[meteorite-list] Asteroid Spotting: Skywatchers to Glimpse Close Flyby (2004 XP14)

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Fri Jun 30 12:43:37 2006
Message-ID: <200606301614.JAA00866_at_zagami.jpl.nasa.gov>

http://space.com/spacewatch/060629_night_sky.html

Asteroid Spotting: Skywatchers to Glimpse Close Flyby
By Joe Rao
SPACE.com
30 June 2006

It's not often you get a chance to spot an asteroid in our night sky.
And though the task will be challenging, experienced backyard
astronomers will give it a go this weekend.

A large asteroid will make an exceptionally close approach to our planet
early on July 3, passing just beyond the Moon's average distance from
Earth. The space rock is named 2004 XP14.

There is no chance of a collision, but professional astronomers are
keeping an eye on the object too.

Asteroid 2004 XP14 is an Apollo asteroid, a class that cross Earth's orbit.
And there are two other classes of asteroids that possess orbits that can
also take them tantalizingly near to the Earth: the Atens and Amors.

How close will 2004 XP14 be?

An astronomical unit (AU) is equal to 92,955,807 miles (149,597,870 km).
The latest calculations show that 2004 XP14 will pass closest to Earth
at 04:25 UT on July 3 (12:25 a.m. EDT or 9:25 p.m. PDT on July 2). The
asteroid's distance from Earth at that moment will be 0.0028898 AU,
which translates into 268,624 miles (432,308 km), or just 1.1 times the
Moon's average distance from Earth.

Celestial shooting gallery

Many older astronomy texts (those written before 1980) often would cite
an extremely close approach in 1937 by the asteroid Hermes, which
on Oct. 30 of that year passed within 460,000-miles (740,000 km.) of
Earth. That was usually referred to as the all-time closest approach of
a celestial body (other than the Moon) to the Earth.

It was always thought that Hermes very close approach - less than twice
the Moon's average distance from Earth - was highly unusual; almost a
unique case.

But in the last quarter century, we've come to realize that the approach
of an asteroid to within less than half a million miles of Earth is far
from uncommon.

A case in point: so far in 2006, we have already had two asteroids
approach closer than Hermes did in 1937. But these two asteroids were
estimated to be no larger than about 66-feet/20-meters across. 2004
XP14 on the other hand, is probably about 30 times larger, though for
now astronomers can only say that it's between a quarter-mile and a
half-mile wide.

And as close as 2004 XP14 will come [Map
<http://www.space.com/php/multimedia/imagedisplay/img_display.php?pic=060626_2004XP14_02.jpg&cap=View+from+Above%3A+Asteroid+2004+XP14+as+seen+on+June+17+as+its+path+approaches+the+orbit+of+Earth.+The+asteroid+will+be+closest+to+Earth+at+12%3A25+a.m.+EDT+July+3.+Credit%3A+NASA/JPL>],
another object on the Potentially Hazardous Asteroid docket is destined
to pass much closer to Earth and possibly could pose a threat to our
planet. On April 13, 2029, the asteroid 99942 Apophis is
expected to pass a mere 18,600 miles (30,000 km.) above Earth's surface.

While there is no chance that a collision will occur, there are some,
like former Apollo astronaut Rusty Schweickart, who have voiced concerns
that after the scarily close 2029 approach that Apophis' orbit could end
up in resonance with Earth's orbit. In fact, if Apophis were to pass
through a narrow "gravitational keyhole" there would be a small
possibility of a collision in 2036 or 2069. Right now, however, the
probability of such an impact is placed at 1-in-28,000.

So we now know that close encounters with asteroids happen with far
greater frequency than was once thought and that Earth has close brushes
with such cosmic rocks and boulders fairly regularly. These typically
range from the size of a house to perhaps half a mile or more in
diameter. Fortunately, the overwhelming majority of these stones miss
the Earth, but close encounters like the one with 2004 XP14 this weekend
gently reminds us that we're literally in a celestial shooting gallery.

How to sight it

Normally with such a relatively small asteroid as 2004 XP14, its peak
brightness would fall into the Pluto category, that is, it becomes no
brighter than magnitude 13 to 15 and is only available to the
most assiduous amateur astronomers and professionals with large
instruments and sophisticated equipment.

However, the combination of its size, plus its very close approach
should cause the asteroid to brighten briefly to 11th magnitude. This
is still about a hundred times fainter than the faintest star visible to
the unaided eye. Yet, those who have access to at least an eight-inch
or (preferably) larger telescope with moderate-to-high magnification and
blessed with dark, transparent skies and steady seeing probably have a
good chance of catching a glimpse of it.

And another factor that should allow observers to make a positive
identification is the asteroid's quick motion among the background
stars - probably more noticeable than carefully watching the minute hand
of a clock.

In fact, during the night of July 2-3, 2004 XP14 will appear to streak
rapidly across the star background, moving at roughly 7 to 8 degrees
per hour. The asteroid will appear to speed on a northward
trajectory. As darkness falls across North America on Sunday evening,
July 2, the asteroid will be situated along the border of the
constellations Aries, the Ram and Taurus, the Bull. It will then rocket
between the stars of Perseus and Andromeda and between 7:00 and 9:00 UT,
it will cut straight across the famous W of Cassiopeia [Sky Map
<http://www.space.com/php/multimedia/imagedisplay/img_display.php?pic=2004-XP14_map_02.jpg&cap=The+asteroid+2004+XP14+as+it+moves+through+Cassiopeia>].


For telescope users, here are the RA and Dec. positions for the
asteroid's encounter with Cassiopeia:

July 3 7h UT RA 1h 38.5m Dec. +55 deg. 25 min.

July 3 8h UT RA 1h 07.3m Dec. +61 deg. 00 min.

July 3 9h UT RA 0h 29.4m Dec. +65 deg. 27 min.

For more technically inclined SPACE.com readers, a custom ephemeris (a
table giving the coordinates of the asteroid for any number of specific
times during a given period) can be generated by going to
http://tinyurl.com/hqkn8.

2004 XP14 will approach Earth ten more times during the next 82 years,
but this weekend's will be by far, the closest. On July 4, 2061, it
will make its next closest approach to Earth: 3.12 million miles/5.04
million km away.

As far as we now know, the next very close approach of a Potentially
Hazardous Asteroid will come on November 8, 2011, when 2005 YU55 skims
Earth at a distance of 98,000 miles (158,000 km.) That?s less than half
the distance of this weekend?s close encounter with 2004 XP14.
Received on Fri 30 Jun 2006 12:14:39 PM PDT