Earth’s magnetic poles drift over time. This is something that every airplane pilot or navigator knows. They have to account for it when they plan their flights.
They drift so much, in fact, that the magnetic poles are in different locations than the geographic poles, or the axis of Earth’s rotation. Today, Earth’s magnetic north pole is 965 kilometres (600 mi) away from its geographic pole. Now a new study says the same pole drifting is occurring on Mercury too.
In addition to being the only solvent that is capable of supporting life, water is essential to life as we know it here on Earth. Because of this, finding deposits of water – whether in liquid form or as ice – on other planets is always exciting. Even where is not seen as a potential indication of life, the presence of water offers opportunities for exploration, scientific study, and even the creation of human outposts.
This has certainly been the case as far as the Moon and Mercury are concerned, where water ice was discovered in the permanently-shadowed cratered regions around the poles. But according to a new analysis of the data from the Lunar Reconnaissance Orbiter and the MESSENGER spacecraft, the Moon and Mercury may have significantly more water ice than previously thought.
A handful of spacecraft have used ion engines to reach their destinations, but none have been as powerful as the engines on the BepiColombo spacecraft. BepiColombo is a joint mission between the European Space Agency (ESA) and the Japan Aerospace Exploration Agency (JAXA.) It was launched on October 20, 2018, and has gone through weeks of in-flight commissioning. On Sunday it turned on its powerful ion thrusters for the first time.
“We put our trust in the thrusters and they have not let us down.” – Günther Hasinger, ESA Director of Science.
Missed the planets in the dusk sky in early 2018? This summer’s astronomical blockbuster sees the return of all the classical naked eye planets in the dusk sky, in a big way.
The Sky Scene in July
This coming July 2018 features a rare look at the solar system in profile: you can see Mercury and Venus low in the dusk looking westward immediately after sunset, with Jupiter high to the south, Saturn rising in the east, and Mars rising just behind. This isn’t a true grouping or grand conjunction, as the planets span a 170 degree swath of the ecliptic from Mercury to Mars (too bad they’re not in orbital order!) but a product of our Earthly vantage point looking out over the swath of inner solar system in the evening sky.
Can you manage a “planetary marathon” and collect all five this coming Fourth of July weekend? Here’s a quick rundown of all the planetary action from west to east:
Mercury’s July apparition – fleeting Mercury is always the toughest of the planets to catch, low to the west. -0.3 magnitude Mercury actually forms a straight line with the bright +1st/2nd magnitude stars Castor and Pollux in Gemini the Twins later this week on the evening of June 27th. Mercury reaches greatest elongation 26 degrees east of the Sun on July 12th, presenting a half illuminated, 8” disk. The angle of the evening ecliptic is canted southward in July, meaning that the position of the planets in the evening sky also favors southern viewers. July also presents another interesting mercurial challenge, as Mercury passes in front of the Beehive Open cluster (Messier 44) in the heart of the constellation Cancer on the night of July 3rd/4th.
Venus this summer – higher up at dusk, brilliant Venus rules the evening sky, shining at magnitude -4. Venus is so bright that you can easily pick it up this month before sunset… if you know exactly where to look for it. Venus reaches greatest elongation 46 degrees east of the Sun on August 17th, presenting a featureless half-illuminated disk 25” in diameter near a point known as dichotomy. Venus also flirts with the bright star Regulus (Alpha Leonis) in July, passing a degrees from the star on July 10th. Fun fact: Venus can actually occult (pass in front of) Regulus and last did so on July 7th, 1959 and will do so next on October 1st, 2044.
Jupiter Rules – The King of the Planets, Jupiter rules the sky after darkness falls, crossing the astronomical constellation Libra the Scales. Fresh off of its May 9th opposition, Jupiter still shines at a respectable magnitude -2 in July, with a disk 36” across. Jupiter heads towards quadrature 90 degrees east of the Sun on August 6th, meaning the planet and its retinue of four Galilean moons cast their respective shadows off to one side. In fact, we also see a series of fine double shadow transits across the Jovian cloud tops involving Io and Europa starting on July 29th.
