March 7, 2012
Bad news, meteor maniacs. The moon will spoil the view of this year’s Perseid meteor shower. Sorry. This year the Perseids peak on Aug. 12/13, i.e., the night of Aug. 12 until daybreak the next morning. That also happens to be the night of the full moon, which rises at sunset and sets at sunrise and blocks the view of most meteors.
Meteors are the streaks of light caused by the collision of Earth with pieces of space debris called meteoroids. Earth travels around the sun at 30,000 miles per hour. If a hunk of space crud, to use the technical term, is just sitting there, Earth’s velocity is enough to make it slam into our atmosphere with incredible force. The resulting friction heats up the meteoroid and leaves a glorious streak of light. Technically speaking, you’re not seeing the meteoroid, but the hot, ionized gasses of the atmosphere around it.
Up to a trillion meteoroids crash into our atmosphere every day, but the resulting meteor trails are visible only from a small location. Many aren’t visible at all because most meteoroids are no larger than a speck of dust. Most meteors are not visible in or near the well-lit environs of cities and towns because the streetlights brighten the sky. Also, consider that most of the planet is covered by vast stretches of uninhabited water.
Also, if the moon is up, forget about seeing any but the brightest meteors. Our nearest celestial neighbor acts like a giant streetlight in the sky. Still, from dark, rural locations on any given moonless night, you might see 5-10 bright meteors every hour.
Meteor showers happen when Earth in its orbit around the sun passes through the trail of meteoroids left by a passing comet. Because Earth takes a year to make one solar circuit, our planet passes through the same debris trail at the same time every year. At the peak of a shower like the Perseids, when Earth is passing through the thickest part of the cloud, as many as 100 streaks per hour may be visible from any moonless, rural location.
Earth plows through the debris trail as it travels through space. It also turns on its axis once per day. For the best view, you have to wait until your part of the Earth turns into the direction of its travel around the sun. If you’re on the trailing side of Earth’s path, you won’t see many meteors.
Motorcyclists know what I mean. You’re going to get a lot more bugs in your face if you’re facing forward on the motorcycle than if you’re sitting backward. From Central Ohio, the best time to observe meteors starts at about 1:30 a.m. and ends as the rising sun washes out the view (around 4:30 a.m. in summer).
Let’s summarize the conditions that have to be achieved to produce a lot of meteors. If nothing else, the list will help you plan future meteor field trips.
1. The sky has to be crystal clear. Hazy or overcast skies block the view.
2. You have to observe near the peak time.
3. Our part of Earth has to be facing into earth’s orbit. That makes the best period to observe the Perseids, if you really must go, from 1:30 a.m. to 4:30 a.m. in the wee hours of Aug. 12 and 13.
4. The moon has to be out of the way after 1:30 a.m.
5. For the best effect, you have to be far from city lights, security lights, billboard lights, etc.
6. Patience is the watchword. Take a lounge chair, and stay in it. Look in the direction away from the nearest cities. (Meteors will appear over the whole sky.) Use your peripheral vision to see as much of the sky as possible. The flow of meteors won’t be regular. Minutes may pass before you see one, and then you might see several in a row. If skies are clear, stick it out until dawn. The absolutely best time to see streaks is right before morning twilight.
7. Take along insect repellent. The local mosquito population has been praying for a stationary stargazer buffet. You fit the bill.
8. Most of all, remember that you don’t have to wait for a meteor shower to see meteors. Any clear, moonless night will produce a few meteors every hour, especially the hours between local midnight and morning twilight.
Tom Burns is the director of Ohio Wesleyan University’s Perkins Observatory. He can be emailed at firstname.lastname@example.org.