So, the first thing that I teach them is how to use a planisphere. The one that we use with our students is the one by David Chandler, shown here. For those of you new to astronomy, a planisphere is a very simple device that can be set to show what the sky looks like at different times on different days of the year. The sky looks different at different latitudes, so planispheres are made for different latitude ranges. The stars and constellations are labeled, and so once you know how to use the planisphere, you can use it to identify stars and constellations. There’s computer software that does the same thing, but this is much easier to carry around with you.

The first thing to do to try to use the planisphere is to figure out what direction you are facing. So, for those of us in the northern hemisphere, that often means finding the north star. A very widespread misconception is that the north star is the brightest star in the sky. I am not sure why this is such a common belief. I never heard that when I was growing up, but the majority of my students have heard that. Unfortunately, it is wrong. In fact, Polaris, the north star, is not even one of the ten brightest stars. It looks like just another star. The only thing special about it is that it is very nearly over the Earth’s north pole, so it appears to practically stay put in the sky.

But, as I said, there is a common mistaken belief that the north star is the brightest in the sky. So, when we went out and the students started looking for the north star, a large number of the class turned and faced towards the brightest thing that they saw up there. Unfortunately, that object was not Polaris, it was the planet Jupiter, and Jupiter was almost due south at the time. I’ve included a sky view below created by Stellarium software. This shows Jupiter and its position in the sky. Right below Jupiter is a group of stars that makes a pattern that generally resembles a teapot. This is part of the constellation Sagittarius. Off to the west of Jupiter is a reddish star named Antares.

Jupiter is actually quite bright. It was in opposition July 9.   At that time, it was the closest that it will be to Earth until next August.  It was also brightest then.  But, it is still pretty bright.  At magnitude -2.5, it is about 60 times brighter than Polaris.  Also, at the time that we were out there, it was at almost the same altitude in the sky that Polaris would be.   Both Polaris and Jupiter were a little over 30 degrees above the horizon.  Jupiter is about as far south as it gets in the sky.  Normally, it is farther north, so it would appear higher in the sky when in the southern sky.  But, it has not been this far south in about 12 years.  It will be about this far south again in another 12 years.  Being low in the sky is not good for observing.  That means that you look through more air to see it, so there is more distortion.  Of course, all that I’ve been saying about Jupiter being low in the sky is for us here in the northern hemisphere.  For my readers down in the southern hemisphere, Jupiter should be passing high in the sky in the evenings.

So, my students learned a bit this first night of sky familiarization.  There’s still a lot more to learn.

-Astroprof

Last week, we had a whole week to “prepare” for the fall semester.  Actually, we spent the entire week going to meetings.  We had meetings, meetings, and yet more meetings.  In fact, most of us never got fully ready for the fall semester (particularly those of us who taught in the summer) until this past weekend.  Today was the first day of classes.  The administrators don’t seem to realize that it takes time to prepare for class.  I guess that all they need to do to get ready for the semester is to  have meetings, so a week of meetings doesn’t phase them any.  The rest of us have work to do.

At any rate, today was the first day of the semester.  I came in early to get ready.  Wow.  If I had not, then I’d never have found a parking spot.  By shortly after I arrived, the parking lots were filled.  We have a record number of students enrolled in the college.  In fact, we have nearly double the number of students that were here when I started full time ten years ago.  At the same time, we have fewer parking spaces.  As with most colleges and universities, parking lots become fair game when new construction is needed.  The students don’t bother to read the parking rules that come with their parking permits, so they park in faculty parking.  Some don’t care about the tickets.  Others park elsewhere, freeing up another space for more students to park in faculty parking.  I know that if I arrive at the wrong time, I’ll have to park clear across campus in the overflow parking.

Enrollment is up, so that means that we need more faculty.  We hired quite a few new full time faculty, but we also hired a boat load of part time faculty.  All those people also need to park.  And of course, there is absolutely no additional faculty parking since when I started years ago.

