Old

This morning, July 31, 2008, I attempted to complete my set. A very old waning (shrinking) crescent Moon must be spied in the narrow window between moonrise and sunrise. The USNO site gave me a one-hour window between the two. If still visible at sunrise (6:17 a.m.), the old crescent would be only 22 hours shy of New Moon.

Equipped this time with the same 10x50 binoculars and observing partner, plus an eight-inch reflector telescope, I drove to a spot with a good view of the eastern sky. I had with me a sky map showing where the Moon would rise relative to the eastern stars. Luckily, Castor and Pollux, the two brightest stars in Gemini, would make a line pointing to the twiggy Moon’s entrance.

Eastern horizon before sunrise on 7-31-08
Chart created with Your Sky

We waited for moonrise. A somber owl hooted again and again. A distant pack of coyotes yipped and barked. We enjoyed various galaxies and globular clusters in the telescope, as well as the naked-eye treat of zippy Delta Aquariid meteors emanating from the constellation Aquarius. If you can get to a dark-sky location, the “shooting stars” of this meteor shower will be active until August 19. They are short and swift, but I did see one that left a glowworm trail lasting for several seconds.

At the appointed minute of moonrise, we began searching--I with binoculars and my partner with telescope. It took several heart-pounding minutes for the crescent to clear the low mountain ridge to the east. Finally, I heard “Got it!” to my left. It was in the telescope. About 15 seconds later, I bagged it in the binos, just lifting off the ridge. Then we both spotted it naked eye, a mere wisp in the rapidly lightening sky.

Very Old Moon of 7-31-08

In the telescope, the lunar sliver was scintillating orange and green, much like a twinkling star scintillates in atmospheric murk near the horizon. As it rose, we began to see the faintest hint of craters in the sliver. I held my digital camera near the telescope’s eyepiece, carefully moving it around and snapping a photo each time the crescent floated into the viewfinder. A tripod would’ve been just the ticket; it was difficult to keep my hands steady. But I bagged my precious trophy, nonetheless.

At twenty-five minutes to sunrise, the naked-eye crescent was no longer visible in the pale blue sky. We continued to watch the Moon through the telescope. I wondered aloud if we would still see it at sunrise. The tessellated clouds overhead shifted from gray and white to rose and cream.

At the minute of sunrise, the Moon looked like a cat’s whisker in a bowl of milk, but we could still see it. The Sun was still blocked behind the eastern mountain ridge. We had the whisker for five minutes past sunrise, then it vaporized.

But the show wasn’t over! We suddenly noticed a bright object over the eastern ridge. At first we thought it was Venus, until we slapped our punch-drunk selves awake, remembering that Venus was currently too close to the Sun to be visible. Aha, could it be? Sure enough, a look through the telescope confirmed the bright, bulbous shape of a weather balloon. Something serendipitous.