…and Saturn makes five: Stately Saturn never fails to impress. Also just past its June 27th opposition, the rings are still tipped open narrowing down only slightly from last year’s widest angle of 27 degrees, assuring an amazing view. Shining at magnitude 0 and subtending 42” (including rings) in July, Saturn traverses the star-rich fields of the astronomical constellation Sagittarius the Archer this summer. Look at Saturn, and you’re glimpsing the edge of the known solar system right up until William Herschel discovered Uranus on the night of March 13th, 1781.
Enter Mars: We saved the best for last. The Red Planet races towards a fine opposition on July 27th. This is the best approach of Mars since the historic 2003 opposition, and very nearly as favorable: Mars shines at magnitude -2.8 at the end of July, and presents a 24.3” disk. More to come as Mars approaches!
And as with many an opposition, dust storm season has engulfed Mars. Be vigilant, as the ‘Red’ Planet often takes on a sickly yellowish tint during a large dust storm, and this cast will often be apparent even to the naked eye. NASA’s aging Opportunity rover has fallen silent due to the lack of sunlight and solar power, and it’s to be seen if the rover can ride out the storm.
The path of the Moon – The Moon makes a good guidepost as it visits the planets in July. The first eclipse season of 2018 also begins in July, with a partial solar eclipse for Tasmania, SE Australia and the extreme southernmost tip of New Zealand on July 13th and wrapping up with a fine total lunar eclipse favoring Africa, Europe, Asia and Australia on July 27th. Note that this eclipse is only 14 hours after Mars passes opposition… we expect to see plenty of pictures of a ruddy Mars near a Blood Moon eclipse.
The Moon also makes a handy guide to catch each of the planets in the daytime sky… though you’ll need binoculars or a telescope to nab Mercury or Saturn (also, be sure the Sun is physically blocked out of view while hunting for Mercury in the daytime sky!) Here are the respective passes of the Moon near each planet in July:
Unfortunately, the telescopic planets Uranus and Neptune are left out of the July evening view; Uranus is currently crossing the constellation Aries and Neptune resides in Aquarius, respectively. Pluto is, however, currently in the direction of Sagittarius, and you can also wave to NASA’s New Horizons spacecraft en route to its New Year’s Day 2019 KBO destination Ultima Thule (nee 2014 MU69) near the waxing gibbous Moon on the night of July 26th.
And finally, another solar system destination in Ophiuchus the Serpent Bearer beckons telescope owners in July: asteroid 4 Vesta.
All of this is more than enough planetary action to keep planetary observers and imagers up late on forthcoming July evenings.
Back in 2012, scientists were delighted to discover that within the polar regions of Mercury, vast amounts of water ice were detected. While the existence of water ice in this permanently-shaded region had been the subject of speculation for about 20 years, it was only after the Mercury Surface, Space Environment, Geochemistry, and Ranging (MESSENGER) spacecraft studied the polar region that this was confirmed.
Based on the MESSENGER data, it was estimated that Mercury could have between 100 billion to 1 trillion tons of water ice at both poles, and that the ice could be up to 20 meters (65.5 ft) deep in places. However, a new study by a team of researchers from Brown University indicates that there could be three additional large craters and many more smaller ones in the northern polar region that also contain ice.
Despite being the closest planet to the Sun, and experiencing scorching surface temperatures on its Sun-facing side, Mercury’s low axial tilt means that its polar regions are permanently shaded and experience average temperatures of about 200 K (-73 °C; -100 °F). The idea that ice might exist in these regions dates back to the 1990s, when Earth-based radar telescopes detected highly reflective spots within the polar craters.
This was confirmed when the MESSENGER spacecraft detected neutron signals from the planet’s north pole that were consistent with water ice. Since that time, it has been the general consensus that Mercury’s surface ice was confined to seven large craters. But as Ariel Deutsch explained in a Brown University press statement, she and her team sought to look beyond them:
“The assumption has been that surface ice on Mercury exists predominantly in large craters, but we show evidence for these smaller-scale deposits as well. Adding these small-scale deposits to the large deposits within craters adds significantly to the surface ice inventory on Mercury.”
