#64 - Jupiter's Four Large Moons

Grab your binoculars. . .
Many of those bright points of light that we call "stars" are not stars at all. Some are planets, many are distant galaxies, and others are clouds of gas and dust called nebulae (plural for nebula). Although you can't always see them, Venus, Mars, and Jupiter (planets - NOT stars) are three of the brightest objects in the night sky - However, they aren't always in the right place for us to see them. When this picture was posted in March of 2004, it was an especially good time to see Jupiter. To find out what planets are currently visible in the night sky, CLICK HERE. IF in fact Jupiter is visible, check it out with a good pair of binoculars - You should be able to see some of its four large moons. Jupiter had 95 officially recognized moons as of March 2025, but the first four (the big ones) were discovered by Galileo in 1610. They are named Io, Europa, Ganymede, and Callisto.

Jupiter at its best . . .
The best time to see Jupiter is when it is at opposition. This happens when it is on the side of the Earth opposite the Sun. When it is opposite the Sun, Jupiter is visible all night, rising in the east in the evening and setting in the west around sunrise the next morning. On the other hand, when the Earth and Jupiter are on different sides of the Sun, Jupiter cannot be seen for months.

To find our where the planets are in relationship to the Sun (and each other), CLICK HERE, set the "size" at 1000, and then select "update".

Galileo rocked the boat . . .
Upon hearing at age 40 that a Dutch optician had invented a glass that made distant objects appear larger, Galileo crafted a telescope and began to look at the heavens. His discovery of the moons, along with other discoveries, revolutionized astronomy and challenged some of the religious and philosophical views of the time. Galileo's report that Jupiter is orbited by moons contradicted the geocentric theory, which held that the Earth was the only center of motion in the universe. With his telescope, Galileo also found that Venus went through phases like our Moon; a phenomenon that could not be explained in terms of an Earth-centered system. Furthermore, his discovery of sunspots showed that it had "blemishes," countering the Aristotelian view that the Sun was perfect. In his old age Galileo was forced by The Inquisition to recant his belief in the Copernican (heliocentric) Theory that the planets orbit around the Sun.

Term: The Inquisition, heretic