The September Equinox

Most people know that something called the “equinox” happens twice every year around March 21 and September 21, but don’t really know what that means. Here are the real facts about the equinox.

The sun crosses the celestial equator on September 22 at 4:44 p.m. EDT. On this date the sun rises due east and sets due west, and the day and night are of equal length. Image Credit: Starry Night Software

The Earth moves in two different ways. First, it spins on its polar axis, a line through the north and south poles, once every 24 hours, causing the alternation of day and night. Secondly, it moves in its orbit around the sun once every 365 1/4 days, causing the annual cycle of seasons. The equinox occurs when these two motions intersect.

Because the Earth is very massive, its mass has an enormously powerful gyroscopic effect. For this reason, its poles always point in the same direction, although a major earthquake can cause tiny wobbles in this axis. Most importantly, the Earth’s motion around the sun has absolutely no effect on the direction the poles are pointing, which has very important consequences for Earth’s seasons.

Astronomers mark the positions of objects in the sky relative to the Earth’s poles of rotation: those are the red lines you see in the chart. The most important line is the celestial equator, which divides the sky into northern and southern hemispheres.

The Earth’s pole of rotation is tilted 23.4 degrees relative to the plane of its orbit. This tilt is always towards the same point in the sky, called the celestial pole, no matter where in its orbit around the sun the Earth happens to be. This tilt has the effect on the surface of the Earth that the sun appears to move across the sky at an angle to the celestial equator. This is marked by the green line in the chart, called the “ecliptic” because eclipses happen along this line.

Twice a year, the sun crosses the celestial equator, moving from the northern hemisphere to the southern hemisphere or from the southern hemisphere to the northern hemisphere. These two crossings are very important for the inhabitants of Earth, because they mark the change in the direction the sun’s rays fall on the Earth.

Specifically, on September 22, the sun will move from the northern hemisphere to the southern hemisphere. It will pass overhead everywhere along the Earth’s equator on that date. It will rise exactly in the east and set exactly in the west. After that date, the sun will shine more on the southern half of our planet, and less on the northern half. Summer will be over in the northern hemisphere, and winter will be on its way. Also, winter will be over in the south, and summer will begin.

The sun will continue on its path southward for the next three months, reaching its southernmost point on December 21, the date called “solstice.” In the northern hemisphere, the days will become shorter, the nights longer, and the temperatures colder, all the result of the sun’s being south of the celestial equator.

It’s always important to remember that this is part of a cycle, and that after December 21 the sun will start moving northward again, and spring will be on its way.

First Quarter Moon

The next few nights are the best this month to observe the surface features of the moon. The sun will be rising along the center line of the moon, casting the mountains and craters in high relief.

Image Credit: Starry Night Software

The sun will be rising along the center line of the moon, casting the mountains and craters in high relief.

Beginners in astronomy are often surprised that the best time to study the moon is not at full moon, which will occur on Thursday the 19th this month. At full moon the sun is high overhead in the center of the moon, and the surface looks like the desert at high noon. The best time is when the sun is falling obliquely, casting long shadow, which is what you see at the first and third quarters.

Third quarter is a bit of a problem because it occurs when the moon is in the dawn sky. First quarter, on the other hand, occurs when the moon is high in the sky at sunset, perfect for evening observing.

The moon is so close to us that you don't really need a telescope to study it. Even without any optical aid, the major features of the moon can be clearly seen, if you take the time. In fact, you can see more detail on the moon with your naked eye than you can see on any of the planets with a powerful telescope.

When you look at the first quarter moon, you are seeing a sphere lit by the sun from the right side (in the northern hemisphere; left side in the southern hemisphere). The surface of the moon varies in reflectivity, so that you see a pattern of light and dark. The lighter areas are the older mountainous regions, mostly on the southern half of the moon; the darker areas are younger lava flows, mostly in the north.

Early observers mistook these for seas and oceans, and named them accordingly. Later astronomers realized that the moon is an airless waterless body, and that its “seas” are dryer than the driest deserts on Earth. The water which has been discovered recently on the moon is buried deep beneath the surface.

If you examine the moon more closely in binoculars or a telescope, your attention will be drawn to the “terminator,” the narrow band down the middle of the moon where dark meets light. This is where the sun is rising.

