In the constellation Perseus, the star having Bayer designation Beta Persei is called Algol.  This is a shortened form of the original Arabic Al Ra’s al Ghul, or “the head of the demon.”  Needless to say, this star is often called “the demon star.”  Interestingly enough, Pliny regards this star as the head of the Medusa, the Gorgon killed by the Greek hero Perseus.  The Hebrews called this star Rosh ha Satan, Satan’s head.  It isn’t really surprising that multiple eastern Mediterranean cultures would have similar names for a star, since they all talked to one another.  What is surprising, though, is that the Chinese called this star Tseih She, meaning “the piled up corpses.”  Hmm.  So, what is so terrible about this star that has everyone thinking ill of it?

We don’t really know for sure what the ancients were thinking.  However, we do know that this star is one of only a handful of naked-eye variable stars.  Normally, Algol is the second brightest star in Perseus, shining with magnitude of 2.1.  However, every 2.87 days, Algol dims to be the sixth or seventh brightest star, at magnitude 3.4.  This dimming actually takes hours, but it is most obvious to the naked eye about an hour or so before or after the minimum brightness.  The actual period between minima is about 68 hours, 48 minutes, and 56 seconds.  To the ancients, who regarded the stars as fixed and unchanging, it would have been an ill omen when a star began to fade like this.  Hence, it is the eye in the head of the Medusa, or even the eye of the Devil himself. 

The variable nature of Algol is not directly reported in ancient texts.  By the Middle Ages, people seem to have forgotten it.  The first report of Algol’s variable nature seems to be that of Geminiano Montanari of Bologna in 1667.  He reported that about every three days, Algol seemed dimmer.  John Goodricke, an astronomer noted for his many contributions to the area of variable star astronomy, reported in 1782 that the variation in brightness was regular and always of equal magnitude.  He proposed that perhaps Algol was composed of two stars too close together to be seen as a single star that passed in front of one another on a regular basis.  This, in fact, is exactly what is happening with Algol.  A dimmer star periodically moves in front of a brighter star, making the pair seem to become much dimmer.  Midway between the minima, there is a very small dip in brightness as the brighter star passes in front of the dimmer one.  This secondary minimum is far too little of change to be reliably observed with the naked eye.  Binary stars whose orbits block one another from our view are called eclipsing binaries.  Algol is sort of the prototype of this class of variable star.

Algol is about 92 lightyears away from us.  The primary star is a spectral type B star.  This is an unusually hot and bright star.  The dimmer companion was always lost in the light of the primary star.  However, in 1978 astronomers at McDonald Observatory, located in the Davis Mountains in west Texas, managed to isolate the spectrum of the dimmer companion.  The companion star is a late G type subgiant star.  A subgiant star is one that has ended its life on the Main Sequence and is dying.  Algol thus consists of a physically large cool star of mass less than the mass of the Sun orbiting a hot main sequence star of several times the mass of the Sun.  This is a problem in that the more massive stars are supposed to die before the less massive ones.  So, what gives?  The famous astronomer Fred Hoyle gave us the answer.  He suggested that the two stars are very close together.  We know this to be true. When the more massive star began to die, it began to expand.  Again, we know this happens with stars.  Well, in a binary star system, there exists a point between the two stars where each star’s gravity pulls equally.  To one side or the other of this point, and one star will dominate.  Well, when the dying star expanded to the point that its outer edges reached this point, then it began to lose mass to the lower mass star.  Eventually, the high mass star lost most of its mass.  The formerly low mass star then became hotter and brighter.  The formerly high mass star was left with less mass than its companion, but it was still dying, so it was still a distended object.  We, therefore, call a star like Algol a semi-detached binary star.  The dying companion is still losing some mass to what is now the primary star.  The orientation of the orbits of these two stars means that the secondary does not completely cover the primary star during eclipse.  Rather, about 21% or so of the primary is still visible during maximum eclipse.  The secondary star is still a couple times brighter than our Sun, so that gives an idea of just how bright the primary star is.

