Libra: the Balance or the Scorpion Blocker

.....Libra is the first of the constellations along the Zodiac that I have written about here. (A curious reader might look at the current star map and wonder why I didn’t start with Virgo, much higher in the sky right now; the reason is that I am not just working my way around the sky, but that on this first pass I’m centering on the brightest of deep-sky objects, things that can be seen with a small telescope. Of the various types of deep-sky objects, the hardest to view are galaxies, and Virgo is so chock full of them that I am saving this constellation for last.)

.....What is the Zodiac? Well, the ecliptic is the path that the Sun takes through the sky, and the planets all stay within 7° of this line (If we skip Mercury, all the planets are within half this distance of the ecliptic). The ecliptic passes through twelve constellations (traditionally; as the constellations were given boundaries by the International Astronomical Union in 1930 the ecliptic passes through thirteen constellations), and these constellations are the Zodiac. Besides being the only zodiacal constellation with no Messier objects, Libra is also the only zodiacal constellation named after an inanimate object.

.....Our constellations can be traced back to the forty-eight the Greeks had (there are eighty-eight constellations now), but the constellations of the Zodiac are much older. This makes sense because while many of the constellations can be thought of as “sky-decorations” the Zodiac allowed the ancients to track the seasons. Of the zodiacal constellations, Libra might one of the youngest.

.....Libra as the balance represents that the Sun would be in this sign at the Autumnal Equinox, when the day and night would be equal lengths, or at least it was. According to the boundaries as they are now, the Sun would be in Libra at the equinox from about 2200 BC until about 700 BC. Even when not using the strict modern boundaries, the wobble of the Earth around its axis (which I discussed in a post on Ursa Minor) would have carried the equinox into Virgo, where it is now (and where it will be until AD 2450). This seems to indicate that Libra as a scales must have existed when the equinox was well inside Libra, but there are many references to these stars as Chelae, the claws of the scorpion. First, as seen below, the stars of Libra work well as the claws of the scorpion, whereas with Libra as a scales, the scorpion’s claws seem a little pathetic. The (seriously cool) names of the stars could refer to this, with Zubeleschamale translating as “the northern claw” and Zubelelgenubi as “the southern claw”. This is contested in some sources (alright, I admit it – in an unsourced article on Wikipedia) in that the Arabic (zubānā) and Akkadian (zibanitu) words for “scorpion” and “scale” are the same. Life becomes more complicated with the constellation having either four claws or four scales, but Richard Allen’s Star Names: Their Lore and Meaning considers Zubelalgubi as a degenerate version of the name “Zubelelgenubi”, and Zubenelhakrabi (the scorpion’s claw) as belonging to g Scorpii, which was apparently due to a need to invent two new claws when the other ones became Libra.

.....Why were the scorpion’s claws made into the balance of Libra (assuming, of course, that this is what happened)? Sure, there would be pressure to have twelve constellations on the Zodiac, one per month, and the reason of having a balance at the point where day and night are balanced make sense, but I have another idea why an inanimate object was added to the Zodiac where it was …

Five minutes before the first sexual harassment lawsuit

.....Unfortunately, Libra is pretty boring as far as deep-sky objects are concerned. There are no open clusters or nebulae in Libra, and the galaxies and one globular cluster in Libra fall far from being easy to find. I’ll address these on my next pass. Zubenelgenubi is a fairly easy double star to split, with the companion star being dimmer, but not tremendously dimmer (magnitudes of 2.8 and 5.2), and about 4 minutes of arc apart, or about one-eighth the size of the Moon in the sky. I could split this double star with a pair of binoculars, so this represents an excellent opportunity to do the same, and take the first step towards learning how to observe and split double stars.

Ursa Minor, or Shakespeare Screws Up

Caesar: …” I am as constant as the northern star,
Of whose true-fix’d and resting quality
There is no fellow in the firmament.
The skies are painted with unnumber’d sparks,
They are all fire and every one doth shine,
But there’s but one in all doth hold his place”

Julius Caesar, Act III, scene I, lines 60-65

…..Shakespeare was a hack. More on this later.

…..A blog on Ursa Minor, the Little Dipper, is going to demand that I go pretty far afield to try and make this interesting because this is a pretty inconsequential constellation. The Little Dipper is probably the most famous constellation that almost no one can find. The constellation is always above the horizon literally until you reach South America as you go south, but except for the three brightest stars, including the Pole Star, Polaris, the rest of the constellation is so faint that it can be lost under pretty much any background light.