Why the huge increase in enrollment?  Well, as a state institution, our tuition is much lower than the private universities.  And, that means that we pick up a lot of students that would have gone there.  Our tuition is even less than that at the state’s big universities so that means even more students.  And, with the economy down, more people go to college.  All that means that not only is the college’s student enrollment up, but we have a record number of physics and astronomy students.  All of our faculty are maxed out, with teaching schedules at the maximum overload level.  Most of our part time faculty are also at the maximum load permitted.  And, we just barely covered all of the classes being offered this semester.

But, with me getting back to a more “normal” schedule, I hope to be back to blogging more.  I’ll try to keep my readers up on the latest astro-news and happenings.  So, keep tuned in!

-Astroprof

-Astroprof

As I start to write this, the orbit counter on Hubble Space Telescope’s HubbleSite reads 100001.  That means that the Hubble has traveled 2.72 billion miles in the last 18 years that its been in orbit.  Of course, it didn’t really go very far.  It is only a few hundred kilometers above Earth’s surface at all times.  From going around giving public talks and from talking with my students, I realize that a lot of people are quite uninformed about how Hubble gets its fantastic images.  I find that a lot of people seem to think that it flies around to different planets, nebulae, galaxies, etc, and photographs them.  That would be nice, but that isn’t what it does.  In fact, its 2.72 billion miles traveled wouldn’t even get it to Neptune.  Rather, the amazing images come from the fact that the Hubble doesn’t have to look through Earth’s atmosphere.  Looking through the atmosphere both blurs the image, and attenuates certain wavelengths of light.  Outside of Earth’s atmosphere, certain wavelengths of light can be observed that are difficult or impossible to observe on the ground.  In fact, Hubble can see a wide range of wavelengths of light well in excess of what humans can see.  Of course, astronomers want to be able to study objects in these kinds of light, so what we often do is to display those wavelengths as certain colors in an image.  Naturally, if the object already has light of those colors, then you’d want to display those colors as some other color, and so forth.  The end result is an image that has far more detail and color than the original object would appear if you could see it in visual light, no matter how good of a telescope that you were using.  The Hubble team uses a color palette that is not commonly used by other astronomers.  The end result is an image that has a lot of scientific information (what astronomers want) and looks beautiful (what the public generally wants).  An example of such an image is the star forming region in star cluster NCG 2074 seen below.  This image was taken yesterday and released as part of the announcement of Hubble’s completion of 100000 orbits around Earth.

The Hubble telescope is alive, but not doing well right now.  It is getting old, and many components are past their useful lives.  Also, the telescope was designed to be serviced every 3 years during a Space Shuttle mission.  The last servicing mission was in March, 2002, over six years ago.  Several instruments have failed, along with some of the gyroscopes that keep the telescope pointed where it needs to point.  Also, it is gradually spiraling back to Earth.  Without another Space Shuttle mission to boost it to higher orbit, it will reenter the Earth’s atmosphere on its own sometime after about 2010.  However, NASA has plans for one final servicing mission, STS-125, due to launch in a couple of months.  They have a lot to do.  It won’t be possible for them to replace everything on Hubble that really ought to be replaced.  That would take two servicing missions.  But, they’ll get most of it, and they’ll boost Hubble to as high of an orbit as they can.  That will give us some time until the final goodbye to this instrument that has become one of NASA’s best success stories.  Pretty much everyone has heard of the Hubble Space Telescope and knows of at least some of what it has done.  I would image that it is by far NASA’s most popular mission right now among the general public.  And, during its 18 years on the job, it has become one of astronomers’ most useful tools.