Together, they examined data from MESSENGER’s Mercury Laser Altimeter (MLA) instrument. This instrument was used by MESSENGER to measure the distance between the spacecraft and Mercury, the resulting data being then used to create detailed topographical maps of the planet’s surface. But in this case, the MLA was used to measure surface reflectance, which indicated the presence of ice.
As an instrument specialist with the MESSENGER mission, Neumann was responsible for calibrating the altimeter’s reflectance signal. These signals can vary based on whether the measurements are taken from overhead or at an angle (the latter of which is refereed to as “off-nadir” readings). Thanks to Neumann’s adjustments, researchers were able to detect high-reflectance deposits in three more large craters that were consistent with water ice.
According to their estimates, these three craters could contain ice sheets that measure about 3,400 square kilometers (1313 mi²). In addition, the team also looked at the terrain surrounding these three large craters. While these areas were not as reflective as the ice sheets inside the craters, they were brighter than the Mercury’s average surface reflectance.
Beyond this, they also looked at altimeter data to seek out evidence of smaller scale deposits. What they found was four smaller craters, each with diameters of less than 5 km (3 mi), which were also more reflective than the surface. From this, they deduced that there were not only more large deposits of ice that were previously undiscovered, but likely many smaller “cold traps” where ice could exist as well.
Between these three newly-discovered large deposits, and what could be hundreds of smaller deposits, the total volume of ice on Mercury could be considerably more than we previously thought. As Deutsch said:
“We suggest that this enhanced reflectance signature is driven by small-scale patches of ice that are spread throughout this terrain. Most of these patches are too small to resolve individually with the altimeter instrument, but collectively they contribute to the overall enhanced reflectance… These four were just the ones we could resolve with the MESSENGER instruments. We think there are probably many, many more of these, ranging in sizes from a kilometer down to a few centimeters.”
In the past, studies of the lunar surface also confirmed the presence of water ice in its cratered polar regions. Further research indicated that outside of the larger craters, small “cold traps”could also contain ice. According to some models, accounting for these smaller deposits could effectively double estimates on the total amounts of ice on the Moon. Much the same could be true for Mercury.
But as Jim Head (who also served as Deutsch Ph.D. advisor for this study) indicated, this work also adds a new take to the critical question of where water in the Solar System came from. “One of the major things we want to understand is how water and other volatiles are distributed through the inner Solar System—including Earth, the Moon and our planetary neighbors,” he said. “This study opens our eyes to new places to look for evidence of water, and suggests there’s a whole lot more of it on Mercury than we thought.”
In addition to indicating the Solar System may be more watery than previously suspected, the presence of abundant ice on Mercury and the Moon has bolstered proposals for building outposts on these bodies. These outposts could be capable of turning local deposits water ice into hydrazine fuel, which would drastically reduce the costs of mounting long-range missions throughout the Solar System.
On the less-speculative side of things, this study also offers new insights into how the Solar System formed and evolved. If water is far more plentiful today than we knew, it would indicate that more was present during the early epochs of planetary formation, presumably when it was being distributed throughout the Solar System by asteroids and comets.
The Solar Planets are a nice mixed bag of what is possible when it comes to planetary formation. Within the inner Solar System, you have the terrestrial planets – bodies that are composed primarily of silicate minerals and metals. And in the outer Solar System, you have the gas giants and bodies that are composed primarily of ice that lie just beyond in the Trans-Neptunian region.
Of these, the question of which planet is the smallest has been the subject of some controversy. Until recently, the smallest planet was considered to be Pluto. But with the 2006 IAU Resolution that put constraints on what the definition of a planet entails, that status has since passed to Mercury. So in addition to being the closest planet to the Sun, Mercury is also the smallest.
Size and Mass:
With a mean radius of 2440 km, Mercury is the smallest planet in our Solar System, equivalent in size to 0.38 Earths. And given that it has its experiences no flattening at the poles – like Venus, which means it is an almost perfectly spherical body – its radius is the same at the poles as it is the equator.
And while it is smaller than the largest natural satellites in our Solar System – such as Ganymede and Titan – it is more massive. At 3.3011×1023 kg in mass (33 trillion trillion metric tons; 36.3 trillion trillion US tons), it is equivalent to 0.055 Earths in terms of mass.
