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 Northern Lights - maybe tonight!

.....On Monday, the Sun released a tremendous amount of material and energy in the general direction of Earth, and that material is now encoutering the Earth.  The tremendous burst of charged particles, when they interact with the Earth's magnetic field, get forced to follow the field lines until all the particles are spun into a tightening flow as the magnetic field lines get closer as they bend to Earth near the north and south magnetic poles.  What happens then is the same as what happens in the flourescent bulbs in your office.  The fast-moving charges energize the electrons around the gases they are passing through, leading to a glow in the sky, the northern lights.  If you have the opportunity to go outside and look north tonight, take the chance and look towards magnetic north. Maybe you'll see (as I used to, in the Upper Penninsula of Michigan) a greenish semicircle of light around magnetic north ... or maybe something cooler, one of those nights when the whole sky seems like a curtain of fire ...

Moony Monday!

.....I said "Moony Monday" for the Total Lunar Eclipse that will occur early Tuesday morning because I couldn't think of anything that went with Tuesday. The universe is not rewarding this, however, since there is a winter storm warning with 5-8 inches of snow on the way, finishing up with frozen rain. I hope someone else out there gets a chance to see this.

.....To see this, all you need is a good view of the skies (from the Americas, and best set up for North America). If you have a telescope, or even binoculars, that will make things even better, but it isn't necessary.

The first stage is when the Moon enters the Earth's penumbra, the shadow where part of the Sun, but not all of it, is blocked. This will be pretty much undetectable. The Moon enters the penumbra at: 11:46 PM (CST/ UT -6, which is 12:46 AM Tuesday in the Eastern Time Zone, and 10:46 PM in Mountain Standard Time, and so on.)

.....The Moon enters the umbra, the central shadow at 12:51 AM (again, CST, the best time zone) , and totality, with the Moon entirely in the umbra from 1:57 AM to 3:14 AM. On Earth, a total eclipse is completely dark, but in a lunar eclipse the light passing through the Earth's atmosphere is scattered into the shadow. In the same way that the sky appears blue because blue light is scattered first, and the setting Sun appears red because red light is scattered last, the totally eclipsed Moon will appear a deep red, sometimes getting so faint that the full &^$%&^% Moon is hard to find in the sky.

.....The Moon leaves the umbra at 4:17 CST, so the party is then pretty much over.

.....Since this lunar eclipse happens on the Winter Solstice (when the Sun is at its lowest point in the sky), the Full Moon (exactly on the opposite side of the sky) will be at its absolute maximum possible highest. I'm honestly fairly amazed that no group has come forward claiming some mystic significance for the occasion. There is definite non-mystic significance, because this is the last total lunar eclipse visible from North America until April of 2014.

.....If you do get a chance to see it, please let me know; I'll be watching the snow fall, grading final exams.

An apology

.....Wow, looking at the time that has gone by, while I very much want to provide a blog that is aimed at those who might not be in the middle of the country with years of experience, I've first gotta go with my teaching responsibilities. Still, I am working toward building up a "Year around the Sky" to start in May. I will still be updating this as often as I can.

Aquila: The Eagle Has Landed

..... The southern star in the summer triangle is Altair, which means "the Eagle". (Vega, in Lyra, also means "the [Diving] Eagle.") Altair is the brightest star in the constellation Aquila (the Eagle) which is shown in the map below along with the constellations Sagitta and Scutum, which a reasonable reader at this point might conjecture mean "the Eagle" and "the Eagle", respectively, but surprisingly this turns out not to be the case.

.....Altair is the closest of the stars in the Summer Triangle, being about 16.77 light years away. The light that reaches the Earth on the night of September 20th, 2010, left the surface of Altair on December 13, 1993.

.....The constellation Aquila is a fairly large constellation in the center of the summer(/autumn) Milky Way. The view of the Milky Way in the sky even shows a split, with the Milky Way having apparently separated into two bands. This appearance is actually due to tremendous clouds of neutral hydrogen gas and dust between us and the center of our galaxy. We're looking in the direction of a tremendous number of stars, which makes it surprising that Aquila has no deep sky objects of interest in the reach of a small telescope.

.....This lack of cool stuff is why I added the constellations of Scutum and Sagitta to this map; I'm going to describe the telescopic objects in these two constellations in Aquila's place, since Aquila is easy to find, but doesn't have anything of its own.

.....This constellation also stands out to me because I now live in an area in which eagles are reasonably common sights. Just last weekend on our drive along the Mississippi to town, we saw two eagles flying over the road. Upriver in Wabasha is the National Eagle Center, located here because it is the northernmost point along the Mississippi the does not freeze over, so there are many bald eagles that winter in this area. In January and February it is possible to see dozens of eagles along the river, and I don't think that there has been any times in which I have gone there that I have not seen any eagles in wild.

Deep Sky Objects in Lyra (L2/M57, M56)

.....There are two Messier objects in Lyra, and the up side to Lyra's small size is that I can fit the entire constellation figure on the finder chart for both objects. Lyra contains one of the most impressive, and easiest to find, Messier objects.

Messier 57 / Leckenby 2: The Ring Nebula

.....The Ring Nebula, aka M 57, aka NGC 6720, aka L2 (my designated second object on the "Leckenby list", my list of deep sky objects that a starting observer has a really good chance to locate) is located between the bottom two stars of Lyra, Sulaphat and Sheliak. In a good pair of binoculars, the Ring Nebula can be seen a little bit closer to Sheliak than Sulaphat.
...In a telescope, the Ring appears as a, well, ring. The Ring Nebula is a "planetary nebula" (due to its round appearance), and in the simplest model of a planetary nebula, it represents what will someday happen to the Sun. When nuclear fusion finally stops at the core of the Sun, the core will collapse without that energy being added to it, and that collapse will release energy that will bounce off the outer part of the Sun like an expanding soap bubble. As it turns out, things are a little bit more complex; the Ring isn't actually a spherical bubble of gas, but more of a cylinder that we are looking at edge-on.

.....Below are two images, one of which might be a mistake to include. The one on the left is a sketch I made of the Ring Nebula through my personal telescope. This is probably fairly close to how this object might look to the typical backyard observer. The other image is a Hubble image of the Ring. This object will *never* look like this in your backyard, I'm sorry.

Messier 56

.....Messier 56 isn't viewed as often as, say, the Ring Nebula, because M56 is a globular cluster, and there are dozens of globular clusters visible during the summer. Given a choice between M56, and something like the Hercules Cluster or M5 in Serpens, most people will go for one of the biggies. The most dramatic globular clusters appear as a bright central blur that resolves itself into individual stars as you get farther to the edge. That resolution does not appear with M56, at least it didn't with me. (The seeing the last night I looked at it was not the clearest, however.)

.....the Messier Objects were originally compiled into a list by Charles Messier because he was looking for comets, and these were things that kinda looked like comets, but weren't. Author Stephen James O'Meara has noted that M56 is special to him because it has a hazy, comet-like appearance, so it shows what Messier found distracting when he made a list of what we now recognize as a tour of the wonders of the sky when Messier was just trying to list the garbage that kept getting in his way.