Perseid meteors are already starting to fall in a display that promises to dazzle sky-watchers this month.
the Perseid meteor shower will peak on the evening of August 12, just four days after the new moon of August 8, so the dark sky should be favorable enough for the annual display, which is one of the most reliable displays of “shooting stars”. This contrasts sharply with next August, when meteors will coincide with a full moon.
Although Perseid rates are highest in the early morning hours of August 12-14, in total, the meteor shower will last around two weeks, July 25 through August 18.
Following: Perseid meteor shower 2021: when, where and how to see it
Related: Night sky, August 2021: what you can see this month [maps]
On the evening of August 12, the moon will set around 10:30 p.m. local time. The display is expected to peak later in the night for observers across the northern hemisphere, particularly in the early twilight of the morning. According to International Meteor Organization (IMO) 2021 weather calendar, the Perseids are expected to peak for about 12 hours, centered around when the ecliptic longitude of the sun is 140.0 ° to 140.1 ° (equinox 2000.0), or August 12 from 3 p.m. to 6 p.m. EDT (1900- 2200 GMT).
Observers from Eastern Europe are ideally positioned for Perseid Peak, but North Americans are not far behind. A single observer under a dark, clear sky can theoretically see 60 members of the shower every hour, however, observers with unusually dark skies often register even larger numbers.
The Perseids are particularly attractive for introducing the public to astronomy as it is a celestial highlight that can be enjoyed without telescopes or other equipment. When planning a public awareness event, keep in mind that the number of visible meteors can be significantly increased by selecting a very dark site free from bright light, haze, and smoke.
At the maximum of the Perseids, these meteors seem to diverge from a point called the “radiant” located near the famous double star cluster in the northern part of the constellation perseus. As the night progresses, the radiant gradually rises higher in the sky to the northeast until dawn ends the observation.
In the United States, the radiant is so far north that it is above the horizon for most of the country when night falls. Thus, some Perseids may be visible from the start of the sighting, although far fewer meteors appear before midnight, even on the night of the maximum downpour.
During this time, the radiant is always low or below the horizon for places south of the equator like Australia, New Zealand and South Africa, where few, if any, Perseids can being seen.
Meteors appearing near the radiant – in Perseus and the neighboring constellations of Cassiopeia, Andromeda and Auriga – have shortened runs while those further away will tend to be longer and faster.
The safest fireworks in the world
Perseids appear white or yellowish and are well known for exhibiting many bright, fragmented meteors with fine, long streaks. The shower comes from the grime of Comet Swift-Tuttle, which orbits the sun, on average, about every 130 years.
Whenever the comet passes near the sun, as in 1992, it releases a trail of tiny particles along its orbit. Earth passes near the comet’s orbit in mid-August and interacts with these tiny chunks of cometary material, which enter our atmosphere at about 60 kilometers per second.
Despite the fact that most of this rubble is no larger than grains of sand, friction releases the kinetic energy of the particles in short-lived flashes of light. The energy released per gram of meteoroid weight far exceeds the energy efficiency of the most powerful man-made explosives.
A slightly larger particle – say the size of a pea or a pebble – can create the effect of a “shooting star” as bright as Jupiter or even Venus, while a meteoroid the size of a child’s marble can evolve into a dazzling fireball and blaze across the skies with a glow close to that of a full moon. If it explodes silently in flight, as sometimes happens with deadly cold objects that are suddenly heated to over 1,000 degrees Fahrenheit (540 degrees Celsius) in the span of a heartbeat, it is called a fireball. .
Such exceptionally bright objects are admittedly rare, but just seeing one makes an entire night of sky viewing is worth it.
My most memorable sighting of the Perseids is one that I haven’t really seen. It was on a cruise ship in the Mediterranean, where, like many of my traveling companions, I was watching the Perseids. Suddenly, the entire deck of the ship lit up for a brief moment as if a flash had gone off. We all turned around and saw a glowing trail with a small drop on one end. What just happened was obvious: a fireball ended in a burst of light, leaving a vapor trail that twisted and warped, and took nearly a minute to finally disappear.
Related: How to see the best meteor showers of 2021
To fully appreciate the Perseids, make sure you are comfortable. Instead of standing and staring at the sky open-mouthed (and risking a stiff neck), stretch out in an insulated sleeping bag or better yet, on a reclining lounge chair covered with a heavy blanket.
Expect the effective temperature to be much lower than your local meteorologist predicts: when you sit near the rapidly cooling ground, even though the air is just a little humid, you can get quite cold. In addition to diapers, have food to snack on, as well as a drink (but no alcohol, as this will interfere with your alertness).
When you first go outdoors, allow your eyes time to adjust to the dark; after about 20 minutes in the dark, the pupils of your eyes open like wells, collecting four or five times the light they usually do. The longer you stay in the dark, the more stars and meteors you will see. If you are using a flashlight, cover the lens with red cellophane, as weak red light affects your eyes much less than white light.
Also consider collecting observations that you can provide to scientists. Amateur spotters can make useful observations by counting meteors for several consecutive hour-long intervals over as many nights as possible during the duration of the downpour. All you need is a pencil, notepad, and a lawn chair or blanket. To be truly meaningful, your count should be taken from a wide open area where nothing interferes with your visual field.
Observe the sky closely and, without looking down, note each time a meteor is seen. Meticulous hour-long counts are invaluable in determining when the shower is reaching its maximum strength and how quickly activity is increasing or decreasing. Record the start and end times of the observation session, and the times of all interludes when you are not looking at the sky.
If two or more people are watching, do not register a meteor just because someone is screaming! When groups observe, the counts of each individual should be reported separately, and not combined with those of other members of the group; aggregated results of this type are meaningless, as they cannot be transformed into a standard hourly rate for a single observer.
It is also important to separately count sporadic meteors – those that do not emanate from the Perseid radiant and, as such, are not Perseids. On average, expect around 5-10 sporadic meteors per hour. The Perseids, on the other hand, can be identified by the fact that their tracks, if they extend backwards across the sky, lead to the radiant point of Perseus. If a pencil or straight stick is held in line with the meteor’s track, it will intercept the radiant. If the meteor does not pass this test, it is not a Perseid and can be classified as sporadic.
For more details on meteor counting, the International Meteor Organization offers some suggestions.
You can also try your hand at counting by magnitudes, drawing tracks on sky maps to determine radiant heat, recording colors, speeds and other characteristics of a downpour. But attempting an overly elaborate schedule can lead to disappointment in the heaviest of rain, as meteors have a way of arriving in clusters that defy both counting, magnitude estimation, and plotting. If you are observing alone, just do hourly counts and estimate the magnitudes; if you are in a group, assign each observer a limited schedule.
There are a few other reliable meteor showers at other times of the year, but the Perseids are probably the easiest to spot. the Geminids are even more prolific, but they occur in mid-December, often on very cold nights. The Perseids arrive when mosquitoes are the main dangers to the stargazer.
But keep in mind that the term “meteor shower” is a misnomer. If it is a shower, it is very widely dispersed; it’s more like waiting for the occasional drip from a faucet. But if you’re lucky enough and don’t try too hard, you might spot some beautiful shooting stars.
Good luck and clear skies to all!
Joe Rao is an instructor and guest speaker at the Hayden Planetarium in New York. He writes on astronomy for Natural History magazine, Farmers’ Almanac and other publications. Follow us on Twitter @Spacedotcom and on Facebook.