Catch Mercury Brushing Past Venus in a Spectacular Dusk ‘Quasi-Conjunction’ This Week


Missing Venus? The third brightest natural object in the heavens returns to prime time dusk skies in 2015 after being absent and lingering in the dawn for most of 2014. But there’s another reason to hunt down the Cytherean world this week, as elusive Mercury chases after it low in the dusk. If you’ve never seen Mercury for yourself, now is a great time to try, using brilliant Venus as a guide.

The circumstances surrounding this pairing are intriguing. We have to admit, we missed this close conjunction whilst filtering through research for the Top 101 Astronomical Events for 2015 due to those very same unique attributes until an astute reader of Universe Today pointed it out.

December 31st Bob King
Venus and Mercury setting over the Duluth, Minnesota skyline on December 31st. Credit and copyright: Bob King.

On the evening of January 5th, Venus shines at magnitude -3.3 and sits about 18 degrees east of the Sun in dusk skies.  You’ll have a narrow window of opportunity to nab Venus, as it’ll sit only 10 degrees above the southwestern horizon as seen from latitude 40 degrees north about an hour after sunset. Make sure you have a clear, uncluttered horizon, and start sweeping the field with binoculars about half an hour after sunset.

Do you see a tiny point of light about a degree and a half to Venus’s lower right? That’s Mercury, just beginning its first dusk apparition of seven for 2015, the most possible in a calendar year. Shining at -0.7 magnitude, Mercury is currently about 8 times fainter than Venus, and drops to +1.4 magnitude by late January.

If you watch the pair on successive evenings, you’ll see Mercury — aptly named after the fleet-footed Roman god — racing to rapidly close the gap. Mercury crosses the one degree separation threshold from January 8th through January 12th, and sits just 39’ — slightly larger than the apparent size of the Full Moon — right around 7:00 PM EST/Midnight Universal Time on January 10th, favoring dusk along eastern North America just a few hours prior.

Credit Jose
Venus and Mercury as seen from Venezuela on January 2nd. Credit and copyright: Jose Rozada.

This also means that you’ll be able to squeeze both Mercury and Venus into the same low power telescopic field of view. They’ll both even show the same approximate gibbous phase, with Venus presenting a 10.5” sized 95% illuminated disk, and Mercury subtending 6” in apparent diameter with a 74% illuminated visage. Venus will seem to be doing its very own mocking impersonation of the Earth, appearing to have a single large moon… Neith, the spurious pseudo-moon of Venus lives!

One curious facet of this week’s conjunction is the fact that Venus and Mercury approach, but never quite meet each other in right ascension. We call such a near miss a “quasi-conjunction.” This is the closest pairing of Venus and Mercury since 2012, though you have to go all the way back to 2005 for one that was easily observable, and the last true quasi-conjunction was in October 2001. Miss this week’s event, and you’ll have to wait until May 13th 2016 to catch Mercury — fresh off of transiting the Sun a week earlier — passing just 26’ from Venus only 6.5 degrees west of the Sun. This is unobservable from your backyard, but SOHO’s LASCO C3 camera’s 15 degree wide field of view will have a front row cyber-seat.

Venus 2015
The dusk path of Venus through early 2015. Credit: Starry Night Education software.

In 2015, Venus will become ever more prominent in the dusk sky before reaching greatest elongation 45.4 degrees east of the Sun on June 6th, 2015. The angle of the January ecliptic at dusk is currently shoving Mercury and Venus southward for northern hemisphere observers, though that’ll change dramatically as we head towards the March equinox. Venus reaches solar conjunction sans transit (which last occurred in 2012 and won’t happen again til 2117 A.D.) on August 15th before heading towards its second elongation of 2015 on October 26th in the dawn sky.  And don’t forget, it’s possible to see Venus in the daytime as it approaches greatest elongation. Venus is also occulted by the Moon 4 times in 2015, including a fine daytime occultation on December 7th for North America.

Mercury through January 2015.
The path of Mercury through January 2015. Credit: Starry Night Education software.

This month, Mercury reaches greatest eastern elongation on January 14th at 18.9 degrees east of the Sun.  Mercury begins retrograde movement later this month — one of the prime reasons this week’s conjunction is quasi — before resuming direct (eastward) motion as seen from our terrestrial vantage point. Though it may seem convenient to blame your earthly woes on Mercury in retrograde as astrologers will have you believe, this is just an illusion of planetary orbital motion. And speaking of motion, Mercury transits the Sun next year on May 9th.

John Barantine
Venus and Mercury as seen from Tucson, Arizona on January 3rd. Credit and copyright: John Barentine (@JohnBarentine)

Mercury and Venus factor in to space exploration in 2015 as well. NASA’s MESSENGER spacecraft wraps up its successful mission  in orbit around Mercury in a few months, and the Japanese Space Agency takes another crack at putting its Akatsuki spacecraft in orbit around Venus this coming November.