Ordinary binoculars can give a surprisingly detailed view of the moon, especially if they are steadied by mounting them on a tripod. Many binoculars have a tripod socket hidden under a small cap in the hinge between their two halves, but you will need a small L-shaped adapter to connect this to a standard camera tripod. You will be amazed at the improvement a tripod mount makes to the view.

The 10x50 size binocular is the most popular among astronomers. Its 10 times magnification and 50mm objective lenses provide excellent views of both nearby objects like the moon and distant objects like star clusters and galaxies. In recent years more powerful binoculars have become widely available at amazingly low prices. The 15x70 size gives particularly good views of the moon, but must be mounted on a tripod.

Because the sun is rising over the terminator, even the slightest variation in topography is exaggerated by the rising sun. Look especially for craters and isolated mountains on the plains. With the extra magnification afforded by a small telescope, you can actually watch the sun rise over craters in real time.

With a good map of the moon you can become familiar with the “geography” of the moon. More than a thousand craters bear the names of famous astronomers of the past.

Neptune reaches Opposition

This week, on August 27, the planet Neptune reaches opposition.

On August 27 Neptune reaches opposition in Aquarius, making it visible all night. Credit: Starry Night Software

When a planet is in opposition, it lies directly opposite the sun in Earth’s sky. It is highest in the sky when the sun is lowest, which is local midnight. When Daylight Saving Time is in effect, this is close to 1 a.m. local time.

Because Neptune is directly opposite the sun. it rises at the same time as the sun sets, and sets at the same time as the sun rises, so is visible all night.

Now that Pluto has been demoted to “dwarf planet” status, Neptune is the most recent planet to be discovered, on September 23, 1846, and the farthest planet from the sun, at an average of 2,798,310,157 miles (4,503,443,661 km.)

As planets go, Neptune is extremely dim, requiring at least a binocular to become visible. Even in a powerful telescope, it is a tiny blue-green disk with no detail to be seen. Unless you look carefully, you could easily mistake it for a star.

In fact, that happened several times before Neptune’s official discovery. Most famously, Galileo twice observed Neptune while studying Jupiter’s moons in 1612 and 1613, but mistook it for a star both times.

After the discovery of Uranus by William Herschel in 1781, mathematicians calculated the possible location of another planet farther from the sun, but no one looked seriously for it until 1846. The first to actually spot it was German astronomer Johann Gottfried Galle on September 23.

Because it takes Neptune 164 years to circle the sun, it spends an awfully long time in any one constellation. For example, Neptune has been in Aquarius since January 24 2011 and won’t move on into Pisces until May 22 2022. In fact, it has only just completed its first trip around the sun since its discovery, and is again very close to the spot where it was discovered.

Since Neptune is so far from the Earth, it presents too small a disk to be studied well with even the largest telescopes. The only good view we’ve ever gotten of Neptune was in 1989 when the Voyager 2 probe passed within 2740 miles (4400 km.) of Neptune’s cloud tops. At that time it recorded two large blue spots in Neptune’s atmosphere, apparently similar to the Great Red Spot on Jupiter. Voyager 2 also confirmed the existence of a faint ring around Neptune, a ghostly echo of Saturn’s ring system.

The Summer Triangle

Have you ever wished you knew more about the stars overhead? It’s easier than you think.

Lie back on a warm summer night and look straight up. You’ll see three bright stars: Vega, Deneb, and Altair. These mark the corners of the “Summer Triangle” and are your guides to the three constellations of Lyra, Cygnus, and Aquila. Credit: Starry Night Software

All you need to do is lie back on a warm summer evening and look up towards the zenith. It will help if you can find a spot free from light pollution on a night when the Moon isn’t in the sky.

The first thing you will notice is that some stars are brighter than others. The brightest stars are said to be “of first magnitude” and there are three that should leap out at you. The brightest is Vega, almost directly overhead at 10:30 p.m. Daylight Time this week. Next brightest is Altair, down towards the southern horizon, and third is Deneb, off towards the northeast. These three form the “Summer Triangle” and are as characteristic of the summer sky as Orion is of the winter sky.

Since these three stars appear to be about the same brightness, you might think that they were all about the same distance away, but you’d be wrong. Stars come in many colors and brightnesses, and sometimes a very distant, very bright star can look as bright as a very close, relatively dim star. Vega and Altair are both relatively close to the Sun, 25 and 17 light years away, but Deneb, which rivals them in brightness, is a whopping 3300 light years away, making it one of the farthest objects you can see with your unaided eye. In fact, Deneb is an absolutely brilliant star, but so far away that its brightness is greatly dimmed by distance.

