Posted on by David Dickinson

Catch the Moon pairing with Mercury & Venus Tonight

Looking west at sunset from latitude 30 degrees north. The ecliptic and Mercury's orbit along with a 10 degree field of view outlined for reference. All graphics created by the author using Starry Night).

If you’ve never seen Mercury, this week is a great time to try.

Over the past few weeks, observers worldwide have been following the outstanding tight triple conjunction of Mercury, Venus and Jupiter low to the west at dusk.

Jupiter has exited the evening sky, headed for conjunction with the Sun on June 19th. I caught what was probably our last glimpse of Jupiter for the season clinging to the murky horizon through binoculars just last week. If you’re “Jonesin’ for Jove,” you can follow its progress this week through superior conjunction as it transits the Solar Heliospheric Observatory’s LASCO C3 camera.

This leaves the two innermost worlds of our fair solar system visible low to the west at dusk. And tonight, they’re joined by a very slender waxing crescent Moon, just over two days after New phase.

The Moon, Venus and Mercury as seen from 30 degrees north tonight at 9PM EDT.
The Moon, Venus and Mercury as seen from 30 degrees north tonight at 9PM EDT.

The evening of June 10th finds a 4% illuminated Moon passing just over 5 degrees (about 10 Full Moon diameters) south of Venus and Mercury. Venus will be the first to appear as the sky darkens, shining at magnitude -3.9 and Mercury will shine about 40 times fainter above it at magnitude +0.3.

Ashen light, also known as Earthshine will also be apparent on the darkened limb of the Moon. Another old-time term for this phenomenon is “the Old Moon in the New Moon’s Arms.” Ashen light is caused by sunlight being reflected off of the Earth and illuminating the nighttime Earthward facing portion of the Moon. Just how prominent this effect appears can vary depending on the total amount of cloud cover on the Earth’s Moonward facing side.

....and the orientation of the Moon, Mercury and Venus on the night of June 12th and ~9PM EDT.
….and the orientation of the Moon, Mercury and Venus on the night of June 12th and ~9PM EDT.

This week sets the stage for the best dusk apparition of Mercury for northern hemisphere viewers in 2013. Orbiting the Sun every 88 Earth days, we see Mercury either favorably placed east of the Sun in the dusk sky or west of the Sun in the dawn sky roughly six times a year. Mercury’s orbit is markedly elliptical, and thus not all apparitions are created the same. An elongation near perihelion, when Mercury is 46 million kilometers from the Sun, can mean its only 17.9 degrees away from the Sun as viewed from the Earth. An elongation near aphelion, 69.8 million kilometers distant, has a maximum angular separation of 27.8 degrees.

This week’s greatest elongation of 24.3 degrees occurs on June 12th. It’s not the most extreme value for 2013, but does have another factor going for it; the angle of the ecliptic. As we approach the solstice of June 21st, the plane of the solar system as traced out by the orbit of the Earth is at a favorable angle relative to the horizon. Thus, an observer from 35 degrees north latitude sees Mercury 18.4 degrees above the horizon at sunset, while an observer at a similar latitude in the southern hemisphere only sees it slightly lower at 16.9 degrees.

Venus and the Moon make great guides to locate Mercury over the next few nights. It’s said that Copernicus himself never saw Mercury with his own eyes, though this oft repeated tale is probably apocryphal.

We also get a shot at a skewed “emoticon conjunction” tonight, not quite a “smiley face” (: as occurred between Jupiter, Venus and the Moon in 2008, but more of a “? :” Stick around until February 13th, 2056 and you’ll see a much tighter version of the same thing! A time exposure of a pass of the International Space Station placed near Mercury and Venus could result in a planetary “meh” conjunction akin to a “/:” Hey, just throwing that obscure challenge out there. Sure, there’s no scientific value to such alignments, except as testimony that the universe may just have a skewed sense of humor…

Through the telescope, Venus currently shows a 10” diameter gibbous phase, while Mercury is only slightly smaller at 8” and is just under half illuminated. No detail can be discerned on either world, as a backyard telescope will give you the same blank view of both worlds that vexed astronomers for centuries. These worlds had to await the dawn of the space age to give up their secrets. NASA’s MESSENGER spacecraft entered a permanent orbit around Mercury in 2011, and continues to return some outstanding science.

