Astronomy

Looking northeast

2 A.M., August 13

Polaris

Radiant

Algol

Pleiades

Capella

Aldebaran

ARIES

PERSEUS

TAURUS

AURIGA

10°

34 ASTRONOMY • JULY 2018

Most astronomy clubs host observing
sessions either on the night of the shower’s
predicted maximum or on a weekend night
close to it. If you’re not doing serious
meteor counting, all you’ll need to bring is
a lawn chair, some snacks, and your eyes.
Telescopes do a great job of magnifying
objects, but they severely restrict your field
of view, a negative for meteor watching.
Binoculars also restrict your view, so don’t
observe the shower through them. Instead,
if you have binoculars nearby, you can use
them to catch a close-up view of a meteor’s
smoke trail after spotting it with your
naked eye.

What’s going on?
Meteors are tiny dust-size particles of rock
and metal that Earth passes through as
it orbits the Sun. Astronomers call these
particles meteoroids when they are f loat-
ing freely in space, but when they burn up
in the atmosphere, they become meteors.
If they survive the fiery ordeal of passage
through our thick blanket of air to land on
the ground, they are then known as mete-
orites. No meteorites come from meteor
showers — the particles are too small.
Most meteor showers originate with
comets. When a comet swings around the
Sun, our star’s heat boils off ice and with it,
trapped dusty debris. When the debris
trail’s orbit crosses Earth’s orbit, we experi-
ence a meteor shower. The exception to the
comet rule is the Geminid shower, which
occurs in December. That event’s particles

• To be visible, a meteor must be within about
  120 miles (200 kilometers) of an observer.


• Meteors become visible at an average
  height of 55 miles (90 km). Nearly all
  burn up before they reach an altitude
  of 50 miles (80 km).


• No shower meteor has survived
  its flight through the atmosphere
  and been recovered.


• The typical bright meteor is produced
  by a particle no larger than a pea
  with a mass of less than 1 gram.
  
  
  • The average total mass of meteoritic
    material entering Earth’s atmosphere is
    estimated to be between 100 and 1,000 tons
    (91,000 and 910,000 kilograms) per day.
  
  
  • The typical hourly rate for meteors
    on a “non-shower” night is about
    6 meteors per hour.
  
  
  • A meteoroid enters the atmosphere with a
    velocity between 50,000 and 165,000 mph
    (81,000–265,000 km/h).
  
  
  
  

METEORS: FASCINATING FACTS

only from the darkest sites. During its next

close passage in 2126, it will shine slightly

brighter than 1st magnitude.

By the way, astronomers call this par-

ticular shower the Perseids because if you

trace all the meteor trails backward, they

meet within the boundaries of the constel-

lation Perseus the Hero. The point of origin

(the direction in space toward which Earth

is heading) is called the radiant. A good

visual approximation of the radiant is

the famous Double Cluster in Perseus

(NGC 869 and NGC 884).

2018 forecast

Scientists who study meteor showers predict

the Perseids will peak between 4 p.m. EDT

August 12 and 4 a.m. EDT August 13.

Based on these times, meteor watchers

All Perseid meteors seem to originate from a point near the Hero’s head, called the radiant.
To see the maximum number of meteors, look roughly 45° away from the radiant. ASTRONOMY: ROEN KELLY

originate with dust coming from the aster-

oid 3200 Phaethon.

Astronomers designated the Perseids’

parent comet as 109P/Swift-Tuttle. The

number identifies it as the 109th periodic

comet whose orbit astronomers have calcu-

lated. The common name comes from the

discoverers, Lewis Swift of Marathon,

New York, and Horace Parnell Tuttle,

who worked at Harvard Observatory in

Massachusetts. Each discovered the comet

in July 1862. It shone at magnitude 7.5 at

the time of the discovery and brightened to

about magnitude 2 by early September. It

sported a tail between 25° and 30° long and

was quite impressive. The comet visits our

part of the solar system every 133 years. In

November 1992, it brightened to 5th mag-

nitude and was visible without optical aid

A Perseid meteor

leaves a colorful trail

over Lake Nockamixon

in Quakertown,

Pennsylvania,

on August 13, 2016,

at 3:32 A.M. EDT. The

imager used a Canon

60Da with a Sigma

18–35mm lens at f/1.8.

He took a 7-second

exposure at ISO 800.