By Night Sky Columnist
updated 4/16/2004 1:51:41 PM ET 2004-04-16T17:51:41

A newly discovered comet should soon be visible to armchair astronomers via images posted to the Internet from the Solar and Heliospheric Observatory. 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 this spring.

However, comets are unpredictable, and casual observers may find it challenging to see any of the objects.

Retired but still working
The newest comet was discovered by William Bradfield of Yankalilla in 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. He then lost sight of it until April 8.

Daniel Green of the Central Bureau for Astronomical Telegrams announced the find on 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 observers.

Eighteen comets over a 32-year time span comes 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 cataloged as C/1995 Q1).

What to expect
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.

Image: Comet
NASA / ESA
A comet slips past the sun at lower left in a 1998 SOHO image, taken by the LASCO C3 instrument.
The projected brightness of this comet is somewhat uncertain, although right now predictions indicate that it could get as bright as second 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, 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 — 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.

Skywatching opportunity
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 23, skywatchers should concentrate on the east-northeast horizon beginning about 90 minutes before sunrise.

Unfortunately, the comet is expected to fade quickly down to magnitude 4 or 5 as it recedes from both the sun and Earth. On this astronomer's scale, larger numbers represent dimmer objects. The brightest objects are zero or first magnitude, with superbright 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.

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