-Astroprof

Images courtesy NASA, STScI

A little over a half century ago, the first satellite was placed into orbit by the Soviet Union. A few months later, the United States followed with Explorer 1. However, Explorer 1, wonderful as it was, was not what the president and his administration had been hoping for. For one thing, they wanted it to be clear that the United States was for pursuing peaceful endeavors in space. Granted, no sooner was the first satellite in orbit, but the Pentagon was trying to figure out how to use this for a military advantage, such as surveillance of our enemies. Still, Explorer 1 had science as its goal, not war. But, it was lifted into space by a modified weapon of war. A Jupiter missile had been adapted to launch Explorer 1. For months, the United States had been trying to get into space using the Vanguard rocket (itself, developed by the Navy, of course, but less militaristic). President Eisenhower really wanted a civilian agency to launch the US into space. Vanguard was being led by the NSF. But, it was the Army Ballistic Missile Agency, under Wernher von Braun, that put the first American satellite into orbit.

Now, the Soviet Union was not so concerned on how it looked for the military to be associated with spaceflight. Sputnik was launched by an R-7 missile: the first operational ICBM. Granted, as a weapon system, the R-7 left a lot to be desired, but the fact remains that it was developed as a weapon first. Even today’s Soyuz rockets are based on the R-7. But, Eisenhower wanted there to be a separation between the US military and space exploration. Granted, there often isn’t much separation, as even today unmanned rockets are frequently launched from military launch pads (or at least launch pads on a military base).

So, the Eisenhower administration pushed to create a separate civilian space agency. Eventually, Congress passed the National Aeronautics and Space Act. This act created NASA, the National Aeronautics and Space Administration. Space engineering is quite similar to aeronautical engineering, so it made sense to combine the aeronautical research, astronautical research, and aerospace research into one agency. The United States, though, already had a government aeronautical research program, headed by NACA, the National Advisory Committee for Aeronautics. So, NACA was absorbed into NASA, along with several military installations, creating a civilian space agency. Since the military had rockets, and they had trained test pilots, there has always been a close association between the military and NASA, but NASA itself is a civilian agency.

The National Aeronautics and Space Act was signed into law by President Eisenhower 50 years ago today. NASA was not actually created then, however. The provisions of the new law didn’t kick in until October 1, 2008, but that step required the signing of the act 50 years ago today.

-Astroprof

Images courtesy of NASA

The asteroid 2008 BT18 was discovered January 31, 2008, but the LINEAR program. 2008 BT18 is one of those potentially hazardous objects. Tomorrow it passes Earth, but at a very safe distance. In fact, for as far as we can reliably compute its orbit, it will continue to miss Earth. In fact, it may never run into Earth. But, it comes close enough that it needs to be watched. Above is an orbital diagram, courtesy JPL, showing the current position of the body. As with many Earth crossing asteroids, its orbit is not just near Earth. In fact, the semimajor axis of its orbit is 2.22 AU, out in the asteroid belt. But, it has a very elliptical orbit, ranging from about 0.89 AU out to almost 3.55 AU. Interestingly, the orbit of 2008 BT18 has a semimajor axis that is very close to one of the asteroid belt’s Kirkwood gaps. That may have something to do with its large eccentricity.

If that were all that there was to this asteroid, it would still be interesting to write about. However, there is more! It is close enough to Earth already that the giant radar at the Arecibo observatory is able to monitor the object. What researchers have found is that 2008 BT18 is not one asteroid, but two! A story at Spaceweather.com labels 2008 BT18 as a binary asteroid. However, the Arecibo radar image, shown here, seems to show the secondary as just a dot. Wouldn’t that mean that it is more like a moon than a binary asteroid? Well, that is hard to say just yet. Getting the size right on radar images is tough. But reports are that the primary (larger object) is about 600 meters across, and the secondary (smaller object) is about 200 meters acrossSo, we’ll have to wait a bit to see if 2008 BT18 is really a binary asteroid, or an asteroid with a moon. But, what is the difference? In either case, these bodies, as they orbit the Sun, will orbit each other around the center of mass point between them. If that center of mass point is located within the larger body, then the smaller one is a moon. If the center of mass point is located outside of the primary body, then they form a binary asteroid. The sticking point, though, is that if the orbit of the secondary is elliptical enough, then sometimes the center of mass point will be inside the primary, and sometimes outside of it. Then, what do we call these things? Also, as you can see from the radar image, the primary is not spherical. That is pretty typical of asteroids. Only the largest ones would be expected to be spherical. But, that might mean that the center of mass is sometimes inside the primary and sometimes outside of it depending upon the primary’s orientation! Now, I don’t know anything about the orbit of the secondary, so I am just listing the possibilities. But, this does illustrate how these things can get complicated.