As you continue to watch the sky, you may begin to see patterns in the fainter stars. The human brain always tries to find patterns in random shapes, as when we look for the shapes of animals in the clouds. The same is true for stars.

Stars are pretty much randomly distributed across the sky, but from time immemorial humans have grouped them into patterns which we call constellations. Each of the three stars in the Summer Triangle is a member of such a constellation.

If you look closely at Vega, for example, you may notice a small parallelogram of stars just to its south. This reminded ancient astronomers of the musical instrument the lyre, so they named this group of stars Lyra. If you have binoculars, use them to take a closer look at Vega and the stars nearby. Even a small binocular is enough to confirm one of Galileo’s first discoveries when he turned his telescope on the sky: many stars which appear single to the naked eye turn out to be double or multiple with a bit of magnification. Several of the stars near Vega are obvious doubles, even with only 6 or 7 times magnification.

Now take a closer look at Deneb. It stands at one end of a chain of bright stars stretching to the south of Vega. There is a second shorter chain of stars which crosses the first chain at right angles. Different cultures have seen different patterns. The ancient Greeks saw this as a swan and named it Cygnus. Deneb is the tail of the swan, the short chain marks the swan’s wings, and the long chain its outstretched neck, with a brighter star Albireo at the head. Others see this as a Christian cross, and call it the Northern Cross, to distinguish it from Crux, the Southern Cross.

If you are under a dark country sky, you will see that the swan is flying along the faint silvery Milky Way. This is the glow from millions of distant stars, too far away for the individual points of light to be resolved. This was another of Galileo’s discoveries.

Altair marks the head of a different bird: Aquila the Eagle. This has broader wings than the swan, and a distinctive curved tail.

Look for some of the smaller constellations in this part of the sky, in particular Delphinus the Dolphin, one of the few constellations which actually resembles its namesake.

Don’t be dismayed if you can’t readily see these patterns. Sometimes the objects the ancients saw in the sky owed more to imagination than to reality.

Lunar Encounters

What’s that bright “star” next to the moon?

What’s that “star” next to the moon? Over the course of the next month, the moon will pass close to three bright “stars,” which are actually planets, starting with Venus on Friday August 9.  Image Credit: Starry Night software

As the moon moves around the Earth in its orbit, it passes close to many more distant objects in the night sky. Because the moon is nearby and in full sunlight, its light often swamps the objects close to it. Only a few objects are bright enough to show up when close to the moon.

The brightest objects in the sky, other than the sun and moon, are the planets. They follow the same path across the sky as the moon, called the ecliptic because that’s where eclipses take place. So encounters between the moon and planets are very common.

This month, the moon will pass close to three of the brightest planets: Venus, Saturn, and Jupiter.

First up is Venus, this Friday, August 9, just after sunset. Because the ecliptic makes a very shallow angle with the horizon at this time of year, both Venus and the moon will be low in the southwestern sky, so make sure you have a low horizon in this direction. The moon will be only three days old, so will present a very narrow crescent. Be sure to look for “the old moon in the new moon’s arms”: the full disk of the moon lit by the ghostly light reflected from the Earth.

Three nights later, on Monday August 12, the moon will have moved on so that it is framed between the planet Saturn, to the left, and the bright star Spica, to the right. If you have a telescope, take a good look at Saturn, as it will soon be vanishing behind the sun.

The moon’s final encounter for the month won’t be until the morning of Saturday August 31. On that morning early risers will be treated to the waning crescent moon just to the right of the planet Jupiter.

With the moon appearing close to three different bright planets over a span of a few weeks, it’s easy to see how some people, who just happened to look at the moon on these three nights, would be convinced that there is always a “star” next to the moon. In reality, the moon is passing close to three different bright objects located far apart in the sky.

Three Ladies of the Night

Have you ever seen an asteroid? These bodies, though small in size, are very numerous, but very few amateur astronomers have ever seen one. The next couple of weeks give an opportunity to view three asteroids in one night: Flora, Juno, and Iris.

The next couple of weeks provide a great opportunity to track down three of the brightest asteroids. Image Credit: Starry Night software

These asteroids were among the first eight to be discovered. Juno was the third asteroid discovered, in 1804, very soon after Ceres in 1801 and Pallas in 1802. It was discovered by German astronomer Karl Ludwig Harding, and named after Juno, the highest of the Roman goddesses.