On top of that, Mercury is significantly more dense than bodies its size. In fact, Mercury’s density (at 5.427 g/cm3) is the second highest in the Solar System, only slightly less than Earth’s (5.515 g/cm3). The result of this is a gravitational force of 3.7 m/s2, which is 0.38 times that of Earth (0.38 g). In essence, this means that if you could stand on the surface of Mercury, you would weight 38% as much as you do on Earth.
In terms of volume, Mercury once again becomes a bit diminutive, at least by Earth standards. Basically, Mercury has a volume of 6.083×1010 km³ (60 billion cubic km; 14.39 trillion cubic miles) which works out to 0.056 times the volume of the Earth. In other words, you could fit Mercury inside Earth almost twenty times over.
Structure and Composition:
Like Earth, Venus and Mars, Mercury is a terrestrial planet, meaning that is primarily composed of silicate minerals and metals that are differentiated between a metallic core and a silicate mantle and crust. But in Mercury’s case, the core is oversized compared to the other terrestrial planets, measuring some 1,800 km (approx. 1,118.5 mi) in radius, and therefore occupying 42% of the planet’s volume (compared to Earth’s 17%).
Another interesting feature about Mercury’s core is the fact that it has a higher iron content than that of any other major planet in the Solar System. Several theories have been proposed to explain this, the most widely-accepted being that Mercury was once a larger planet that was struck by a planetesimal that stripped away much of the original crust and mantle, leaving behind the core as a major component.
Beyond the core is a mantle that measures 500 – 700 km (310 – 435 mi) in thickness and is composed primarily of silicate material. The outermost layer is Mercury’s crust, which is composed of silicate material that is believed to be 100 – 300 km thick.
Yes, Mercury is a pretty small customer when compared to its brothers, sisters and distant cousins in the Solar System. However, it is also one of the densest, hottest and most irradiated. So while small, no one would ever accuse this planet of not being really tough!
March has been a busy month for planet and comet watchers. Lots of action. Venus, the planet that’s captured our attention at dusk in the west for months, is in inferior conjunction with the Sun today. Watch for it to rise before the Sun in the eastern sky at dawn in about a week.
As Venus flees the evening scene, steadfast Mars and a new planet, Mercury keep things lively. For northern hemisphere skywatchers, this is Mercury’s best dusk apparition of the year. If you’d like to make its acquaintance, this week and next are best. And it’s so easy! Just find a spot with a wide open view of the western horizon, bring a pair of binoculars for backup and wait for a clear evening.
Plan to watch starting about 40 minutes after sundown. From most locations, Mercury will appear about 10° or one fist held at arm’s length above the horizon a little bit north of due west. Shining around magnitude +0, it will be the only “star” in that part of the sky. Mars is nearby but much fainter at magnitude +1.5. You’ll have to wait at least an hour after sunset to spot it.
Have a telescope? Check out the planet using a magnification around 50x or higher. You’ll see that it looks like a Mini-Me version of the Moon. Mercury is brightest when closest to full. Over the next few weeks, it will wane to a crescent while increasing in apparent size.
If you like planets, don’t forget the combo of Jupiter and Spica at the opposite end of the sky. Jupiter climbs out of bed and over the southeastern horizon about 9 p.m. local time in late March, but to see it and Spica, Virgo’s brightest star, give it an hour and look again at 10 p.m. or later. Quite the duo!
You’re not afraid of getting up with the first robins are you? If you set your alarm to a half hour or so before the first hint of dawn’s light and find a location with an open view of the southeastern horizon, you might be first in your neighborhood to spot Terry Lovejoy’s brand new comet. His sixth, the Australian amateur discovered C/2017 E4 Lovejoyon the morning of March 10th in the constellation Sagittarius at about 12th magnitude.
The comet has rapidly brightened since then and is now a small, moderately condensed fuzzball of magnitude +9, bright enough to spot in a 6-inch or larger telescope. Some observers have even picked it up in large binoculars. Lovejoy’s comet should brighten by at least another magnitude in the coming weeks, putting it within 10 x 50 binocular range.
