Ursa Major (Constellation)

"Thou art as opposite to every good
As the Antipodes are unto us,
Or as South to the Septentrion"

Henry VI, Part III Act I, scene iv, lines 134-135

.....A constellation is one of a set of eighty-eight star patterns recognized as "official" by the International Astronomical Union.  The reason that there is an official set is that constellations are used as a way to identify a number of different types of stars, so having official constellations allows us to define official boundaries.  There are plenty of useful groups of stars, many of which I'll talk about, that aren't constellations, and these I will refer to as "asterisms".  The most famous asterism is probably the Big Dipper - the Big Dipper is only a part of the larger constellation, Ursa Major.

.....Ursa Major makes a good starting point because for most of America, it is a circumpolar constellation; that is to say, the star is close enough to the pole that it never sets below the horizon, and so it can be seen all year long. I will continue on over the next year, constellation by constellation, as they pass their high point in the evening sky.

.....In June skies, the Big Dipper will start the night near the zenith (directly overhead) , and in July the Dipper is still high in the northwest by 11 PM.  Many of the stars of the Big Dipper have individual names, a measure of the importance of the stars of this constellation.

.....Another method was derived by Johann Hevelius in a star atlas published in 1603. He tried to name the brightest star in a constellation “alpha of that constellation”, so the brightest star in Ursa Major should be a Ursae Majoris (then b, g, d, and so on). Ursa Major is an unfortunate starting point for introducing this system, because in this case, as you can see, Hevelius simply started by making a pattern of the Big Dipper. Here is a map of the Big Dipper with stars named in this system:

 

.....All of the early catalogs began with Ursa Major and Ursa Minor (again, more commonly recognized by the Big Dipper and Little Dipper).

.........The stars of the Big Dipper have been recognized as a constellation from the earliest times. Homer seems to have recognized the Big Dipper (as a bear) as the only circumpolar constellation as “Arctos, sole star (here taken as constellation) that never bathes in the ocean wave” The Big Dipper appears in the Bible, in the book of Job “He [God] made the Bear and Orion, the Pleiades and the constellations of the South (9:9)”, and “Can you bring forth the Mazzaroth in their season, or guide the Bear with its train (38:32)?” Note that the Dipper is not represented as a bear with an incongruously large tail, but as a bear with three followers (cubs? hunters?). (It is unknown what Mazzaroth represents. It could refer to a southern constellation using the pattern of parallelism in Hebrew poetry, or it could represent the zodiacal constellations as a set. It could also represent a handy gardening tool with a built-in mulching attachment; we just don’t know.)

.....The Big Dipper is one of the oldest star patterns. I feel that I’m being fair in saying “the Big Dipper” here, as opposed to “Ursa Major”, because “Ursa Major” itself is an expansion of the Big Dipper. Sure, it was an expansion that took place several hundred years BCE while the other circumpolar constellations were created at this time, but the Big Dipper was old even then. It is impossible to know just how old, but the idea of the Big Dipper as a bear is surprisingly widespread, in bold defiance of the fact that it looks absolutely freakin' nothing like a bear. (The idea that Ursa Major is old enough to go back to a time in which bears looked a lot more like dippers has, unfortunately, little evidentiary support.) The writer Thomas Hood took a different tack:

“Imagine that Jupiter, fearing to come too nigh upon her teeth, layde hold on her tayle, and thereby drewe her up into the heaven; so that shee of herself being very weightie, and the distance from the Earth to the heavens very great, there was great likelihood that her taile must stretch. Other reason know I none.”

.....Admittedly, the Germanic nation did not consider this a bear, but a wagon (which makes sense, seeing the bowl as the wagon and the handle as the bar that the animals would be attached to); what is surprising that a number of North American cultures also saw a bear here. (To their credit, they only saw the bowl of the dipper as a bear; the three stars of the handles were hunters chasing the bear, catching it in the fall when the bear, low in the evening sky, would drip blood onto the trees, changing their colors.