Both planets are catching up to us from the far side of their orbits. Mercury will pass within 2 degrees of Venus on June 20th, making for a fine wide field view in binoculars.

And now for the wow factor of what you’re seeing tonight. The Moon just passed apogee on June 9th and is currently about 416,500 kilometers or just over one light second distant. Mercury meanwhile, is 0.86 astronomical units (A.U.), or almost 133 million kilometers, or about 7 light minutes away. Finally, Venus is currently farther away from the Earth than the Sun at 1.59 A.U.s, or about 13.7 light minutes distant.

All this makes for a great show in the dusk skies this week. And yes, lunar apogee just after New sets us up for the closest Full Moon of 2013 (aka the internet sensation known as the “Super Moon”) on June 23rd. More to come on that soon!

 

Posted on by David Dickinson

New Crater Names Approved for Mercury’s South Pole & More

Mercury's southern polar region as seen from MESSENGER. (Credit: NASA/Johns Hopkins UniversityApplied Physics Laboratory/Carnegie Institution of Washington).

Move over, Tolkien & Tryggvadóttir. Yesterday, an announcement was made that the International Astronomical Union (IAU) approved proposed names for nine new craters on the planet Mercury. The names honor deceased writers, artists and musicians following the convention established by the IAU for naming features on the innermost world.

The announcement comes as NASA’s MESSENGER spacecraft has completed mapping of the surface of Mercury earlier this month. A good majority of these features were established at Mercury’s southern polar region, one of the last areas of the planet to be mapped by MESSENGER.

The craters honored with a newly assigned moniker are:

Donelaitis, named after 18th century Lithuanian poet Kristijonas Donelaitis, author of The Seasons and other tales and fables.

Petofi, named after 19th century Hungarian poet Sandor Petofi, who wrote Nemzeti dal which inspired the Hungarian Revolution of 1848.

Roerich, named after early 20th century Russian philosopher and artist Nicholas Roerich, who created the Roerich Pact of 1935 which asserted the neutrality of scientific, cultural and educational institutions during time of war.

Hurley, named after the 20th century Australian photographer James Francis Hurley, who traveled to Antarctica and served with Australian forces in both World Wars.

Lovecraft, named after 20th century American author H.P. Lovecraft, a pioneer in horror, fantasy and science fiction.

Alver, named after 20th century Estonian author Betti Alver who wrote the 1927 novel Mistress in the Wind.

Flaiano, named after 20th century Italian novelist and screenwriter Ennio Flaiano who was a pioneer Italian cinema and contemporary of Federico Fellini.

Pahinui, named after mid-20th century Hawaiian musician Charles Phillip Kahahawai Pahinui, influential slack-key guitar player and part of the “Hawaiian Renaissance” of island culture in the 1970’s.

L’Engle, named after American author Madeleine L’Engle, who wrote the young adult novels An Acceptable Time, A Swiftly Tilting Planet & A Wind in the Door. L’Engle passed away in 2007.

Five of the newly named craters in the south pole region of Mercury (circled in red). Note that the final portion of the USGS map, although recently released, has yet to be filled in! (Credit: USGS).
Five of the newly named craters in the south pole region of Mercury (circled in red). Note that the final portion of the USGS map, although recently released, has yet to be filled in! (Credit: USGS).

The nine new crater names join 95 others named thus far. The MESSENGER surface mapping campaign has been ongoing since the spacecraft’s first flyby of Mercury in January 2008. MESSENGER entered permanent orbit around world on March 18th, 2011.

MESSENGER missions operations engineer Ray Espiritu was instrumental in getting Pahinui’s name in the running.

“I wanted to honor the place where I grew up and still call home,” Espiritu said. ”The Pahinui crater contains a possible volcanic vent, and its name may inspire other scientists as they investigate the volcanic processes that helped to create Mercury, just as investigation of the Hawaiian volcanoes helps us understand the volcanic processes that shape Earth as we know it today.”

Pahinui Crater. (Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington).
Pahinui Crater. (Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington).

Lovecraft is another interesting selection on the list. The name of the famous horror writer was in the running last month for the naming of Pluto’s moons P4 & P5, and New Horizons principle investigator Alan Stern hinted that Lovecraft may still find a home on a surface feature as New Horizons reveals Pluto & Charon in July 2015. It would be a fitting tribute to a fine writer. Could we end up with Lovecraft marking not only the solar system’s “hubs of hell” on Mercury, but its frozen outer wastelands as well?

There was more news yesterday in the realm of astrogeology and the planet Mercury. The IAU Working Group for Planetary System Nomenclature also made the distinction between features described as valles and catenae on the surface of Mercury. Catenae are described as crater chains, and MESSENGER has sufficient resolution that several valles have been revealed as such. Catenae on Mercury are named after radio astronomy observatories, while valles are named after abandoned cities of antiquity. Thus, Haystack Vallis is now Haystack Catena, Goldstone Vallis is now Goldstone Catena, and Arecibo Vallis is now Arecibo Catena, and, well, you get the idea.

Arecibo Catenae (formerly known as Arecibo Vallis) as imaged by MESSENGER in 2008. (Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington).
Arecibo Catenae (formerly known as Arecibo Vallis) as imaged by MESSENGER in 2008. (Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington).

MESSENGER has proven to be a boon for planetary science. The spacecraft was launched in 2004 and took almost 7 years and 6 flyby assists (one past the Earth, two past Venus and three past Mercury) to become the first spacecraft to orbit the tiniest planet in our solar system. Mercury was first seen up close by Mariner 10 in 1974 and even then we only mapped 45% of its surface. Scientists had to wait until MESSENGER to fill in the remainder of Mercury’s map.

The next mission to Mercury isn’t until the planned arrival of the joint ESA/JAXA BepiColombo mission in 2022.

And don’t forget to watch for Mercury as it reaches greatest elongation on Easter Day low in the dawn sky. I managed to catch sight of it low to the east with binoculars for the first time this apparition this morning about 40 minutes prior to local sunrise. It’s amazing to think that ground-based professional telescopes & even amateur astronomers can actually image fuzzy details on the planet’s surface that match up with what MESSENGER is revealing!

All fascinating stuff to contemplate as  we welcome the newest named craters to our ever expanding map of Mercury… now, will there ever be a Miskatonic University within the walls of Lovecraft crater?

-Explore these recently named craters and more  using the USGS inactive Astrogeology Science Center.

-Also check out this animation of the south polar region of Mercury and more as imaged by MESSENGER.

 

 

 

Posted on by David Dickinson

See Mercury at its Greatest Elongation for 2013

Mercury gives a clue to Super-Mercuries
Astronomers have found a star system with two planets like Mercury, but bigger. Our own Mercury could supply clues to their composition and formation. (Credit: NASA/Johns Hopkins University/Applied Physics Laboratory.Carnegie Institution of Washington).

A fine apparition of the planet Mercury graces the dawn skies this week, leading up to its greatest elongation from the Sun for 2013.

It seems that nearly every appearance of the planet Mercury is touted as the “best” these days. Such was the case with the inner-most world’s dusk showing early last month. Truth is, all elongations of Mercury (and Venus, for that matter) are not created equal, and visibility of each apparition isn’t the same for observers worldwide. We’ll show you why.

Mercury orbits the Sun once every 88 days. With an orbit interior to our own, it never strays far from the Sun in the sky and thus can only appear low in the dawn or dusk. Its orbit is also elliptical, with an eccentricity of 0.206, the greatest of any planet in our solar system. This means that greatest elongations can vary considerably, from 17.9° away from the Sun in the sky near perihelion of the planet to 28.7° near aphelion. And although reaching greatest elongation near aphelion means the tiny world is above the muck of the horizon, it also means it’s also intrinsically a bit fainter; Mercury can vary in brightness from magnitude -0.2 at a perihelic-elongation to half a magnitude fainter at +0.3 for an aphelic-elongation.

A comparison of elongations of Mercury as seen from the Earth at perihelion versus aphelion. (Created by the author).
A comparison of elongations of Mercury as seen from the Earth at perihelion versus aphelion. (Created by the author).

But there’s more. Compounding this situation is the angle of the ecliptic, or the imaginary plane of the orbit of the Earth. Near the March equinox the ecliptic rides high in the dusk to the west and low in the dawn to the east for northern hemisphere observers. In the southern hemisphere, the reverse is true. It’s a strange sight for a northerner to head “Down Under” and watch the Sun rise in the east, transit to the north and set to the west!

The path of Mercury looking east ~45 minutes prior to sunrise from latitude 30 degrees north from March 26th through April 30th, (Created by the author using Starry Night).
The path of Mercury looking east ~45 minutes prior to sunrise from latitude 30 degrees north from March 26th through April 30th, (Created by the author using Starry Night).

Thus what may be a terrible apparition of Mercury for one hemisphere may be a grand one for another, as is the case this week. Yes, northern observers can catch the fleeting world, if they know exactly where to look for it. For observers based at longitude 40° north, Mercury will never peak above an altitude of 10° in the dawn sky. Observers based near 35° south will however see the planet reach its maximum possible elevation of over 25° degrees above the horizon.

We would qualify this as “The best dawn appearance of Mercury for 2013… as seen from the southern hemisphere.” Greatest elongations of Mercury occur in pairs, with dusk-to-dawn apparitions about 45 days apart as the planet passes between us and the Sun, followed by a longer period of about 70 days as the world loops back around behind the Sun. The orbit of Mercury is tilted about 7° with respect to our own. Otherwise, we would see a transit of the planet every inferior conjunction, as last occurred on November 8th, 2006 and will happen next on May 9th, 2016.

The path of Mercury from March 26th through April 26th looking east from latitude 35 degrees south ~45 minutes prior to sunrise. (Created by the author using Starry Night).
The path of Mercury from March 26th through April 26th looking east from latitude 35 degrees south ~45 minutes prior to sunrise. (Created by the author using Starry Night).

Mercury will show a maximum illumination area of 38.5” square arc seconds as seen from the Earth March 30th on just before reaching its greatest elongation west of the Sun on March 31st on Easter Day at 22:00 UT/18:00EDT. Through a telescope, Mercury will display a 7.7” diameter disk with a 50% illuminated “half-Moon” phase. Mercury reaches greatest elongation just 28 hours prior to aphelion which occurs on April 2nd, the closest this has occurred date-wise since April 8th, 2006. This won’t be matched again until March 24th, 2020. Shining at magnitude +0.3, Mercury will then race ahead of the Earth on its inside track and will begin to gradually sink lower on successive mornings in early April. The morning of April 8th may well offer the last good chance to spy the tiny world when the old crescent Moon passes just 8° degrees north of the planet within two days of reaching New phase on April 10th. Mercury reaches superior conjunction opposite to the Earth and on the far side of the Sun on May 11th, 2013, and will again head into the dusk skies for its next greatest eastern elongation on June 12th.

From our Earthly vantage point, Mercury completes 3.15 orbits of the Sun a year. This means that we see 6 greatest elongations on average most years, 3 westerns (dawn) and 3 easterns (dusk). The most elongations of Mercury that you can have in a calendar year are 7, which occurred in 2011 and will happen again in 2015. It’s fascinating to think that until the advent of the Space Age, the orbit and the rough size of Mercury was all we knew about the planet. It would take the first flyby of the Mariner 10 spacecraft to give us a close up view of Mercury in 1974. The precession of the orbit of Mercury was a mystery until explained by Einsteinian physics, and still stands as one of the great proofs of general relativity. Today, we have a permanent ambassador around Mercury, NASA’s MESSENGER spacecraft. MESSENGER has mapped to world in detail, sampled its tenuous exosphere, and observed hints of ancient volcanic activity. MESSENGER will be followed by the joint European Space Agency/Japan Aerospace Exploration Agency mission BepiColombo set to launch in 2015 which will arrive at Mercury in 2022. All fascinating things to ponder as you search for the diminutive world low in the dawn skies this coming Easter weekend!