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Holy Legends - I've heard several legends about the Holy Grail, and I was wondering if there's any evidence of an actual Holy Grail. If there is, that what can it do? Can it grant immortal life like in "Indiana Jones and the Last Crusade?"

It seems likely that there was once a "Holy Grail." Despite some naysayers there seems to be good evidence of the existence of Jesus of Nazareth and a Passover supper attended by him and his disciples just before his crucifixion. It was at this dinner that the sacrament of communion was established using wine and bread. Wine certainly implies that a cup was used (though perhaps a larger communal one - more like a bowl - than we might normally think of a cup today).

After that, though, the story gets a very fuzzy. There is not much in the Bible about a Grail and there is no real significance attached to the cup in that holy set of scripture. Most of the legend of the Grail seems to be connected with an individual named Joseph of Arimathea. Joseph was a rich, follower of Jesus that took possession of his body after the crucifixion. With the help of another follower named Nicodemus, he prepared the body of Jesus to be placed in his own (Joseph's) tomb. During this process, the legend says that he used the grail to catch some of Jesus's blood.

However, the story about Joseph of Arimathea and the Grail doesn't appear in any document we know about until the Robert de Boron wrote his poem Joseph d'Arimathe around the 12th century. The poem says that Joseph was imprisoned for his burial of Jesus's body and the Grail sustained him during this period. He later left the middle-east and traveled to Britain taking the Grail with him. From the Boron story came a whole wealth of Grail fictional literature emerged having to do with King Arthur and his knights and their seach for the Grail.

Boron's poem was clearly a work of fiction, but later writers seem to have taken it at face value. In a history of Glastonbury Abbey written around 1350 AD claims were made that Joseph came to Britain bringing the cup with him and it was at the Abbey.

As for the remarkable powers of the cup, one of the earliest references to this seems to be in the story of The Fisher King written by the French poet Chrétien de Troyes around 1190 AD. Here the Grail seems to have the strange power to keep people alive with them only eating a small mass-wafer (like they would serve during the sacrament of Holy Communion) a day as long as it is served in the cup. However, the Grail clearly does not have the full healing powers in this story as is often described in later tales.

The power of the Holy Grail to heal and give eternal life might actually be connected with pagan stories that pre-dated Christianity in Europe. In many of these stories special lakes or pools had the power to grant eternal life if one drank or bathed in them (One version of this story is the Fountain of Youth). As the myths evolved the pool changed into a bowl (symbolic of a pool) and this legend was later probably mixed with the legend of the Grail when Christianity was brought to Europe.

The Grail story has also been mixed in with the history of the Knights Templar, a order of knights sworn to protect pilgrams to the holy land. In the story the Knights find the Grail and transport it back to Europe. There is no historical record to support this story however.

Another completely separate story has the Grail left in the house of St Mark where the Last Supper took place. Mark then takes it to Rome where it was used as the Papal Chalice until it was moved out of Rome in 3rd century during a period of persecution. From there it went to a Spanish soldier and onto Spanish monks who hid it during the Muslim occupation of Spain during the 6th century. For a while it was held in the treasury of several Spanish Kings until it was given to the Cathedral of Valencia, where it remains today.

So is the Holy Grail actually in a church in Valencia, Spain? Some people might think so. However, there are a number of bowls that are reputed to be "the one, true grail." Another contender for the title is Nanteos Cup. For many years the cup was kept at the Nanteos Mansion near Aberystwyth in Wales. Legend connects this bowl with the story of the Grail held at Glastonbury Abbey. According to the story, monks fleeing Thomas Cromwell's persecution took the cup with them. The monks were hidden by the Powells at Nanteos. When the last monk died the bowl was passed to the Lord Powell and kept by the family ever since. An recent examination of the cup by experts, however, revealed that it is typical of mazer bowls, a type of medieval vessel, probably created in the 14th century - far too recent to be the real Grail. However, there are stories that people have been healed after drinking from the vessel and the current owner of the cup, Fiona Mirylees, still sends water that has been in the cup to people with life threatening illnesses.

