Illustration of MESSENGER in orbit around Mercury (NASA/JPL/APL)
Don’t take these spectacular Mercury images (below the jump) for granted. Three weeks ago, NASA’s orbiting Mercury spacecraft did an engine fire to boost its altitude above the hothouse planet. Another one is scheduled for January.
But all this will do is delay the end of the long-running mission — the first one to orbit Mercury — until early 2015, the Johns Hopkins Applied Physics Laboratory wrote in an update. These maneuvers “extend orbital operations and delay the probe’s inevitable impact onto Mercury’s surface until early next spring,” the organization said in a statement.
Until MESSENGER (MErcury Surface, Space ENvironment, GEochemistry, and Ranging) flew by Mercury for the first time in January 2008, we knew very little about the planet. The only close-up pictures previously came from Mariner 10, which whizzed by a few times in 1974-75. After a few flybys, MESSENGER settled into orbit in 2011.
A 3-D image of Balanchine crater on Mercury obtained by the MESSENGER spacecraft. Scientists are examining the region to learn more about its oddly shaped ejecta, which may have occurred when one impact crater dumped material on top of another pile. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
Mercury’s high density compared to other planets remains a mystery. MESSENGER investigations found a surface that didn’t have a lot of iron in it, but lots of volatile materials such as sodium and sulfur.
The surface had volcanoes on it and still has water ice in permanently shadowed craters near the poles.
Its magnetic field produces weird effects that are still being examined. NASA speaks of “unexplained bursts of electrons and highly variable distributions of different elements” in its tenuous atmosphere, called an exosphere.
This is an Andy Warhol-like image of an unnamed crater near Mercury’s north pole. Data obtained by the MESSENGER spacecraft makes scientists suspect there is water ice inside the 15-mile (24-kilometer) divot. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
“Our only regret is that we have insufficient propellant to operate another 10 years, but we look forward to the incredible science returns planned for the final eight months of the mission,” stated Andy Calloway, MESSENGER mission operations manager at the Johns Hopkins University Applied Physics Laboratory, at the time.
MESSENGER has done several orbital-boosting maneuvers in recent months to prolong the mission as possible. The first one in June adjusted its orbit to between 71.4 miles (115 kilometers) and 97.2 miles (156.4 kilometers), while the second in September went lower: a minimum of 15.7 miles (25.2 kilometers) to 58.2 miles (93.7 kilometers).
As of late October, MESSENGER’s minimum altitude was 115.1 miles (185.2 miles) and it took roughly eight hours for it to orbit Mercury. Once it finally crashes, Europe’s and Japan’s BepiColombo is expected to be the next Mercury orbiting mission. It launches in 2016, but will take several flybys past planets to get there and won’t arrive until 2024.
Ice is lurking at the bottom of these craters on Mercury in this double image. From left to right, the large craters are Chesterton, Tryggvadóttir, and Tolkien. The right-hand image is stretched to show the permanent dark bottoms in each crater. Data is from the NASA MESSENGER mission. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
Artist's impression of the European Space Agency/JAXA BepiColombo mission in operation around Mercury. Credit: Astrium
After facing down a couple of delays due to technical difficulties, Europe’s and Japan’s first Mercury orbiter is entering some of the final stages ahead of its 2016 launch. Part of the BepiColombo orbiter moved into a European testing facility this past week that will shake, bake and otherwise test the hardware to make sure it’s ready for its extreme mission.
Because Mercury is so close to the Sun, BepiColombo is going to have a particularly harsh operating environment. Temperatures there will soar as high as 350 degrees Celsius (662 degrees Fahrenheit), requiring officials to change the chamber to simulate these higher temperatures. Time will tell if the spacecraft is ready for the test.
BepiColombo is also special because it includes not one orbiting spacecraft, but two. Flying in different orbits, the Mercury Planetary Orbiter and the Mercury Magnetospheric Orbiter will try to learn more about this mysterious planet. NASA’s MESSENGER (MErcury Surface, Space ENvironment, GEochemistry and Ranging) spacecraft has spent the past few years orbiting Mercury, but before then, we had very little information on the planet. (And before MESSENGER, only brief flybys from NASA’s Mariner 10 in the 1970s turned up spacecraft-based information on Mercury.)
