According to popular lore, scientists, upon making a discovery, are supposed to exclaim, "Eureka!" However, it's said that, in reality, they are more apt to muse to themselves, or comment to a colleague, "That's funny!" And judging by his notes, that was Galileo's reaction nearly 400 years ago when, using his new telescope, he made the earthshaking discovery that Jupiter has moons.

The night of Jan. 7, 1610, upon seeing a magnified Jupiter for the first time, he noticed "three little stars" which he assumed to be ordinary background stars. "Yet," as he wrote, "they made me somewhat wonder because they seemed to be arranged exactly in a straight line, parallel to the ecliptic."

The next night, he "found a very different state of things, for there were three little stars all west of Jupiter." Curious, he "waited for the next night with the most intense longing, but was disappointed for the sky was covered with clouds."

Over the next several nights, he was able to make observations and each time saw the "stars" in a different pattern. At this point his brilliance and ability to think outside the box came into play, enabling him to infer what he was seeing--and it flew in the face of what was believed about the heavens at that time.

He wrote, "I therefore concluded, and decided unhesitatingly, that there are three stars in the heavens moving about Jupiter, which was established as clear as daylight by numerous other subsequent observations." He even determined "that there are not only three, but four, erratic sidereal bodies performing their revolutions around Jupiter.



His discovery was earthshaking because the prevailing scientific and theological world view held that all heavenly objects orbited Earth which was at the center of the cosmos. Galileo's discovery of bodies orbiting Jupiter provided visual evidence in support of the heretical Copernican theory that the Sun was at the center.

Galileo's four new "stars," which he called Medicean planets, are now named Io, Europa, Ganymede, and Callisto, and are called Jupiter's Galilean moons in his honor.

There's an irony related to Galileo's discovery. As he focused his attention on Jupiter, the planet Uranus, which would not be discovered for another 171 years, was less than 3 degrees away. However, with his crude telescopes, and given Uranus' distance, faintness, and slow movement against the background stars, it is unlikely he would have recognized it as a planet. But if he had, perhaps he would have shouted, "Eureka!"

Sky Calendar:

â ¢ Jan. 15 Thu. morning: The gibbous Moon is to lower left of Saturn.

â ¢ 17 Sat. morning: The 3rd quarter Moon to the right of Virgo's brightest star Spica.

â ¢ 21 Wed. morning: Scorpius' brightest star Antares is just to the upper left of the crescent Moon in the southeast.

â ¢ 26 Mon. The new Moon produces an annular solar eclipse, but it won't be visible from our hemisphere.

â ¢ 30 Fri. evening: The crescent Moon is above Venus.

Naked-eye Planets:

Evening: Brilliant "evening star" Venus is high in the southwest with Mercury the brightest object low in the west southwest at dark FOR the next few nights. Morning: Saturn is the brightest object high in the southwest before dawn.

Stargazer appears every other week. Paul Derrick is an amateur astronomer who lives in Waco. Contact him at 918 N. 30th, Waco, TX 76707, (254) 753-6920 or See the Stargazer Web site at