When the script was written for Indiana Jones and the Last Crusade they combined many of these myths. Where is the real Grail? Well, I suspect that after the Last Supper everybody was so concerned with the events that followed that nobody bothered with the cup and it simply disappeared into the mists of history.

Big Birds of Death - Are there any real accounts of large birds of prey attacking or carrying off people? - Gary S.

As to the first part of your question, there are certainly examples of eagles and hawks attacking human beings that violated their territory. Get a little too close to a nest and you could find yourself on the wrong end of some very sharp talons. One sad example of this happened in Mendocino County, CA, in 1895. According to the New York Times two brothers, age 13 and 11, were climbing a mountain to find a Bald Eagle's nest when the creature suddenly attacked them. The boys escaped, but the younger was badly injured and lost his sight to the eagle's talons and beak.

However, the question about whether an eagle or other large bird has ever attacked a person (with the intent of eating them) and managed to fly off with them is a more complicated question. There are certainly a number of reports of large birds attacking and carrying off small children. For example, in August of 1881 the New York Times reported that an eagle with a seven-foot wingspan swooped down and tried to carry off a 2-year-old boy. Witnesses said that it might have succeeded if the child's clothes had not torn, allowing him to escape.

More recently in 1977 ten-year-old Marlon Lowe was playing with friends near his home in Illinois when two large birds - thought to be condors with wingspans from eight to ten feet across according to witnesses - swept down on the children. One of the birds picked up Marlon by the straps of his sleeveless shirt and carried him into the air. His screams brought his parents outside to see him lifted to the height of two feet for a distance of about 40 feet before the creature let him go.

In both of these accounts, the monster birds did not get far with their human burdens, but there are other stories where the avian giants were more successful. The best documented of these occurred in Leka, Norway, on June 5, 1932 when Svanhild Hansen, a five-year-old, forty-pound girl, was picked up by a huge eagle and carried more than a mile to a high ledge. She was found there safe and asleep by a rescue party. With the exception of a few scratches, she was unharmed. Zoologist Hartvig Huitfeldt-Kaas was so interested in the story he spent a month at the time investigating it and pronounced it "completely reliable."

There are also many less well document stories including the sad tale of five-year-old Marie Delex from the French Alps in 1838. The girl was playing with friends when she was picked up by a large eagle and carried away. The eagle's nest was checked, but only piles of goat and sheep bones were found. Two months later her horribly mutilated remains were discovered by a local shepherd on a rock several miles from where she had disappeared.

In May of 1904 the New York Times published the story of 18-month old girl in England that was apparently picked up by an eagle while she played just outside her parent's cottage door. Searchers at first assumed that the girl had been kidnapped, but a game warden found her body in a rocky crevasse at the crest of a hill. The girl's eyes had been plucked out and part of her cheek was missing.

Despite many stories though the years like these modern experts are skeptical. Mike Jacobson, an eagle management specialist for the U.S. Fish and Wildlife Service, has been quoted as saying, "There used to be stories about eagles carrying off babies and little kids, and none of that has ever been documented. They can pick up and carry four or five pounds, maximum, and actually fly off with it.They can lift a little more and hop it along, but they can't carry it off."

That's from a dead stop, however. An eagle already in motion can lift much more. "On a wide-open beach, I have no doubt that an eagle with a full head of steam could pick up a six- or eight-pound dog and just keep on going," says biologist and predatory bird expert Ronald Clarke. "If it landed to kill a ten-pounder, and then tried to pick up and fly from a dead stop, could it get off the ground? Probably not."

An eagle swooping down on animal on the side of mountain and then carrying it to a lower altitude, might be even able to carry more weight as such a maneuver requires only a downward glide (See a video of an eagle doing this with a small goat http://www.youtube.com/watch?v=r3n4qPpL8T0&feature=related).