…..Ursa Minor, quite frankly, has its name write a check most of its stars can’t cash. The constellation would be quite ignorable if it were not for the star Polaris, and from Greek times to the Renaissance this constellation was sometimes referred to as “Cynosura” (what a translation to this word means is not known, but it probably has something to do with a dog) and sometimes that name only referred to the brightest star in the constellation, so for most of human history the general reaction to the constellation is, “The heck with it, just deal the bright, useful star.” (A reasonable question might also be “Why not just call it, like, “Polaris” or something that shows that since it’s by the Pole, and this brings us to one of Shakespeare’s mistakes. Again, more on this a little later.)

.....Polaris has its name because it is very, very close to the North Celestial Pole. To see why this is doubly lucky, let’s look for a moment at how the sky appears. Obvious statement of the day: the stars are all very, very far away. So far away that even as they move through space, a time traveler stepping from a clear night in first dynasty Egypt to tonight would only notice a shift in a handful of the stars with respect to each other, and even then only if that time traveler had some pretty good measuring tools. Because of this, it is useful to treat the sky as a dome, or as a globe that we see the inside of from the Earth. To map this, we use the Earth to help us. Consider the Earth as spinning inside this gigantic sphere; one thing that we could "see", projected against the heavens would be the sky appearing to turn as we spun beneath it. Projected on the sky, we could trace north and south poles above the Earth's north and south poles (called the North and South Celestial Poles, reasonably enough), and the Celestial Equator above the Earth's equator. The North Celestial Pole is less than half a degree of arc away from Polaris, so if you were to sit and watch the sky over the course of a night (an eminently worthy endeavor), the stars would appear to whirl around the sky, with only Polaris remaining still. (The South Celestial Pole has no stars of note anywhere near it.)

.....Even Polaris has gotten a reputation beyond its actual means. Because of the usefulness of Polaris, (perhaps) the true idea that Polaris will help you find where you are has led to the (false) idea that Polaris is inordinately easy to find. As I discussed in my post on the Big Dipper, and repeated in my map on the previous post, Polaris can be identified by using the two stars at the end of the bowl of the Big Dipper (which is relatively bright), but a surprisingly common misconception is that Polaris is the brightest star in the sky. How this came about, I certainly don't know. (Polaris is actually the 47th brightest star in the sky.) This has led one friend of mine to increase the "Don't Get No Respect" quotient for this constellation by arbitrarily and willfully defining the brightest visible star as "the North Star". (Hi, Trish!)

…..Besides the three brightest stars, the others are fourth, fourth, fourth, and fifth magnitude, this definition of brightness stretching back to the ancient Greeks when the astronomer Hipparchus divided the stars by their brightness, ranking the stars from “first rank” (the brightest) to “sixth rank” (the dimmest). The other stars that observers expect to see from the constellation figure are dim enough so that a hazy evening, a bright Moon, or the ubiquitous nearby Wal-Mart (in case you didn’t think that Wal-Mart was evil enough) will make these stars impossible to see. In seventh grade, when I got my first chance to study astronomy institutionally, one of our assignments was to sketch constellations we found in the sky. I saw a lot of students turn in the Little Dipper, but none of them got the right stars, a trend that I notice up to today. (A second thing is that I notice Wal-Mart is apparently in Microsoft’s spell-checker; Scorpius: No, Capricornus: No, Wal-Mart: yes – be afraid, be very afraid …)

.....Going back to that hypothetical time traveler, however, the sky as a whole would have shifted noticeably, because the Earth does not sedately simply rotate on its axis, that axis is tracing out a circle on the sky like a tremendous top, with a period of 26,000 years. This wobble is now pointing at Polaris, getting even closer as this century goes on, but in Julius Caesar's time, Polaris was more than ten degrees away from the pole (the "Secret Devil Sign", in memory of the recent death of Ronnie James Dio), making a definite loop during the night. Our time traveler would have seen Thuban (also on the map) as the North Star, and if you wait for about 13,000 years you will see Vega, in Lyra, as the pole star, and that truly is one of the brightest stars in the sky. This is Shakespeare's astronomy mistake in Julius Caesar.