Good news. E4 Lovejoy is moving north rapidly and is now visible about a dozen degrees high in Aquarius just before the start of dawn. I’ll be out the next clear morning, eyepiece to eye, to welcome this new fuzzball from beyond Neptune to my front yard. The map above shows the eastern sky near dawn and a general location of the comet. Use the more detailed map below to pinpoint it in your binoculars and telescope.
Spring brings with it a new spirit and the opportunity to get out at night free of the bite of mosquitos or cold. Clear skies!
KENNEDY SPACE CENTER VISITOR COMPLEX, FL – America’s pioneering astronauts who braved the perils of the unknown and put their lives on the line at the dawn of the space age atop mighty rockets that propelled our hopes and dreams into the new frontier of outer space and culminated with NASA’s Apollo lunar landings, are being honored with the eye popping new ‘Heroes and Legends’ attraction at the Kennedy Space Center Visitor Complex (KSCVC) in Florida.
With fanfare and a fireworks display perfectly timed for Veterans Day, ‘Heroes and Legends’ opened its doors to the public on Friday, November 11, 2016, during a gala ceremony attended by more than 25 veteran and current NASA astronauts, including revered Gemini and Apollo space program astronauts Buzz Aldrin, Jim Lovell, Charlie Duke, Tom Stafford, Dave Scott, Walt Cunningham and Al Worden – and throngs of thrilled members of the general public who traveled here as eyewitnesses from all across the globe.
Aldrin, Scott, and Duke walked on the Moon during the Apollo 11, 15 and 16 missions.
Also on hand were the adult children of the late-astronauts Alan Shepard (first American in space) and Neil Armstrong (first man to walk on the Moon), as well as representatives from NASA, The Boeing Company (sponsor) and park operator Delaware North – for the engaging program hosted by Master of Ceremonies John Zarrella, CNN’s well known and now retired space correspondent.
The stunning new ‘Heroes and Legends’ attraction is perfectly positioned just inside the entrance to the KSC Visitor Complex to greet visitors upon their arrival with an awe inspiring sense of what it was like to embark on the very first human journey’s into space by the pioneers who made it all possible ! And when every step along the way unveiled heretofore unknown treasures into the origin of us and our place in the Universe.
Upon entering the park visitors will immediately and surely be mesmerized by a gigantic bas relief sculpture recreating an iconic photo of America’s first astronauts – the Mercury 7 astronauts; Scott Carpenter, Gordon Cooper, John Glenn, Gus Grissom, Wally Schirra, Alan Shepard, and Deke Slayton.
“With all the drama of an actual trip to space, guests of Kennedy Space Center Visitor Complex in Florida will be greeted with a dramatic sense of arrival with the new Heroes & Legends featuring the U.S. Astronaut Hall of Fame® presented by Boeing. Positioned just inside the entrance, the attraction sets the stage for a richer park experience by providing the emotional background and context for space exploration and the legendary men and women who pioneered our journey into space,” according to a description from Delaware North Companies Parks and Resorts, which operates the KSC visitor complex.
“Designed to be the first stop upon entering Kennedy Space Center Visitor Complex, Heroes & Legends uses the early years of the space program to explore the concept of heroism, and the qualities that define the individuals who inspired their generation.”
“I hope that all of you, when you get to see Heroes and Legends, you’re inspired,” said Kennedy Space Center Director Bob Cabana, a former space shuttle astronaut and member of the Astronaut Hall of Fame, during the ceremony.
“The children today can see that there is so much more they can reach for if they apply themselves and do well.”
“I think people a thousand years from now are going to be happy to see these artifacts and relics,” Apollo 15 command module pilot Al Worden told the crowd.
“We have so much on display here with a Saturn V, Space Shuttle Atlantis. People will think back and see the wonderful days we had here. And I guess in that same vein, that makes me a relic too.”
Furthermore, ‘Heroes and Legends’ is now very conveniently housed inside the new home of the U.S. Astronaut Hall of Fame (AHOF) – making for a unified space exploration experience for park visitors. AHOF previously was located at another off site park facility some seven miles outside and west of the Visitor Complex.
The bas relief measures 30 feet tall and 40 feet wide. It is made put of fiberglass and was digitally sculpted, carved by CNC machines and juts out from the side of the new into the new 37,000 square foot U.S. Astronaut Hall of Fame (AHOF) structure.