MESSENGER has turned up quite a few surprises. It’s showed us more about the nature of Mercury’s tenuous atmosphere and it’s discovered probable water ice (!) in permanently shadowed areas, among other things. The European Space Agency and Japan hope to push our understanding of the Sun’s closest planet when BepiColombo gets there in 2024.
On Oct. 30, 2014, the Mercury Planetary Orbiter (part of the BepiColombo mission) was moved into the European Space Agency’s space simulator for testing ahead of the expected 2016 launch. Credit: ESA–A. Le’Floch
There are so many questions that Mercury presents us, and BepiColombo is trying to answer a few of those. For example, Mercury’s density is higher than the rest of the other terrestrial planets for reasons that are poorly understood. Scientists aren’t sure if its core is liquid or solid, or even it has active plate tectonics as Earth does. Its magnetic field is a mystery, given that Mars and Venus and the Moon don’t have any. And there are tons of questions too about its atmosphere, such as how it is produced and how the magnetic field and solar wind work together.
The two spacecraft will be carried together to Mercury’s orbit along with a component called the Mercury Transfer Model (MTM), which will push the spacecraft out there using solar-electric propulsion. Just before BepiColombo enters orbit, MTM will be jettisoned and the Mercury Polar Orbiter will ensure the Mercury Magnetospheric Orbiter receives the needed resources to survive until the two spacecraft move into their separate orbits, according to the European Space Agency.
As for why it takes so long to get out there, to save on fuel the mission will swing by Earth, Venus and Mercury to get to the right spot. Once the two spacecraft are ready to go, they’re expected to last a year in orbit — with a potential one-year extension.
Psst! Ever spy the planet Mercury? The most bashful of all the naked eye planets makes its best dawn appearance of 2014 this weekend for northern hemisphere observers. And not only will Mercury be worth getting up for, but you’ll also stand a chance at nabbing that most elusive of astronomical phenomena — the zodiacal light — from a good dark sky sight.
DST note: This post was written whilst we we’re visiting Arizona, a land that, we’re happy to report, does not for the most part observe the archaic practice of Daylight Saving Time. Life goes on, zombies do not arise, and trains still run on time. In the surrounding world of North America, however, don’t forget to “fall back” one hour on Sunday morning, November 2nd. I know, I know. Trust me, we didn’t design the wacky system we’re stuck with today. All times noted below post-shift reflect this change, but it also means that you’ll have to awaken an hour earlier Sunday November 2nd onwards to begin your astronomical vigil for Mercury!
The apparent daily path of Mercury as seen from 30 degrees north from October 21st to November 14th. Created using Starry Night Education Software.
Mercury starts the month of November reaching greatest elongation on Saturday, November 1st at 18.7 degrees west of the Sun at 13:00 Universal Time UT/09:00 EDT. Look for Mercury about 10 degrees above the eastern horizon 40 minutes before sunrise. The planet Jupiter and the stars Denebola and Regulus make good morning guideposts to trace the line of the ecliptic down to the horizon to find -0.3 magnitude Mercury.
Mars, Mercury and the International Space Station caught during an evening apparition in 2013. (Photo by author)
Sweeping along the horizon with binoculars, you may just be able to spy +0.2 magnitude Arcturus at a similar elevation to the northwest. The +1st magnitude star Spica also sits to Mercury’s lower right. Mercury passes 4.2 degrees north of Spica on November 4th while both are still about 18 degrees from the Sun, making for a good study in contrast.
Later in the month, the old waning crescent Moon will present a challenge as it passes 2.1 degrees north of Mercury on November 21st, though both will only be 9 degrees from the Sun on this date.
Mercury also passes 1.6 degrees south of Saturn November 26th, but both are only 7 degrees from the Sun and unobservable at this point. But don’t despair, as you can always watch all of the planetary conjunction action via SOHO’s sunward staring LASCO C3 camera, which has a generous 15 degree field of view.
Mercury (the bright ‘star’ with spikes) transits SOHO’s LASCO C3 camera. Credit: NASA/ESA/SOHO.
At the eyepiece, Mercury starts off the month of November as a 57% illuminated gibbous disk about 7” in diameter. This will change to a 92% illuminated disk 5″ across on November 15th, as the planet races towards superior conjunction on the far side of the Sun on December 8th. As with Venus, Mercury always emerges in the dawn sky as a crescent headed towards full phase, and the cycle reverses for both planets when they emerge in the dusk sky.