So don’t fear the bone-chilling January temps (or Mercury in retrograde) but do get out there these coming evenings and check out the fine celestial waltz being performed by the solar system’s two innermost worlds.


How to See Planet Mercury at its Best in 2014

Looking west on January 31st 30 minutes after sunset. (Created using Stellarium).

 There’s an often told anecdote that astronomer Nicolaus Copernicus never spied Mercury. And while this tale is almost certainly apocryphal, it does speak to just how elusive the innermost planet of our solar system really is.

Never seen Mercury for yourself? This final week of January offers a good time to try, as Mercury reaches greatest elongation east of the Sun on Friday, January 31st.

This will offer northern hemisphere viewers one on the best chances to spot the fleeting world low to the west immediately after local sunset. And although we get on average six apparitions of Mercury per year – three each in the dawn and dusk – all apparitions aren’t created equal.

The approximate moment of greatest elongation occurs on January 31st at 10:00 UT / 5:00 AM EST, when Mercury is 18.4 degrees east of the Sun. This is only 0.5 degrees shy of the smallest elongation for Mercury that can occur, as the planet reaches perihelion just three days later on February 3rd at 0.3075 Astronomical Units (AUs) from the Sun. The last time this was surpassed was the evening elongation of February 16th, 2013th, and the next time it’ll be topped is October 16th, 2015 at just 18.1 degrees from the Sun.

Path of Mercury from January 27th to February 12th. (Created using Starry Night).
Path of Mercury from January 27th to February 12th as seen from latitude 30 degrees north. (Created using Starry Night Education Software).

And though this elongation is closer than usual, this also works in the Mercury-spotter’s favor. At greatest elongation, Mercury will present a 50% illuminated 7 arc second disk, readily apparent in a small telescope. But a also means that Mercury will appear almost a full magnitude brighter than it does when it reaches greatest elongation near aphelion, as it last did on March 31st of last year, and will do again on March 14th of this year.

Mercury will shine at magnitude -0.4 low towards the west into this coming weekend. We managed to pick up Mercury with binoculars on January 16th and have since managed to start tracking the planet unaided since January 18th.

Mercury also has another factor going for it, in terms of the angle of the evening ecliptic. Following ahead of the Sun, Mercury occupies a space that the Sun will trace up its apparent path along the ecliptic as it begins its long slow crawl northward towards the Vernal Equinox on March 20th. This means that Mercury is almost perpendicular above the western horizon at dusk and is currently getting a maximum boost above the atmospheric murk.

Mercury also gets joined by a razor thin waxing crescent Moon just over 24 hours past New sliding by it on the evening of Friday, January 31st. Look for the Moon five degrees to the right of Mercury on the 31st. The Moon will be a much easier catch on the February 1st when its 10 degrees above Mercury. And can you spy the +1 magnitude star Fomalhaut in the constellation Piscis Austrinus just 20 degrees to the south of Mercury?

The orientation of the Moon and Mercury on the evening of February 1st. Credit: Stellarium.

And speaking of the Moon, this week’s New Moon is the second of the month, a feat that repeats in March 2014 and leaves the month of February “New Moon-less…” such an occurrence in either instance is informally known as a Black Moon.

Orbiting the Sun once every 88 days, Mercury completes about 4.15 circuits of the Sun for every Earth year. From our Earthbound vantage point, however, Mercury seems to only orbit the Sun 3.15 times a year. Thus 6 elongations (3 in the dusk and 3 in the dawn) will occur every year, through 7 can occur, as last happened in 2011 and will occur again next year in 2015.

August 15th, 2012.
Mercury (to the lower left) and the Moon on August 15th, 2012. (Photo by author).

After this weekend, Mercury will resume its plunge towards the horizon through early February. Mercury will begin retrograde (westward) apparent motion against the starry background on February 6th before resuming direct (eastward motion) on February 27th. And although astrologers may  find that “Mercury in retrograde” is a convenient “blame magnet,” they’re also falling prey to a logical fallacy known as retrofitting, as Mercury spends a longer fraction of time than any other planet “in retrograde” at about 20%!

From there, Mercury heads towards inferior conjunction between the Earth and the Sun on Saturday, February 15th, passing just 3.7 degrees north of the solar disk. You can catch Mercury entering into the field of view of the Solar Heliospheric Observatory’s (SOHO) LASCO C3 camera from February 12th to February 18th.

And although Mercury misses this time, we’re not that far away from the next transit of Mercury across the face of the Sun on May 9th, 2016.

Up for more? An even tougher challenge is to attempt to spot Mercury… in the daytime. We’ve noted this possibility before as Mercury reaches maximum elongation from the Sun while still in the negative magnitude range. Of course, you want to physically block the Sun out of view, and don’t even try sweeping the sky near the Sun visually with binoculars or a telescope! You’ll need a clear, blue sky for maximum contrast and a polarizing filter may help in your quest… but this should be possible under exceptional conditions.

Good luck, and be sure to send those Mercury pics in to Universe Today!