September 19, 2026: Venus reaches its greatest illuminated extent tonight, appearing larger through a telescope while showing an evening crescent phase. Learn why the Evening Star shines so brilliantly before sunset.
by Jeffrey L. Hunt
Chicago, Illinois: Sunrise, 6:35 a.m. CDT; Sunset, 6:53 p.m. CDT. Times are calculated by the US Naval Observatory’s MICA computer program. Check local sources for sunrise and sunset times.
Venus as an Evening Star
Venus at Greatest Illuminated Extent
Tonight, Venus is at its greatest illuminated extent.
When the moon is observed, the size of the lunar orb changes little during a lunation because of the moon’s slightly elliptical orbit. Its phase waxes to Full when the illuminated portion covers the greatest area of the sky. Thus, the Full moon is the moon’s greatest illuminated extent.
Venus’ visibility is different. Its distance from Earth changes dramatically during an apparition. During the current evening appearance, the planet’s distance has varied by more than 400%. As Venus emerged from bright evening twilight earlier in the apparition, it was farthest from Earth and displayed a nearly Full phase. As the Evening Star climbed into the evening sky, it showed a gibbous phase through a telescope. By August 15, Venus reached greatest elongation, appearing as an evening half phase, while it was about half its earlier distance from Earth and roughly twice as large in a telescope’s eyepiece.
Venus Tonight
Tonight, the planet appears more than 60% larger through a telescope than it did a month ago and displays an evening crescent phase, 25% illuminated. While the illuminated fraction is shrinking, the planet’s rapidly increasing apparent size more than compensates for the decreasing phase. As a result, the illuminated area visible from Earth reaches its maximum tonight, known as greatest illuminated extent.
As Venus descends into evening twilight, it reaches greatest brilliancy on September 23. After the sun and moon, it is the brightest celestial body in the sky. Tonight, find it less than 5° above the west-southwest horizon. Locate a clear view in that direction.
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