Why aren’t all appearances of Mercury the same? Mercury orbits the Sun once every 88 days, making greatest elongations of Mercury far from uncommon: on average, we get three dawn and three dusk apparitions of the innermost world per year, with a maximum of seven total possible. Two main factors come into play to assure that not all appearances of Mercury are created equal.
A depiction of the evening motion of Mercury and Venus as seen from Earth. Credit: NASA.
One is the angle of the ecliptic, which is the imaginary plane of our solar system that planets roughly follow traced out by the Earth’s orbit. In northern hemisphere Fall, this angle is at its closest to perpendicular at dawn, and the dusk angle is most favorable in the Spring. In the southern hemisphere, the situation is reversed. This serves to place Mercury as high as possible out of the atmospheric murk during favorable times, and shove it down into near invisibility during others.
The second factor is Mercury’s orbit. Mercury has the most elliptical orbit of any planet in our solar system at a value of 20.5% (0.205), with an aphelion of 69.8 million kilometres and perihelion 46 million kilometres from the Sun. This plays a more complicated role, as an elongation near perihelion only sees the planet venture 18.0 degrees from the Sun, while aphelion can see the planet range up to 27.8 degrees away. However, this distance variation also leads to noticeable changes in brightness that works to the advantage of Mercury spotters in the opposite direction. Mercury shines as bright as magnitude -0.3 at closer apparitions, to a full magnitude fainter at more distant ones at +0.7.
In the case of this weekend, greatest elongation for Mercury occurs just a week after perihelion, which transpired on October 25th.
Mercury transits the Sun earlier this year as captured by the Curiosity rover on Mars. Credit: NASA/JPL.
Mercury is also worth keeping an eye on in coming years, as it will also transit the Sun for the first time since 2006 on May 9th, 2016. This will be visible for Europe and North America. We always thought it a bit strange that while rarer transits of Venus have yet to make their sci-fi theatrical debut, a transit of Mercury does crop up in the film Sunshine.
The first week of November is also a fine time to try and spy the zodiacal light. This is a cone-shaped glow following the plane of the ecliptic, resulting from sunlight backscattered across a dispersed layer of interplanetary dust. The zodiacal light was a common sight for us from the dark skies of Arizona, often rivaling the distant glow of Tucson over the mountains. The zodiacal light vanished from our view after moving to the humid and often light polluted U.S. East Coast, though we’re happy to report that we can once again spy it as we continue to traverse the U.S. southwest this Fall.
The zodiacal light captured by Cory Schmitz over the Drakensberg Mountains in South Africa. (Used with permission).
None other than rock legend Brian May of Queen fame wrote his PhD dissertation on the zodiacal light and the distribution and relative velocity of dust particles along the plane of the solar system. Having a dark site and a clear flat horizon is key to nabbing this bonus to your quest to cross Mercury off your life list this weekend!
A view of the crater Prokofiev on Mercury. The crater is the largest one on the planet's north pole area to have "radar-bright" material, a probable sign of ice. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington.
New pictures of water ice at Mercury’s north pole — the first such optical images ever — could help scientists better understand how water came to planets in the rest of the Solar System, including Earth. The image you see above came courtesy of NASA’s MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft.
Mercury is a hot planet (it’s the closest one to the Sun), so the only way the ice survives is in deep shadow. This makes it hard to spot unless scientists use some clever techniques. In this case, they examined some scattered light from Prokofiev, the biggest crater in Mercury’s north pole suspected to hold the deposits.
The pictures show that Prokofiev’s surface water ice likely arrived after the craters underneath. And in an intriguing find, there is probably other water ice sitting under dark materials believed to be “frozen organic-rich compounds,” stated the Johns Hopkins University Applied Physics Laboratory.
“This result was a little surprising, because sharp boundaries indicate that the volatile deposits at Mercury’s poles are geologically young, relative to the time scale for lateral mixing by impacts,” stated lead researcher Nancy Chabot, the Instrument Scientist for MESSENGER’s Mercury dual imaging system.
Illustration of MESSENGER in orbit around Mercury (NASA/JPL/APL)
“One of the big questions we’ve been grappling with is ‘When did Mercury’s water ice deposits show up?’ Are they billions of years old, or were they emplaced only recently?”, added Chabot, who is a planetary scientist at the Johns Hopkins University Applied Physics Laboratory in Maryland. “Understanding the age of these deposits has implications for understanding the delivery of water to all the terrestrial planets, including Earth.”