To date 93 astronauts have been inducted into the Astronaut Hall of Fame spanning the Mercury, Gemini, Apollo and Space Shuttle programs.
“I don’t consider myself a hero like say, Charles Lindbergh,” said Jim Lovell, a member of the Astronaut Hall of Fame and Apollo 13 commander, when asked by Zarrella what it feels like to be considered an American space hero. “I just did what was proper and exciting — something for my country and my family. I guess I’m just a lucky guy.”
The astronauts are also quick to say that they were supported by hundreds of thousands of dedicated people working in the space program to make Apollo happen.
“It important to remember all the dedication and hard work that it took from those of us involved in the astronaut program, but also the support we received from Kennedy and all the contractors involved in Apollo,” said Apollo 16 moonwalker Charlie Duke.
“400,000 people made it possible for 24 of us to go to the Moon.”
“So dream big, aim high!” exclaimed Duke.
“Hopefully this is an inspiration to you and your kids and grandkids.”
Construction of the facility by Falcon’s Treehouse, an Orlando-based design firm began in the fall of 2015.
“We’re focusing on a story to create what we consider a ‘launch pad’ for our visitors,” said Therrin Protze, the Delaware North chief operating officer of the Visitor Complex. “This is an opportunity to learn about the amazing attributes of our heroes behind the historical events that have shaped the way we look at space, the world and the future.
“We are grateful to NASA for allowing us to tell the NASA story to millions of guests from all over the world,” Protze said.
Visitors walk up a sweeping ramp to enter the Heroes and Legends experience.
After visitors walk through the doors, they will be immersed by two successive video presentations and finally the Hall of Fame exhibit hall.
Here’s a detailed description:
• In the stunning 360-degree discovery bay, What is a Hero?, guests will explore how society defines heroism through diverse perspectives. Each examination of heroism starts with the following questions: What is a hero; Who are the heroes of our time; and What does it take to be a hero? During the seven-minute presentation, the historic beginning of the space race is acknowledged as the impetus for America’s push to the stars in NASA’s early years and the rivalry between the United States and the Soviet Union during the Cold War.
• Through the Eyes of a Hero is a custom-built theater featuring a multi-sensory experience during which guests will vicariously join NASA’s heroes and legends on the most perilous stages of their adventures. Artistically choreographed lighting and 3D imagery will be enhanced by intense, deeply resonant sound effects to create the sensation of being “in the moment.” The seven and one-half minute show takes guests on an intimate journey with four space-age heroes to fully immerse them in the awe, excitement and dangers of the first crewed space program missions.
• The third experience, A Hero Is…, offers interactive exhibits that highlight the nine different attributes of our history making astronauts: inspired, curious, passionate, tenacious, disciplined, confident, courageous, principled and selfless. A collection of nine exhibit modules will explore each aforementioned attribute, through the actual experiences of NASA’s astronauts. Their stories are enhanced with memorabilia from the astronaut or the space program.
Priceless historic artifacts on display also include two flown capsules from Mercury and Gemini; the Sigma 7 Mercury spacecraft piloted by Wally Schirra during his six-orbit mission in October 1962 and the Gemini IX capsule flown by Tom Stafford and Gene Cernan for three days in June 1966.
The human rated Mercury Redstone-6 (MR-6) is also on display and dramatically mated to the Schirra’s Sigma 7 Mercury capsule.
Another room houses the original consoles of the Mercury Mission Control room with the world map that was used to follow the path of John Glenn’s Mercury capsule Friendship 7 between tracking stations when he became the first American to orbit Earth in 1962.
Further details about ‘Heroes and Legends, the U.S. Astronaut Hall of Fame and all other attractions are available at the Kennedy Space Center Visitor Complex website: https://www.kennedyspacecenter.com/
Stay tuned here for Ken’s continuing Earth and Planetary science and human spaceflight news.
