Mercury and Venus is the closest planet to the Sun in our Solar System. Because it is so close to the Sun, it is only observable in the early morning, just after sunrise, or at dusk. In fact, ancient Greek astronomers once believed Mercury was actually two separate objects. It usually appears as a bright “star” with a golden hue. As an evening star, appears in the western sky setting about an hour after the Sun; as a morning star, it appears in the eastern sky rising about an hour before the Sun.
Venus is the bright Evening Star that shines low in the west-southwest, 20 minutes after sunset; Venus itself sets about 80 minutes after the Sun. On the evening of September 9, the thin crescent moon hangs 4 degrees to the upper right of the Evening Star.
Mercury is the closest planet to the Sun in our Solar System. Because it is so close to the Sun, it is only observable in the early morning, just after sunrise, or at dusk. In fact, ancient Greek astronomers once believed Mercury was actually two separate objects. It usually appears as a bright “star” with a golden hue. As an evening star, appears in the western sky setting about an hour after the Sun; as a morning star, it appears in the eastern sky rising about an hour before the Sun.
In the evening hours, Venus dominates the low west-southwest sky for the first 90 minutes or so after sundown. It separated by about 15 degrees — equal to about 1.5 times the width of your fist held at arm’s length. Finally, Mercury is visible in the southwest evening sky, during the first half of the month, but is much lower than Venus and is a bit of a challenge to find. Both are wonderful telescopic targets shining brilliantly and noticeably fainter.
In our schedule, remember that when measuring the angular separation between two celestial objects, your clenched fist held at arm’s length measures roughly 10 degrees.
Mercury reaches its greatest elongation at 27 degrees east of the sun, it is also well to the south of it and may briefly be visible with binoculars before it sets only 45 minutes after sundown from mid-northern latitudes. Observers in the Gulf Coast states and the Desert Southwest are more favorably located to see this zero-magnitude planet as it follows the sun by an hour during the first half of the month.
Mercury is undergoing a very poor apparition in the evening sky until September 15: use binoculars to look for the tiny planet very low in the west 20 minutes after sunset. Mercury is gradually becoming fainter and harder to see with each passing evening during this period. Mercury will be passing between Earth and the Sun (inferior conjunction) on October 9, and will reappear in the morning sky a few days later.
When the year opens, Venus will be visible very low near the east-southeast horizon about 90 minutes before sunrise. Within several weeks it moves too close to the Sun to be seen. Superior conjunction is on March 26. Venus will be out of view until late spring when it emerges above the west-northwest horizon soon after sunset. It will gradually increase in prominence through the balance of the year. Its greatest angular distance (elongation) east of the Sun is on October 29.
After the Moon, Venus is the brightest natural object in the night sky. It is both the Earth’s closest neighbor in our Solar System and the planet most similar to Earth in size, gravity, and composition. We can’t see the surface of Venus from Earth, because it is covered with thick clouds. Venus has the densest atmosphere of the four terrestrial planets (Mercury, Venus, Earth, and Mars), which consists mostly of carbon dioxide. Always brilliant, and shining with a steady, silvery light.
Venus, which has been languishing low in the dusk all summer, at last manages to stay above the west-southwest horizon as late as the end of evening twilight. On the evening of Sept. 5, the goddess of love (magnitude -4.0) makes a beautiful passage by the 1st-magnitude star Spica; look for Spica less than 2 degrees to Venus’s lower left. The following evening you’ll find it 2 degrees to Venus’s lower right. On Sept. 9, a three-day-old crescent moon sits about 4.5 degrees to the upper right of Venus. About 5 degrees below both, you’ll perhaps still see Spica (binoculars will help).
All three objects, moon, planet and star, will form a large, loose triangle, visible low in the west-southwest sky about 40 minutes after sunset. In telescopes, Venus still appears rather unimpressive, displaying a rather small gibbous disk, 70-percent illuminated by the sun.