.........There has been some conjecture that the Big Dipper is the remnant of some Paleolithic bear cult, but this might be reading too much into this. Beyond the elephant, the bear is the largest land creature, so the most important group of stars is probably predisposed to be called “the bear”. If there is anything to the idea that the Dipper was considered a bear even before the migrations to America, it might be as William Whitney (American philologist of the nineteenth century) supposed, looking at how the Sanskrit word Riksha can mean either “star” or “bear”, depending on the gender of the word. The seven most important stars in the sky could then have been the "seven bears", or just eventually lumped together as "the bear". Or, maybe a North America culture just picked "bear", and the constellation name spread. There is currently no way to know.

....I was considering also discussing the number of times that different constellations appear in literature, but starting with the Big Dipper made this prohibitive, since references to it are so common. If you run across a literary reference to a constellation, please let me know. (I'll cite you -- you're name will be in a blog ... wow!) I did find three appearances of the Big Dipper in Shakespeare as well. In addition to the quote that begins this entry (the Septentrion, or “seven stars” is the Dipper), the Big Dipper is also referenced in Henry IV, Part I, where it is used as a timepiece (I'll discuss this more when we talk about the Little Dipper, and using the stars to the north as a clock) and a reference in King Lear where Shakespeare has one of the villains of the piece speak in what we would now consider to be enlightened skepticism about astrology. I'll go into more detail on this when I talk about the first zodiacal constellation on our tour -- Ophiuchus! (Don't recognize this as apart of the Weekly World News zodiac? I'll explain soon ...)

.....Confining ourselves to the stars of the constellation itself, take a look at the center star of the handle, the bright star Mizar. Mizar has a magnitude of 2.23, a fairly bright star. Close to Mizar in the sky, close enough to be seen with the eye, if your eyes are good, and easily with a pair of binoculars, is a fainter star, Alcor. Alcor has a visual magnitude of 3.99, which means that we are receiving about five times as much light from Mizar as we are from Alcor; we don't see Mizar as five times as bright, because our eyes don't work such that twice the light equals twice the brightness. If that were true, then your head would all but explode as you went inside and turned the lights on after being out looking at the stars!

.........Mizar and Alcor are separated by a distance in the sky that is about 1/3 the apparent size of the Moon in the sky. Many cultures have used this star as a test of vision, requiring a reasonably sharp eye to see this as two stars and not one. There has been a question as to whether Mizar and Alcor are actually part of a double star system, or if the are simply close to the same line of sight in the sky. This is somewhat similar to seeing two people sitting together on a bus and assuming that they are married. It does seem that these two stars are indeed orbiting each other, but widely separated. The closer star, Mizar is about 78 light years away, which means that the light you see tonight left the star's surface in early June in 1931, and has spent all that time traveling through space. Alcor is about three light years away from Mizar, or about 190,000 times the distance between the Earth and the Sun. If these stars are orbiting each other, it will take about 43 million years for each orbit. Mizar is itself a double star, but you will need a telescope to see that. Both stars are about the same brightness, and much closer. They orbit each other in only about 104 days, a much smaller separation.

Star Names

.....Aargh.  This is the second try at this.  I've been having a number of problems with Firefox tonight, so I don't think I will be using that for posting anytime soon.  Welcome back, Internet Explorer.

....."Now that class is over, I understand how we can find out a star's mass, and size, and temperature, and composition, but what really gets me is how we can find out their names." - The punchline to what I devoutly hope is a fictional anecdote.

.....Consider the view of the night sky below.  (Credit where credit is due; here is the source of the image.)  Pick a star, any star, in the field of view.  (This is the easy part.)

.....Now, imagine how you would tell someone else which star you picked.  In order to convey what we're looking at to another, we need some way of mapping the sky.  The starting point that I'll be using in most of these will be constellations, patterns based on Romans overwriting names from the Greeks who stole a good number of the patterns from the Babylonians, who might have taken some from India.  Cosmopolitan theft.

.....An alternative would be to name individual stars, instead of groups of stars.  The downside of this is that there are more than five thousand stars visible to the eye.  If you have problems keeping track of all your relatives, imagine how difficult this would be!

.....About the brightest two hundred or so stars have individual names (I'll be including these on individual star maps for each constellations as we go), and as we'll see, most of these stars have Arabic names.  Our multicultural thefts continue!  The reason for this is that the Greek need for precision in tracking directions by the sky was not very demanding.  The Mediterranean is a physically forgiving place to navigate, especially if you just have to decide between "north along the coast" or "south along the coast".  If you needed to keep track of exactly how you were traveling in order to hit an oasis across a wide-open span of desert, you want more exact road signs, yourself.