At present Juno is located in the western part of the constellation Aquarius, and is about magnitude 8.6. It is too faint to be seen with the unaided eye, but can be easily seen in binoculars or a small telescope. In amateur telescopes it is too small to look any different than a star, hence the name "asteroid" meaning "star-like."

The first asteroids were discovered quite by accident. In 1846, British astronomer John Russell Hind decided to change that by beginning a systematic effort to search for asteroids using the newly published Berlin star maps. He plotted objects along the ecliptic, adding stars that were too faint to be on the maps, and looking for any star that seemed to move. He was rewarded the next year by his discovery of two new asteroids, Iris on August 13 and Flora on October 18.

Iris is named after the Greek goddess of the rainbow and Flora after the Roman goddess of flowers. Juno is the largest of the three, 145 miles (233 km.) in diameter, and Flora the smallest at 80 miles (128 km.), with Iris in between at 125 miles (200 km.) As you can see, they are all quite tiny bodies. Juno has been photographed by the Hooker Telescope at Mount Wilson, and is a rough potato shape with a very large crater on its surface.

Image Credit: Hooker Telescope at Mount Wilson

Currently Iris is in central Aquarius at magnitude 7.6, making it the brightest of the three, and Flora is in Sagittarius at magnitude 8.6. Iris is just south of the globular cluster Messier 2, Juno just north of Messiers 72 and 73, and Flora just west of globular cluster Messier 75.

If you want to replicate the methods used by these early 19th century astronomers, you could plot the "stars" in the neighborhoods indicated on successive nights, and then look for the ones that move. Or you could use the more modern approach of printing finder charts using a modern planetarium program on your computer. All three are moving slowly westward, from left to right for observers in the northern hemisphere.

It’s really quite remarkable that we can see these tiny chunks of rock, farther away than Mars, with ordinary binoculars. Don’t miss this chance.

Spot Mercury at Dawn

Most skygazers have never seen the planet Mercury because it never strays very far from the sun. This week is one of the rare opportunities to catch Mercury just before sunrise.

On the morning of Tuesday July 30, Mercury will be at its furthest from the sun, just under Jupiter and Mars. Credit: Starry Night software

Two things about Mercury make it a tough target. First and foremost, it never strays far from the sun because of its location in the inner solar system. It is always observed against a bright twilight sky, either half an hour after sunset or half an hour before sunrise, and always low in the sky.

Secondly, it is a tiny object. Now that Pluto has been demoted to "dwarf planet" status, Mercury, at 1550 miles (2440 km.) in diameter, is the smallest of the eight planets, 38 percent of Earth's diameter.

The challenge in observing Mercury is to find a tiny speck of light, low in the sky, against bright wilight. This week offers one of the rare opportunities when conditions are at their best.

Mercury will be farthest from the sun in our sky on July 30. The weeks just before and after this date are equally favourable.

The best time will be about 40 minutes before sunrise, a balance between Mercury's altitude above the horizon and the brightness of twilight. Scanning the sky with binoculars will help to spot the tiny speck of light. Once spotted in binoculars, you should just be able to see Mercury with the unaided eye.

Because of Mercury's low altitude, a low cloudless eastern horizon is necessary. The task is made easier by the presence of two much brighter planets in the dawn sky, Jupiter and Mars. Mercury will be below and to the left of these two objects.

Once you spot Mercury, locate it relative to landmarks on your horizon, and see how high you can follow it as it rises and the sky becomes brighter. If you have a telescope, this task becomes easier.

Seen in a telescope, Mercury will look like a tiny gibbous moon. As it rises higher in the sky, it will clear the turbulence, and the view will improve.

Congratulations...you have succeeded in observing one of the most elusive objects in the sky. It is said that the great 16th century astronomer Johannes Kepler never managed to see Mercury.

More Close Encounters

This month is full of encounters between astronomical objects. Last week we had the Moon and Spica in Virgo in the evening, and Mars and Messier 35 in Gemini in the morning, and this week we have Venus and Regulus in Leo in the evening, and Mars and Jupiter in Gemini in the morning.

