January 2019 presents a great time to catch the two brightest planets in Earth’s sky, Venus and Jupiter. Maybe you’ve seen them already. The waning crescent moon swept past them in the first few days of January, but now the moon has moved too close to the sun to be easily visible. Yet the planets remain, poised to dazzle us for the remainder of this month. Look eastward to view dazzling Venus, a brilliant beauty of a planet, shining much more brilliantly than any star. The king planet Jupiter – also extremely bright, but not as bright as Venus – can be found below Venus in the east before sunup.
Venus and Jupiter rank as the second-brightest and third-brightest heavenly bodies to light up the nighttime, respectively, after the moon.
On January 6, 2019 – if you live in just the right place on Earth (China, Korea, Japan, Russia, North Pacific Ocean and Alaska’s Aleutian Islands) – you might see the new moon taking a “bite” out of the sun. This partial solar eclipse will happen on January 5 or 6 (depending on your time zone). Afterwards the moon will return to the evening sky.
Thus the moon will disappear from the morning sky on January 6, the same date on which Venus will reach a milestone as the morning “star.” In the parlance of astronomers, it’s said that an inferior planet – like Venus or Mercury – reaches its greatest elongation from the sun when at its greatest angular distance from the sun on the dome of Earth’s sky. Venus’ coming greatest elongation will occur on January 6, 2019.
Venus is an inferior planet by virtue of the fact that it orbits the sun inside of Earth’s orbit. That’s why we can never see Venus opposite the sun in our sky. Consider a full moon; it looks full to us because its daylight side is facing us. In order to do that, the moon must be opposite the sun on the sky’s dome. As an inferior planet, Venus can’t do this. It can’t ever be opposite the sun as seen from Earth.
In fact, Venus can never get as far as 90 degrees from the sun on the sky’s dome, as viewed from Earth. The moon at its first quarter or last quarter phase resides 90 degrees from the sun in Earth’s sky. At most, Venus’ angular distance from the sun somewhat exceeds 45 degrees.
When Venus swings out to its greatest elongation as a morning “star” on January 6, 2019, it’ll be 47 degrees west of the sun on the sky’s dome. When Venus swings maximally west of the sun, this world is generally rising a maximum or near maximum amount of time before sunrise. From most places worldwide, Venus is now rising more than three hours before the sun.
Venus is well known for its eight-year cycle, by which this world swings out to its greatest western elongation 5 times every eight years. More exactly, this Venus cycle is a few days shy of eight years, so, some eight years from now, Venus will reach its greatest western elongation of 47 degrees on January 3, 2027.
And Jupiter? It is a superior planet, meaning it orbits the sun beyond Earth’s orbit. Thus its movement in our sky is very different from that of Venus, more of a yearly cycle, more determined by Earth’s smaller orbit and faster motion. Jupiter was recently behind the sun from Earth’s perspective, but it has now returned to the east before dawn. We’re still seeing it nearly along our line of sight to the sun. Jupiter will now – very steadily – rise earlier and hence climb higher in the east each morning. Ultimately, as Earth and Jupiter pursue their paths around the sun (Earth faster, Jupiter slower), Jupiter will be rising at midnight … and then at sunset. That’ll happen when Earth is passing more or less between the sun and Jupiter on June 10, 2019.
Watch Venus – as well as Jupiter – for the rest of this month. After Venus’ greatest morning elongation on January 6, 2019, Venus will slowly but surely sink in the direction of sunrise, as Jupiter climbs away from the rising sun. These two worlds are bound to meet before dawn, and so they will, for a conjunction in the morning sky on January 22, 2019.
As it flees ahead of us in its smaller orbit, Venus will remain a morning “star” for months to come. It’ll finally leave the morning sky – traveling behind the sun from Earth’s perspective – on August 14, 2019.
Bottom line: Venus reaches a milestone – greatest elongation – on January 6, 2019. This gem of a planet is now rising a maximum time before sunrise. Don’t miss the Jupiter/Venus conjunction on January 22.
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.