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The Perseid Radiant
The Annual Perseid Meteor Shower
Professor Michael D Smith
University of Kent
Acknowledge: many colleagues, International Meteor Organisation, ESA, NASA The annual Perseid Meteor Shower • 
Looking north ……….
The Perseid Meteor Shower: Fact Sheet Runs annually from July 17 to August 24. • 
The Perseid Meteor Shower: Fact Sheet Runs annually from July 17 to August 24. • 
The Perseid Meteor Shower: Fact Sheet Runs annually from July 17 to August 24. Peaks this year on the night of August 12 and the morning of August 13. 1
The Perseid Meteor Shower: Fact Sheet Expect to see around 60 -­‐ 100 meteors per hour this year. The best viewing will be between the hours of 11pm and 3am. But the peak is between 19:00 on the 12th until 08:00 on the 13th. No guarantee (UT – Universal Time = GMT, BST: +1h) The waning gibbous moon will block out some of the meteors this year, but the Perseids are so bright and numerous that it should still be a good show. Try looking in the opposite direction of sky from the Moon. Meteors will radiate from the constellation Perseus, but can appear anywhere in the sky……..
The Origin
Perseids have been observed for at least 2000 years.
The first information on them came from the Far East .
In the period 1864-1866, Schiaparelli (1871) proved by
calculations of the Perseid orbit that this stream shared the
orbit of Comet 1862 III (109P/Swift-Tuttle).
This was the first proven association between a meteor
shower and a comet.
It is produced by comet Swift-Tuttle.
It is periodic, period 133 years
Solid nucleus is about 26 kilometers
Currently, orbit is locked into 1:11 resonance with Jupiter
Returned in 1737, 1862, 1992 …..
So what are Meteoroids? Meteors? Meteorites? •  Small pieces of space debris (usually parts of comets
or asteroids) that are on a collision course with the
Earth are called meteoroids.
•  When meteoroids enter the Earth's atmosphere
they are
called meteors. They are travelling at
speeds of
up to 60-70 km per second.
•  If they
survive and strike the surface of
the Earth they are called meteorites.
Meteors – as Shooting Stars •  Meteoroids range in size from grains to
metre-sized rocks.
•  Enter Earth’s atmosphere and become
meteors or “shooting stars”.
•  Most meteors are tiny specks of dust. •  Larger meteors produce fireballs. Hannover, 1995!
Several hundred tons of meteoroids enter the Earth's atmosphere each day (100 million kg/year ). Most are very small pieces (milligrams) that burn up quickly in the atmosphere and never reach the surface. Perseid Shower, 1996!
Peekskill, 1992!
So what are Meteoroids? Meteors? Meteorites? •  The typical size of a meteor that produces a visible streak of light ranges from about the size of a grain of sand to the size of a small pebble. •  Average weight is only around 1 gram! •  Metre –sized rocks occasionally •  Fireballs (large, brilliant meteors) are periodically seen. These may weigh up to several undred kilograms or more. 2
Meteor Shower Designations •  Meteor showers are usually named for the constellation in which their radiant lies at the peak of the shower… Ex.: Perseid shower = Perseus Ex.: Leonid shower = Leo Ex.: Geminid shower = Gemini The Physics. Why do meteors generate a streak of light?? •  As they travel through our atmosphere, meteors collide with air molecules. •  This knocks away materials and strips electrons from the meteor. •  When the stripped atoms recapture electrons, light is emitted. •  The colour of the light depends on the temperature and the material being “excited.” 3 Questions… 1. True/False: The material or element that makes up a meteor is the main factor that determines the colour of the glowing trail left behind True 2. This major meteor shower has a peak time around early/mid August: a. Geminids b. Leonids
c. Orionids
d. Perseids d. Perseids 3. What is the point in the sky from which all of the meteors seem to come during a shower called? Radiant Meteor Showers and Comets •  Occur on a regular schedule Some Meteor Showers
Date of Meteors / Hour
at Max
Jan. 4
Aug. 12
Comet 1862 III
Oct. 21
Comet Halley
Nov. 17
Comet P/Tempel-Tuttle
Dec. 14
3200 Phaethon
Are all meteors the same colour?? Iron
The material or element that makes up a meteor is the main factor that determines the color of its glowing trail. -­‐ Magnesium
Impact Hazard: Barringer Crater in Arizona
1.2 kilometers across and 200 meters deep
formed about 49,000 years ago
impact of a 50 meter nickel/iron meteorite.
traveling at a speed of 11 kilometers per second.