Of course, there are always sightings of giant unknown birds - like those in the American Indian thunderbird legend - whose huge wingspans that might be able to carry very heavy loads. However, most experts doubt these stories, if for no other reason, then legions of bird watchers in the United States that could hardly miss noticing a bird with a twelve-foot-plus wingspan.

If not today, then scientists tell us that certainly in the past there were eagles and other large birds that could kill a child and fly away with them. The Haast's Eagle of New Zealand is only known from fossil remains, but it is estimated they weighed as much as 40 pounds and were still living at the time that New Zealand was first populated by humans about 750 years ago. The evidence about Haast's seems to match legendary stories told by Maori people of New Zealand about a bird so powerful it could sweep down and kill a small child. With a lift capacity of as much as ¾ of their weight, they could undoubtedly have flown off with the victim too.

Death Ray for Sale? - This is the link to "death ray tubes." These are a workable model of a death ray gun, you can buy it for 350 US$ and it works for carving rock. It does exist and as seen in the site united nuclear.. So are lots of other sci-fi inventions… And they do work too.. You get warnings to not direct them toward humans… They will melt... - Agnar Kiil

The "Death Ray" offered by United Nuclear, is not the death ray as was once envisioned by the mysterious inventor Nikola Tesla in the 1930's that has garnered so much press over the years. That weapon was better known as a charged particle beam. Tesla designed a device that would send a beam of particles out at high speed and saw it as a defensive weapon that would ensure peace. He claimed such a device would be able to "bring down a fleet of 10,000 enemy airplanes at a distance of 200 miles from a defending nation's border…"

Though no nations at the time acted on Tesla's idea, during the cold war both the Soviet Union and the United States experimented with charged particle weapons, but could not make them practical.

The "Death Ray" on the United Nuclear site is actually an infrared laser (Infrared means the light the laser is generating is of frequency too low to be visible to the human eye). Lasers, of course, have become common devices found in such everyday objects such as DVD players, supermarket checkout terminals and screen pointers. The ones offered by United Nuclear, of course, are of considerably more power. A laser pointer uses about 1 mill watt of power, where the United Nuclear infrared laser can be bought with a power supply of up to 100 watts. This is enough to cut thin metal and crack rock. Commercial sealed CO2 lasers, however, can often be found at powers of 3000 watts or more and can be used to cut carbon steel as thick as a ½ inch.

Even lasers with power levels less than a watt can be dangerous, however, if directed into a human eye. The light the laser puts out is "coherent" with all the light particles (or photons) going in the same direction, at the same frequency in the same phase. This results in the beam focusing a lot of energy into a very small space causing the target to heat up and burn or melt. Even a fairly low powered laser that enters an eye will be concentrated on the retina causing damage and potential blindness. For this reason engineers and scientists working with lasers always wear eye protection.

As powerful as lasers are, the military up to this point, has not found them to be effective weapons. The amount of power they require limits their mobility, especially compared with traditional weapons like bombs and rockets. Lasers have still been used on the battlefield, however, to guide traditional weapons to their targets. First a laser is pointed toward a target, say a tank. Then the laser light reflected back from the tank can be used to guide a rocket or bomb accurately to its destination.

The U.S. military has not completely given up on lasers, however, and has recently has some success with electric lasers that are small enough to fit into a truck and have an output of over 100 kilowatt. With this much power they hope they will be able to use them in the future to zap incoming rockets or mortars.

About the site itself: United Nuclear seems like a fascinating place to purchase off-beat science items and reminds me a lot of Edmund Scientific, a similar company in operation near where I grew up. Although Edmund is now only a catalog and web business, when I was in High School it had a showroom complete with a demonstration area for lasers and other cool science products. My high school science teacher advised us geeks that this was a good place to take a girl for a cheap date.

I see that United Nuclear has a showroom in Laingsburg, Michigan, and if anybody living in the area has a girl friend who is into death rays, it sounds like you might want to take her there for an inexpensive outing.