….As far as anachronisms in Shakespeare go, though, this one is not the biggest, even in that play. In Act II, scene i, line 191, Brutus says “Peace! Count the clock.”, and in Act II, scene ii, lines 114-115, Caesar asks “What is’t o’clock?”, to which Brutus responds, “Caesar, ‘tis stricken eight.” Mechanical clocks in the time of Caesar (actually invented in the thirteenth century AD) would actually be less of an anachronism than, say, giving Macbeth Iron Man’s armor…

“Is this a transistor I see before me, the bipolar junction toward my hand?”

.....Oh sure, you might say that Shakespeare didn't know any better but he was able to come up with more appropriate way to discuss time earlier in the scene I just quoted, when Brutus says "I cannot, by the progress of the stars,/ Give guess how near to day." - lines 2-3.

…..Ursa Minor is an important place being filled by a rather boring occupant that is still bright enough to fulfill a useful purpose. (Like Al Gore - Zing!) Yes, I know that this would have been funnier ten years ago. Let me try this again ...

…..To sum up, Ursa Minor is a dim, dark, empty place with only a couple of bright points – kind of like Lower Michigan (Double Zing!)

The May Sky

.....There are many books and websites to help people who are good at astronomy become really good at astronomy, and many books and websites to (apparently) help people who live in the country where the sky gets what could actually considered to be dark (or at least where you don't have a direct line-of-sight to eight outdoor lights), but a lot of this can be counterproductive if you are just trying to start out, or if you just live where the sky is bright enough to hide a lot of the stars from you. Hopefully, this blog can be useful in both of these cases, but I realized that I might lose some of the benefits of talking about constellations if you aren't able to easily find those things in the first place, so I made a series of maps.

.....All of these maps show the sky as it is seen from the latitudes of the northern US about eleven PM (tonight), or about when the sky finally gets dark. The first map just shows the brightest stars, so while the constellation figures are missing stars, hopefully this stripped-down maps will help you find those constellations to begin with. (As you might see in just a moment here, sometimes star maps that have all visible stars can seem a lttle "busy", and be hard to follow. Also, in all maps the constellations in blue are the ones that have already been discussed in some depth in a blog post, and the constellations in red are the ones that I have yet to get to. Looks like a busy summer.)

.....Heck, even just giving these constellations might not be that helpful. After all, what I have is a representation of the sky as the inside of a giant bowl, flattened out and seen from the inside. In the spring and early summer, the Big Dipper can be used to find the North Star at the tail of Ursa Minor (the Little Dipper), Regulus, the brightest star in Leo, and following the arc of the stars of the handle leads to Acrturus, in Boötes, and then on to Spica, in Virgo.

.....With that (hopefully) as a means to help you find the constellations of the brighter stars, here is a map of the whole sky, helping you if you do live somewhere where the whole sky can be seen, and perhaps frusting you a little bit if you don't.

.....Note that the planets Mars and Saturn are both visible in our evenings! Both planets are about as bright as the star Spica, the brightest star in Virgo (and the end of the great arc from the Big Dipper's handle) Mars does not show much (to me, at least) beyond a disk in a telescope, but Saturn looks so phenomenal as to almost seem fake in even the smallest telescope. If you have anything, even an old department store cardboard 'scope, give Saturn a try!

.....As always, individual maps can be downloaded from this site.

Boötes-licious

.....Astronomy, by definition, is a study that encompasses the universe, and so there is are many different new things that a study of astronomy can bring you across. For example, I learned that the symbol on the second “o” in “Boötes” is not an umlaut, but a dieresis, indicating that both letters are to be pronounced. I have been presuming that this makes the pronunciation “Bu-u-tez”. I could well be wrong, but since the constellation is never going to get offended, who cares?

.....In legend, Boötes is a herdsman with his dogs (the constellation Canes Venatici) chasing the Great B ear (Ursa Major) forever around the pole, from the latitudes of the northern United States only getting six hours below the horizon a day to rest from the chase. A quick look at the star map will show that this legend is proof that the ancient Greeks had no knowledge of kites. If we were to remake the constellations today (a scheme which has been tried before, remind me to tell you about that sometime), Boötes would almost certainly be “the kite”.