Learn more about Heroes and Legends at KSCVC, GOES-R weather satellite, OSIRIS-REx, InSight Mars lander, SpaceX missions, Juno at Jupiter, SpaceX CRS-9 rocket launch, ISS, ULA Atlas and Delta rockets, Orbital ATK Cygnus, Boeing, Space Taxis, Mars rovers, Orion, SLS, Antares, NASA missions and more at Ken’s upcoming outreach events:
Nov 17-20: “GOES-R weather satellite launch, OSIRIS-REx launch, SpaceX missions/launches to ISS on CRS-9, Juno at Jupiter, ULA Delta 4 Heavy spy satellite, SLS, Orion, Commercial crew, Curiosity explores Mars, Pluto and more,” Kennedy Space Center Quality Inn, Titusville, FL, evenings
Have you caught sight of Mercury yet? This coming week is a good time to try, looking low to the west at dusk. We just managed to to nab it with binoculars for the first time during the current apparition this past Sunday from the rooftop of our Air BnB in Casablanca, Morocco.
Mercury is a tough grab under any circumstance, that’s for sure. Brilliant Venus and Jupiter make great guides to finding the elusive planet in late July, as it ping-pongs between the two. The waxing crescent Moon joins the scene in the first week of August, and for a very lucky few, actually occults (passes in front of ) the diminutive innermost world shortly after passing New.
Here’s the low down on everything Mercurial, and circumstances for the coming weeks.
Mercury passes 18′ from the star Regulus on Saturday, July 30th at 19:00 Universal Time (UT), representing the closest passage of a planet near a first magnitude star for 2016.
The Moon then reaches New phase, marking the start of lunation 1158 on August 2nd at 20:45 UT. The Moon then moves on to occult Mercury on Thursday, August 4th at 22:00 UT, just over 48 hours later. The occultation is visible at dusk for observers based in southern Chile and southern Argentina. The rest of us see a close pass. Note that although it is a miss for North America, viewers based on the continent share the same colongitude and will see Mercury only a degree off of the northern limb of the Moon on the night of August 4th. Mercury shines at magnitude +0.01, and presents a 67% illuminated disk 6.3” in size, while the Moon is a slender 5% illuminated.
How early can you see the waxing crescent Moon? Catching the Moon with the naked eye under transparent clear skies isn’t usually difficult when it passes 20 hours old. This cycle, first sightings favor South Africa westward on the night of August 3rd.
Mercury reaches greatest elongation 27.4 degrees east of the Sun 12 days after this occultation on August 16th.
How rare is it? Well occultations of Mercury by the Moon are the toughest to catch of all the naked eye planets, owing to the fact that the planet never strays far from the Sun. Nearly all of these events go unwitnessed, as they occur mainly under daytime skies. And while you can observe Mercury in the daytime near greatest elongation with a telescope, safety precautions need to be taken to assure the Sun is physically blocked from view. Astronomers of yore did exactly that, hoping to glimpse fleeting detail on Mercury while it was perched higher in the sky above the murk of the atmosphere low to the horizon.
In fact, a quick search of ye ole web reveals very few convincing captures of an occultation of Mercury (see the video above). The closest grab thus far comes from astrophotographer Cory Schmitz on June 3rd 2016 based in South Africa:
Can’t wait til next week? The Moon crosses the Hyades open star cluster this week, occulting several stars along the way. The action occurs on the morning of Friday, July 29th culminating with an occultation of +1 magnitude Aldebaran by the 23% illuminated Moon. Texas and Mexico are well-placed to see this event under dark skies. A small confession: we actually prefer occultations of planets and stars by the waxing Moon, as the dark edge of the Moon is leading during ingress, making it much easier to witness and the exact moment the Moon blots out the object.
Still want more? The Moon actually goes on to occult Jupiter on August 6th for the South Pacific. Viewers farther west in southeast Asia might just spy this one in the daytime. This is the second occultation of Jupiter by the Moon in a series of four in 2016.
Keep and eye on those planets in August, as they’re now all currently visible in the dusk sky. The Moon, Regulus and Venus also form a tight five degree triangle on the evening of August 4th, followed by a slightly wider grouping of Venus, Jupiter and the Moon around August 25th.
More to come on that soon. Be sure to check the planet Mercury off of your life list this coming week, using the nearby waxing crescent Moon as a guide.