Algol is obviously a binary star.  However, by the middle of the 20^th Century, it had become clear that that wasn’t the whole story.  As it turns out, there is a third star to Algol!  This third star orbits some 50 million miles from the other two, in a different plane.  This star, also a star hotter and more massive than our Sun, never blocks our view of the other stars.  This is about the only way that a triple star system could be stable:  two stars orbiting very close together with one much farther out orbiting the other pair.  Another example of a star like this is Alpha Centauri, where there are two stars orbiting close together and one more much farther out.

Interestingly enough, Algol is not the only naked-eye variable in Perseus.  Right near Algol in the sky is the star Rho Persei.  As it turns out, Rho Persei is also a variable star.  Rho Persei is what we call a semi-regular variable, meaning that it varies, but without a clear cut pattern.  Also, Rho Persei only varies by 0.7 magnitudes over several months, so it is hard to notice its variation with the naked eye.

For those of you who want to see Algol, you’ll either have to stay up really late, get up really early, or wait until later this summer.

-Astroprof

Fifty years ago, the award winning classic science fiction movie Forbidden Planet was released.  The movie predates me, but I did get to see it on television when I was young.

I have always rather enjoyed science fiction.  Growing up, I used to watch scifi movies on TV whenever I got a chance.  There was often one showing on Saturday afternoons, and for several years, there was a station that showed a scifi movie every Friday night.  There was also a station that showed movies every weekday afternoon, with one day per week set aside as science fiction day.  It was one of these afternoons, I think, that I first saw the movie.  It made an impression that stuck with me, so when the movie came out on DVD a few years back, I just had to get it.

For those of you who don’t know the movie, the screenplay for Forbidden Planet was written by Cyril Hume, the movie was directed by Fred Wilcox and produced by Nicholas Nayfack.  Forbidden Planet had an all star cast (or least a cast that were to be stars) including Walter Pidgeon, Leslie Nielson, Richard Anderson, and Anne Francis.

In the annals of science fiction films, this movie is a giant.  It is a well thought out story with several sub-plots running.  The movie has the sort of optimistic American ideals of the 1950’s and elements of the sort of fear of technology of that era.  The movie also had a fairly sophisticated commentary on the state of humanity.  Even the dialogue is good.  For the 1950’s, the special effects were stupendous.  Personally, I don’t think that any special effects equaled those of Forbidden Planet until Star Wars in the 1977.  I showed this movie one night to the students of our astronomy club when it was too cloudy to go outside.  The story is still good, and the special effects even hold up today, though they don’t look quite as sophisticated as we are used to seeing now-a-days.  Several of the plot devices and ideas formed the basis of much of what we have come to think of as standard ideas in science fiction.  You can see the legacy of Forbidden Planet in Star Wars, Star Trek, and all sorts of other stories.

