The highlight of 2004 for skywatchers was meant to be two naked-eye comets visible at the same time, which hasn't happened since 1911.
Instead, there will be three.
The third comet, known as Comet Bradfield, was discovered in early April and surprised everyone.
This is the 18th comet discovered by William Bradfield of Australia, making him the most prolific comet hunter in history, Colorado Mountain College astronomy professor Jimmy Westlake said.
By the time Bradfield discovered the comet, it already was close to the sun and bright enough to be seen by the naked eye.
The comet was traveling behind the sun Friday but will reappear this weekend in the early morning sky.
It will travel through the sky at the same time as two other predicted comets -- Comet LINEAR and Comet NEAT.
"This is very unusual," Westlake said. "It's certainly a once-in-a-lifetime experience if they develop as it is predicted they might."
Comets NEAT and LINEAR have been on the astronomical radar for years.
NEAT was discovered by its namesake, a computer program called the Near Earth Asteroid Tracking Program, which scans the sky looking for asteroids that pose a threat to Earth.
Comet LINEAR was discovered by a similar program -- the Lincoln Near Earth Asteroid Research program.
"Both of these comets are on what we think is their first trip to the inner solar system," Westlake said.
The comets have an orbit estimated to be so long that it takes a million years or more to make one trip around the sun. A picture of Comet NEAT was featured on NASA's Astronomy Picture of the Day Web site.
It showed a bright body with a long tail. A similar picture of Comet LINEAR was featured on the same Web site Thursday. LINEAR can be seen by the naked eye just as the sky is getting bright in the morning, before the sun has come up and a few stars are still visible.
"But Comet NEAT will actually put on a better show for us," Westlake said.
In the first week of May, NEAT will rise higher and higher in the evening sky as the month progresses best seen right around sundown. Comets are basically dirty snowballs traveling through space, a mixture of frozen water, carbon dioxide, methane and frozen ammonia. Mixed in with the ice are dust size particles of rocky debris.
As the snowball comes close to the sun, it turns back into a gas.
"The comets swell and vaporize, and the solar wind from the sun blows that fuzzy cloud away from the snowball creating a tail," Westlake said.
When comets are coming toward the sun, they travel headfirst. As they move away from the sun, the comet travels tail first.
"Comets are the frozen leftovers from the formation of our solar system 4.6 billion years ago," Westlake said.
"They are of interest to scientists because they may be pristine material from the early formation of our solar system. It's like studying relics from our ancient past."