.....Ironically, most of the stars whose names we've looked at so far come from the Latin.  "Polaris" comes from "Stella Polaris", the pole star, now located close to directly overhead at the Earth's North Pole, so it seems motionless as the rest of the Northern Hemisphere skies rotate around it.  The Greek name was "Phoenice", from their name for the constellation, along with a lot of other names in pretty much all cultures.

.....The name of the star Arcturus comes from the Greek, and apparently mean "bear-watcher".  I'll go more into the significance of this when I talk about its constellation, 

Boötes, next month.

....."Regulus" was coined by Nikolai Kopernik (Copernicus) himself, meaning "little king"

.....Spica is also from the Latin, "Spicum", or "spike" for the sheaf of wheat usually shown with Virgo (which I will not cover in depth until out next go round, next spring - I have my reasons.

.....Rising in the east, we can see three bright stars which we will later investigate as the "Summer Triangle".  "Altair", which means "eagle" in Arabic, "Vega", which means "diving eagle/vulture" in Latin, and "Deneb" which surprisingly has nothing to do with eagles, meaning "tail".  But that is for the future ...

The Brightnesses of Stars

.....One of the biggest problems with just getting into astronomy is learning a new language , made all the more confusing because it looks so much like English.  There are a lot of terms which, don't worry, become familiar very quickly, but if you just pulled an astronomy book or magazine off the shelf in a bookstore, can seem to make little sense.  I'm going to try to avoid new terms (just for the sake of new terms) where I can, and where I think it's important, I'll call special attention to them, like now.

.....It is hard to start off a column with an apology for two thousand years of common use (so I waited until the second paragraph! woo hoo!), but there is a habit that started with a Greek astronomer about 2300 years ago.  This astronomer, Hipparchos, divided the stars in six categories with the brightest stars as "stars of the first rank" and the dimmest stars as "stars of the sixth rank".  This seems to make sense until we track this this forward into the nineteenth century, and people are able to take photographs of stars and make absolute measurements of the amount of light coming from a particular star, as opposed to simply "brighter than that other star over there", when astronomers decided to keep the magnitude system.

.....This means that a star with a magnitude of 6.00 is the faintest star that can be seen with the naked eye (I normally use "unaided", but I want this blog to show up under Google searches for 'naked';  heck - naked naked naked) and a star with a magnitude of 1.00 is quite bright.  The Sun has an apparent magnitude of -28.  This can be hard to track.  Still, at this level, we can still use the magnitude system in a reasonable way.

.....Consider this map below, which is the June 2011 sky as it might appear in a magazine such as Astronomy or Sky & Telescope, which shows stars down to fifth magnitude (going all the way to sixth magnitude would add about 1,600 tiny dots to the map; not a great deal of use is added.

.....(I chose to only include stars and asterisms that have come up in the blog.  Since this blog is fairly young, that's not a lot.)  Even if I had put all the names on the map, consider looking up at a sky like this:

.....If you are just starting out, this can be pretty darned intimidating, plus, unless you live someplace away from cities/car dealerships/McDonald's.  I certainly can't walk out my back door and see fifth magnitude stars!  We can speak of how many stars we can see by talking about a "limiting magnitude".  A reasonably dark, moonless suburb, with no direct lines of sight to street lights, might have a sky with a limiting magnitude of fourth magnitude:

.....As you can see, even with a limiting magnitude of four, "holes" are appearing in the patterns.  Move a little bit closer to town (or let the gibbous Moon rise), and we have a limiting magnitude of three:

.....That last one is about what the sky looks like from my back window on a good night.  You'll notice lots of holes in constellation patterns; some entire constellations have vanished.  At this point, the lack of stars (which might have seemed beneficial to a beginner who did not want to be overwhelmed) now works against us.  This is why I started with the Big Dipper and a few bright stars.  After all, toss in some thin clouds and we go to second magnitude.  (Notice that when we are looking at this map there are a few sets of bright stars.  The three bright stars rising in the east we will come back to, in time.)