Dudleytown Hauntings - I was wondering what the Curator's thought was on the stories of the Dudleytown hauntings in Connecticut . Could Dudleytown be haunted by the spirits of the old town that once resided there? - Tim A.

I have to admit that I have no special knowledge of the Dudleytown legend. However, it is a fascinating story and thanks for suggesting we talk about it here in Ask the Curator. Let me go over the account so that anybody not familiar with the tale will know what we're talking about.

The legend of Dudleytown supposedly starts in 1510 when Edmund Dudley was beheaded for plotting to overthrow the King of England. The story has it that a curse was placed on his family. In 1747 brothers Abiel and Barzillai Dudley, supposedly Edmund's descendants, settled in the area giving the town its name. The location was too rocky and dark for farming so the town people made a business out of making charcoal from the abundant trees. The town prospered for while, but then, according to the legend, things turned bad.

As the story goes it all started when one of the Dudley brothers when insane. Then there were a series of unfortunate accidents and mysterious deaths. A woman was struck by lightning while sitting on her porch. People got sick, children disappeared and houses burned down. Finally, in despair, the villagers abandoned the town. Soon the dark woods closed in around it and now only the ever present owls inhabit the area. According to the legend most other animals avoid it.

So is the place really haunted? Well, if you talk to Dudleytown's neighbors they will tell you it is all a bunch of hokum and the legend has caused all kinds of problems for them. A number of years ago some of the property owners in the area formed an association - Dark Entry Forest, Inc. - purchased the land designated the location a nature preserve. For many years it was possible to visit the location without a problem. However, after the 1999 release of the movie The Blair Witch Project the area was inundated by thrill seeking teenagers and paranormal investigators. Now The Blair Witch Project was supposed to have taken place in Maryland, but the location in the film, a dark woods, was so similar to Dudleytown that people in Connecticut decided this local location was a good place to try and have a Blair Witch type adventure. The problems this caused - like late night drinking parties and theft from the historic ruins - forced Dark Entry Forest, Inc. to close the location to visitors.

(Dudleytown isn't the only historic site to have problems caused by it supposed haunted connections - See The Haunted Church of Gravity Hill )

Teenagers continued to find their way into the town, however. In one incident, perhaps even a little bit like the Blair Witch movie, a group of five teens found themselves so lost that at 1:30 in the morning they had to call 911 to get rescued. Fortunately, instead of losing their lives, as in the film, they each just got a $77 ticket from the Connecticut State Police for trespassing.

Some argue that the association is just trying to down play the ghostly history to avoid any more paranormal mayhem, but at least one author agrees with them that the legend is all bunk. The Rev. Gary P. Dudley, of Texas, became interested in the story because of the connection with his name. After researching the historical records he wrote The Legend of Dudleytown: Solving Legends through Genealogical and Historical Research (Heritage Books, 2001). In his book Dudley argues that most of the stories associated with the town are complete fiction or have been twisted to fit the legend. For example, the wife of Dr. William Clarke, who owned a vacation home on the site, supposedly went mad and killed herself when she was left alone there one night. Dudley found that Mrs. Clarke did indeed commit suicide, but that occurred in New York City, not in Dudleytown.

So is Dudleytown really haunted? Well, according to people who have visited the site the surrounding hills and heavy forest certainly make it dark and gloomy location worthy of a haunting. However, spooky places do not necessary mean there are spooks (Check The Science of Ghosts and Hauntings).

If you want to see what Rev. Dudley has to say about it, buy his book or visit his website at http://www.legendofdudleytown.com/

Earth: The Heat is On! - How can so much of the interior of the earth be hot molten lava, and have the ground stay around a cool 55 degrees? Why does the heat not work its way to the surface? Where's the convection? - John

The very center of the Earth is estimated to have a temperature of around 12,000°F. As you move outward from the center of the planet the temperature drops off till just below the outer crust of the Earth it is only about 1,202 to 2,192°F. All the rock below the crust is either molten or semi-molten and it does support a convection current with the hottest rock moving upward, losing its heat near the surface and then sinking back down. These convection currents are slow, but powerful and are responsible for the movement of the tectonic plates on the surface of the Earth. The movement of the plates, in turn, is responsible for such events earthquakes, tsunamis and volcanic eruptions.

