Tonight’s the night! As seen from North America, the planets Venus and Jupiter – the two brightest points of light in all the heavens – will be in conjunction in your early evening sky. This pair of planets will shine rather low in the southwest, to the upper left of the thin waxing crescent moon.
The scene will be beautiful. It’s not to be missed, assuming you have a sky that is free of autumn cloudiness. Just be sure to catch the crescent moon, Venus and Jupiter at dusk or early evening, because they’ll set by mid-evening.
What’s all the hullabaloo about the word conjunction? Generally speaking, conjunction refers to two celestial bodies pairing up close together on the sky’s dome. More specifically, conjunction means that two heavenly bodies – such as Venus and Jupiter – are north and south of one another on the imaginary celestial sphere surrounding Earth.
Since ancient times, astronomers have imagined the heavenly ceiling as a fixed sphere of stars. The Earth’s equator projected onto this fictitious stellar sphere is called the celestial equator. The Earth’s north and south poles projected onto the stellar sphere are called the north and south celestial poles, respectively. Any half-circle running from the north to the south celestial pole is an arc of right ascension. Right ascension on the sky’s dome is the equivalent of longitude here on Earth.
When Venus passes to the south of Jupiter at 6 p.m. Eastern Time, these planets will be in conjunction and on the same arc of right ascension. That is our modern interpretation of this event. It’s also fun to contemplate how ancient stargazers might have interpreted the coming together of two such brilliant planets, plus the moon, and I got a cloudy rainy day and won't be able to see it!
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