.....The second constellation that I’m looking at in this post is the Northern Crown, Corona Borealis. If I may digress for just a moment, when I was much younger, carrying my telescope out to an extraneous plot of land behind our house, one of our neighbors asked me about what constellations were visible, and when I got to this one, he said,” No. That’s not it. I’ve seen that before and that’s not it!!!” (He didn’t shout, but he was speaking very definitively and I’ve learned that nothing is more definitive on the internet than using three exclamation points.) I realized pretty quickly that he was thinking about the northern lights, the *aurora* borealis, but I cannot remember if I tried to explain that, or just thought, “Whatever, old dude” (or whatever the early 80’s version of that was) and went on.

.....At least Corona Borealis looks kind of like a circlet of stars, but recreating Boötes would allow us to reimage the second constellation that we are looking at today, Corona Borealis away from being the Northern Crown into, say, the Kite-Eating Tree from Peanuts.



.....(I know that the kite appears larger than the tree; it’s foreshortening. The tree is in the background, waiting for the kite to slip up, drift away and get caught. If this story seems too grim for backyard astronomy, please reread the original myth.)

.....As far as telescopic objects in these constellations go, there are pretty slim pickings for the suburban astronomer. The North Galactic Pole is on this map, which means that these constellations are as far away from the pale band of the Milky Way in the sky as it is possible to get. There are a few galaxies in these two constellations, but all of them are close to the limit of visibility for a backyard telescope on the best of nights. I shall try and find each one, and then come back with an update, but I really would not be expecting very much.


.....While Boötes and Corona Borealis don't have any bright deep-sky objects, they do have a couple of bright double stars that small telescopes can reach. Most stars aren't like our Sun, traveling alone through space (yes, I like the planets, but they are very tiny things compared to a star), but travel in packs of two, three, or even more. The vast majority of these stars are so far away that we can't even see them as individual stars, but some of the closer ones can be "split", as it were, in a small telescope. The two things that I look for when looking for interesting double stars are that the stars are of close to the same brightness (so one does not overwhelm the other) and are far enough apart againts the sky to be split. It also helps if the pair is bright enough to be found easily in the sky. The brightest and best in these constellations is Izar (epsilon Boötis). The two stars have magnitudes of 2.5 (bright enough to see from suburbia) and 4.9 (bright enough to be seen from some nice, quiet farmland), but they are quite close together, with a separation of 2.8 seconds of arc, or about 1/600th the size of the full Moon. (This is a useful measure for me, in that my 8" telescope, at low power, can just barely fit the whole Moon in the field of view.) You will need to use a higher magnification eyepiece to see this pair as two stars.


.....If you can find Alkalurops (Mu Boötis), that will be much easier, and the two stars will be distinct as separate stars under even what is typically the lowest magnification lens for a given telescope, 1.8 minutes of arc (1/33rd of a degree, or about 1/16 the size of the full Moon) with stars of magnitudes 4.3 (can be seen on a good night, maybe not actually in a city) and 7.0 (invisible without the telescope/binoculars. I'll give you more once I have a chance to go hunting myself, until then, please don't hestitate to let me know what you like to see (or what you'd like my help to know about something you're seeing, in other words).

Not Dead!

I just wanted to announce that this blog is not dead! After the demands of the school year choked it back last fall, this summer will see many, many (okay, maybe just "many") posts, with hopefully a large backlog to carry me through the winter. I will be focusing especially on people who might have gotten a telescope as a gift who is now taking it out as the nights start to get warmer ...

The Geminid Meteor Shower

.....Tonight (Sunday, December 13th) is the peak of the Geminind meteor shower. This is one of the best meteor showers of this year (if it is not currently snowing where you are - sigh). The Geminid meteor shower comes from a trail of dust in the orbit of 3200 Phaeton.

.....This is unusual in that most meteor showers are due to the Earth crossing that path of a comet, and hitting (at about 60+ kilometers per second) the little pieces of dust that once, on some long previous pass, boiled off of the comet and helped reflect sunlight, resulting in the comet's bright tail. Phaeton is classified as an asteroid, not a comet, but it could simply be a comet so darn old that all of the ice (the shiny bit of a comet) has long since been evaporated by the Sun.