Binary asteroids, or asteroids with moons, are not all that uncommon.  In fact, a lot of asteroids seem to be double lobed, perhaps being a binary asteroid in which the two bodies have drifted together.  We also have known that asteroids can have moons since August of 1993, when the Galileo spacecraft flew past the asteroid 243 Ida, discovering a moon as seen in the image below.  That moon eventually was named Dactyl (243 Ida I).

We are still learning about asteroids.  So, you can see why I now cover them early in the semester rather than at the end as a footnote to the Solar System.  And, I seem to be winning converts to my way of thinking.  After explaining what I do to other astronomy faculty, several have decided that my approach is a good idea and they are restructuring their courses to follow the same approach.

-Astroprof

Images courtesy JPL, Arecibo

My previous post was about how I’ve not been blogging much lately. The Sun’s been pretty quiet lately, too. In fact, there has been very little to look at on the Sun for a while. It has now been quite a long time since I’ve taken my students out to look at the Sun during the astronomy classes. The image above, courtesy of SOHO, is not just an orange circle. It is actually an image of the Sun. I know, it doesn’t look all that exciting. It’s not totally featureless, but it is far less impressive than images a few years ago. As I said, there hasn’t been much to look at for some time. For the last couple of years, there have frequently been no sunspots to observe. The lack of sunspots is a symptom of not much magnetic activity going on. Of course, for a lot of people, that is good, because lack of magnetic activity means that there is a low probability of a big solar flare and the accompanying radiation and geomagnetic storms. That means that satellites, power grids, communications, etc. don’t have to worry about disruptions due to solar activity.

But, is there something wrong with the Sun? Why are there no sunspots? A recent news story called attention to the fact that there have been no sunspots for a while. To discuss that, though, we need to first realize that the Sun does not have constant activity. For hundreds of years, astronomers have observed that sometimes there are more sunspots than at other times. Eventually, it became apparent that the Sun tends to build up activity to where it has a lot of spots, and then activity wanes until there are few, or even none. The Sun stays quiet like that for a while, and then activity picks up, and eventually the Sun’s face is routinely covered in spots again. The time that it takes for the Sun to go through this cycle is about 11 years, give or take a year. The Sun does not follow a set schedule, so some cycles are a little quicker than others, and some last a little longer.  Below, courtesy of NASA, is a graphic showing solar sunspot activity for the last four centuries.

You notice that every decade, or so, Solar activity drops off.  Sometimes it drops to near zero and hangs that way for a year or so.  But, during an extended period of time in the late 17th Century, there were practically no sunspots at all for several decades.  During this period of time, sunspots were the exception, rather than the rule.  In fact, it was a big deal if an astronomer observed a sunspot then.  We call this period of time the Maunder Minimum.  But, sunspots are a symptom, not a cause, of solar activity.  So, few sunspots means that the Sun itself is being pretty quiet.  The Maunder Minimum also corresponds to a period of time when Earth’s climate was a bit screwy.  In fact, in much of Europe (where we have the best weather records from the period), there was a general cooling — a period known as the Little Ice Age.   The MSU press release that I cited above raises the specter that another Maunder Minimum event may be on the horizon.