The story of the movie is loosely based on Shakespeare’s The Tempest.  The story starts with an interplanetary flying saucer from Earth coming to investigate why an expedition to the planet Alair-IV has apparently vanished.  This saucer is part of a galactic space quasi-military space fleet (similar to Star Fleet).  The captain and crew land on the planet, ignoring a broadcast warning that to land was to face great danger.  Upon landing, a robot named Robby meets them and takes the captain, Commander Adams, and the ship’s doctor to meet the sole surviving member of the expedition, a man named Morbius.  There they find Morbius living with his daughter Altaria and their robotic servant, Robby.  Morbius claims that the original expedition had been killed by some sort of creature that for some reason has left him and his daughter alone for all these years.  Morbius claims to have found knowledge left over from an ancient civilization that used to live on the planet.  Commander Adams wants to take them back to Earth, but Morbius refuses, so Adams decides to use parts of his spaceship to fabricate an interstellar communication system to report home and get orders to deal with the situation.  Soon, somehow the communicator is sabotaged.  Adams suspects Morbius, but there is no proof.  Eventually, a crewmember is gruesomely killed, and Adams heads to Morbius’ residence to demand answers.  There, he and the doctor find that Morbius has discovered found actual working artifacts of the ancient beings called the Krel.  They had a teaching tool that had taught him how to build Robby the robot.  Underneath the Morbius residence is a massive Krel facility that goes on for miles and miles.  It has been self sustaining and self repairing for millennia, though even Morbius has no idea what it does for sure.  He suspects that the Krel were on the verge of developing a technology that would do all their work for them with just a thought.  Adams and the doctor are impressed, but this does not help explain the loss of a crewmember.  They go back to the spaceship where disintegrator cannon have been set up to protect the ship and crew.  That night, a giant invisible monster attacks.  The monster seems to resist their every weapon, and then it suddenly disappears.  Decades later, I still had an image of the giant creature caught in the disintegrator beams where it became sort of visible.  The special effects are obviously animation by hand drawing, but it still gives me a chill when I see it.  Adams and the doctor go back to the Morbius residence, where they confront Morbius again.  While Adams and Morbius argue, the doctor gets his brain boosted in the Krel machine, and he realizes the monster is actually a creature created by Morbius’ subconscious mind.  The giant Krel machine had created it in response to Morbius’ subconscious (the Freudian id) desire to put an end to the people who disagreed with his wishes.  Eventually his own daughter disobeys him and challenges him, and his Id Monster attacks.  He eventually sacrifices himself to save his daughter.  Adams takes Altaria and they leave for Earth.  Their last act was to set the self destruct on the giant Krel machine.

Robby the robot is interesting in that he had built in programming that prohibited him from harming any human being.  This predates Asimov’s laws of robotics.  As I suggested, the Earth saucer is reminiscent of the Star Trek, with an organization like Star Fleet, and an intrepid captain and doctor rushing off into danger (though no Vulcan science officer!).  The disintegrator ray guns seem to work a lot like phasers.  Scenes of the Krel machine are seen in other science fiction movies and shows that follow, and they bear some resemblance to scenes in the interior of the Death Star in Star Wars.  There are even force fields like seen in Lost in Space.

There are a couple of interesting commentaries here, as well.  One, of course, which was a common theme in science fiction in the 1950’s and 1960’s was taking a shot at technology.  Frequently in these movies some technological advance gets out of control and everyone is in peril.  In Forbidden Planet, at least, the technology is rather neutral.  It is the use of the technology that gets everyone in trouble.  In many of these movies, some technological or scientific advance is made without any regard for its moral consequences.  Here, the Krel machine was designed with the high and noble goals of freeing the peaceful Krel from work so that they could concentrate on learning, poetry, art, and such.  The problem was their baser instincts that the machine keyed on, and the Krel wound up killing themselves off.  Then, when Morbius came to be connected with the machine, anyone crossing him got killed.  The commentary here is that we all have a selfish and brutal side to us that we must keep under control.  In Star Wars terms, we can all be tempted to the dark side.  Again, this is a little different from other movies of the era, where some mad scientist is totally immoral.  Here Morbius is essentially a good and caring person who would never consciously harm anyone.  His subconscious, though, wishes harm to those who challenge him. 

The movie is very interesting and thought provoking, and it deserves to be a classic.  I think that even people who don’t normally like science fiction would find something of value here.  If you haven’t seen Forbidden Planet, then you should!  It is well worth your time.

-Astroprof

I have always liked going to a planetarium.  Growing up, trips to the planetarium allowed me to learn the night sky in a way that I could not have otherwise done.  A knowledgeable person would point out stars and constellations on the dome of the planetarium, time could be sped up and slowed down to see the motions of the planets, and you could see what the sky would look like without light pollution (something that growing up in Houston, Texas, was hard to fathom).  So, I thought that perhaps a planetarium blog entry might be in order.