As you note, the average underground temperature when you get about four feet or so underground runs about 50 to 55°F. It isn't hotter because the crust, which is almost completely a solid, acts like a thick insulating blanket. Because it is solid it does not support a convection current that would more easily bring heat energy to the surface.

Just because the average temperature near the surface is about 55, does not mean there are not spots where it isn't significantly lower or higher in temperature. For example, in locations where the crust is thick, or the surface temperature is consistently low, you can get a condition called permafrost. This is where the subsurface temperature is freezing even down to a depth of several hundred feet. We usually associate these regions with places near the poles, like Alaska, but permafrost can actually be found in lower latitude locations like the Suwaki cold anomaly in the north-eastern corner of Poland.

Where the crust is thinner, more heat escapes to the surface causing higher than average sub-surface temperatures. The crust tends to be thinnest under the sea, so much of the Earth's heat escapes into the oceans. Places where to tectonic plates join are also locations where heat can escape more easily. For example, the edge of the pacific plate is known as the famous "ring of fire" and is responsible for 75% of all the recorded volcanic activity. Some of the volcanoes involved include those from the coast of North America (including Mt. St. Helens and Mt. Rainer), Japan (Mt. Fuji), the Philippines (Mount Pinatubo) and New Guinea and Micronesian (Mount Tambora).

There are also "hotspots" where the crust thins and a molten rock plume comes very close to the surface. One of the most famous hotspots created the island chain of Hawaii, which has active volcanoes despite being in the middle of the Pacific plate. The world's most famous hotspot is probably Yellowstone where high subsurface temperatures cause spectacular phenomenon like hot springs, mud pots, steam vents and geysers. The subsurface temperatures at the Norris Geyser Basin at Yellowstone have been found to be as high as 401 °F at only a depth of 265 feet. Yellowstone is also one of the known locations of a "super volcano" which, when it erupts, can lay waste to continent sized regions.

Why to these hotspots exist? Scientists think that either upward flowing convection currents from deep within the earth melts and thins the crust in these locations, or the crust itself melts creating a convection current to carry heat to the surface.

Where does the Earth's internal heat come from in the first place? Some of it is residual heat from the planet's formation, but planet has also picked up kinetic energy from the impact of asteroids, including a collision with another planet-sized body that created the moon. However, about 80% of the all the heat is thought to come from the natural decay of certain radioactive isotopes found underground. Some scientists theorize that the center of the earth may even form a natural atomic reactor generating energy at the core of the planet.

Many Channels - Two Wires? - A cable vision wire for a TV only has two wires in it. But it can have over a hundred different signals(channels) coming through it at the same time, even more if you count the sound and picture as separate signals. How can all those different signals come through at the same time? - John.

This is really the same question for a number of similar problems: How can we have get signals from multiple radio stations all coming through the same airspace at the same time? How can we have multiple video channels on a single fiber optic cable? How can we hear different sounds at the same time with our ears? The answer in every case is because the information is coming at us as waves vibrating at different frequencies.

Let's take the simple case of two musical instruments: A tuba and a piccolo. A tuba produces long, waves of sound. We hear this as a low pitch. Because the waves are far apart they reach us less quickly than closer waves so we call this a low frequency (of waves).

A piccolo produces a high pitch which means it sends us shorter waves that come at us more often giving us a higher frequency.

If we could see these waves as they come to our ears we would see that they appear not as separate waves, but as two sets of waves piled on top of each other. However, our ears can easily separate the sounds by wavelength so we tell the tuba apart from the piccolo.

