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” !
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 firstname.lastname@example.org or contact me for more info. Good luck!
I may have been the only one in this area who saw the “mini-moon” (a full moon at apogee) last May 21. No media covered it, but give us a full moon at perigee (coming this Nov 14) and you will see a lot of print about “supermoons”.
The term was invented by an astrologer (name withheld to not give undeserved credit) who defined it as “a new or full moon which occurs with the Moon at or near (within 90% of) its closest approach to Earth in a given orbit”. Right away there are two problems: first, the moon’s orbit is not a fixed path that repeats exactly month to month so you are taking 90% of a moving target. Arguments then arise as to how many “supermoons” you can get in a year. Secondly, it is very difficult to actually see a new moon, -you risk eye damage since new moons are always close to the Sun. Even during solar eclipses when the moon is silhouetted against the Sun you need to use proper solar filters during the partial phases. “Danger, Will Robinson, Danger!”
Orbiting objects would always be the same size if their orbits were perfectly circular, but circular orbits are extremely rare. Our moon follows quite an elliptical path being father away at “apogee” and closer at “perigee”. Furthermore the actual difference between the two varies. For example, on Sep 18 at 1 pm, perigee distance is 361 896 km. Two weeks later (Oct 4 at 7 am) apogee distance is 406 096 km for a difference of 44 200 km. The next three occasions give a difference of 48 801 km in late Oct, 50 045 km in Nov and 47 409 km in Dec. The difference is never the same. The moon’s apparent size does change between the extremes but the 14% range in size is only an average.
So if the moon is closer to the Earth at perigee, shouldn’t it look bigger? Yes, but they are never seen side-by-side. Most people, if they happen to see both, rely on memory to compare the two moon sizes. If you go to the trouble of taking photos, they need to be with exactly the same camera, the same lens, and the moon must be close to the same location on two separate dates. Since the moon’s path across the sky is different in subsequent months, and it’s phase is not synchronized exactly to its orbit, and the weather sometimes works against you, it is not an easy task. I have succeeded getting photos only a few times in many years of trying. (OK, it was not a big priority.)
Image of Perigean Full Moon Jun 2013 (left) and Apogean Full Moon (right) John H. Photo
At the risk of adding to the media hype, the best “supermoon” this year is Nov 14 with perigee less than 3 hours from full moon, -a small and fairly rare time difference. Although the “mini-moon” last May 21 was a media “non-event”, do (“or do not") check out the next “mini-moon” on Jun 8, 2017. Do (“or do not, there is no try") to take pictures of both, this is the only way to really see the difference. Clear skies!
by John Hlynialuk
With the current heat wave holding Ontario in its grip, I am reluctant to talk about particles burning up in our atmosphere and adding more heat to the situation. But, rest assured, the extra energy is only going to make for an interesting night of viewing and not raise our local temperature one iota.
I am of course, talking about the annual Perseid meteor shower. These meteors (the more correct name for shooting stars), appear to stream from the head of the constellation Perseus for the same reason that falling snow appears to come from a point in the road ahead of your moving car. Every August, the Earth passes into a stream of particles (most snow-flake size and smaller) left behind by a comet called Swift-Tuttle.
The shower, already underway because the comet debris is rather wide, can be seen from July 17 to Aug 24, but the main peak of activity falls on the nights around Aug 11 to Aug 13. During the darkest hours after the moon sets (12:36 am Aug 11, 1:12 am Aug 12 and 1:52 am Aug 13) you can see shooting stars fall out of the sky at a rate of 90 per hour or more. This number includes all visible meteors over the entire celestial hemisphere so it is not likely that a single observer will see this many, but expect one per minute on average on those nights. Observing in a group of 4 or so, each covering one-quarter of the sky, is a fun way to get close to the maximum number. In addition, some recent predictions indicate that there may be a burst of higher activity during the night that may raise the number to twice that many.
Over a dozen bright Perseids appear on this composite image taken Aug 12, 2013 by John H.
Perseid meteors hit the atmosphere at 60 km/s, or over 200,000 km per hour and are among the fastest travelling meteoroids, -the proper name before they enter the atmosphere. Most other meteor showers’ particles move much slower (if 30 km/s is slow!). In any case, the energy carried by the particles (remember kinetic energy from physics class?) is mostly converted into light when they encounter the thin upper atmosphere which even at 80 to 120 km is still thick enough to act like a brick wall to meteoroids. The rapid deceleration creates a shock wave that heats the particle to incandescence, producing the glowing trail of light we see from the ground. Some Perseids are a bit more massive than average (maybe the size/mass of a grape) and those meteors may leave a glowing train that persists for several seconds. Some of these trains have been seen with binoculars to persist for several minutes. So bring binos if you have a pair.
The diehard meteor watchers of BAS will be watching in the wee hours after midnight from Aug 11 to 13 from the Fox Observatory and the public is welcome to join us. But, any dark site is suitable even if only a part of the sky is visible. Lying out on a lawn chair watching celestial fireworks is a great way to spend time with family and friends and get a break from the daytime heat.
Shooting stars really are “cool”.