Stargazing: Venus at Greatest Brightness, September Equinox

A gleaming heavenly beacon is bidding adieu to summer. Venus, in its long-running show as the “evening star,” reaches its final month of brilliance, topping out at its greatest brightness Sept. 18-22. As the third brightest object in the sky, the closest planet to the Earth will be bright enough to cast faint shadows on dark nights. For the rest of the month, Venus will sink speedily towards the horizon, vanishing from view by October. November marks its return to our skies as the “morning star,” reaching greatest brilliancy near Sun., Nov. 29.

An interesting paradox occurs when Venus reaches its gleaming peak. Due to its closeness to Earth, it will be at its observable largest. However, because of where the planet is in its orbit, only 28 percent of the disc is illuminated. Through a telescope, Venus is seen as a crescent. But the crescent shape is enormous, giving greater disc area to reflect more sunlight. The thin crescent shape is offset by the bigger expanse of reflection.

The phases of Venus are what Galileo saw and studied in 1610, which ultimately overturned the Earth-centered model of the solar system, 416 years ago.

On Tues., Sept. 22, nearly everyone on Earth will experience equal hours of day and night. With the September Equinox, those in the Northern Hemisphere will welcome the official first day of Autumn.