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.
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?
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.
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!
An occultation occurs when one foreground celestial object completely obscures another. Technically, a total solar eclipse is an occultation of the Sun by the Moon, although it’s never referred to as such. The term finds modern usage mainly for the blocking of stars and planets by the Moon. Very occasionally, an asteroid or planet can occult a distant star as well.
And yes, the modern astronomical term “occultation” traces its hoary roots back to the days when astronomy was intertwined with the pseudoscience of astrology. To this day, the term still makes some folks wonder if astronomers are secretly casting horoscopes. Trust us, you’re still on a solid astronomical footing to use the term “occultation.”
Unfortunately, the January 25thoccultation of Saturn by the Moon will only grace part of Antarctica, southern Argentina and Chile, and the Falkland Islands post-sunrise. The rest of us still will see a very photogenic pass of Saturn near the waning crescent Moon on the morning of Saturday, January 25th. The Moon will pass just about a degree — two times its apparent width — south of Saturn for northern hemisphere observers.
Both the Moon and Saturn will reside in the astronomical constellation of Libra this weekend during closest passage. The pair will rise around 2 AM local. After their brief tryst, the Moon will head towards New on January 30th while Saturn will continue to rise successively earlier as its heads towards opposition and the start of evening Saturn observing season on May 10th, 2014.
January 2014 is also notable for having two New Moons, an occurrence informally known as a Black Moon. This occurs again this year in March, and February 2014 is devoid of a New Moon. February is the only month that can be “missing a Moon phase” as it’s the only one shorter the synodic period of 29.5 days, in which the Moon returns to like phase.
In the telescope, Saturn will present a +0.8 magnitude disk 16” across (38” with rings from tip-to-tip). Saturn’s rings are tipped open to our line of sight by about 22 degrees in 2014, and are widening towards a maximum of 27 degrees in 2016 through 2017. If you have an equatorial telescope with tracking capability, it may be possible this weekend to follow Saturn up into the daytime sky. Though Saturn isn’t quite bright enough to see in the daytime unaided, it might just be possible to spy using binoculars on the 25th using the nearby crescent Moon as a guide. Saturn is a tough daytime target to be sure, but it’s not impossible to acquire with a little skill and patience.
The current cycle of occultations of Saturn began on December 1st, 2013 and ends on November 22nd, 2014. The cycle will move progressively northward through the year.
The Moon and Saturn put on a repeat performance over almost the same exact location (this time in darkness) on April 17th, 2014, and the best event in the cycle for North America will be the August 31st daytime occultation of Saturn by the waxing crescent Moon.
Now for the wow factor of what you’re seeing. On Saturday morning, the Moon is just over 371,000 kilometres distant, or a little over a light second away. Saturn is over four thousand times more remote at just over 10.1 astronomical units (AUs) distant, which works out to 1.5 billion kilometres, or over 83 light minutes away. And although the Moon is over a 112 times larger in apparent diameter than Saturn as seen from the Earth, the globe of Saturn is actually over 34 times bigger.
And though we’ve been to the Moon lots since the dawn of the Space Age, only two spacecraft (Voyagers 1 and 2) have made brief flybys of the ringed world, and only one – Cassini – has orbited it. Note that China’s Chang’e-3 lander and rover are about to experience their second sunset this weekend as well from the lunar surface since landing on the Moon last month.
And although lots of planets get occulted by the Moon in 2014, no stars brighter than +1st magnitude lie in its path. In fact, the next cycle of bright star occultations by the Moon doesn’t resume until the Moon meets Aldebaran in January 29th, 2015.
There are, however, over a 100 lesser events involving the Moon occulting naked eye stars worldwide in 2014. Two such events occur this week as well, when the 48% illuminated Moon occults the +4.5th magnitude star Lambda Virginis for west-central South America on the morning of January 24th, and the occultation of the +2.8th magnitude star Alpha Librae (Zubenelgenubi) for central Asia on January 25th.
Don’t miss these celestial events, and be sure to send those pics in to Universe Today… there’s something for everyone happening in the sky this week worldwide!