However, let’s not be too quick to rush out and buy parkas.  After all, the Sun is at solar minimum right now.  It is supposed to be at a lull of sunspot activity.  And, as I wrote a few months ago, the next sunspot cycle is already showing signs of getting started.  It just takes a while.  Today, an article at Science@NASA suggests that there is nothing at all wrong with the Sun.  It may be that the current sunspot minimum is lasting a shade longer than average, but so what?  An average is an average.  By definition, there are times that are going to be longer and shorter than the average!  What would be really be indicative of something being amiss would be if this minimum were lasting longer than at any time since the Maunder Minimum.  But, that is not the case.  There have been other minima lasting this long during the 20th Century.  So far, the current minimum, though a little longer than average, is less than one standard deviation from the average length.  You won’t need to start getting antsy until it is about two standard deviations late.  Whenever anything is even slightly out of dead average, it seems that you always have somebody coming along claiming catastrophe is about to strike.

Interestingly, I read a novel a few years ago by Roger Zelazny and Thomas Thomas entitled Flare about the end of a Maunder Minimum type of event.   It was quite an interesting read, and I recommend it.  In the book, a Maunder Minimum started right at the beginning of the 21st Century, during which time humans moved forward in space exploration and colonization.  Suddenly, sunspot activity began again, and all hell breaks loose.  According to the book, the lack of activity from the Sun counteracted global warming due to greenhouse gases.  Sadly, even if all the people who are convinced that the Sun is indeed about to go into a Maunder Minimum (which I doubt), evidence seems to be mounting that the current level of greenhouse gas emissions would more than make up for any cooling that might result.  And, it is not even clear if events like the Little Ice Age are global or regional.  So, just sitting around hoping that the current solar activity lull leads to an extended period of inactivity is a poor plan for dealing with global warming.  And, indications are that this may be just the lull before the storm.  Some solar researchers seem to be calling for an unusually active solar cycle about to happen.

-Astroprof

Images courtesy SOHO, NASA

-Astroprof

Any of you who write space related blog postings might consider submitting them to the Carnival of Space to get more exposure.  To do so, just email a link to your submission to carnivalofspace@gmail.com.

-Astroprof

The remote location delayed word reaching scientists in major cities. The remote location also meant that travel to the site was an expedition rather than just a trip. Considerable planning was needed, as well as gathering of supplies. Before scientific expeditions could make it into the area, the world fell into war. The Great War, now known as World War I, pretty much kept everyone occupied for a number of years. After the war, Russia was deep into the throes of revolution. So, it was over two decades before scientists made it into the area. What they saw shook the world. An entire forest was devastated by the explosion.

Right away, speculation began to run rampant. Nobody had seen something like this. But, just a few years later, that changed. During World War II, weapons scientists began to realize that for very large bombs, the overpressure can do more damage than the immediate explosive fireball. And, to maximize the coverage of that overpressure, the bomb should be detonated above the ground. The blast damage from the atomic bombs dropped on Japan at the end of the war displayed similarities to the Tungaska blast pattern, only the Tunguska blast was much, much larger.  Soon, a favored hypothesis was that the blast was caused by some sort of air burst. But, an air burst of what?

The Solar System is a shooting gallery. There are a lot of things flying around out there. Most of these things are small, so when they run into Earth, they simply appear as meteors (shooting stars). A few, though, survive passage through Earth’s atmosphere to strike the ground. These are meteorites. The larger the meteorite, the bigger the explosion when it hits the ground, and the bigger the crater. Earth has plenty of craters.

But, the Tunguska event shows signs of an atmospheric explosion, not a crater. There have been numerous attempts to find a crater, but so far all have been fruitless. At present, there are still a few claims that have yet to be evaluated by the scientific community, but most today feel that there is no crater. So, how could something so big hit Earth and not leave a crater? Well, it obviously had to be something that did not make it to the ground. So, what could that be?

