Celestial Fireworks

They night sky is a fascinating place, particularly if you live under reasonably dark skies.  If you’re blitzed by light pollution, as are those who live in or near major cities, however, it can seem a pretty barren place, devoid of all but the brightest of stars.  In that case you might almost never look up, because what is there to see?

Sometimes, though, nature puts on a show that cuts through even the worst light pollution.  Such a show is in progress right now.  If you go outside just after sunset and look to the west, you’ll see two bright objects very close together and getting closer each day.

The brightest of the pair is Venus, the most brilliant object in Earth’s sky except for the moon and the sun.  No star and no other planet ever shines as brightly as Venus, so it’s instantly recognizable, even if you don’t know anything about astronomy.  Have a look tonight (or on the next clear night) and you’ll see what I mean.

The other object, roughly to the south (left) of Venus is giant Jupiter.  Aside from Venus itself, no planet is brighter than Jupiter, and no star is as bright.  So it, too, is instantly recognizable.  If it’s brighter than anything except Venus, it’s Jupiter.

JupiterVenus20150624The image above shows the evening sky at about 9:00 PM in Baltimore, Maryland on June 24, 2015, the day I’m writing this.   If you trace a line from Venus through Jupiter you’ll come to Regulus, the brightest star in the constellation of Leo, the lion.  Regulus is bright as stars go; it’s the 21st brightest star in the sky.  The two brightest stars in the sky right now are Arcturus, an orange star high up in the sky, and Vega, to the east and one of the three bright stars in the well-known “summer triangle.”  Finding them and comparing them to Jupiter and Venus can be interesting.

But here’s the really neat part: as the month wears on, Venus and Jupiter will grow closer and closer together, until on June 30th they are only about one-third of a degree apart.  How big is one-third of a degree?  Well, the full moon is roughly half a degree in diameter, so on the last day of June, Venus and Jupiter will be closer together than the full moon is wide.

In case you’re interested, this phenomenon–the closest approach of two celestial objects in the sky–is called appulse.  Another term sometimes used is conjunction, but technically conjunction occurs when two objects are at the same right ascension, which is essentially longitude projected onto the sky.  Venus and Jupiter will reach conjunction on July 1st, but they will be slightly farther apart than on June 30th.

By the by, “closeness” in this context is only how the objects appear in our sky.  In reality, Venus and Jupiter are nowhere near each other in space.  They just happen to line up along about the same line of sight from Earth.  Venus is 59 million miles away, while Jupiter is 561 million miles away.  The current positions of the inner planets and Jupiter are shown below.


An event of this brilliance doesn’t happen too often, so be sure to get outside and have a look as often as possible between now and the end of the month.  And keep looking after that, as Venus and Jupiter continue their dance, gradually separating again in early July.