Conjunction of Jupiter and Venus: What is a conjunction?
A conjunction is when two astronomical objects are either at the same right ascension (hour angle as plotted on a star atlas) or the same ecliptic longitude, as observed from Earth. Conjunctions of the bright planets occur when they appear to move past each other in the sky. Sometimes they seem to nearly meet, although they are millions of miles apart.
What is Ultra Close Conjunction?
Whereas a normal conjunction occurs at the instant the two bodies have the same right ascension or the same ecliptic longitude, this time separation between two bodies is at an absolute minimum, making it a special case called Ultra conjunction or Appulse.
Conjunction of Jupiter and Venus
Venus revolves around the sun once in about 225 days. Because our planet is moving, Venus catches up to and passes by Earth every 584 days. Jupiter is a slower moving participant in this celestial waltz as it revolves around the sun once in nearly 12 years.
A conjunction between Venus and Jupiter, in and of itself, is not a rare event; it occurs about eight to 12 times per decade, on average. Usually, in such cases, the smallest angular distance between these two planets is about a degree or two, with 1 degree equal to the width of two full moons. While not a “once-in-a-lifetime” event, these close conjunctions are infrequent enough to attract the attention of even the casual sky watchers.
But the August 27 occurrence will be a rather special case. It is a very close approach of the Venus to Jupiter, making this an ultra close conjunction.
Conjunction of Jupiter and Venus: Why is this conjunction special?
The two brightest planets in the night sky, Venus and Jupiter, will come close together on Aug. 27, 2016, in their closest encounter until 2065.
On Saturday, Aug. 27, sky watchers will get a chance to see Venus and Jupiter paired in an extremely close configuration.
As Jupiter is going down, Venus is gradually coming up. When the two planets pass each other on Aug. 27, it will be, in a way, the passing of the torch; Jupiter will relinquish the title of “evening star” to Venus.
Where and when to see?
Before the 27th, find a location that can provide you with a clear and unobstructed view of the western sky. The two planets will lie only 5 degrees above the western horizon about 30 minutes after sunset in bright twilight; brighter Venus will shine just above Jupiter. You can judge how high above the horizon 5 degrees is by making a fist and holding it out at arm’s length. Place the bottom of your fist on the horizon, and the top part is 10 degrees. So the two planets will be only half that width above the western horizon a half hour after sundown.
If the sky is hazy, you might also want to scan the horizon with binoculars to help you pick them out. Be sure to take a look, it will take until 2065 to catch an approach closer than this.
How Close Jupiter and Venus will appear?
To get a better idea of how close this is, check out the northwest sky as soon as it gets dark, and locate the seven stars of the Big Dipper. Look at the middle star in the handle of the Dipper; that’s Mizar. With normal eyesight, you should be able to make out a fainter star just above Mizar, shining about one-fifth as brightly. That’s Alcor. The ancient Arabs considered it to be a test of good eyesight. Mizar and Alcor are separated by 12 arc minutes. Remember that point when you see them in the sky. Also remember that at the moment of their ultra conjunction on the 27th, the distance between Venus and Jupiter will be only one-third that which separates Mizar from Alcor.