On the night of Sunday July 21, the planet Venus passes just north of the bright star Regulus in Leo in the western sky just after sunset.  Credit: Starry Night software

Although Regulus is one of the brightest stars in the sky, Venus is far brighter, and will be by far the easier to see. Once you spot Venus, look below and to its left to spot Regulus. If you’re south of the equator, Regulus will be above and to the left of Venus.

Later that night, an hour before dawn, look in the northeastern sky to see Jupiter and Mars rise together. Jupiter will be the brighter of the two, with reddish Mars above and to its left. If you’re in the southern hemisphere, Mars will be below and to the left of Jupiter.

Later that night, an hour before sunrise, the planet Mars passes Jupiter.  Credit: Starry Night software

If you have access to a telescope, these twin planets will make an interesting sight. Jupiter will be accompanied by its four bright moons, Io, Europa, Ganymede, and Callisto. What will be most noticeable is the tremendous difference in size between the two planets. Both are on the far side of the Sun, but still Mars is much closer than Jupiter. Even so, Jupiter will appear more than eight times larger in diameter than Mars.

The planets move relatively slowly as compared to the moon, so that, if you miss these events on Sunday night and Monday morning, try again the following night and morning, and these encounters will still be close enough to be fascinating.

The Milky Way Galaxy

When people ask me what I do, I tell them I study galaxy mergers and evolution. Sometimes they will nod, smile and listen for awhile, and then more often than not, the question will come:  "What exactly is a galaxy?".  I then realize that most people are never taught in school what a galaxy is, and I certainly wasn't before I went to study astronomy at university.  If you are lucky enough to be under a dark, clear sky on a summers night, understanding what a galaxy is becomes so much easier!  (or alternatively, fire up Starry Night at home :) ).

We live within a fairly large spiral disk galaxy, about two thirds from the centre, in one of its spiral arms. During the summer, a faint cloud-like band, known as the Milky Way, arches across the night sky.  If you were in space, far above the Earth, you would see that this band of light actually goes all the way around the sky, forming a great circle around us.  This is because we are inside of the disk of the Milky Way, and the band of light is actually composed of parts of the galaxy which are very far away.  With a telescope, you can see that the Milky Way is composed of millions of individual stars, but to the unaided eye, they all blur together to form a cloud.  You might notice that there are gaps and dark spots in the Milky way.  These are actually massive clouds of gas and dust which block the light from the stars beyond them.

Most of the stars we see in the sky are part of the spiral arm our solar system is located in, known as the Orion arm.  The stars you can see with your naked eyes are like houses in our neighbourhood, while the stars in the other arms are like distant parts of a massive city.  The centre of the Milky Way galaxy is located in the direction of Sagittarius, where a super massive black hole lives.  That black hole is the centre of our galaxy, with all the stars orbiting around it, just like our Sun is the centre of our solar system with the planets orbiting around it, but on a much, much larger scale.  What is a black hole you ask?  We'll look at that in my next post!  For now, make sure you find the time this summer to get out of the city, to a place free from light pollution, and enjoy the view from Earth of our amazing galaxy, the Milky Way!

Close Encounters in the July Sky

If you only glance at the sky now and then, you may think it's pretty much the same every night. Regular sky watchers know better, and are aware of the constant changes the sky undergoes.

On the night of Monday July 15, the first quarter moon sails just north of the bright star Spica in Virgo.  Credit: Starry Night software

Take the moon, for example. Although most people know that the moon revolves around the Earth, they may never have noticed this movement with their own eyes. This week we get a chance to do exactly that.

The problem is that much of the time the moon is in an open reach of sky, and there are no fixed points to mark its movement. This week it passes close to the bright star Spica and the planet Saturn in the constellation Virgo.

On Sunday night, July 14, the moon will be well to the right of Spica (in the northern hemisphere...reverse left and right if you're south of the equator) in the evening sky.

On Monday night, July 15, the moon will be immediately above Spica. In fact, if you live in Central America or Africa, the moon will pass right in front of Spica, in what is called a lunar occultation.

On Tuesday night, July 16, the moon will have moved well to the left of the moon, and will be just below the planet Saturn.

On Wednesday night, July 17, the moon will be well to the left of Saturn.

Let's go back to Monday night, when the moon is closest to Spica. This will not be the only astronomical encounter this night. Stay up until the wee hours of the morning, and you'll see Mars and Jupiter rise an hour before sunrise. If you look at Mars in binoculars or a small telescope, you will see that it is close to one of the brightest star clusters in the sky, Messier 35 in Gemini.