In the case of radio waves it is an electric field that carries the waves. Different radio stations operate at different frequencies and the electronics in the radio, like our ears do with sound, separate them so the radio tune into just one station while ignoring the other.

Now one caution here: radio waves are slightly different than sound waves because radio waves act as "carrier" waves that transport the information on them by changing the height of the waves (amplitude modulation or AM) or changing the frequency just slightly higher or lower (frequency modulation or FM). Because radio waves are used as carriers they transport all kinds of information on top of them including music, cell phone conversation, and video. Much of the information carried is now coded digitally on top of the signal, such as in the case of HDTV.

Whatever the information that is carried, at the bottom level it is still the fact that the waves are transmitted and received at different frequencies that allow them to be separated.

This is also the case with cable TV. The waves are transmitted through wires by electricity, but are very similar to the radio waves that move through the air. Your cable box sorts out the channels by frequency so you can then select one to appear on your TV.

In many places the older cable systems that depended on wire and electricity are now being replaced with fiber optic lines that carry light. What's the advantage? Well, light signals operate at higher frequencies than radio signals. This means more information can be carried on a fiber optic line allowing for more video channels.

What Makes a Dinosaur? - I read on your web site and came across some dinosaurs with descriptions elsewhere that said even though they lived in this [Mesozoic] Era and were marine reptiles or flying reptiles, they were still not considered dinosaurs. Can someone explain why?....and just as important, what exactly were they considered then if not dinosaurs? - Sydney L.

People tend to think that any reptile that lived during the Mesozoic Era qualifies as a dinosaur. However, dinosaurs actually have a pretty precise definition. The term "dinosaur" was created in 1842 by the famous zoologist Sir Richard Owen from the Greek words deinos meaning "terrible, powerful, wondrous" and sauros meaning "lizard." Owens also defined the characteristics of the basic taxon (or group).

Dinosaurs are part of a larger collection of reptiles called Archosaurs that include things like crocodiles and alligators. However, two things divide dinosaurs from all other archosaurs. First, they are by definition terrestrial. They lived on the land (so they did not include flying reptiles or aquatic reptiles). The second thing is that they have an upright gait. That is, their legs were straight, perpendicular to the ground and supported the weight of the body. This is a characteristic that they share with today's mammals and gives both groups the ability to walk or run more easily. Most other land reptiles (like lizards) have a sprawling gait with their legs out to the side and their feet not underneath their bodies.

The flying reptiles that lived at the same time as the dinosaurs include the huge Quetzalcoatlus, which with a wingspan exceeding thirty feet was the largest flying animal ever, and Rhamphorhynchus which had a long trailing tail with a diamond-shaped fin on the end. The flying reptiles, including these two, had their own group name: the Pterosaurs. (Note that there is also a species in the group called Pteranodon and you don't want to mix this up with the group name).

The aquatic reptiles that lived during the time of the dinosaurs included the famous Elasmosaurus, a type of plesiosaur with a long neck, saucer shaped body and four diamond shaped fins and the ichthyosaur Ophthalmosaurus, a dolphin shaped reptile that grew to a length of 18 feet. There is no overall name for this collection, except "ancient, extinct marine reptiles." However, most of these creatures fell into three groups, the mosasaurs, the ichthyosaurs and the plesiosaurs.

Interestingly enough, recent developments in understanding which animals are related to which may force the dinosaur group to include flying creatures. Evidence has been mounting that modern birds are descended from dinosaurs. Since under strict classification rules a group descended from another is included in the parent group, birds are dinosaurs and dinosaurs are not extinct (It is important to note, however, that the Pterosaurs are still not dinosaurs as they are not birds). Some scientists now refer to the original dinosaur group as "non-avian dinosaurs" and birds as "avian dinosaurs." This is somewhat clumsy, however, and in common speaking people still use the word dinosaurs to refer to the original group of extinct land reptiles that include the familiar species Stegosaurus, Triceratops, and Tyrannosaurus rex.