The Asteroid and the Dinosaur WHEN: 65 million years WHERE: what is now Yucatan WHAT: a 10-­‐kilometer wide asteroid at an impact speed of 11 km/second RESULTS: (1) threw huge amounts of matter into the atmosphere (2) created the 180 km Chicxulub Crater (3) generating 600 meter waves (emptied the Gulf of Mexico!?). (4) months of darkness interfering with photosynthesis and climate. Stones: Chondrite Meteorites"
Contain round grains of minerals."
By far the largest number of
meteorites - 85% "
Similar in composition to
asteroids, mantles and crusts
of the terrestrial planets."
Formed: accretion, thermal
processing by a shock wave"
(5) extinction of many species, including the last of the dinosaurs. Chondrites: variety Achondrites – Stoney No round chondrules Pallasites and mesosiderites Fe-­‐Ni and rock fragments Igneous: core/mantle boundary and mixing of different material Achondrites pes
Iron Meteorites"
Primarily iron and nickel alloy: easily recognised
-­‐ Represents the cores of differenCated asteroids -­‐ Formed by melCng/crystalizaCon Originate in planetary cores of planetesimals
(large ancient asteroids).
Meteorite finds
Carbonaceous Chondrites"
Desert Finds
May contain organic compounds (e.g. amino-­‐acids) that EETA79001-Martian
may hold keys to how life developed in the Solar System. Antarctic finds
ALHA81005 – Martian
Meteorites and Meteorwrongs
Only 132 found on Earth!
Ejected from Mars surface during
Trapped gases are identical to those
measured by Viking 1 & 2 missions
Fusion crust
(ablation dents)
Viking missions carried
gas chromatography mass
spectrometers to analyse
Mars to Morocco:Tissint
•  Fell 18th July 2011 in Morocco pristine!
Moon Meteorite ALH84001 •  7kg found after the fall
•  1kg is now in London Natural History Museum
•  Offers a unique insight into the Red Planet
Lunar Meteorites
•  Discovered in Antarctica 1984
•  About 40 found on Earth
•  Dislodged from Mars about 16 million years
•  All found in hot or cold deserts
•  Ejected from moon during
•  Fell to Earth 13,000 years ago
•  May contain fossil evidence that may
indicate that primitive life existed on Mars
more than 3.6 billion years ago.
Formation of the the Moon
•  Has less iron than the Earth
•  Lacks many "volatile elements"
•  Resemble Earth's mantle
•  Oxygen isotopes are identical to Earth’s •  Moon is made of “earth-­‐like” material Several otheheories:
•  Theory: Collision with Mars-­‐size body – Theia
Binary system (co-
Comets Dirty snowballs -­‐ small objects of ice, gas, impact up to 20 million years
•  Go into orbit
Chemistry and mineralogy
identical to Apollo samples
What are meteor showers??? - result when the
Earth encounters
cometary orbits
The annual nature of
meteor showers hints
to the nature of the
orbits of meteoroids.
Comet Swift Tuttle goes
out to 52 AU and swings
in to 0.96 AU, just inside
earth’s orbit.
Comet Parts dust, tiny traces of organic material Image from Image credit: K. Jobse, P. Jenniskens and NASA Ames Research
Image from: Nucleus, Coma
Dust tail – white “smoke” reflects sun. 600,000 to 6 million miles long
Ion tail – Solar UV breaks down CO gas, glow blue. 10’s of millions of miles
So why study meteorites?
•  Unique insights into how the planets formed
•  Develop theories about the formation of the
solar system
•  Develops the understanding of neighbouring
•  Search for extraterrestial life
Rosetta’s 6th August appointment
On March 2, 2004, ESA’s Rosetta’s 6th August rendezvous
Rosetta was launched. It sent footage of Main-­‐
Belt asteroid (21) Lutetia on 10 July 2010 h To catch comet 67P/Churyumov-Gerasimenko in
2014 and accompany it into the interior solar
To deploy Philae in November to make first
controlled landing on a comet. Philae will use
harpoons to anchor itself to the come
New problem: the rubber duck
Peekskill, 1992