Later that night, an hour before sunrise, the planet Mars passes the open cluster Messier 35 in Gemini. Jupiter is approaching from the east.  Credit: Starry Night software

Now we will see how the planets move as well. Because they are farther away, they seem to move much more slowly than the moon. A few months ago we were watching Mars and Jupiter fade into evening twilight as they moved behind the sun. Now they have emerged into morning twilight to begin their next apparition in our night sky. If you're an early riser, keep an eye on them over the next couple of weeks as they approach each other, pass on the morning of July 22, and then draw apart again.

Venus and the Beehive

On the night of Wednesday July 3, the planet Venus will have an interesting encounter with a swarm of bees.


On the evening of Wednesday July 3, Venus skims just north of the Beehive star cluster. Credit: Starry Night software

Venus has only recently emerged from behind the Sun, so you may not have seen it yet as an “evening star.” Venus is of course a planet, which shines by light reflected from the sun, and not a star, a huge ball of glowing plasma in the far reaches of space. To the naked eye, stars and planets look the same, so ancient astronomers called them all “stars.”

The ancients did note that some “stars” appeared to move, so gave them a special name, “planets,” which means “wandering stars.” In particular they noticed that two especially bright planets never wandered very far from the sun. At first they thought these were two different objects, one in the morning sky, one in the evening, but at some point realized that these were really aspects of the same object, which they named “Venus.” The next step was the realization that Venus’ movements could be explained by a body revolving in a circle around the sun, peeking out first on one side, then the other.

Venus is still quite close to the sun in the sky, so you will need a low western horizon to catch a glimpse of it as it sets about an hour and a half after the sun. On Wednesday night, use your binoculars to follow it down as it gets closer to the horizon. If you’re lucky, you may catch a glimmer of hundreds of tiny stars just below it.

These stars are members of one of the closest star clusters to our sun, the Beehive Cluster in the constellation Cancer. This cluster is located 590 light years from the sun, only the Hyades and the Pleiades being closer. It contains just over a thousand stars, of which about 300 are similar to our sun. At least two of the stars in the cluster have planets, and we can only imagine how glorious the night sky must be on a planet situated in the middle of a star cluster. In fact, Isaac Asimov has written a famous science fiction story, “Nightfall,” set on such a planet.

Because it is readily visible in a dark sky with the unaided eye, the Beehive Cluster is known by different names in different cultures. Its resemblance to a swarm of bees has given it the name “the Beehive.” It has also been called “Praesepe,” Latin for “manger.” It is seen as a hay-filled manger surrounded by asses waiting to eat. The nearest stars to it are named Asellus Borealis and Asellus Australis, the Northern Ass and the Southern Ass. Astronomers know it as Messier 44, the 44th object in Charles Messier’s famous catalog.

Although the Beehive is easily visible with the naked eye in a dark sky, seeing it tonight will be a challenge. Venus is only visible close to sunset, and the sky will not be completely dark and hour and a half later when Venus sets. Besides observing from a location with a low western horizon, use binoculars to follow Venus down towards the horizon. Venus itself should be easy to see, as it’s the brightest object in the night sky after the moon, but the stars of the Beehive will be difficult without binoculars.

Your favourite space mission

One of my favourite features of Starry Night is its large database of space mission data. Sometimes I just like to position myself near Cassini spacecraft and replay its visually stunning passage through Saturn's rings. The view is breathtaking and the idea that humans have actually built a spacecraft which has done this exact thing is mind boggling.

Other times I look at the entire space mission path of Voyager missions, admiring the engineering and planning marvel that led to well used gravitational slingshots. A simple curved line becomes exciting when you put it in its proper context.

Yet, these space missions, almost entirely forgotten, still give us valuable insight about what lies in unfamiliar regions of the solar system. The latest information coming from Voyager 1, currently the furthest man-made object, presents some new questions about the edge of the solar system and the effects playing out there.

What is your favourite space mission? Do you use Starry Night to replay it? How can we make the experience more enjoyable or the information more readily available?

Cassini doing what it does best

MOOCs

I'm a big fan of Massive Open Online Courses (MOOCs). I think they'll ultimately revolutionize the way that Universities operate, and they're certainly making them rethink things already.

