The potential
The potential for a bright comet show for the spring of 2004 is based on an improved orbit that places the new comet NEATs closest point to the Sun, or perihelion, at a distance of 89.4 million miles (143.9 million kilometers) on May 15, 2004.
The comet was nearly a billion miles (1.6 billion kilometers) from the Sun when it was discovered. At that time it was shining at magnitude 20, or more than 398,000 times dimmer than the faintest star visible to the unaided eye. Most comets would be completely invisible at such a tremendous distance, even to the telescope that found it, so the implication is that Comet NEAT C/2001 Q4 may be an unusually large and active object.
The comet has brightened noticeably since its discovery, but is still very faint -- only about magnitude 14, still some 1,600 times fainter than the threshold of naked-eye visibility. It is located within the faint constellation of Fornax, the Furnace. It cannot be observed at the present time, since this part of the sky is only above the horizon during the daytime.
Sizzle of fizzle?
Most new comets are notoriously unpredictable, and there is no guarantee that comet NEAT wont fizzle. The big question is whether this activity is the sign of a truly great comet or just a temporary flare-up of an ordinary one.
A "new" comet in a parabolic orbit that is, a comet that has never passed near the Sun before may be covered with very volatile material, such as frozen carbon dioxide, nitrogen, and carbon monoxide. These ices tend to vaporize far from the Sun, giving a distant comet a surge in brightness that can raise unrealistic expectations. Several such flops appeared last century.
If you are at least 35 years old, you might remember the big build-up and subsequent letdown for comet Kohoutek during the Christmas season of 1973.
Kohoutek was discovered more than nine months before it was due to sweep around the Sun. At the time of its discovery in March 1973 it appeared unusually bright for a comet so far out from the Sun (more than half a billion miles). Some touted it as potentially the "Comet of the Century." Most astronomers hoped that if it was so bright and unusual at its discovery, that it would keep on being bright and unusual as it neared the Sun.
But it merely remained unusual rather than getting very bright.
In fact, except at the time of its perihelion, when astronauts on board the Skylab Space Station caught a glimpse of it shining brilliantly next to the Sun, to earthbound observers Kohoutek hardly appeared very bright at all. Many who looked skyward often through light polluted city skies could barely perceive the object without binoculars or telescopes.
Comet Cunningham in 1940-41 and Comet Austin in 1990 proved similarly disappointing.
Not-so-NEAT calculations
On the other hand, a comet that is in an elliptical orbit and returning to the Sun from the distant past has probably shed its highly volatile materials, so what we would be seeing is the true underlying level of its activity. Comet Hale-Bopp, which brightened the night sky during the late winter and spring of 1997, fell into this class.
Unfortunately, as of this writing, calculations by orbital experts suggests that Comet NEAT may be traveling in a parabolic orbit, hinting that it may indeed be a new comet, like Kohoutek. This however, doesnt automatically mean that Comet NEAT will fizzle-out, since not all-new comets become duds. Comet Arend-Roland is an outstanding exception, a first-timer that put on a spectacular show in April 1957.
If it indeed stays on its current prescribed path, Comet NEAT will pass closest to the Earth on May 7, 2004 at a distance of just under 30 million miles (48.3 million kilometers). It will appear to rise out of the evening twilight during the first week of May 2004 and move northward from Canis Major, through Cancer by midmonth and on into Ursa Major by months end.
And another thing
If the prospects for one bright comet doesnt excite you, how about two?
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Two comets?
Here's where both comets will be on May 15, 2004, in relation to the orbits of Earth and Venus around the Sun. The tails of both comets point away from the Sun, because it is the Sun's radiation and solar wind that strips the comet of its surface material, creating the head and tail that reflect sunlight and make a comet visible from Earth. | | | |
On Oct. 29, 2002, The IAU announced the discovery by the LINEAR survey of a comet that may also become a bright naked-eye object in May 2004.
Designated C/2002 T7 (LINEAR), the comet is currently shining at around 15th magnitude. The latest orbit suggests that it will come closest to the Sun on April 23, 2004 at a distance of about 57 million miles (91 million kilometers). Comet LINEAR, however, appears to be on projected May 2004 track that would take it eastward through the constellations of Pisces, Cetus, Eridanus, Lepus and Canis Major. This would be too low in the sky and too close to the Sun, except perhaps for those at far-southerly latitudes such as Australia, South Africa.
Should either comet evolve into a bright first-magnitude object as some forecasts suggest, either or both could end up becoming striking sights one year from now, with NEAT adorning our evening sky soon after sunset and LINEAR appearing first in the morning and then later in the evening.
But if either or both turns out to be duds, they will appear as nothing more than fuzz-balls in small telescopes.
Well just have to wait and see. One thing is for sure: the countdown is on!
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Joe Rao serves as an instructor and guest lecturer at New York's Hayden Planetarium. He writes about astronomy for The New York Times and other publications, and he is also an on-camera meteorologist for News 12 Westchester, New York.
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| Degrees measure apparent sizes of objects or distances in the sky, as seen from our vantage point. The Moon is one-half degree in width. The width of your fist held at arm's length is about 10 degrees. 1 AU, or astronomical unit, is the distance from the Sun to Earth, or about 93 million miles. Magnitude is the standard by which astronomers measure the apparent brightness of objects that appear in the sky. The lower the number, the brighter the object. The brightest stars in the sky are categorized as zero or first magnitude. Negative magnitudes are reserved for the most brilliant objects: the brightest star is Sirius (-1.4); the full Moon is -12.7; the Sun is -26.7. The faintest stars visible under dark skies are around +6. |
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