June 5, 2020

AstroEvent: A Fine Meeting of Two Planets.

Jupiter & Venus the night of March 13th.

(Graphics created by the Author in Starry Night).

“What are those two large things in the night sky?” Back in 1999 I fielded almost daily questions such as this as Jupiter & Venus moved ever closer together in the evening sky, climaxing in a 9’ arc minute pairing on February 23rd. Get ready for such questions once more as the two planets approach each other again this week. Both are well placed high in the western sky at sunset 46° degrees east of the setting Sun and attaining a minimum separation of 3° degrees apart on March 13th, when dazzling Venus is north of Jupiter at 22:00 UT/18:00 EDT (Hey, we’re on ye ‘ole daylight savings time now; UKers will follow suit on March 25th!) Both reach a technical conjunction in Right Ascension about 36 hours later, with Venus shining at magnitude -4.3, while Jupiter is around -2.1, a little over 6x times difference in brightness. this is the best bright planet pairing for 2012 and is a hard one to miss! Note that those “drive-time astronomers” asking about the pair will almost always confuse “size” with “brightness” (they were HUGE, man…) an interesting observation in human perception in of itself. In actuality, Venus is currently about 58% illuminated and 20” wide (1/90th the average diameter of a Full Moon) and mighty Jupiter is fully lit at 35” arc seconds across. Venus will now vault towards a dramatic pass near the Pleiades next month on April 3rd-5th before descending to transit the Sun for the last time in our lifetimes on June 5th-6th, 2012, while Jupiter slowly descends into the dusk twilight for a conjunction with the Sun on May 13th. Venus is really truckin’ with a current apparent motion of over 1 degree a day!

3 planets (Venus, Jupiter & Mercury low on the horizon) & a space station! (Photograph by Author).

All of this is, of course part of the perception from our Earthly vantage point. Venus is currently 0.81 A.U.s away, while enormous Jupiter which has a diameter almost 12x times lager (as reckoned by its equatorial radius) and is 7 times more distant at 5.63 A.U.s from Earth. These two rank as the 3rd and 4th brightest natural objects in the sky behind the Sun and the Moon and both can cast shadows under the right conditions.

Conjunctions between the two aren’t all that rare, as they occur any time Jupiter ventures near the Sun into the domain of Venus as seen from Earth. What does make this pairing exceptional is the fact that it occurs in Aries at a well placed northern declination at a favorable angular distance from the Sun. Thus, the pairing is visible for mid-northern latitude observers for several hours after local sunset. Venus and Jupiter will also have another close pairing low in the dusk on May 28th, 2013 less than 1° degree apart, and another good morning pairing on May 28th, 2013 about 1° degree apart.

In the bizzaro astronomy department, we miss out on the pair being joined by the crescent Moon and forming a triple “Smiley face” conjunction as occurred on December 1st, 2008. The next shot at this form of cosmic irony is a skewed “face” occurring the morning of February 13th, 2056 for European longitudes;

The coming “great skewed smiley” conjunction of 2056!

Never let it be said that the cosmos doesn’t have a sense of humor!

Looking elsewhere in the skies, keep an eye on Comet C/2009 P1 Garradd as it reaches its northernmost declination of +71° at the start of this week and shines at around magnitude +7 in the constellation Draco. Garradd makes a good binocular target this spring and visits the environs of NGC 4236 the night of March 13th, passes 5 degrees southeast of the spiral galaxy M81 (photo op!) and also passes very near the +4.1 magnitude star Lambda Draconis on 17th, making it an excellent guide post to locating the icy-interloper.

Another interesting pairing occurs on March 15th when the Moon occults the open cluster M21 in the constellation Sagittarius on March 15th centered on 12:45 UT for observers in the US & Canadian Northwest. The Moon will be a waning crescent just past last quarter phase, and observers may have a chance to watch several stars in the +6.5 magnitude cluster emerge from behind the dark limb of the Moon.

Finally, the planet Mars is fresh off of opposition earlier this month and makes an interesting pass by the galaxies of M95 & M96 in the constellation Leo this week. In fact, Mars will be within half a degree of the pair from March 15th to the 19th, and will pass within 0.13 degrees of M96 at 14:00 UT on the 16th! This will be a tough visual challenge, however, as the galaxies shine at magnitude +11.4 (M95) and magnitude +10.1 (M96), while Mars glows at a dazzling -1.0, more than 63,000 times as bright! I was able to catch a steady flicker from a 10th magnitude star very near Mars while on the hunt for the Martian moons of Deimos and Phobos earlier this month, but keep in mind that that is a point source, while a deep sky object such as a galaxy has that faint magnitude scattered over its apparent surface area!  Thanks goes out to Ed Kotapish for pointing out the Mars passages by the galaxies in Leo, as well as indulging us in our crazy visions of smiley-faced conjunctions in the sky… may the heavens smile down on a back yard observing site near you!


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