Every 133 years, comet Swift-Tuttle completes another orbit. When it returns to the inner solar system and is heated by the sun, enough gas and water vapor are released to make it visible from Earth. The last time this happened was 1992. However, comet Swift-Tuttle is of interest this and every year, since it is the source of the dust and debris that causes the Perseid meteor shower.
The Perseid meteor shower is one of the best of the year, and this year, it happens during a new moon, so the skies will be extra dark. The shower can last up to a week, but the peak this year is expected tonight (Saturday) and Sunday night.
The intersection of the Earth’s orbit with that of comet Swift-Tuttle is always in the same place. From our perspective, it is in the direction of the constellation Perseus. The meteors can be seen in any part of the sky, but the radiant, or point where the meteors appear to originate is in Perseus, thus the name Perseids for the meteor shower. Within Perseus, the radiant is a bit toward the more recognizable constellation Cassiopeia. Look for the sideways “W” in the northeastern sky to identify Cassiopeia.
In a typical year, this shower will produce about 60 meteors per hour, or one per minute. Because they are not evenly spaced, some minutes will have none and some will have several. In some years, the rate can be much higher. For the best view, find a place where you can see as much of the sky as possible and get comfortable. Lie on a blanket or recline in a chair, since standing up with your neck tipped up is a sure way to shorten your viewing session.
Give yourself 20 to 30 minutes for your eyes to get completely dark-adapted. Don’t use a flashlight after your eyes have adjusted, or at least, cover any lights with red cellophane. If you can watch with someone else, you should each look toward a different part of the sky and point out any meteors you see to each other. If you have a piece of paper, making a mark when you see one is the best way to keep track of how many you see. At least for me, counting marks on a paper is much more reliable than trying to remember some running total while I am being wowed by a giant fireball.
Although seen since ancient times, it wasn’t until the 1992 visit that comet Swift-Tuttle was observed with enough precision to verify this was the previously observed comet. It was then noted that future encounters bring this comet extremely close to Earth. Close enough that it has been called the single most dangerous object known to humanity.
It is much bigger than what is thought to have ended the reign of the dinosaurs. Fortunately, we don’t have to worry about a collision for the next few thousand years. Unfortunately, calculations farther into the future than that are very unreliable.
This monthRight after dark tonight (Saturday), the planets make great markers for the zodiac. Because the moon is only a tiny crescent that sets by 9 p.m., just look for the brightest things in the sky to see the planets. Venus, Jupiter, Saturn and Mars make a line across the southern sky, and none is more than 30 degrees above the southern horizon.
Venus, the brightest one, is in the west.
Jupiter is slightly less bright than Venus, and is toward the southwest.
Saturn is just above the teapot asterism of Sagittarius and is close to the Milky Way.
Mars is the bright reddish one in the southeast. As long as there is not too much smoke in the air, Mars will be significantly more orange than the others.
Charles Hakes teaches in the Physics and Engineering Department at Fort Lewis College and is the director of the Fort Lewis Observatory. Reach him at email@example.com.