Another intriguing property comes when scientists compare Mercury to the Moon: because the ice looks different on both relatively atmosphere-less bodies, scientists believe the water came more recently to the Moon. But more study is required.
The 1st Quarter Moon occults Saturn during the last event in the series on August 5th, 2015. Sequence courtesy of Teale Britstra.
Got clear skies? This week’s equinox means the return of astronomical Fall for northern hemisphere observers and a slow but steady return of longer nights afterwards. And as the Moon returns to the evening skies, all eyes turn to the astronomical action transpiring low to the southwest at dusk.
Three planets and two “occasional” planets lie along the Moon’s apparent path this coming weekend: Mars, Saturn, Mercury and the tiny worldlets of 4 Vesta and 1 Ceres. Discovered in the early 19th century, Ceres and Vesta enjoyed planetary status initially before being relegated to the realm of the asteroids, only to make a brief comeback in 2006 before once again being purged along with Pluto to dwarf planet status.
The Moon approaches Saturn on the evening of September 28th as seen from latitude 30 degrees north. Credit: Stellarium.
On Sunday September 28th, the four day old Moon will actually occult (pass in front of) Saturn, Ceres, and Vesta in quick succession. The Saturn occultation is part of a series of 12 in an ongoing cycle. This particular occultation is best for Hawaiian-based observers on the evening of September 28th. Astute observers will recall that Ceres and Vesta fit in the same 15’ field of view earlier this summer. Both are now over six degrees apart and slowly widening. Unfortunately, there is no location worldwide where it’s possible to see all (or two) of these objects occulted simultaneously. The best spots for catching the occultations of +7.8 magnitude Vesta and +9.0 magnitude Ceres are from the Horn of Africa and just off of the Chilean coast of South America, respectively. The rest of us will see a close but photogenic conjunction of the trio and the Moon. To our knowledge, an occultation of Ceres or Vesta by the dark limb of the Moon has yet to be recorded. Vesta also reaches perihelion this week on September 23rd at 4:00 UT, about 2.2 astronomical units from the Sun and 2.6 A.U.s from Earth.
4 Vesta and 1 Ceres share the same field of view this past summer. Credit: Andrew Symes @FailedProtostar.
The reappearance of the Moon in the evening skies is also a great time to try your hand (or eyes) at the fine visual athletic sport of waxing crescent moon-spotting. The Moon passes New phase marking the start of lunation 1135 on Wednesday, September 24th at 6:12 UT/2:12 AM EDT. First sighting opportunities will occur over the South Pacific on the same evening, with worldwide opportunities to spy the razor-thin Moon low to the west the following night. Aim your binoculars at the Moon and sweep about three degrees to the south, and you’ll spy Mercury and the bright star Spica just over a degree apart.
This week’s New Moon is also notable for marking the celebration of Rosh Hashanah, and the beginning of the Jewish year 5775 A.M. at sundown on Wednesday. The Jewish calendar is a hybrid luni-solar one, and inserted an embolismic or intercalculary month earlier this spring to stay in sync with the solar year.
The occultation footprint of Saturn. The dashed line denotes where the event occurs in the daytime, while the solid line marks where it can be seen after sunset. Created using Occult 4.1.0.
The Moon also visits Mars and Antares on September 29th. The ruddy pair sits just three degrees apart on the 28th, making an interesting study in contrast. Which one looks “redder” to you? Antares was actually named by the Greeks to refer to it as the “equal to,” “pseudo,” or “anti-Mars…” Mars can take on anything from a yellowish to pumpkin orange appearance, depending on the current amount of dust suspended in its atmosphere. The action around Mars is also heating up, as NASA’s MAVEN spacecraft just arrived in orbit around the Red Planet and India’s Mars Orbiter is set to join it this week… and all as Comet A1 Siding Spring makes a close pass on October 19th!
And speaking of spacecraft, another news maker is photo-bombing the dusk scene, although of course it’s much too faint to see. NASA’s Dawn mission is en route to enter orbit around Ceres in early 2015, and currently lies near R.A. 15h 02’ and declination -14 37’, just over a degree from Ceres as seen from Earth. The Moon will briefly “occult” the Dawn spacecraft as well on September 28th.
