A group of amateur astronomers has used the 2.1-meter (82-inch) Otto Struve Telescope at McDonald Observatory to make the first "through-the-Eyepiece" sighting of so-called the tenth planet, an object orbiting the Sun in the Kuiper Belt, far beyond Pluto. The group included members of the St. Louis and Rockland Astronomical Societies, and a few others.

The object's official designation is 2003UB313. Its discoverers, led by Dr. Michael Brown of Caltech, have nicknamed it "Xena." The actual discovery and confirmation of the object were made by mining images taken by sensitive electronic imagers mounted on a telescope, called CCDs (charge-coupled devices).

According to Louis Berman of the St. Louis Astronomical Society, Brown confirmed to the group of amateur astronomers before their attempt that, to his knowledge, they were the only people in the world attempting to see "Xena" through the eyepiece of a telescope.

In terms of brightness, "Xena" is what astronomers would call a 19th magnitude object. That means that it's about five million times dimmer than Polaris, the North Star, which is sometimes difficult to see with the unaided eye. "Xena" is just at the limit of what can be seen with the human eye through the Struve Telescope.

The sighting took place on October 9, 2005, at 1:08 a.m. CDT. The first sighting was made by Keith Murdock of the St. Louis Astronomical Society. Confirmation occurred at 1:15 a.m. when Louis Berman, also of the St. Louis group, located the object. Eight more members of the group saw "Xena," in addition to two McDonald Observatory staffers, Kevin Mace and Frank Cianciolo. The observers followed a strict protocol and kept detailed records to verify their observations.

McDonald Observatory's Frank Cianciolo recalls the event:

"Since UB313 would not be high enough to observe until roughly 1:30 a.m. or so, the group planned to observe a number of other objects prior to the "Xena" attempt. The views of these other objects indicated that while we had reasonable conditions, we didn't have the excellent conditions the group had thought we may need to acquire UB313, so there was a bit of tension as the viewing window approached.

"At the proper time, the guys from St. Louis worked with Kevin [Mace] to get the telescope pointed to the coordinates where they had calculated UB313 should be at that precise time. Fortunately, there were no bright stars in the field of view that would cause glare and possibly ruin any chance of seeing the object. Due to some confusion about sky orientation in the eyepiece, Keith [Murdock] spent several long minutes not recognizing the field he expected to see. Once that confusion was cleared up and a small correction to the telescope's point were made, however, it didn't take long for Keith to announce that he believed he could identify, conclusively, UB313.

"After Keith's sighting, it took each observer several minutes to properly understand the orientation of the field and then to hop from brighter stars to fainter stars and finally to see "Xena." At the staggering distance of roughly 90 AU [that is, 90 times the Earth-Sun distance], an object the size of UB313 essentially displays no measurable size. Due to this, it was no easy task to actually identify the incredibly faint fuzzy dot as anything but a star at the very limit of visibility through the 82-inch [Struve Telescope]."

The object, Berman says, "was a very dim, pointlike source that could only be seen through averted vision. If you looked straight at it, you'd never see it."

McDonald Observatory's Mace agrees. "It looked like a faint star," he said. "A little difficult to pick out against the field stars. It's not visually stunning."

However, Mace continued, "how many people on the planet have seen this? Pretty much just our group."

Cianciolo credits the sighting with the group's early preparations. "Had it not been for the excellent charts and CCD images which the St. Louis group spent weeks preparing, there would have been no way to conclusively identify UB313," Cianciolo said. "It is a testament to the incredible skill and dedication some amateurs show to their passion of astronomy that the folks on the dome floor that night are, to anyone's knowledge, the only humans on the planet to have seen UB313 at an eyepiece.

"Truly this has to go down as "extreme astronomy," he said.

These days, it is unusual for large telescopes at professional observatories to even have eyepieces. The astronomers at McDonald don't use the eyepieces for their observations -- images are recorded onto computers. But the eyepiece capability makes three of McDonald's research- grade telescopes accessible to the public a few nights each month. The Struve, as well as the 2.7-meter (107-inch) Harlan J. Smith Telescope, may be the largest telescopes in the world available for public observing sessions. McDonald's smaller 0.9-meter (36-inch) telescope is also used for special public viewing programs.