Tonight – January 12, 2017 – watch for the shining light in the west after sunset. It’s starlike, but brighter than any star. It’s the brightest planet, Venus, and it reaches a milestone in its appearance in our sky tonight, known as greatest eastern elongation. In other words, Venus is as far from the sun now as it will be for this evening apparition.
At greatest elongation, Venus swings out to its greatest angular distance of 47o east of the sun, placing Venus in fine view in the western twilight sky.
Because Venus is now farthest from the setting sun on the sky’s dome, this brilliant beauty of a planet stays out for several hours after dark. You can’t miss it because Venus is the third-brightest celestial body to light up the heavens, after the sun and moon.
Two planets reside close to Venus on the sky’s dome at present. Even though Venus outshines Mars by leaps and bounds, you will still be able to view the red planet Mars a short hop above Venus at nightfall throughout January 2017.
Depending on where you live worldwide, the planets Venus and Neptune are in conjunction and closest together for the year on the evening of January 12 or 13, 2017. You always need an optical aid to view Neptune, but it may be more difficult than usual to view Neptune because of Venus’ glare. After all, these two worlds are only about one-half degree (the moon’s diameter) apart during this particular conjunction.
It might be easier to see the 4th-magnitude star Lambda Aquarii in the same binocular field with Venus. If Venus proves to be too bright, try removing Venus from the binocular field while leaving the star Lambda Aquarii in it. You can actually see faint star Lambda Aquarii with the eye alone on a clear, dark night.
Bird’s-eye view of Earth’s and Venus’ orbits
Venus is an inferior planet that orbits the sun inside Earth’s orbit. Unlike the full moon, which rises in the east around sunset, and sets in the west around sunrise, we can never see Venus opposite the sun in our sky. In fact, we can’t even see Venus 90o from the sun in our sky – like the moon at its first quarter and last quarter phases.
Venus does resemble a little moon, however, in that it appears more or less half-illuminated in the telescope when near greatest elongation. It shows this phase now because – around this time – this world makes a 90o angle with the Earth and sun, with Venus at the vertex of this right angle. Remember, it is easier to view Venus’ phase through a telescope in a daytime or twilight sky because – at true nighttime – the glare of Venus itself can be overwhelming.
Venus is well known for its 8-year cycles, swinging out to its greatest evening elongation some 5 times every 8 years, or once every 1.6 years. After 8 years, Venus returns to nearly the same spot relative to the backdrop stars of the zodiac.
We list the greatest evening elongations of Venus for the next 8 years:
January 12, 2017
August 17, 2018
March 24, 2020
October 29, 2021
June 4, 2023
January 10, 2025
Bottom line: Enjoy Venus, as this inferior planet reaches its greatest eastern (evening) elongation – greatest apparent distance from the sun on our sky’s dome – on January 12, 2017.
Bruce McClure has served as lead writer for EarthSky's popular Tonight pages since 2004. He's a sundial aficionado, whose love for the heavens has taken him to Lake Titicaca in Bolivia and sailing in the North Atlantic, where he earned his celestial navigation certificate through the School of Ocean Sailing and Navigation. He also writes and hosts public astronomy programs and planetarium programs in and around his home in upstate New York.