.....And on a very bad night, if all that we can see are stars of first magnitude or brighter, the sky is fairly empty. 

.....Drat.  I just noticed that I did not add Saturn to the empty star maps.

Rings Around the May Sky

.....I love looking at the stars, and I, like a lot of other people, want to help other people recognize what is there to be seen, but if you look at a star map in a magazine like Astronomy or Sky & Telescope, or at a useful web site such as Heavens Above, you will get a skyful of constellations, but you might not have the experience or confidence to use all this.  As we go through the sky constellation by constellation, I will add these into the mix.

.....So far, we have only covered the Big Dipper and the bright stars that we can find with the Big Dipper ... plus one.  We start with the Big Dipper and stars as it is seen at 10 PM on May first (which is, admittedly, well past).  At the beginning of each month, I will post a view of the night sky at 10 PM.  Will this be uniformly useful?  Often not.  In the summer, it might not even be dark at ten, and in the winter it will have been dark for several hours, but this will still be helpful if you observe within a few hours of 10 PM.  The map is also set up to show the sky from 44 degrees north, pretty close for most of the northern United States and well set up for Europe, but a viewer in the southern US or Japan would only notice a slight shift in the positions of the stars.  SO let's take a look ...

.....Added to this set of stars is the one bright planet visible in the evening sky, Saturn.  (Sorry, SATURN!!)  If you ave a telescope of even the smallest size gathering dust in a closet, you should definitely get that out, because Saturn is one of the few things in the sky that actually looks like it's supposed to.  As I go through the sky, there will be a lot of deep sky objects that can be found in a telescope that (I know from bitter experience) get a response of, "So, is that it?  The little fuzzy bit?"  Saturn, in a telescope looks like *&^%&^* Saturn.  Saturn's rings are clearly visible in even the smallest telescope, and you will definitely know that you have found them.  On a good night, the Cassini division, the dark line between the two rings is visible, and Titan - the largest moon of Titan, and the only moon with an atmosphere (but it's still no Yavin IV)..

The Big Dipper

.....If you step outside on a clear, dark night, the number of stars can be overwhelming.  If you step outside in an area with light pollution, it can be hard to find enough stars to make any patterns out.  There is one pattern, though, that can be seen in almost any semi-clear weather, and that happens to be high in the spring sky, the Big Dipper.  The Big Dipper is the most recognizable part of Ursa Major, which is a circumpolar constellation; that is to say, the stars are close enough to the pole that it never sets below the horizon, and so it can be seen all year long. In May skies, the Big Dipper will start the night near the zenith (directly overhead) , and all summer, the Dipper is still high in the northwest by 11 PM.

.....The Big Dipper can also serve to introduce how stars are tracked individually as well. Of all the stars that can be seen with the naked eye (there are slightly more than 5,000), there are about two hundred that have individual names. These are typically the brightest stars in a constellation, and show the limits of the usefulness of designating stars individually in such a unique manner; after all, could you reliably remember five thousand names? (Heck, have you ever had to correct a grandparent or other family member? Odds are, there aren’t five thousand in the family.) Here is a star map of Ursa Major with all of the named stars shown.

.....Another method was derived by Johann Hevelius in a star atlas published in 1603. He tried to name the brightest star in a constellation “alpha of that constellation”, so the brightest star in Ursa Major should be a Ursae Majoris (then b, g, d, and so on). Ursa Major is an unfortunate starting point for introducing this system, because in this case, as you can see, Hevelius simply started by making a pattern of the Big Dipper. Here is a map of the Big Dipper with stars named in this system:
 .....The stars of the Big Dipper can also be used to provide a sense of scale across the sky. Judging scale is one of the biggest problems in getting used to moving around the sky, because in the sky there are no points of reference that we see on the ground. Fortunately, we have fairly reliable measurement tools at the end of our arms – we can use our hands. (Yes, your hands are almost certainly not the same size as mine, but your arms are also differently sized than mine as well. This balances out.)

