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brightest and fourth-brightest celestial objects in the sky, after the sun and moon.
• Many people see Venus, Jupiter and the moon in a twilight sky. They are so bright that all three objects can withstand a lot of twilight, as shown in the image above. Astronomers recognize three types of twilight, by the way. Astronomical twilight starts in the morning when the sun is within 18o of the horizon, nautical twilight when the sun comes within 12o, and civil twilight when the sun is 6o below the horizon. (For reference, the diameter of the sun or the moon equals one-half degree.)
• It is difficult to see planets and bright stars in the morning sky after the start of civil twilight. At 40 degrees north latitude (the latitude of Denver, Colorado), civil twilight begins about 30 minutes before sunrise, nautical twilight about 70 minutes before and astronomical twilight nearly two hours before. Click here to find out when these different kinds of twilight light up your sky.
• Bottom line: People all over the world have seen the moon pass the planets Venus and Jupiter in the predawn sky this weekend. If you're up before the sun on Monday, July 16, you have another good chance of seeing the three most brilliant orbs of nighttime gracing the predawn sky: the moon, Venus and Jupiter! Don't miss them.
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