[astronomyed] "Planetary Wonderings" August 2007
- From: Mary-Frances Bartels <ki0dz@xxxxxxxxxxxxxxxxxxxxxxxxxxxxx>
- To: astronomyed@xxxxxxxxxxxxx
- Date: Wed, 24 Oct 2007 00:12:49 -0400
*Planetary Wonderings*
*August Focus: Perseid Meteor Shower and Near Earth Objects*
*By Mary-Frances Bartels, NASA Solar System Ambassador*
For Northern Hemisphere observers, August is usually regarded as "meteor
month" with one of the best displays of the year reaching its peak near
midmonth. That display is, of course, the annual Perseid Meteor Shower
beloved by everyone from meteor enthusiasts to summer campers. This
year's peak night will coincide with a new moon, meaning that skies will
be dark and meteors plentiful.
What is a meteor shower? Comets supply fragments that become most
meteor showers. As a comet orbits the Sun, it releases an icy, dusty
debris stream along its orbit. If Earth travels through this stream, we
will see a meteor shower. Comet Swift-Tuttle provides the material for
the Perseids. Depending on where Earth and the stream meet, meteors
appear to fall from a particular place in the sky, maybe within the
neighborhood of a constellation.
Meteor showers are named after the constellation from which meteors
appear to originate, a spot in the sky astronomers call the radiant. For
instance, the radiant for the Leonid meteor shower is located in the
constellation Leo. The Perseid meteor shower is so named because meteors
appear to fall from a point in the constellation Perseus.
This year's peak, showing the greatest number of meteors, is expected
Sunday morning (August 12), late Sunday night and Monday morning (August
13) before dawn. But you'll see some Perseids Saturday (August 11)
before dawn, too. Early in the evening one may see a few of the long,
slow, and colorful earth-grazers near the northeast horizon. The rate
of meteors falling will increase throughout the evening until the
crescendo before dawn when one may see one or two meteors per minute.
Let us now move from meteor showers to special comets and asteroids
known as *N*ear-*E*arth *O*bjects (NEOs). These particular comets and
asteroids have been nudged by the gravity of nearby planets into orbits
that allow them to enter the Earth's neighborhood. NEOs are comprised
of two major groups --- *N*ear-*E*arth *C*omets and *N*ear-*E*arth
*A*steroids. The George E. Brown, Jr. Near-Earth Object Survey Act
(2005), directed NASA to detect, track, catalogue, and characterize the
physical characteristics of larger NEOs.
*P*otentially *H*azardous *A*steroids are a subgroup of NEAs and
occasionally make it to the mainstream media. They have the potential
to come fairly close to the Earth. This potential does /not/ mean a PHA
/will/ impact the Earth. It only means a possibility exists for such a
threat. Two scales measure impact risk associated with PHAs --- the
detailed Palermo Technical Impact Hazard Scale and the more familiar
Torino Impact Hazard Scale. While there are now 876 known PHAs, none
are deemed a real danger to the Earth.
Orbit@Home is a distributed computing project, similar to SETI@Home,
which allows the public to help monitor the impact hazard posed by
Near-Earth objects. (This mention does *not* constitute endorsement of
Orbit@Home. While it appears legitimate, it is *not* mentioned on
NASA's NEO homepage. That said, this project was very recently selected
for funding by NASA.)
*Resource of the Month: *Back in April I mentioned the /What's Up/
website that gives details for viewing the night sky for each day of the
year. It only gives information for nights up to the current date. To
get the same information that includes all the dates in the current week
see http://www.universetoday.com/category/whats-up/ . Only want
highlights for the coming month? One website to check out is
Space.Com's Nightsky website at
http://www.space.com/spacewatch/sky_calendar.html .
*Activity of the Month: *Enjoy the Persied meteor shower!
Suggestions, questions, and comments about "Planetary Wonderings" are
welcomed and may be directed to stargazer @ keeplookinup.net (remove
spaces). Past columns may be found at www.keeplookingup.net
<http://www.keeplookingup.net/> (click on "Planetary Wonderings" on the
right side of opening screen).
*Remember to /keep looking up!/
/ /*
Sources:
· http://neo.jpl.nasa.gov/neo/groups.html Near Earth Objects
· http://stardate.org/nightsky/meteors/
·
http://www.earthsky.org/radioshows/51468/the-2007-peak-of-the-perseid-meteor-showe
·
http://science.nasa.gov/headlines/y2007/11jul_greatperseids.htm?list116241
--
M R Bartels ki0dz@xxxxxxxxxxxxxxxxxxxxxxxxxxxxx(((#))) ^ ^
http://www.qsl.net/ki0dz Central Ohio | ^ - ^
Watkins Products www.watkinsonline.com #092389 ------- (o o)
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