This evening – May 8, 2018 – at 8 p.m. Central Time in North America, our planet Earth passes in between the sun and the outer planet Jupiter. That places Jupiter opposite the sun in Earth’s sky. Therefore, astronomers call this event an opposition of Jupiter. By Universal Time, the opposition of Jupiter actually happens on May 9, at 1 Universal Time (UTC). Click here to translate Jupiter’s opposition time to your time zone).
Because Jupiter is opposite the sun, it’s now rising in the east around sunset, climbing highest in the sky at midnight and setting in the west around sunrise. It shines more brightly than any star in the evening sky, and is the second-brightest planet, after Venus. But Venus only shines for a short while in the west after sunset while Jupiter stays out all night long. At dusk or nightfall, you might catch them both: Venus blazing low in the west and Jupiter, a bit fainter but still brighter than any star, shining in the east.
Jupiter comes to opposition about every 13 months. That’s how long Earth takes to travel once around the sun relative to Jupiter. As a result – according to our earthly calendars – Jupiter’s opposition comes about a month later each year. Last year – in 2017 – Jupiter’s opposition date was April 7. Next year – in 2019 – it’ll be June 10.
Jupiter’s closest approach to Earth for the year always falls on or near this planet’s opposition date. In 2018, Jupiter comes closest to Earth about one and one-half days after its May 8th opposition date, coming to within 409 million miles (658 million km) of Earth on May 10 at 12 UTC. In other words, Jupiter is some 4.4 astronomical units from Earth at opposition.
At this 2018 opposition, Jupiter shines in front of the constellation Libra the Scales. The close 2nd-magnitude star to Jupiter is Zubenelgenubi, Libra’s alpha star. Dazzling Jupiter – a planet in our own solar system, and therefore much closer to us – outshines this star by over 100 times.
Jupiter is sometimes called a failed star. You would need at least 80 Jupiters – rolled into a ball – to be hot enough inside for thermonuclear reactions to ignite. In other words, Jupiter is not massive enough to shine as stars do.
But Jupiter is the largest and most massive planet in our solar system. So when the sun goes down on this May night, you might — if you’re fanciful enough — you might imagine bright Jupiter as a tiny sun all night long.
Bottom line: Be sure to look for Jupiter on the night of May 8-9, 2019 as this world reaches opposition, the point opposite the sun in our sky. About one and one-half day later, on May 10, at 12 UTC, Jupiter reaches its closest point to Earth for this year!