.....Looking for meteor showers is easy, as observational astronomy gets. Just go outside and get comfortable, and look in the general direction of east. Meteor showers have names due to the fact that they are all on pretty much the same orbit, so as the Earth moves through their path, the hits of the particles on the Earth (which heats them several hundred degrees in a few seconds as they burn up in the Earth's atmosphere) all seem to come from the same general part of the sky. In this case, the central point for these meteors is the general area of the constellation Gemini.

.....In the image that accompanies this entry, I have provided a view of the eastern sky from the northern US at about ten o'clock at night, to help you find Gemini. (Hint: start by looking for Orion the Hunter, one of three constellations that actually looks like what it's named after -- a big guy with a belt, sword, club and shield. These are also some of the brightest stars in the winter sky. We're going to come back to Orion soon for my series "So you just got a telescope", for anyone getting a telescope as a holiday present.)

.....The Geminid meteor shower has three things going for this year. First, the Moon is almost new, so the Moon will be providing absolutely no light to interfere with the meteor shower. Second, the Geminid shower has been very strong in recent years. One could expect to see up to 120 meteors per hour in perfect conditions, which, unfortunately includes being far, far away from city lights. Thirdly, the Geminid shower is one that is almost as strong before midnight as it is after midnight, so a little evening viewing should give you a view of some meteors. If the weather is clear, wrap yourself up warmly and give yourself a view!

.....(The peak is expected to be at about 11:10 PM CST.)

A Bright Space Station in the Evening

.....As more is added to the International Space Station (from here on out, just the “ISS”), the space station can appear even brighter in sky on those favorable passes when the large solar panel arrays catch the Sun just right. Over the course of the next week , the ISS will make several passes over the continental United States in which it will appear substantially brighter in the sky than the planet Jupiter, the bright but relatively stationary light in the South. As I’ve written before, you can watch out for these good passages by combining trips to a weather website and one of several websites. (I use www.heavens-above.com, as I note in the links, and you can use the Messier Pro login and password as described in an earlier post.)

.....Oh, one thing that I have not mentioned is that these bright passes will take place in the early evening, and will be very easy to see. I took the opportunity to find a (hopefully) good night for a number of cities of friends, family, and a couple of people who have actually admitted reading this thing. I looked at the Weather Channel’s website, picked nights predicted to be clear, and noted the time and directions to look. I’ve put these in alphabetical order by state. If you’re state isn’t in here, then look at a nearby city, or drop a note in the comments and I’ll find a good time for your city.

.....This will be early enough so that even young kids can see it, so drag everyone you can outside, and then come back here and we’ll compare notes on who was able to see it!

Alabama (Mobile)

.....Yikes! What are you doing inside? The only decent pass for you this week will be this evening (Sunday, November 8th). If you go outside and look to the southwest at 5:11:06 PM, the ISS will appear over the southwestern horizon. The Space Station will be just south of directly overhead, and it will vanish just above the northeastern horizon at 5:17:52.
http://www.heavens-above.com/PassDetails.asp?Session=kebgfgclbbkemgcihfjooook&satid=25544&date=40125.9680109606

Colorado (Denver)

.....Hey, I’m sorry, but you don’t have a great combination. Go here, see you get anything, and then wait for a better week.
http://www.heavens-above.com/PassSummary.aspx?satid=25544&Session=kebgfgclbakbpkhgkmjkhfod

Florida (Orlando)

.....Yikes! What are you doing inside? (Not a lot of good passes for the gulf states this week.) The only decent pass for you this week will be this evening (Sunday, November 8th), and the ISS will only appear about as bright as the brightest star, but it should be visible in evening twilight. If you go outside and look to the southwest at 6:09:53 PM (the same pass as Mobile is seeing), the ISS will appear over the southwestern horizon. The Space Station will reach an altitude of 33 degrees above the horizon, and will hug the western and then the northern horizon until it vanishes into the Earth’s shadow at 6:17:15 PM.

http://www.heavens-above.com/PassDetails.asp?Session=kebgfgclbbkemgcihfjooook&satid=25544&date=40125.9684758333


Georgia (Lookout Mountain)

.....See Tennessee (Chattanooga). You live in Chattanooga, get over it.