Crowded skies: the Moon approaching Saturn, 4 Vesta, 1 Ceres and the Dawn spacecraft on the 28th. The red arrow shows the direction of the Moon. Created using Starry Night Education Software.
Be sure to keep an eye out for Earthshine on the dark limb of the Moon as our natural neighbor in space waxes from crescent to First Quarter. What you’re seeing is the reflection of sunlight from the gibbous Earth illuminating the lunar plains on the nighttime side of the Moon. This effect gives the Moon a dramatic 3D appearance and can vary depending on the amount of cloud and snow cover currently facing the Moon.
Such a close trio of conjunctions raises the question: when was the last time the Moon covered two or more planets at once? Well, on April 23rd 1998, the Moon actually occulted Venus and Jupiter at the same time, although you had to journey to Ascension Island to witness it!
The waning crescent Moon approaches Jupiter and Venus on April 23rd, 1998. Credit: Stellarium.
Such bizarre conjunctions are extremely rare. You need a close pairing of less than half a degree for two bright objects to be covered by the Moon at the same time. And often, such conjunctions occur too close to the Sun for observation. A great consequence of such passages, however, is that it can result in a “smiley-face” conjunction, such as the one that occurs on October 15th, 2036:
Smile: A close pass of the Moon, Saturn, and Regulus in 2036. Credit: Stellarium.
Such an occurrence lends credence to a certain sense of cosmic irony in the universe.
And be sure to keep an eye on the Moon, as eclipse season 2 of 2 for 2014 kicks off next week, with the second total lunar eclipse of the year visible from North America.
Illustration of MESSENGER in orbit around Mercury (NASA/JPL/APL)
A little over a week before NASA’s MAVEN spacecraft fired its rockets to successfully enter orbit around Mars, MESSENGER performed a little burn of its own – the second of four orbit correction maneuvers (OCMs) that will allow it to remain in orbit around Mercury until next March. Although it is closing in on the end of its operational life it’s nice to know we still have a few more months of images and discoveries from MESSENGER to look forward to!
MESSENGER’s orientation after the start of orbit correction maneuver 10 (OCM-10). Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
The first OCM burn was performed on June 17, raising MESSENGER’s orbit from 115 kilometers (71.4 miles) to 156.4 kilometers (97.2 miles) above the surface of Mercury. That was the ninth OCM of the MESSENGER mission, and at 11:54 a.m. EDT on Sept. 12, 2014, the tenth was performed.
At the time of this most recent maneuver, MESSENGER was in an orbit with a closest approach of 24.3 kilometers (15.1 miles) above the surface of Mercury. With a velocity change of 8.57 meters per second (19.17 miles per hour), the spacecraft’s four largest monopropellant thrusters (with a small contribution from four of the 12 smallest monopropellant thrusters) nudged the spacecraft to an orbit with a closest approach altitude of 94 kilometers (58.4 miles). This maneuver also increased the spacecraft’s speed relative to Mercury at the maximum distance from Mercury, adding about 3.2 minutes to the spacecraft’s eight-hour, two-minute orbit period.
OCM-10 lasted for 2 1/4 minutes and added 3.2 minutes to the spacecraft’s 8-hour, 2-minute-long orbit. (Source)
The next two burns will occur on October 24 and January 21.
After its two final successful burns MESSENGER will be out of propellant, making any further OCMs impossible. At the planned end of its mission MESSENGER will impact Mercury’s surface in March of 2015.
Built and operated by The Johns Hopkins University Applied Physics Laboratory (JHUAPL), MESSENGER launched from Cape Canaveral Air Force Station on August 3, 2004. It entered orbit around Mercury on March 18, 2011, the first spacecraft ever to do so. Since then it has performed countless observations of our Solar System’s innermost planet and has successfully mapped 100% of its surface. Check out the infographic below showing some of the amazing numbers racked up by MESSENGER since its launch ten years ago, and read more about the MESSENGER mission here.
“MESSENGER by the Numbers” – an infographic by NASA
Images of the surface of Mercury taken by the MESSENGER (MErcury Surface, Space ENvironment, GEochemistry, and Ranging) spacecraft. Some are in visual wavelengths and some are in other wavelengths. Yellow areas are considered to be younger spots. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
We’re lucky to have a spacecraft looking at Mercury and sending back information like this. NASA’s MESSENGER satellite just beamed back these images of three craters on the hplanet — Kertesz (top), Dominici (middle) and an unnamed crater (bottom).