First of all, since I wanted to talk about more than one planetarium, I figured that it would be useful to know the plural of the word.  The word obviously comes from Latin, and having had several years of Latin, I knew that the plural should be “planetaria,” if normal Latin conventions are used.  However, I often have also heard “planetariums” used as the plural of the word.  So, I naturally decided to look in the dictionary.  Much to my consternation, I find that both words are listed as the plural of planetarium!  Now, if that isn’t silly.  Microsoft Word seems to think that the plural is planetariums, but the majority of people that I personally know who are in the planetarium field (planetarians, they call themselves) use planetaria as the plural.  Since planetaria also fits with my own reasoning from knowing the Latin root of the word, that is what I will use.

So, now that we have the grammar down, what exactly is a planetarium?  Put simply, a planetarium is a device that shows what the sky looks like.  Planetaria in some form have been around since ancient times.  We don’t know who came up with the first one, but there are stories that the Arabs used to have tents with small holes punched through the material.  Inside, the tent during the daytime, you’d see a representation of the night sky.  There were also devices such as astrolabes that could be used to show the relative orientation of stars, the Sun, Moon, etc in the sky at different times of the day.  One might think of these as handheld planetaria.  A more modern version of this would be software that lets you see on your computer screen what the sky would look like at night.  This is universally called “planetarium software.”  Interestingly, many modern planetarium projectors use computers to drive them, and the software so used is also called planetarium software, even though it only superficially resembles the planetarium software that shows visualizations of the sky.  Personally, I use planetarium software on both my desktop computer and on a laptop that I can take into the field.  Also, I have planetarium software on a PDA that has turned into one of the most useful programs that I have ever put on that device.  Anyone who plans on going out observing, especially any amateur, should think about putting planetarium software on a PDA (if you’ve got a PDA, that is!).  You would not believe how often that you use it if it is available.

Related to a planetarium is an orrery.  Most of you have probably seen an orrery, but had no idea what it was called.  An orrery is, simply put, a model of the Solar System.  It usually has the Sun in the middle, and the planets positioned in their proper positions around the Sun.  The planets can then be repositioned to show their motion around the Sun.  A mechanical orrery has gears and motors to move the planets about in the proper speed.  So, an orrery would be a sort of working model of the Solar System.  I have seen some very complex ones that even had moons around the various planets.  A few that I’ve seen have even incorporated projectors to shine the relative planetary positions onto a screen.  That makes such an orrery very close to a planetarium.

But, what I really wanted to talk about was not planetarium software, but rather what I think of as actual planetaria:  i.e. planetarium projectors inside specially built buildings.  This is what I think of as a planetarium.  There is a certain mystic to the large domed room with the strange machine in its middle.  I don’t know how long such planetaria have existed.  The first large precision planetaria seem to date to early in the Twentieth Century, with the construction of such a device by Carl Zeiss in 1924.  I have heard that less sophisticated devices existed before that, but for now we’ll just attribute the first modern planetarium device to Zeiss.  Essentially, such a device is a powerful lamp situated inside a hollow ball.  The ball has holes drilled in its surface to represent stars.  The larger the stars, the larger the hole is drilled.  This star ball is then place inside a room with a domed ceiling.  However, the star ball is very expensive to make.  It can’t be done on an assembly line, so it must be done one at a time by a craftsman.  Also, drilling precision holes in a spherical shape is quite difficult and time consuming.  Until the invention of computer controlled machining, even a template was not possible.  So, that made construction of the planetarium ball very expensive.  Also, you can’t drill holes for planets on a ball like that since they move around.  That meant that in addition to the large star ball, the planetarium projector also needed a separate mechanism to show the planets.  This usually consists of a light source and a set of individually controlled mirrors.  The mirrors are geared to turn together, much in the way that the orrery works, projecting a dot onto the planetarium ceiling at the proper place to represent the planet.  But, since the planet projector is not on the star ball itself, the positions of the planets will be slightly off.  This effect is minimized by making sure that the ceiling onto which the stars and planets are projected is located many times the diameter of the ball away from the projector itself.  Also, the image on the ceiling will be misshapen to an observer sitting far from the star projector.  These are known issues, so a well designed planetarium has the seating clustered near the star ball in the center of the room.  Planetaria designed as public theaters, though, often cram as many seats as possible into the space, resulting in a poor view for anyone not near the center of the theater. 