One of the early contenders was that it may have been something that would not survive the high temperature and pressure of passing through the Earth’s atmosphere. A comet was suggested as fitting the bill. After all, comets are icy bodies, so they would tend to vaporize during entry into Earth’s atmosphere. Of course, it would have to be a smaller body than most comets, so perhaps it was a piece of a comet that had broken off. An likely parent body was even postulated: Encke’s Comet. Comet Encke was known to shed pieces now and then. And, Encke’s Comet comes close to Earth. In fact, in June, Earth is quite near the comet’s orbit, passing through a swarm of debris shed by the comet. This debris gives us the Beta Taurid Meteors, which peak in late June and early July. Furthermore, the bodies approach Earth from the daylight side of the planet, not unlike the object that created the blast. However, this hypothesis has gradually fallen into disfavor.

The top hypothesis today is that a stony asteroid was the progenitor of the Tunguska blast.  But, how can a huge chunk of rock not make it through the atmosphere?  Well, remember the asteroid Itokawa.   That is an example of a rocky asteroid that is not a solid chunk of rock.  It is at best a pile of rubble.  Such a body would hit the atmosphere moving at dozens of kilometers per second and shatter into billions and billions of pieces from the shock of the sudden deceleration.  Those pieces would separate, the debris would pancake, and the air in front of the body would be compressed and heated into a great fireball.  The energy released by the ensuing explosion would be huge.  For a body of only tens of meters across, the resulting explosion could easily be equivalent to that of a hydrogen bomb.  Even for a fairly solid rock, the stress of hitting the atmosphere would be an awful lot to stand.  For rocky bodies, the tiny ones burn up.  The small ones make it to the ground as meteorites.  The medium sized ones blow up in the atmosphere.  The large ones, miles across, would probably make it to the ground.   Favoring the asteroid hypothesis is dust found at the impact site consistent with the composition of asteroids.

So, both the asteroid and comet hypotheses are still alive, but the scientific community is leaning heavily towards an asteroid, based on the evidence currently available.  Also, Earth crossing asteroids in that size range are very common.  Comets or comet fragments of the right size are quite rare by comparison.

But, just how big was the explosion?  For many years, I had heard estimates of about the equivalent of 25 megatons of TNT.  But, in recent years, the estimate had dropped considerably, with about 12 MT being about average.  There have been suggestions that the trees of the area were easier to knock over than had been thought, and so the blast damage was overestimated.   I have heard estimates of blast strength as low as about 3 MT.  That is about what you’d expect from a hydrogen bomb.  This happened a century ago.  But, there is a reason to try to nail down the size of the blast beyond simple curiosity.  The smaller the blast, the smaller the body that caused it.  And, there are a lot more small bodies flying around than large ones.  So, knowing the size of the body responsible for the blast gives us an idea of how likely it is happen again anytime soon.

Estimating the size of the body causing the explosion is difficult.  For one thing, we don’t know how big the blast really was.  For another, we don’t know how fast the impacting body was moving.  Recently, we’ve been able to compute the atmospheric effects far better, and that suggests a much smaller body may have been responsible than had generally been assumed.  If so, then the risk of another Tunguska event goes up.  The smallest bodies that I’ve seen proposed are believed to strike Earth perhaps once every couple hundred years.  Now, that doesn’t mean that we are safe for another hundred years.  Ask the people in Iowa that have had their second hundred year flood in under two decades.  A hundred year flood simply means a 1% chance of flooding each year.  A once every couple hundred year chance of impact really means is that there is a 0.5% chance of impact each year.  Of course, I’ve heard other estimates that were far more comforting, such as a chance of impact once every thousand years or so (about a 0.1% per year).

Over the years, of course, there have been far wilder suggestions of what caused the impact, ranging from a miniature black hole to a chunk of antimatter.  And, there have been suggestions of non-natural causes, too, such as a crashing flying saucer or a scientific experiment gone awry.  But, the simplest and far most likely scenario is of an impact by an asteroid or comet.

-Astroprof

Images courtesy Wikimedia Commons