Why the interesting appearance? That’s because some of these are color composites representing spectral information gathered by the spacecraft. By examining elements that are a part of the surface, scientists can get a sense of how the planet was formed and what parts of it were made when. For example, the yellow parts of those images are believed to be the youngest parts.
MESSENGER made its first flyby of Mercury in 2008 and entered orbit into the planet, which is the closest to the Sun, in 2011. Its discoveries including finding ice and hot flows amid the pictures of its cratered surface.
Artist's conception of NASA's MESSENGER spacecraft above Mercury. Credit: JHUAPL
Look out below! NASA’s MESSENGER spacecraft is at its lowest altitude of any spacecraft above Mercury, and over the next couple of months it’s going to get even lower above the planet.
The spacecraft — whose name stands for MErcury Surface, Space ENvironment, GEochemistry, and Ranging — is doing a close shave above the sun’s closest planet to look at the polar ice and its gravity and magnetic fields.
“This dip in altitude is allowing us to see Mercury up close and personal for the first time,” stated Ralph McNutt, the project scientist for MESSENGER at the Johns Hopkins University Applied Physics Laboratory (APL).
MESSENGER is the first-ever mission to orbit Mercury. It arrived at the planet in March 2011 and has now spent three Earth years or 14 Mercury years examining the cratered planet and its environment. The campaign has revealed many secrets about Mercury, ranging from the discovery of ice deposits to changes in its tenuous atmosphere due to the Sun.
The spacecraft made its lowest approach above the planet on July 25, at 62 miles (100 kilometers) and will keep moving lower due to “progressive changes” in its orbit, APL stated. By Aug. 19, the minimum altitude will be 50 km (31 miles), and then the closet approach will be on Sept. 12 at 25 km (16 miles).
After that, the team will temporarily raise the spacecraft’s orbit again before it makes a planned impact on the planet’s surface in March 2015. The NASA mission is operated and managed by Johns Hopkins University.
Will you see it? Comet Jacques will pass about 3.5 degrees north of brilliant Venus tomorrow morning July 13. This map shows the sky facing northeast about 1 hour before sunrise. Stellarium
Comet C/2014 E2 Jacques has returned! Before it disappeared in the solar glow this spring, the comet reached magnitude +6, the naked eye limit. Now it’s back at dawn, rising higher each morning as it treks toward darker skies. Just days after its July 2 perihelion, the fuzzball will be in conjunction with the planet Venus tomorrow morning July 13. With Mercury nearby, you may have the chance to see this celestial ‘Rat Pack’ tucked within a 8° circle.
First photo of Comet Jacques on its return to the morning sky taken on July 11. Two tails are visible – a short, dust tail pointing to the lower left of the coma and longer gas or ion tail to the right. Credit: Gerald Rhemann
While I can guarantee you’ll see Venus and probably Mercury (especially if you use binoculars), morning twilight and low altitude will undoubtedly make spotting Comet Jacques challenging. A 6-inch telescope might nail it. Look for a small, fuzzy cloud with a brighter core against the bluing sky. Patience is the sky observer’s most useful tool. It won’t be long before the comet’s westward motion combined with the seasonal drift of the stars will loft it into darkness again.
Use this map to follow Comet Jacques as it moves west across Taurus and Auriga over the next few weeks. Planet positions are shown for July 13 with stars to magnitude +6. Jacques’ position is marked every 5 days. Click to enlarge. Source: Chris Mariott’s SkyMap
A week from now, when the moon’s slimmed to half, the comet will be nearly twice as high and should be easily visible in 50mm binoculars at the start of morning twilight.
Comet Jacques is expected to remain around magnitude +6 through the remainder of July into early August and then slowly fade. It will be well-placed in Perseus at the time of the Perseid meteor shower on Aug. 12-13. Closest approach to Earth occurs on August 29 at 52.4 million miles (84.3 million km). Good luck and let us know if you see it.