The Zeiss planetaria were a fantastic success.  However, they were quite expensive, so only a few were built.  These were associated with major museums in large cities, and even then they could only be built if some generous benefactor donated a large sum of money to the museum to build the planetarium.  Armand Spitz, an amateur astronomer and astronomy populizer, decided to design a less expensive planetarium that would be affordable to colleges, schools, and smaller museums.    Spitz was convinced that a planetarium could be used as a fantastic tool for education.  He developed a design for a planetarium projector consisting of a dodecahedral ball of flat plates.  The ball looked sort of funny, but the holes for the stars drilled in the flat plates were easy to produce from a template.  This cut down costs.  This new planetarium design eventually took off, and these smaller, less expensive, planetaria started popping up all over the country.  His company still exists, but they eventually switched production to the more traditional spherical star ball.  A college that I used to teach at had a planetarium with a Spitz projector.  It was absolutely wonderful to teach astronomy using a planetarium.

Of course, technology has continued to advance.  It is now possible to have a computer screen and a fish-eye lens that can project onto the dome of the planetarium anything that is shown on the screen.  This has some advantages over the old star ball.  For one thing, the star ball is limited to showing what the sky looks like from Earth (Granted, if you know how to use it, then you can show the sky from anywhere on Earth, any day, any time of day, any year, and I have done this.).  The computer screen can show the sky from anywhere in the universe that the computer has enough data to generate a sky view.  You can even simulate “flying” from one star system to another.  You can also highlight and zoom in on certain things, something not possible with the star ball projector.  One disadvantage, though, is that for most of the computer generated views, the stars don’t quite look right.  For one thing, to make a brighter star, these projectors usually use bigger dots (especially the earlier ones).  In the sky, the stars all look the same size, just different brightness.  This is more what the sky looks like using a star ball.  Still, the more modern computerized projectors seem to be overcoming this limitation.

While I normally think of the planetarium as a place to see the stars, you can do more with it.  Basically the planetarium building is a room with a high domed ceiling.  The ceiling is reflective so that you can see the stars better, and this makes the entire ceiling basically a giant projection screen.  So, you can also show movies and slide shows in the planetarium.  It also is a place where you can see laser shows.  Sadly, these seem to be more common uses than showing the sky.  The last few planetarium shows that I have been to didn’t even really mention the stars on the ceiling one time all during the show!  In fact, the shows were little more than fancy slide shows with some cool narration.  This misses out on the entire reason for having a planetarium in the first place!!!!   

The other problem seems to be that most planetarium shows produced now-a-days seem aimed at elementary school kids.  While I have no problem with planetarium shows aimed at young children, and I believe that it is essential to get them interested in science early on, I also think that it is a mistake to only aim at the young ones.  We are losing children from the sciences in middle and high school.  When asked why they didn’t want to study science, a group of high school students a few years ago replied that it was because they thought that science was boring, irrelevant, and only for kids.  Clearly something is horribly wrong here.  I can’t imagine anything less boring.  I see science involved in all aspects of my life, so it is far from irrelevant.  And as for being only for kids, I guess that I am young at heart, but still … .  So, perhaps we should have some of these programs aimed at middle and high school, and even some aimed at adults.  I think that we are missing out here.

I wish that we had a planetarium at my college so that I could put together some planetarium shows that used the unique capabilities of the planetarium projector and the planetarium experience.  Alas, planetaria are still expensive to build and to maintain, so we aren’t likely to get one anytime soon (if ever).

Several movies have scenes where the key figures are exposed to a vacuum for some period of time with apparently no ill effects.  2001, A Space Odyssey has our hero doing several seconds of unprotected space walking. The Hitchhiker’s Guide to the Galaxy has our heroes tossed into space without spacesuits, only to be rescued seconds later.  And, the lead character in Sudden Recall is suddenly exposed to the Martian atmosphere, which is nearly a vacuum.  All survived.  How realistic is this?  How would we know how the human body really reacts in space?