Massachusetts (Boston)

.....It won’t be great tomorrow, but from 6:33;37 to 6:40:04, the ISS will hug the western horizon going north, disappearing due north, and never getting more than 10 degrees above the horizon.
http://www.heavens-above.com/PassDetails.asp?Session=kebgfgclbakbpkhgkmjkhfod&satid=25544&date=40126.9844423032

Michigan (the southwestern UP)

..... There are a lot of great passes, a lot of crummy weather. Try tomorrow night from 5:34:41 to 5:40:04. The ISS will rise in the southwest, appearing to be aiming due east. The ISS will only get 26 degrees above the horizon, and will still be 23 degrees above the horizon when it disappears behind the Earth’s shadow.

http://www.heavens-above.com/PassSummary.aspx?satid=25544&Session=kebgfgclbakbpkhgkmjkhfod

Minnesota (Elbow Lake)

.....Okay, really, this a great week for seeing the ISS from the upper Midwest. Minnesota has a lot of passes, and the best days for Elbow Lake will be tomorrow (Monday), but the best pass will be Tuesday. There will be two tries on Monday, the first going from 5:34:12 to 5:39:28. It will rise in the south and skim the southern horizon, moving to due east, never getting more than 12 degrees above the horizon. Monday’s second pass will be from 7:10:04 to 7:11:27. The ISS will be about as bright as the star Sirius, and as you can guess from the time, it won’t be up very long. The ISS will rise in the southwest and disappear behind the Earth’s shadow when it is 25 degrees above the horizon.

.....Tuesday is supposed to be partly cloudy, and you will see another pass of the ISS disappearing on the way. Rising in the southwest, the ISS will pass very close by the planet Jupiter as it moves to the eastern horizon. The ISS will get 31 degrees above the horizon, and disappear into the Earth’s shadow when it is still 20 degrees up.

http://www.heavens-above.com/PassSummary.aspx?satid=25544&Session=kebgfgclbakbpkhgkmjkhfod

Minnesota (Twin Cities)

.....Tuesday is the best day for all of Minnesota this week. From 5:09:08 to 5:16:27, the ISS will be the brightest object in the sky as it moves from the southwest to the northeast, getting 65 degrees above the horizon.

http://www.heavens-above.com/PassDetails.asp?Session=kebgfgclbakbpkhgkmjkhfod&satid=25544&date=40125.9680122685

Minnesota (Winona)

.....The clearest day on the forecast is Tuesday, which is also the day this week of the best pass. On Tuesday, the ISS will rise in the darkening sky in the southwest, rising high overhead at 5:56:15, reaching 67 degrees above the horizon, until it disappears into the Earth’s shadow at 18:02:08, still 34 degrees above the eastern horizon.

http://www.heavens-above.com/PassDetails.asp?Session=kebgfgclbakbpkhgkmjkhfod&satid=25544&date=40128.0007469907

Pennsylvania (Harrisburg)

.....Harrisburg has an exceptional pass today, from 6:14:45 until 6:17:52. The ISS will rise in the southwest, and pass very high in the sky before disappearing into the Earth’s shadow while it is still 66 degrees above the horizon. If you don’t make this, then your next best shot is on Saturday when the ISS will never get above 17 degrees over the western to northern to eastern horizon from 5:19:29 to 5:26:46.

http://www.heavens-above.com/PassSummary.aspx?satid=25544&Session=kebgfgclbakbpkhgkmjkhfod

Pennsylvania (Philadelphia)

.....Philadelphia has an exceptional pass today, from 6:14:47 until 6:17:39. The ISS will rise in the southwest, and pass very high in the sky before disappearing into the Earth’s shadow while it is still 66 degrees above the horizon. If you don’t make this, then your next best shot is on Saturday when the ISS will never get above 17 degrees over the western to northern to eastern horizon from 5:21:56 to 5:25:29.

http://www.heavens-above.com/PassSummary.aspx?satid=25544&Session=kebgfgclbakbpkhgkmjkhfod

Tennessee (Chattanooga)

..... Chattanooga should have good weather on Wednesday and Thursday, so on Wednesday (just after sunset) look from 5:35:46 to 5:51:03 as the ISS, as bright as Jupiter, travels from south of west towards the north, to set in the northeast. The ISS will pass about halfway up the sky, at about 39 degrees above the horizon.

.....Thursday won’t be as bright, but from 6:06:54 to 6:15:36, the ISS will skin the northern horizon, west to east, getting only 15 degrees above the horizon.

http://www.heavens-above.com/PassSummary.aspx?satid=25544&Session=kebgfgclbakbpkhgkmjkhfod