New Comet Bradfield Makes Rare Trio
By Joe Rao
SPACE.com's Night Sky Columnist
A newly discovered comet should soon be visible to armchair
astronomers via images posted to the Internet from the Solar and Heliospheric Observatory (SOHO) spacecraft. Later this month,
sharp-eyed observers may also spot the comet in the morning sky.
The comet, named Bradfield, is racing through the inner
solar system at a time when two other comets are expected to become visible to the naked eye, providing a rare trio of opportunities
However, comets are unpredictable and casual observers
may find it challenging to see any of the objects.
The newest comet was discovered by William Bradfield of
South Australia, while the object was in the constellation Cetus. Bradfield first
spotted it low in the western evening sky with his 10-inch telescope on March 23 and again on March 24. Then lost sight of
it until April 8.
Daniel Green of the Central Bureau for Astronomical Telegrams
announced the find on the following Monday.
The 76-year-old Bradfield is credited with 17 other comet
discoveries dating back to his very first on March 12, 1972. Born in New
Zealand, Bradfield worked many years for the Australian government as a research scientist
on rocket-propulsion systems before retiring in the late 1980s.
All 18 of Bradfield's discoveries bear his name alone,
which means he spotted and reported them well ahead of any other observer. (Some comets are found by two or more observers
at roughly the same time.)
By having access to stars and constellations visible only
at far southerly latitudes, Bradfield can carefully examine regions of the sky that are unavailable to Northern Hemisphere
Eighteen comets over a 32-year time span come out to an
average of one new discovery about every 21 months. But it has been nine years since Bradfield made his last discovery (an
object catalogued as C/1995 Q1).
Green's calculations show that the comet will continue
to approach the Sun in the coming days. It should reach perihelion (its closest approach to the Sun) on April 17, when it
will be just 0.169 astronomical unit (15.7 million miles, or 25.2 million kilometers) from the solar system's central star.
This is well inside the orbit of the planet Mercury.
The projected brightness of this comet is somewhat uncertain,
although right now predictions indicate that it could get as bright as 2nd magnitude. That would be easily seen with the naked
eye. However, because of its very close proximity to the Sun, the comet will be impossible to observe for a week or more.
As it dashes past the Sun however, comet Bradfield will
be visible to those using computers and accessing near-live images from the SOHO Web site (http://sohowww.nascom.nasa.gov/data/realtime-images.html),
primarily in images from the LASCO C3 instrument.
The comet should be within range of the SOHO
imagery from about April 17 through April 19. It will appear to pass closest to the Sun -- 2.6 degrees from its center today,
on April 18.
Last year, the public was captivated by a similar scenario
when SOHO photographed a comet rounding the Sun. Hundreds of otherwise unknown comets have actually been first detected in
SOHO imagery, generating a competition among a handful of armchair astronomers. Just last
week, SOHO officials reported the 750th discovery of a comet using the spacecraft's imagery.
Because it will appear to move rapidly northward after
perihelion, comet Bradfield will ultimately emerge into the morning sky for observers in mid-northern latitudes during the
final week of April.
Beginning April 23rd, skywatchers should concentrate on
the east-northeast horizon beginning about 90 minutes before sunrise.
Unfortunately, the comet is expected to fade quickly down
to 4th or 5th magnitude as it recedes from both the Sun and Earth. On this astronomer's scale, larger numbers represent dimmer
objects. The brightest objects are zero of first magnitude, with super bright objects such as Venus achieving negative magnitudes.
Binoculars will aid observers in sighting comet Bradfield,
as well as any tail that might appear to protrude upwards from the horizon.