If you have noticed a bright light in the eastern sky (perhaps while taking your pet for a walk) you are not alone. Venus in the west is gone (returning soon to the morning sky) and Mercury will not last long as a substitute evening star. Now we turn to the eastern sky to watch our next featured planet, Jupiter, a planet almost as bright as Venus, and in many ways much more interesting.
Jupiter is the largest planet of the 8 planets in our solar system (9 if you still pine for Pluto). Jupiter and our Sun constitute 99.99% of the total system mass and each has a gravity pull so strong that according to current theories, a major planet was prevented from forming in the space between -only jagged chunks of space debris, the asteroids, are found orbiting there. One Jove-centric pundit defined our solar system as “Sun, Jupiter and assorted debris”, and it is true that the “leftovers” don’t amount to much, mass-wise. Earth, of course, has water, an atmosphere, and conditions that allow living organisms to thrive, so it is pretty special. Jupiter is unique, too, but only because it is such an extreme contrast to our own beautiful world.
The gravity of Jupiter is over 2.5 times Earth’s so, if yours truly, at a trim 180 pounds, were on Jupiter, I would need to support 455 pounds just to stand up, -if there was any place to stand. A solid surface like that on Earth cannot be found on Jupiter, and what we see in telescopes are the tops of swirling white and brownish clouds of ammonia crystals and darker-coloured sulphur compounds. Below the clouds (about 50 km thick) is a mixture of very cold hydrogen and helium gas which gets thicker and thicker all the way to the “surface” of a strange ocean of metallic liquid hydrogen. The atmospheric pressure here would crush the strongest pressurized vessel from Earth. So if the gravity doesn’t kill you, the pressure will.
Exploration of Jupiter can only happen from orbit or floating/flying in the upper atmosphere, but even here spacecraft are severely challenged. Wind speeds reach 1600 km/h (10 times those in Earth’s jet streams), and lightning occurs in “superbolts” the equivalent of 100 of the terrestrial variety. Huge storms in the atmosphere of this huge planet are common, -one Jovian hurricane, the Great Red Spot (first seen in 1665 and raging still) is bigger than the entire Earth with wind speeds over 400 km/h (twice those of a category 4 hurricane on Earth). Even Jupiter’s magnetic field is huge, extending several million km into space, so we are lucky that we are 600 million km away, -it is a safe enough distance.
Jupiter reaches a point in our sky called opposition on Apr 7 when it is exactly opposite the Sun and highest in our sky at midnight. This is prime-time for Jupiter, when it is well above the turbulent air near the horizon. But if it is cloudy Apr 7, don’t panic. Planets at opposition are in good viewing position for a month before and several months after the opposition date. For the best views on any clear night, observe the planet when it is away from the disturbing air near the horizon. Summer star parties will obviously feature both Jupiter and Saturn, which itself reaches opposition June 15.
Jupiter is near the star Spica, the brightest star of Virgo, but Spica does not move, so use it as a reference point to watch Jupiter doing what distinguishes planets from background stars, i.e. wander. Jupiter slowly slips westward until June 8 (retrograding), then, in the summer, it starts back towards Spica. By the end of Jupiter-viewing in autumn, the pair will be setting in the west just after sunset, with Jupiter closest to Spica and right above it.
Observing nights at the Fox Observatory will certainly include views of Jupiter with its always-changing arrangement of 4 bright moons. These are even visible in binoculars, but true to its status as King of Planets, Jupiter has 63 more moons circling it, the most of any planet. By Jove, Jupiter really is an attention-getter!
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”.
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!
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.
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.
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.
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 .
Photo Ⓒ 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” !