.....Consider the “distance” between the stars Dubhe and Merak. I put the word “distance” in quotes, because we have to define what we mean by distance. If I describe the physical distance as 45 light years, how does that help you? We’ll use “distance” to refer to the angular distance between two things in the sky, so that an object on the horizon due north will be 180⁰ away from an object just above the horizon due south. In this way, the distance between these two stars is just a little bit more than five degrees. As shown in the diagram below, this distance against the sky is about the same as the angular size of three fingers held at arm’s length. This can also be used as an order to your bartender if the viewing isn’t good. (PARENTS: If you little one comes in, sighs, and says, “Gimme three fingers of Redpop”, then s/he has been reading this blog - or you could simply be a lousy parent.)

.....The stars Dubhe and Phad are ten degrees apart. This is about the distance between your fingertips is you extend your hand as shown below, a form that is either reminiscent of a certain arachnid-based superhero from a company with “marvelous” lawyers, or – if you were a young person in the 70’s or 80’s – the “secret devil sign” beloved by metal bands and freaked out middle-aged PTA moms. Of course, if a freaked-out PTA grandma sees you making a devil sign to the night sky, then you might need to refer back to the “three fingers” – once the police leave.
.....The stars Dubhe and Alioth are fifteen degrees apart, which can be measured by the hand sign below, which I have christened the “dude”. (Pronounced “duuuuuuuuude”.)

.........The Big Dipper can also be used as a guide around the sky as well. A line that passes through Merak and Dubhe will pass very close to the North Celestial Pole, and hence, the North Star. (This is helpful, because while the North Star Polaris is a reasonably bright star, it is nowhere near the brightest star in the sky, though this is a common misconception.)

 

.....A line passing through the other end of the bowl will come very close to the bright star Regulus, in Leo. This star is setting very close to sunset now.

.....If you follow the curve of the Big Dipper's handle, the curve will arc towards the bright star Arcturus, in Bootes (coming soon), and if you go past Arcturus, you will speed on to Spica, in Virgo (next to last of this series, next spring).

An astronomy blog for the average backyard

.....Why add yet one more blog to the blogosphere, a place with (at last count) about four blogs for every person living on Earth? ([i]citation needed[/i])  Even just looking at the amount of knowledge available on the internet makes it seem like certainly everything must be covered by now.  And it is, possibly.  The difference is that most of these resources seem to make the assumption that you are very familiar with astronomy already, and/or that you live fifty miles away from the nearest small town.  This is a blog that is meant to be accessible to anyone, especially those just getting backyard astronomy (although I hope that I can also keep the interest of more experienced readers, as well), and for those teaching introductory astronomy who might like a starting point and some resources.

.....This is a blog about the universe as seen from your backyard, even if that backyard is surrounded on all sides by streetlights. As hard as it may seem to be, everyone starts out at the same level.  When I was about seven, I got my first astronomy book, and I began learning my way around the night sky. In seventh grade, I got a telescope with a lens that (as it turned out), was actually a little smaller than the human eye. For two years, I tried to work with that, balancing the six-inch long tripod on the bars supporting the chain-link fence around our house.  I could find Jupiter, Saturn, the brightest nebula and the brightest galaxy.  I moved on to a “department store telescope” which turned out to be a cardboard tube with a single lens at the end. I worked with this for four years, adding perhaps a dozen more deep-sky objects to the list of things that I could find in the sky.  For my high-school graduation, I got a Schmidt-Cassegrain telescope with a mirror eight inches across. (Some people got cars; if that's you, are you still using that and happy 25+ years later?  I think I'm ahead.)  I hope this establishes my bona fides as someone with a little observing experience, and someone who got here the hard way. You don’t have to do that, and I can help.

.....Many blogs will be tied to something going on in the sky at that time. Over the next couple of months, Saturn, Uranus, Neptune, the Moon, meteors, satellites and more will each have entries. My first run through the sky will be by the constellations visible from mid-northern latitudes, providing a map of each constellation, its location in the sky, the names of some of its brighter stars, and some hopefully interesting background about that constellation. 

.....After that, starting next year, I will go through each of the constellations again, describing some of the clusters, nebulae, double stars, galaxies, et cetera, that can be found in that constellation using binoculars.  After I have made a pass like this, I will start investigating what can be seen with a small telescope.  (If you want to look at more of this material, I will be doing this in a more "target of opportunity" way in my other blog, The Messier Pro.)