Venus: It’s Just a Phase it’s Going Through

Seth Jarvis

Grab your party hats and telescopes, it’s time to celebrate 400 years of observational heliocentrism.

You have a good opportunity this week to observe Venus and see the dynamic geometry of the solar system in action.

While you are looking at Venus, appearing like a diminutive first-quarter moon in your telescope’s eyepiece, consider this:

Exactly four hundred years ago Galileo used his own primitive telescope to observe Venus, and through it he saw that as the nights went by Venus exhibited phases similar to those shown by our moon.

Galileo reasoned that the only way that Venus could present these phases to us on Earth is if Venus and Earth were both planets orbiting the Sun.  Prevailing thought at the time held that Earth was “fixed” in the heavens and that everything in the universe revolved around Earth.

galileo venus phases sketches

Galileo's sketches of the phases of Venus

Galileo’s observations of Venus provided hard evidence in support of Copernicus’ revolutionary assertion that we live in a heliocentric (Sun-centered) rather than geocentric (Earth-centered), universe.

Telling people in the early 1600’s that the Sun, not Earth, was the center of everything was a dangerous thing to do.  For centuries the conventional wisdom was that Earth (and by extension, mankind) was the center of the universe and everything in the heavens revolved around us.  It was the ultimate ego-trip.

Galileo was saying to the world, “Copernicus was right. Earth is a planet, like Venus, and it orbits the Sun. Night and day are the result of our planet rotating.”  That was very upsetting to the dominant belief of the day.  Galileo was charged with heresy, a crime punishable by death. He avoided execution at the hands of the Inquisition only by recanting his belief in a heliocentric universe, and he was sentenced to house arrest for the rest of his life.

For your own observations of Venus as it goes through its phases, you will need a modest telescope with at least 30x magnification.

Venus Aug 24


Look to the west soon after sunset  this week – Venus is the super bright object just above the western horizon.

Don’t dawdle, though.  Venus is moving rapidly from night to night, and will be no longer visible after sunset by about September 6th.

Venus will then be passing between Earth and the Sun for the next couple of months but will re-emerge as the “Morning Star” against the pre-dawn eastern horizon this November through February.

Happy viewing!

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3 thoughts on “Venus: It’s Just a Phase it’s Going Through

  1. “For centuries the conventional wisdom was that Earth (and by extension, mankind) was the center of the universe and everything in the heavens revolved around us. It was the ultimate ego-trip.”

    Well, it wasn’t really the ultimate ego trip. The center of the universe, in Aristotelian cosmology, was the gutter of the universe, where all that was mortal, corruptible, and imperfect was collected. The heavenly bodies, and the vast spheres containing them, on the other hand, were perfect, unchanging, and eternal. Humans were at the center, but that wasn’t by any means viewed as the best or highest place in the universe–quite the opposite. In fact, Copernicus and Galileo could boast that they were elevating the earth to a higher place by elevating it into the celestial realm.

    A good source on this:
    Mano Singham’s article on “The Copernican Myths” in Physics Today, December 2007, page 48; online at

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