WRAL WeatherCenter Blog

It's just a phase (of Venus)

Posted January 31, 2009 3:02 p.m. EST

At tonight's skywatching session at Jordan Lake, those who are getting their first view of Venus through a telescope might exclaim, "It looks like the Moon!"

Not that you need a telescope to see this planet. With just your eyes you can easily spot Venus by looking after sunset for the absurdly bright "star" in the west. (Don't mistake it for the actual Moon, which appears much bigger and brighter.)

But if you do use a telescope to take a closer look at Venus, you'll discover what Galileo Galilei did four centuries ago: Venus exhibits phases, like those of our Moon.

As Venus travels around the Sun, it appears to change shape as differing amounts of the side of Venus facing Earth are lit by sunlight. When Venus is in the part of its orbit where it's closer to Earth, Venus looks more like a crescent. When Venus is further away, on the far side of the Sun, it looks more fully lit.

Galileo's discovery of the phases of Venus was a big deal. It provided important evidence against the prevailing model of the time of an Earth-centered universe, and in favor of a heliocentric model, in which the planets orbit the Sun. This year we celebrate the International Year of Astronomy in part to honor Galileo's contributions to our understanding of the universe.

Tonight (Sat., Jan. 31, 2009), you can join Morehead Planetarium and Science Center for our monthly skywatching session. Put on your warmest clothes, and come to Ebenezer Church Recreation Area, Jordan Lake, between 6:30 and 8:30 p.m. In addition to the real Moon, we'll catch telescopic views of Venus looking somewhat moonlike itself.