The two largest planets in the evening sky right now are the gas giants of our solar system. They are Saturn and Jupiter. Through even a small telescope, Saturn has a remarkable system of rings. Jupiter also features a large disk with gaseous bands. There is also a retinue containing four bright satellites. Their positions change from hour to hour, night to night. Soon after nightfall, both planets can be seen clearly in the southwest evening sky.
Yet, both these giants are still far less bright than Venus, the brightest planet in our sky.
If you look in the south-southwest sky, Venus may be the first planet that you see, even before sunset. After six months of hiding from any inconveniences near the southwestern sky, Venus is now rising in the twilight. Venus is also brightening as it speeds toward Earth in its faster orbit around sun.
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A double identity
Venus orbits the sun within Earth's orbit and alternates between evening and morning sky. It spends about 9.5 months as an "evening" star and approximately the same time as a "morningstar".
These "stars" were actually two distinct celestial bodies, according to ancient Greek astronomers. The morning object was named after Phosphorus (the harbinger light) and the evening object after Hesperus, son of Atlas. Pythagoras, a Greek mathematician and philosopher who lived from 570-495 BC, was the first to realize that Hesperus and Phosphorus were the same thing.
This behavior was not understood by the ancients, and it was a puzzle to them. Galileo began to observe Venus through his crude telescope after he moved to Pisa in 1610. He noticed that one evening a small piece of Venus' disk was missing. After several months, Venus began to appear in the form of a crescent. In other words, it displayed the same phases as the Moon. This was a significant discovery that ultimately ended the long-held notion of an Earth-centered universe.
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As if you were watching an auto race.
Venus travels only a short distance east or west from the sun because, like Mercury, it is an "inferior planet" (orbiting closer to the sun than Earth). Its movement can be compared to watching an auto race from the grandstand. All the action is right in front of you and you only need to turn a small amount either direction to see it. For "superior planets", those located beyond Earth orbit, viewers on Earth, however, are just like the pit crews at the racetrack who must turn in every direction to follow the cars.
Venus appears full, or nearly so, when it is opposite the sun. It is small because it is far away from us. Because Venus travels at a higher speed around the sun than Earth, it appears larger and closer to us. The angle of sunlight hitting it from Earth's vantage point changes as well.
As Venus is about to pass between Earth, the sun and Venus, it appears like a thin crescent. It appears larger than it did when it was six times closer to Earth at this point in its orbit.
This is the schedule that shows how Venus' appearance might change over the next few weeks.
Oct. 29 The greatest eastern elongation: Venus sets approximately 2.5 hours after sunset at the point in the sky that it attains the greatest angular distance (47 degrees). Reminder: Keep your fist straight out to cover about 10 degrees of the sky. Our solar system geometry now shows Venus at a right angle to the sun and Earth. When viewed through a small telescope, Venus appears twice as big as before July 31st. It is now a stunning silvery-white "half moon" and it can be seen more than twice as often. It gradually becomes a fat crescent as it orbits closer to Earth in the nights that follow.
The southwest sky will be a spectacle after sunset on Nov. 7, with Venus and the crescent Moon. Venus will be visible to the upper left of the thin sliver. The full moon's darkened area should be visible, interposed between the sky and the sunlit crescent. This sight is often called "the old and young moons in each other's arms". It was first recognized by Leonardo da Vinci (1452-1519) as earthshine. The moon was then reflected the dim, bluish-gray light. Earth's light is reflected sunlight. Therefore, earthshine is actually sunlight that is reflected off Earth and onto the moon. On the evening of December 6, another similar pairing between Venus and the moon will occur.
Dec. 3 The greatest brilliance: Venus shines at a magnitude -4.9, setting two hours and 45 mins after the sun. It shines brightly now, so that the naked eye can see it in the deep blue sky without any haze. While it continues to approach Earth, it appears to curve in towards the sun in our sky. It is now a beautiful, large crescent visible through a telescope. As the night passes, it becomes thinner and smaller. Even with steady-held binoculars, the crescent can be seen clearly. Venus is now 38 million miles (61,000,000 kilometers) away from Earth. Venus' disk appears 26% brighter than it did a month ago.
Dec. 19 Disk 12/12 Illuminated: Although the crescent of Venus is continuing to shrink, its approach to Earth has seen it grow in length. It is now at 29 million miles (47,000,000 km) from Earth, but it is also making a rapid descent toward the sun. It is now setting 10 minutes after sunset. Its appearance is quite similar to its two cusps. Are you able to see the crescent’s "cusp extensions", threadlike, wisps light that extend beyond its points?
Dec. 26 Disk only 6% illuminated. It is crucial to locate Venus as soon as possible while it is high up in the sky and in a steady atmosphere. It is best to locate Venus well before sunset. As seen from mid-northern Latitudes, Venus rises about 15 degrees above the southwest skyline and sets 100 minutes later. Venus, now located at 27 million miles (43,000,000 km) from Earth and turning more towards us is a sign that it is closer to us than ever. It will disappear from the evening sky in a week.
Jan. 8 Inferior conjunct: Venus will transition from being an evening star to becoming a morning star, and will appear as if it is passing between Earth and the sun. On January 14, Venus will rise as a new morning star rising in the east-southeast at Mid-Dawn. It should be visible from any location with open east-southeastern views for another week, approximately 45 minutes to an hours before sunrise.