Well, it turns out that we do have a pretty good idea what happens to a human body in a vacuum.  We can get a pretty good estimate of what would occur from looking at divers who suddenly depressurize from depth to one atmosphere.  All sorts of bad things can happen.  But, we have an even better model.  Animals, and humans, actually have been exposed to vacuum conditions, so we have first hand data.

In the earliest days of spaceflight, the space agencies considered the possibility of a breach in the integrity of a spacecraft to be a very real possibility.  It still is, but is now thought to be much less likely than it was then.   Naturally, there was concern about what would happen to the astronaut.  Everyone knew that you’d die without air, but the question was whether or not a human could live long enough to put on a spacesuit’s helmet, or to close the visor if the helmet were already in place.  If a spacesuit were punctured on a spacewalk, how long would an astronaut’s companion have to get him to the safety of a pressurized spacecraft?  These were questions that animals helped to answer.  Personally, while I agree that the answers to the question are important, I don’t think that I could ever purposefully do that to an animal.  Nor, would I want to be anywhere around before, during, or after the experiment. 

In addition to animal tests, there have been human tests for exposure to very low pressures, such as those experienced by the sudden decompression in a high altitude aircraft.  Extrapolation of these test results lets us figure what may happen with no pressure rather than low pressure.  And, there have been accidents.  Humans have accidentally been exposed to vacuum, or to pressures so low as to be effectively vacuum as far as human physical responses go. 

An actual human exposure accident occurred during the early tests for Apollo at the Johnson Space Center in Houston.  JSC has several vacuum chambers, with at least two large enough for humans to work and move about in while in a vacuum.  These chambers not only operate at a vacuum, but they also have lights, heat lamps, and chilling coils to simulate both thermal and radiation conditions experienced in space.    In one space simulation in 1966, a technician at the Manned Spacecraft Center in Houston (later it was renamed the Johnson Space Center) was testing a spacesuit in such a vacuum chamber.  The suit tore and rapidly depressurized.  An emergency repressurization procedure was initiated and the subject was rescued by medical personnel standing by for just such an emergency.  The technician was exposed to vacuum and low pressure conditions for under a minute, and though he has severe problems at the time and shortly after, he eventually fully recovered.  Other accidents also occurred, not all of which resulted in survival of the victim.  Still other incidents involved ruptures in pressure suits resulting in partial body decompression.  And, in 1971, Soyuz 11 had a failure resulting in sudden decompression during reentry.  The cosmonauts onboard did not survive.  Animal studies coupled with medical accounts (for the accident survivors) or autopsy reports (for those that did not survive) give us a pretty good idea of how the human body responds to vacuum exposure.  These incidents, though, were accidental, and were not carefully controlled experiments, so the data is a bit incomplete in places.  Needless to say, there are few volunteers for controlled experiments detailing vacuum exposure!

So what does happen?  There has been all sorts of speculation by laymen and science fiction writers.  Many suggest that the victim will simply explode (after all it is called explosive decompression!).  Well, obviously this can’t be right, since some people survive!  There is also speculation that the victim’s blood would boil.  This, too, did not happen with the technician in Houston, nor with many of the animals.  Why would this speculation even occur, though?  Doesn’t water boil at 100C?  Yes, and no.  As pressure drops, the boiling point of water drops.  At sufficiently low pressure, the boiling point drops all the way to freezing, and water exists only as a solid or a gas.  The atmospheric pressure on Mars is this low!  However, remember that you are a fairly sealed system.  So, unless something bad happens (which I’ll mention later), even if the pressure outside your body drops, then the pressure inside your body should remain high enough (at least on the arterial side of the circulatory system) to just avoid your blood boiling. 