I've tried my hand at a few for fun, review and professional development (See: Khan Academy, Coursera and many more), but haven't tied any relating to astronomy. Have you? Have you found a good one?

What about amateur astronomy? Could it reliably be taught by video, or is there just no substitute for getting out there and doing it yourself?

Scorpius and its Stingers

Most of the constellations seem pretty much random arrangements of stars to modern eyes. Scorpius is one of the few which actually resembles its namesake, the Scorpion.

For observers in the Northern Hemisphere, the constellation Scorpius appears low in the southern sky on warm June evenings.   Credit: Starry Night software

As seen by observers in the Northern Hemisphere, Scorpius appears like a giant scorpion peeking over our southern horizon. With a fairly small body, marked by the red giant star Antares, the scorpion has three stars in front representing its claws, and a long curving tail behind, ending in two bright stars marking its stinger. If you live in Canada or the northern USA, part its tail will be below the horizon, but more southern observers will see the whole beast.

Antares (Alpha Scorpii) is one of the brightest stars in the sky, and one of the few with an obvious red color. This color reminded ancient observers of the red planet Mars, hence its name, which means “not Mars,” Ares being the Greek for Mars. In large amateur telescopes, this red giant is seen to have a tiny companion star. Because of the primary star’s vivid red color, the companion often appears greenish, which is an optical illusion, since there are no green stars.

Of the stars making up the Scorpion’s claws, Graffias (Beta Scorpii) and Nu Scorpii are both double stars. Both are easily split in even the smallest telescope. The stars in Graffias are relatively close, 14 arc seconds apart, while those in Nu Scorpii are much farther apart, 41 arc seconds, visible in binoculars. Both pairs are quite unequal in brightness, about 2 magnitudes difference between the two stars.

The stinger at the end of the scorpion’s tail consists of two stars, Shaula and Lesath. These appear as a double star to the naked eye, sometimes called the “Cat’s Eyes.” They point to one of the brightest and most beautiful open star clusters in the sky, Messier 7. This was first described by Claudius Ptolemy in the 2nd century AD, so sometimes is known as “Ptolemy’s Cluster.” Just above this cluster is another one, equally bright and beautiful, known as Messier 6 or the “Butterfly Cluster.” Both are visible to the naked eye, but reveal their true beauty in binoculars or a small telescope.

Just above these clusters, and just over the border in the constellation Sagittarius, is the black hole at the center of our Milky Way Galaxy. The black hole itself is of course invisible, but the area is rich in stars.

Moving back up to Antares, if you look just below it with binoculars, you will see a fuzzy patch. In a moderate sized amateur telescope this resolves into one of the finest globular clusters in the sky, known as Messier 4 or the “Cat’s Eye.” Yes, it’s confusing to have two “Cat’s Eyes” in the same constellation, but one a pair of stars and the other a globular cluster.

About half way between Antares and Graffias is another smaller globular cluster, Messier 80, also a fine sight in a telescope.

Scorpius thus offers many treats to any stargazer, whether equipped with binoculars, a telescope, or nothing but their own eyes.

Supermoon

My kids are really excited to go camping this weekend.  Not because of the birds and animals, plants and trees, the rocks, the beautiful lake, the different sounds, dad’s barbeque or the activities we have planned.  Instead they are full of anticipation for this Sunday’s “supermoon”.  

I told them about the supermoon last week while casually checking out the moon with the naked eye.  The name brought on curious looks of suspicion – is dad pulling our leg? I mean you put anything with a “super” in front of a word and kids will think its some type of character with superhuman powers.  After reassuring my 3 year old that the supermoon was indeed a “good guy”, I tried to explain that the supermoon was simply the largest full moon of the year.  

For us older folk, a supermoon is a full moon that occurs at the same time the moon is at perigee (point closest to Earth in it’s orbit).  At these times the moon can appear up to 30% brighter and 14 percent bigger to us here on Earth. Sunday’s supermoon will be the largest full moon of 2013. 

Take a moment to share the supermoon with others this Sunday and If you take any photos - cape and all  – we’d love to see them!

First Day of Summer

The summer solstice begins today (June 20) for places west of the Central Time Zone in North America and tomorrow (June 21) for places in the Eastern Time Zone.  You can use Starry Night to figure out the exact time of the solstice at your location.

Here is a question. Why isn’t the summer solstice, the longest day of the year, also the hottest day of the year?