Леониды /english/
Leonids Made Easy
What are the Leonids?
The Leonids are a meteor shower. They are
called the Leonids because they appear to radiate out of the constellation Leo.
A Meteor, also known as a "shooting star," is a particle from space.
Its typical size ranges from that of a grain of sand to that of a pea. A meteor
appears when it enters Earth's atmosphere and burns up high overhead. Meteors can
be seen on any night, but Earth enters clouds of particles several times each
year and the result is a meteor shower.
What Do the Leonids Look Like?
All meteors appear as brief streaks of
light moving a short distance across the sky. Some meteors move slow and some
move fast. Here is a video of a bright, slow meteor. Note that a streak
persisted for a little while after the meteor vanished. This "streak"
is called the train and is basically a trail of glowing dust left in the wake
of the meteor.
The Leonids are fast meteors and they
leave lots of trains. They enter Earth's atmosphere traveling at speeds of over
158,000 miles per hour (mph). For comparison an Indy race car can reach a top
speed of about 250 mph, the fastest jet has a top speed of 2190 mph, and an
orbiting spacecraft has an average speed of 20,000 mph.
Besides being fast, the Leonids usually
contain a large number of very bright meteors. The trains of these bright
meteors can last from several seconds to several minutes.
Where Do the Leonids Come From?
Most if not all meteor showers are
produced by comets. In the case of the Leonids the parent comet is named
Tempel-Tuttle and it makes an appearance in our skies every 33 years. Comets
are composed of ice and dust. Every time a comet approaches the sun the ice
melts and dust is released. Eventually the dust spreads completely around a
comet's orbit, but most of the dust stays close to the comet. When Earth passes
through the dense cloud of dust the result is a spectacular meteor shower or a
meteor storm. Meteor storms produce several thousand meteors per hour.
When Do the Leonids Occur?
Every November 17-18 Earth crosses the
orbit of comet Tempel-Tuttle and the Leonids become visible. An observer with
clear, dark skies can see 10 or 15 Leonid meteors every hour on that morning.
Unless an observer is living at a very high northern latitude (generally within
the Arctic Circle), the Leonids are only visible during the morning hours.
Since Tempel-Tuttle passed closest to the
sun in February of 1998, the years 1998 and 1999 were expected to produce very
strong displays. During 1998 the Leonids peaked over Europe with hourly rates
of 250-300, while in 1999 astronomers are predicting an even better display
over western Europe and the Atlantic. During the mornings of November 17 and 18
observers anywhere in the Northern Hemisphere should see greater than normal
displays. Start watching sometime after about 11:30 p.m. local time (because of
Earth's rotation, local time literally means "your time"). The
radiant will still be about an hour from rising, but you will have the
opportunity to see the "Grazers". These are Leonids that are not
dropping down into Earth's atmosphere, but are instead grazing the atmosphere.
These appear as reddish meteors that advance from east to west across a large
part of the sky. In 1998 there were reports that several east coast television
stations were receiving calls that rockets were seen crossing the sky. These
"rockets" were in fact the Leonid grazers. As the radiant rises near
12:30 a.m. local time, the Leonids will travel shorter distances across the sky
as they drop down into the atmosphere. Their color will also change to white
and blue-white. Some of the brightest will actually appear slightly greenish.
As the morning progresses, meteor rates should generally increase. Keep
watching until morning twilight begins.
How Do You Observe the Leonids?
The point from where the Leonid meteors
appear to radiate is located within the constellation Leo and is referred to as
the radiant. The radiant is located in the western portion of that
constellation in what is commonly referred to as the "sickle" or
"backwards question mark." The radiant location with respect to the
horizon is shown below.
(Image produced by the Author using
Starry Night 2.0 and Adobe Photoshop 5.0. It represents the view from
mid-northern latitudes at about 3:00 a.m. local time.)
To best observe the Leonids wear
appropriate clothing for the weather. Lie outside in a reclining lawn chair
with your feet pointing towards the east (the general direction of the
radiant). Do not look directly at the radiant, but at the area above and around
it. The Leonids can be observed into morning twilight. Other minor meteor
showers will be going on at the time and stray meteors, more commonly called
sporadics, will frequently be seen that do not belong to a meteor shower. When
you see a meteor mentally trace it backwards and if you arrive at the
"sickle" of Leo it is probably a Leonid.