Solar System planets Mercury, Venus, and Jupiter will be in close proximity for the next few days near the western horizon just after sunset. The approximate locations of the first six planets in our Solar System for this week are shown below. A theoretical line has been drawn to show how an observer on Earth would see the alignment of the three planets.
From most of the US, Mercury will be seen passing almost directly to the north of Venus on Friday night, although the planets will be below the horizon here before the actual conjunction occurs. Mercury and Jupiter line up next in the wee hours of Sunday, though once again, the planets will have already set in the US. Finally, Venus and Jupiter come closest on Monday night in the US, but the actual conjunction, which occurs Tuesday, will not be seen due to daylight in the US at the time.
After that, these three planets won’t dance this close to each other, as observed from Earth, for about 13 years.
The conjunction of two planets means they appear in our sky at either the same right ascension or the same ecliptical longitude. All of these conjunctions are in right ascension, meaning the planets will appear in our sky directly north or south of each other as they pass.
Viewing conditions
The best time to look is about 30 to 60 minutes after the local sunset time. Mercury will be very faint but visible. It’s on its way to its greatest elongation at 24.3°E in the evening of June 12. Venus is the brightest “star” in the night sky and Jupiter’s the second brightest, so you should have no trouble spotting them.
If the skies are clear over Iowa City or Baltimore during the conjunction, I’ll try to post photos of the near approach. If you’d like me to post your pictures, please send them to photos (at) schoolsnapshots.org, and be sure to tell me in the email who you are, where you took the photos, what day and time it was, and any special things I should know about the photo.
Circumstances of the conjunctions
Mercury will be 1°22′ north of Venus (15° West elongation to the sun) on Saturday, May 25 at 03:52:17 UTC (10:52 PM Chicago Time, Friday). On Monday, May 27 at 09:47:09 UTC (4:47 AM, Chicago), Mercury will be 2°22′ north of Jupiter (17° East elongation to the sun). And finally, at 20:39:31 UTC on Tuesday, May 28 (3:39 PM Chicago), Venus will be 1° north of Jupiter (15.9° East elongation to the sun).
For all the actual conjunctions, the planets will not be visible from the US. This means what we will see here is more of a “close approach.” Note that this is a phenomenon of observation only. The planets are actually very far away from each other; they just look close in the sky as observed from Earth.
Distances of planets from Earth
This week, all three planets are on the opposite side of the sun from the Earth. Mercury is at a distance of 113 million miles (182 million km), Venus at 154 million miles (248 million km), and Jupiter at 562 million miles (904 million km), from Earth.
The difference between superior and inferior conjunction
Normally, astronomers refer to conjunctions with the sun. When the inner planet is on the opposite side of the sun as Earth, the conjunction is called a superior conjunction. When the planet’s on the same side of the sun as the Earth, it’s called an inferior conjunction. This is illustrated below:
