Mercury (Evening Star) and Crescent Moon

by: John Hlynialuk

The variable weather of March prevented stargazers in the Bruce and Grey area from seeing Venus and Mercury as double evening stars on March 19. Though the daytime sky was a spectacular blue, a dense cloud moved in above the western horizon at sunset, hid the planets and even obliterated the Sun as it sank below the edge of Lake Huron. Amateur astronomers were again teased by the goddess of astronomy, Urania, but, on that occasion, she perversely hid her beauties from sight.

Though this is not the first time that clouds have defeated local stargazers, (weather cancellations average about 50%) we all understand the following: "whether or not it is clear to you...the universe is unfolding as it should":
Desiderata, Max Ehrmann. If you read "weather" instead of "whether", the line has a slightly different meaning to be kept in mind as we attempt to observe future sky sights.

The next test of local stargazer’s dedication comes when Urania offers a series of crescent moon appearances near Mercury and Mars in the western sky from Mar 29 to Apr 1 (weather permitting, of course). The thin crescent Moon is a very pretty sight and should be high enough above the western horizon on Mar 29 to stand out in bright twilight. (See diagram). Right beside it, the only bright “star” in the area is the planet Mercury. This is an opportunity to spot that elusive planet if you have never seen it before, -it will be in the western sky playing the role of “Evening Star” for a few weeks. On March 30, the crescent Moon moves upwards and will be just left of Mars. On March 31, it appears close to Aldebaran, the “angry red eye” of Taurus the Bull. Aldebaran is indeed a red giant star, 44 times larger than the Sun, and does have a slight tinge of red to it. After April 1, the Moon continues moving eastward, increasing its phase (waxing) and brightening the sky as it does so. The Moon is first quarter on April 3 and full on April 11. April’s Full Moon is also called the “Egg Moon”, the “Grass Sprouting Moon” or the “Paschal Moon”.

Moon Mar29-31
Diagram from Starry Night Simulation Curriculum

Unlike Venus which had a three month period of visibility, the two planets presently in the western sky will not be around for long. On April 1, Mercury starts back towards the Sun and will be lost in the Sun’s glare by the time of full moon. Mars follows Mercury and is hidden in the Sun’s glow a few weeks later. The show is over by the third week of April.

Most of Mercury’s disappearing act is due to the rapid decrease in the amount of sunlight that reflects our way from its surface. Both Venus and Mercury exhibit phases as they orbit the Sun and on March 29, Mercury is half illuminated, -a first quarter phase. By Apr 6, this is reduced to a thin crescent (like the crescent Moon on March 29 and 30) and with less light reflected our way, the brightness of Mercury drops rapidly. With the weather in March so changeable, if you want to add Mercury to your life-list of astronomical objects, you need to observe on any clear night in the next two weeks or so.

If you join the Bluewater Astronomers on Saturday, March 25 at the Fox Observatory for the Messier Marathon, and you arrive before Mercury sets, ask one of the guides to show you the planet in a telescope. At medium power it is possible to see the planet as a thin crescent like a miniature crescent Moon. If you have a telescope of your own, Mercury is a neat sight, -this month is your best opportunity to see it for the entire year. Don’t miss it!

Venus and Mars in Western Sky after Sunset

Two very different planets are visible in the evening sky right now. Venus is obvious even in twilight, -a very bright Evening “Star” high above the SW horizon. Then there is Mars, much dimmer and slightly reddish -to the left and slightly up from Venus- looking like an average background star. Both are visible in February and March, Venus catching your eye instantly, its light so intense that most times clouds cannot block it. And now that you know where to look, you should be able to spot the Red Planet as well.

Image above shows Venus and Mars above the western horizon Feb 18, 2017
Canon 6D 10 s ISO 3200 f/8 24 mm lens

Venus, on Feb 17, was its brightest for this apparition since it had the largest sunlit surface facing us and was on the inside track of its orbit so it was also larger in area due to proximity. The two effects work against each other, -as the planet gets closer and larger, less and less of its surface is light from our perspective. There is a happy medium, however, on Feb 17 when the two produce a maximum lit surface. See SKY SIGHTS entry for Feb 17 for more.

Image above shows Venus on Feb 18, 2017 at its maximum brightness. (-4.6)
Canon 6D eyepiece projection through 20 mm eyepiece on C-9.25 Edge HD 1/40 s ISO100 f/40 eff. foc.len.

The difference in visual appearance of the two planets is based mostly on distance. Venus in its orbit is approaching the Earth right now and on March 24, it passes between us and the Sun at a mere 41 million kilometres. On rare occasions, it can even shave another 3 million km off that figure. Mars is about 6 times farther than Venus right now and on the opposite side of the solar system from Earth. In a year or so, however, Mars and Earth will be much closer, only 56 million km apart and so Mars will shine as a bright planet in our sky once again. But because Mars is smaller than Earth, (half of Earth’s diameter) and reflects less light our way (16%) it can never get as bright as Venus in our sky. Venus is an Earth-sized planet and its thick atmosphere of clouds reflects 75% of the sunlight in our direction. Mars and our Moon are very poor reflectors with similar albedos (the technical term for reflectivity) of 16% and 12% respectively, about the same as a slate blackboard.

Both planets, Venus and Mars are named after mythological gods. The Roman goddess of love was Venus and in Greek mythology, she was Aphrodite. She is always depicted as demur, lovely and beautifully curvy. The Roman god of war, Mars, and the equivalent Greek war god, Ares are shown in statues and paintings as bold, handsome and certainly manly (and deadly in battle). As the story goes, Mars and Venus at one point were a couple and produced twin offspring which judging by their names were probably poorly behaved: Deimos (meaning terror or dread) and Phobos (panic/fear). These names are used for the two real moons of the planet Mars.

So in the summer of 2018, a much brighter Mars will be the planet to observe with surface features like ice caps and dust storms visible in a telescope. (Even Deimos and Phobos may be glimpsed). But Venus, though closest and brightest in our sky right now, will forever remain mysterious, never dropping her thick veil of clouds and revealing her surface features (unless you have radar eyes, of course). Do enjoy the naked eye or binocular views of Venus right now because by April, Aphrodite’s month, she passes behind the Sun and disappears from our western sky. Later in spring, Venus returns to the east as an equally bright Morning Star, but by then she has left Mars far behind. This is only a temporary separation as the two are back together in a spectacular “embrace” in October -stay tuned.

Penumbral Lunar Eclipse Feb 10

There is an “oh-so-close” lunar eclipse happening on Feb 10. Technically it is a miss, and even if the skies are perfectly clear, the best we can hope for is a slight darkening of part of the Moon’s face at the prime time of 7:44 pm. Even then, you might not notice anything unless you know exactly what to look for. Here’s what you need to know, (in case you’re interested).

Eclipses are caused by shadows. The Sun sends light out in all directions and during a lunar eclipse, the Earth blocks the Sun’s light and the Earth’s shadow falls onto the full Moon. Things have to be lined up perfectly, so eclipses don’t happen every month, -the most we get is seven a year, about half of each type. In 2017, we get two solar and two lunar eclipses, a bit fewer than average.

Lunar eclipses would happen more often except that the Moon’s orbit around Earth is tilted and Earth’s shadow goes over or under the Moon most times. Secondly, there are two parts to the Earth’s shadow that can cover the Moon, an easily-seen dark central area, the umbra, and a surrounding penumbra, but it allows most of the sunlight through and is barely detectable. A penumbral eclipse is what we will get on Feb 10.

LEcl.Feb 10

The shadow of Earth extends past the Earth and forms a dark cone stretching out to a point about 1,400,000 km away in space. That’s almost 4 times as far as the Moon is from us, so at the Moon’s distance, the shadow’s cross-section (a circle) is still big, almost 3 times as wide as the full Moon. For that reason, lunar eclipses last several hours and solar eclipses, with a much smaller Moon shadow, -only a few hundred km across- last only a few minutes.

The shadow of Earth on Feb 10 comes close but does not actually contact the umbra (it gets 99% of the way there). The second lunar eclipse this year, on August 7, is a bit better but still only partial and worse yet, for the whole eclipse, the Moon is below our horizon, -the best view will be in the Middle East.

The one bit of good news for Feb 10 is that it may be possible to see a darkening due to the slightly darker, inner part of the penumbral shadow. The outer penumbra is just too faint to see when it touches the face of the Moon at 5:34 pm. By 7:44 pm, however, a darkening on the upper left edge of the Moon (about 10:30 on the clock) may be discernible for perhaps 20 minutes either side of the prime time. The only way to tell for sure is to take a picture at 7:44 pm and compare it to another taken two hours later when the eclipse is over and the Moon is back to full brightness.

If it is clear Friday night, Feb 10, the Fox Observatory at the Outdoor Education Centre near Oliphant will be open to the public and members of the Bluewater Astronomical Society will be there to show you the Moon. You are welcome to take a souvenir photo through the telescope, -even a cell phone will work. If the weather cooperates, there will be time to observe the eclipse, take photos and have a hot chocolate to ward off the chill. Do join us.

Here is an image from the April 4, 2015 lunar eclipse taken before umbral contact to simulate the appearance of the Feb 10 event. Notice the darkening in the upper left of the Moon's disk, -this is about where to expect darkening for the Feb 10 eclipse. This image was taken 10 minutes before umbral contact and the inside edge of the penumbra should be darker than this for Feb 10. Skies will need to be perfectly clear!

Image by John H. Apr 4, 2015, Canon 60Da, 400 mm telephoto at f/5.6, 1/250 s, ISO 200

PS: The next good total lunar eclipse visible locally happens in two years on Jan 21, 2019 but only a year from now, on Jan 31, 2018, there is a good lunar eclipse visible from the west coast of North America if you are free to travel then. (I hear the skiing is good out there at that time, too). Mark your calendars!

Maps to the Fox Observatory are found on our HOME page.

Vermin of the Skies

by John Hlynialuk

On my astronomy calendar, the new year is marked by the anniversary of a night over 200 years ago (1801) that created a crisis in planetary astronomy. It was not immediately recognized as such, and the alarms were only heard in astronomical circles at first. The general public was mostly unaware that their universe was changing.

The event was the discovery of Ceres, an object that was called a “planet” for a while, then an “asteroid” and now is referred to as a “minor solar system body”.

Guiseppe Piazzi, an Italian astronomer celebrated the first night of 1801 by discovering an unusual moving speck in a place where astronomers expected planets to be, and it came to be named Ceres (the Roman goddess of agriculture). Discoverers are allowed to suggest names, although the International Astronomical Union has final approval. There is some leeway in suggested names, however, and it’s OK (and a great idea) to name an asteroid after your spouse, -several discoverer’s wives have been immortalized in the heavens. However, the IAU will not allow naming a new asteroid or comet after your cat, for ex. Neither can anyone name a star after a loved one, not officially anyway. (Those websites are, in fact, a scam).

Twenty years before Piazzi’s discovery, on March 13, 1781, William Herschel added a 7th planet, Uranus, to the list so Ceres raised the planet count to eight.

Then in rapid succession, three additional “planets” was discovered, Pallas in 1802, Juno in 1804 and Vesta in 1807. The count stayed at 11 until 1845 when the astronomical “cup” overflowed.

In 1845 Astraea was discovered and the planet number went to twelve. Now things started to get complicated. In September 1846, an object was discovered that was different. The previous discoveries were star-like objects between the orbits of Mars and Jupiter, but this one was the most distant object ever observed. Furthermore, large telescopes showed that the object had a disk and colour similar to that of Uranus. Planet 13 (actually Neptune) was more like planet 7 (Uranus) than planets 8 thru 12.

From 1847 on, new “planets” were discovered at the rate of about one a year and astronomers uncharitably started to refer to these objects as the “vermin of the skies”, -not because they were ugly, (which they are -think debris from the exploding Death Star in Star Wars spreading out through space), but because there were so many of them.

The situation was resolved when William Herschel suggested that these objects should be put into a separate category of small “star-like” bodies that would be called “asteroids”. It was an intelligent suggestion especially as the numbers of asteroids continued to grow. There were enough ways to challenge students without asking them to memorize (in proper order) hundreds of new “planets”.

Astronomers now list more than 200 asteroids over 100 km in size, Ceres, the one that started it all, is 945 km across and Vesta is 545 km in diameter. The IAU recognizes 20 364 with names and there are thousands more that are simply given catalogue numbers. In all, there may be several million asteroids, but thankfully, most orbit between Mars and Jupiter and seldom stray to the vicinity of Earth to pose a danger.


In June 2014, both Vesta and Ceres were in the same part of the sky near the star Heze in Virgo.
Image was taken with a Canon 60Da with a zoom telephoto set at 285 mm focal length f/5.6, 30 s exposure (on a tracking telescope) ISO 2000. The image is a crop from the original and shows stars down to about 9th magnitude. Vesta magnitude was about 6.1, Ceres was at 7.3 .
2014 by J.Hlynialuk

Asteroid 4Vesta is bright enough to be seen with the naked eye but binoculars make the task easier. See it for yourself over the next few months, -the finder chart shows where to look. Join the two brightest stars of Gemini, -Castor and Pollux- and extend the line down (eastwards) and you are in the right general area. Vesta should be the brightest object in view, but there is only one certain way to identify it. Make a quick star sketch (or take a photo) and then come back in a few days to see which “star” has moved. (This is how Vesta was originally discovered). Spot Vesta and you can add a named asteroid to your life list of astronomical objects. Only 20 363 more to go.

Detailed finder charts (both Vesta and Ceres) and photo hints are under the
CHARTS & FORMS tab. Good luck hunting “minor solar system bodies” !

Thin Moon Challenge

Thin Moon Challenge Issued"
John Hlynialuk
Lorraine Rodgers and Aaron Top have laid down a challenge (sort of...). In a recent discussion between some BAS members (Brett T., Lorraine R. and John H.) it was determined that the thinnest new moon sighting (confirmed by image) was over 5 years ago on Feb 3, 2011. That evening, Lorraine and Aaron observed a 21-hour old crescent above the western horizon just east of Sauble Beach (they moved inland to get away from the winds at the shore). The very thin crescent is just visible above the tallest tree branches in Aaron's image below.

Canon 50D with 85 mm f/5.6, 1/15 s, ISO 640 at 6:21 pm Feb 3, 2011
Aaron Top image

So far, this is the thinnest (youngest) crescent moon seen by local amateur astronomers, - an admirable achievement, although it is not a world record. The "official" visual sighting record is held by Steven James O'Meara who spotted a 15 h 32 min moon in May 1990. The youngest moon seen with optical aid is 11 h 40 min by Mohsen G. Mirsaeed of Tehran on Sep 7, 2002. The Sky&Telescope article on thin moons is here: S&T Thin Moons
Note that there is an image taken with the Moon at 0.0 hours age, i.e., at the exact moment of New Moon. Remarkable and true! This was done in daytime by Thierry Legault on July 8, 2013. More information here:
Youngest Possible NM As an added comment, if the Moon were a perfect sphere, there will always be a thin crescent of light except at the central moment of a total solar eclipse. The Moon is a real world, of course and has terrain that can reflect light. The S&T article link in the previous paragraph explains this nicely.

Thin Moon Challenge: The info you need
The table below includes both last crescent and new crescent moon viewing opportunities in the next few months. Data is from Starry Night but do the moon age calculation yourself by working from the time of NM to the time of observation. Do the math yourself, do not rely on a program to do it for you, we have found discrepancies of several hours between different astronomy software programs.
Note that not all of those events listed will break the record, but you might want to try for an observation or an image or two with a fatter crescent and earthshine for practice. Note that an observation by a single observer must be confirmed by a second witness to be eligible for the record. Also acceptable is an image of the thin moon in question (with horizon in the view and original camera data intact) and please make sure your camera clock is accurate to the nearest minute or so. Send all reports and/or images to the editor of SGN or contact me for more info. Good luck!

Thin Moons Nov Dec Jan 2017