Looking Up: Satellites share show in meteor watch
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How did you do looking for Perseid meteors this past week? If you had an opportunity to look, you might have seen why the old-fashioned concept of patience is still needed today. The average count under IDEAL conditions is seeing one meteor a minute, but more likely you had to wait many minutes.
We had the bright moon (unless you went out very late), and many of us contend with light pollution, and obstructions such as trees and rooftops. In addition, if we didn’t wait till after midnight when the meteor shower was strongest, the number seen would be sharply cut.
Nevertheless, time under the stars need never be a waste of time. Anyone enjoying the heavens above can appreciate the chance to slow down a bit and take time just to look, without even a telescope or binoculars. It’s amazing what you can see.
The Perseid meteor shower, one of numerous showers in the year, peaked on Aug. 11 and 12. A few may still be seen.
When clouds cooperated early this past week, I managed to see four Perseid meteors one night, between about 11:30 p.m. and 12:30 a.m., and three meteors on another night, between 10:30 and 11:15 p.m. On the first occasion, the moon had set and the Milky Way Band stood out gorgeously. Facing southward right into the heart of the Milky Way Galaxy -- yet never leaving my deck -- it was thrilling to see one bright meteor coursing in front of the Milky Way, soon followed by another. The brilliant head of the meteor was tracing out a dimmer, gray trail as it continued its fiery plunge in Earth’s upper atmosphere.
On another night last week there wasn’t a single meteor noticed in an hour’s watch, but the view was still exciting. Four Earth satellites came into view mostly at different times, all of them about as bright as a first-magnitude star. They each slowly moved across the sky and faded to invisibility. Science fiction buffs might say the spacecraft teleported through a black hole or vanished in an alien phaser attack. Not quite! You can easily see many satellites any clear night; there are thousands circling the world. They fade out of view as they enter the shadow of Earth.
Each of them faded out at different parts of the eastern sky, at varying heights above the horizon, in that hour’s time. By this, one can deduce the distance of the satellite, knowing the dimensions of Earth’s shadow, which extends back from the spherical Earth in a the shape of a cone and tapers to a point about 860,000 miles behind Earth.
Picture an ice cream cone. Better yet, buy one or make one. Before eating it, consider Earth to be the scoop of ice cream. It’s hard to find the right flavor to match Earth’s colors! Hopefully you picked one of those wafer cones that ends in a sharp point -- the end kids like to chew off and suck the melting ice cream. This is likened to the shadow of Earth, referred to as the “umbra.” There is also a secondary shadow around the cone called the “penumbra,” which isn’t totally dark. We usually talk about the shadow when there is a lunar eclipse, but as we have seen, our orbiting spacecraft are eclipsed continually as they enter the shadow, much closer to Earth than the moon.
The moon, by the way, dips into this shadow during an eclipse, only about a third of the way into the length of the cone.
A lovely pair
Two of the satellites were most unusual. They were very close together -- about 2 degrees apart, and one was leading the other. Equally bright, the pair crossed from south toward north, disappearing in the shadow close to overhead, in the constellation Cygnus the Swan.
This pair may have been a tethered satellite system, in which two satellites are connected by a wire for scientific research.
Full moon is on Aug. 16, and last quarter is on the 23rd. Be sure to look for brilliant Jupiter low in the south during the evening. During evening twilight, look very low in the west for brilliant Venus. Dimmer planet Mars is to the upper left of Venus, and Mercury and Saturn are to the lower right (Mercury currently appears second brightest of these four planets). Their positions will shift from night to night. Binoculars will help find the dimmer planets in the glow of dusk.
P.S. Enjoy your ice cream cone.
Keep looking up!
Peter W. Becker is managing editor at The Wayne Independent in Honesdale, Pa. He has been an amateur astronomer since the age of 12, in 1969. He may be reached at email@example.com.