But what does happen?  Well, it isn’t really pretty, but here is a synopsis of what I gather is likely to occur, based on studies human and animal vacuum exposure.  First, it depends upon how quickly the lungs empty.  If the victim is smart enough to quickly exhale, then massive internal injuries can be prevented.  On the other hand, if the victim tries to hold his breath, or has some sort of airway obstruction, then the lung tissues can rupture, spilling air into the body cavities.  This causes massive system failure, and the victim, if holding his breath, can no longer hold his breath.  The rapid reduction in pressure in the lungs now results in reduction of pressure within the body, and bodily fluids do begin to boil.  Such an event is always fatal, even if pressure is rapidly returned to normal. 

If the victim exhales, though, then several things happen.  First to occur is that there is no air for the blood to exchange oxygen and carbon dioxide with.  In fact, worse than no air, the blood flow through the lungs can even lose oxygen to space!  This can occur only for about 10 to 15 seconds with a human before loss of consciousness.  Hypoxia and impaired judgment begin to occur within about 7 or 8 seconds, though.  So, anything the victim must do to save himself must be instinctive, and drilled and trained to the point of being nearly automatic, without much thought.  Given the surprise factor likely in a sudden accident, there may be only five seconds or so to react.  If exposed to sudden explosive decompression, the victim must remember to exhale at once.  This must be automatic and drilled into the subject.  There are only a couple of seconds before serious, and often irreversible, damage to the lungs occurs.  The 1966 accident victim at the Manned Spaceflight Center remembered to exhale.  He did report the rather strange feeling that occurred as water in the saliva on his tongue began to boil.  A more serious problem is that water on the surface of the eye also begins to boil, drying the eye, resulting in severe pain almost immediately.  Hypoxia results in loss of vision after 10 seconds or so.  This loss of vision often remains for a while after the victim is returned to atmospheric pressure. 

The external pressure on the body is suddenly released, and this causes pressure in the soft tissues to fall, resulting in some water vapor forming in those tissues.  This water vapor then presses on the veins, increasing pressure.  The water vapor also causes the tissues to distend, swelling to nearly double their normal size.  The body appears bloated.  Some capillaries can rupture, causing bruising.  In an incident on a high altitude balloon flight, a glove lost pressure.  The pilot’s hand became bloated and he experienced great pain.  After several seconds, the hand became useless.  In another incident, a potentially fatal accident occurred during a spacewalk on STS-37.  During this mission, the astronaut punched a tiny hole in the hand of his spacesuit.  However, the pressure in is spacesuit pressed his hand against the hole.  The vacuum at this hole caused tiny ruptures below the skin, and his blood actually clotted to seal the edges of the hole to his flesh.  Upon returning to the shuttle, he had a small, very red, and very painful lesion on his hand.  He was quite fortunate.

As a response to loss of oxygen in the blood, the heart begins to beat very rapidly, as if the victim were doing heavy exercise.  However, there is no oxygen to get.  Eventually, the heart beat slows, and with the slowing heart, the blood pressure drops.  When the blood pressure on the arterial side of the circulatory system drops to equal that on the venous side, then blood no longer will flow.  After about 45 seconds or so, effective circulation stops, even though the heart continues to pump.  The body goes into convulsions shortly after cessation of consciousness, then paralysis sets in.  Starved for oxygen the heart itself stops after 60 to 90 seconds, though some reports report fibrillation beginning prior to the time that it stops beating, sometimes even during the first minute of exposure.  A second set of convulsions hits at the end, then the heart stops.  To my knowledge, no subject has ever survived this point, even if oxygen is immediately restored.  In some animal studies, sometimes, distension of the stomach can press on the diaphragm, compressing the thoracic cavity, causing heart fibrillation or cardiac arrest prematurely.  None survived this event, either.

So, if you are ever in a spacecraft or a spacesuit, and you suddenly experience explosive decompression, then you need to remember at once to exhale, then you need to position yourself for assistance.  You’ve only got seconds before you are helpless.  Then, you just have to hope and pray that someone gets you back into pressure within a minute or so.  Subjects who manage to avoid some of the more unpleasant events above seem to achieve a complete recovery if they get oxygen again within 45 to 60 seconds.

So, that is what happens to a human body in a vacuum.

-Astroprof