The summer astronomical action heats up this week, as the waning crescent Moon joins the inner planets at dawn. This week’s action comes hot on the tails of the northward solstice which occurred this past weekend, which fell on June 21st in 2014, marking the start of astronomical summer in the northern hemisphere and winter in the southern. This also means that the ecliptic angle at dawn for mid-northern latitude observers will run southward from the northeast early in the morning sky. And although the longest day was June 21st, the earliest sunrise from 40 degrees north latitude was June 14th and the latest sunset occurs on June 27th. We’re slowly taking back the night!
The dawn patrol action begins tomorrow, as the waning crescent Moon slides by Venus low in the dawn sky Tuesday morning. Geocentric (Earth-centered) conjunction occurs on June 24th at around 13:00 Universal Time/9:00 AM EDT, as the 8% illuminated Moon sits 1.3 degrees — just shy of three Full Moon diameters — from -3.8 magnitude Venus. Also note that the open cluster the Pleiades (Messier 45) sits nearby. Well, nearby as seen from our Earthbound vantage point… the Moon is just over one light second away, Venus is 11 light minutes away, and the Pleiades are about 400 light years distant.
Looking east the morning of Tuesday, June 24th at 5:00 AM EDT from latitude 30 degrees north. Created using Starry Night Education software.
And speaking of the Pleiades, Venus will once again meet the cluster in 2020 in the dusk sky, just like it did in 2012. This is the result of an eight year cycle, where apparitions of Venus roughly repeat. Unfortunately we won’t, however, get another transit of Venus across the face of the Sun until 2117!
Can you follow the crescent Moon up in to the daytime sky? Tuesday is also a great time to hunt for Venus in the daytime sky, using the nearby crescent Moon as a guide. Both sit about 32 degrees from the Sun on June 24th. Just make sure you physically block the dazzling Sun behind a building or hill in your quest.
From there, the waning Moon continues to thin on successive mornings as it heads towards New phase on Friday, June 27th at 8:09 UT/4:09 AM EDT and the start of lunation 1132. You might be able to spy the uber-thin Moon about 20-24 hours from to New on the morning prior. The Moon will also occult (pass in front of) Mercury Thursday morning, as the planet just begins its dawn apparition and emerges from the glare of the Sun.
The position of the Moon and Mercury post-sunrise on the morning of June 26th. Credit: Stellarium.
Unfortunately, catching the event will be a challenge. Mercury is almost always occulted by the Moon in the daytime due to its close proximity to the Sun. The footprint of the occultation runs from the Middle East across North Africa to the southeastern U.S. and northern South America, but only a thin sliver of land from northern Alabama to Venezuela will see the occultation begin just before sunrise… for the remainder of the U.S. SE, the occultation will be underway at sunrise and Mercury will emerge from behind the dark limb of the Moon in daylight.
The ground track of the June 26th occultation. Credit: Occult 4.0.
Mercury and the Moon sit 10 degrees from the Sun during the event. Stargazer and veteran daytime planet hunter Shahrin Ahmad based in Malaysia notes that while it is possible to catch Mercury at 10 degrees from the Sun in the daytime using proper precautions, it’ll shine at magnitude +3.5, almost a full 5 magnitudes (100 times) fainter than its maximum possible brightness of -1.5. The only other occultation of Mercury by the Moon in 2014 favors Australia and New Zealand on October 22nd.
This current morning apparition of Mercury this July is equally favorable for the southern hemisphere, and the planet reaches 20.9 degrees elongation west of the Sun on July 12th.
You can see Mercury crossing the field of view of SOHO’s LASCO C3 camera from left to right recently, along with comet C/2014 E2 Jacques as a small moving dot down at about the 7 o’clock position.
Mercury (arrowed) and comet E2 Jacques (in the box) as seen from SOHO. (Click here for animation)
And keep an eye on the morning action this summer, as Jupiter joins the morning roundup in August for a fine pairing with Venus on August 18th.
The Moon will then reemerge in the dusk evening sky this weekend and may just be visible as a 40-44 hour old crescent on Saturday night June 28th. The appearance of the returning Moon this month also marks the start of the month of Ramadan on the Islamic calendar, a month of fasting. The Muslim calendar is strictly based on the lunar cycle, and thus loses about 11 days per year compared to the Gregorian calendar, which strives to keep the tropical and sidereal solar years in sync. On years when the sighting of the crescent Moon is right on the edge of theoretical observability, there can actually be some debate as to the exact evening on which Ramadan will begin.
Don’t miss the wanderings of our nearest natural neighbor across the dawn and dusk sky this week!