Silencing the Bang - How does a gun silencer stop the loud sound of a gunpowder explosion? - John

As exotic as a gun silencer (or to use the more official term "suppressor") seems, it really is very similar in many ways to something we see every day: a car muffler. Both were invented by Hiram Maxim in the beginning of the 20th century. Maxim was a clever inventor who also created the first modern machine gun and tried his hand at building flying machines.

In both cases a silencer or muffler needs to take a high pressure shock wave that to our ears is a loud "bang" and lower the pressure before it gets to us. This is done by allowing the gasses inside the gun barrel (or exhaust pipe in the case of a car) to expand in a closed container.

A basic silencer that is screwed on to the end of a gun can be as simple as a large, empty can with holes at each end to allow the bullet to pass through. As the bullet travels through the silencer, the gas behind it expands into the can and the pressure is lowered. More sophisticated silencers may also have "baffles" that further suppress the sound by adding additional smaller chambers near the final exit hole.

Some of these devices also utilize water, liquid, a gel or grease inside to cool the hot gases and which will further decrease the pressure and sound. This is an effective approach, but often these materials are partly vaporized each time the weapon is fired and must be replenished after a limited number of shots. Some disposable silencers are designed to only work for a handful for rounds before they lose their effectiveness.

While silencers can lower the sound of high pressure gas coming out of the barrel of a gun, there are other sounds a weapon makes that it has little effect on. In particular, if supersonic rounds are used the bullet will break the sound barrier with a loud crack after it leaves the front of the silencer. For this reason sub-sonic rounds are often used with silenced weapons, but this reduces the range and effectiveness of the bullet.

While we often picture silencers as always being screwed onto the end of a gun, some are built right into the weapon. Many are not as effective as often seen in the movies and may not even lower the volume of a gunshot enough that the marksman can avoid wearing hearing protection. However, in many cases it is not necessary to lower the sound of the shot as much as change the character of it so that it is not easily identifiable as a gunshot. In an urban setting this allows the sound of the shot to blend it with the ambient noise.

In many countries and jurisdictions silencers are highly regulated. They are legal to own in the United States in most places, but require an expensive permit.

Stars or Galaxies? - When I look up at the night sky, how many of those stars are really stars and how many are galaxies? - John

First, let's start with defining the difference between a star and a galaxy, for those not familiar with these terms. A star is a giant ball of hydrogen gas massive enough support a fusion process that generates heat and light. Our local example is the sun. There are also dimmer white and brown dwarf stars and these are usually stars that have burned off enough of their material that they can no longer really support fusion.

A galaxy is a group of stars bound together by their gravity. A galaxy often takes the shape of a flattened, rotating disc (left). The stars are pulled into arms that give the galaxy the appearance of a whirlpool when viewed from above. Not all galaxies have this shape. Scientists speculate that galaxies with other shapes may be the result of a collision between two galaxies. Galaxies typically are composed of billions of stars. Scientists all speculate that most galaxies may have a supermassive black hole at the very center.

On a good, dark night if your vision is exceptional, you might be able to spot some 2,500 stars in the sky with your unaided eyes. However, only a handful of galaxies can be seen without binoculars or a telescope. There is, of course our own galaxy (the Milky Way) and if you live in the Southern hemisphere you may be able to spot the large and small Magellanic Clouds. In addition if you know where to look you might be able to find the great Andromeda Galaxy (M31), the Triangulum Galaxy (M33) and the Centaurus A Galaxy (NGC5128).

That's at best six compared to twenty-five hundred. And not all of those galaxies can be seen from one location on the Earth.

That, of course, doesn't mean there are not a lot of galaxies in the sky. They are just mostly too dim to be seen without a telescope.

A related question might be, are there more stars in own galaxy that galaxies in the visible universe? Current estimates put the number of stars in the Milky Way Galaxy at around 100 billion. That's a lot, but it's only a drop in the bucket when compared to the estimated number of visible galaxies: Over seven trillion.

And that's, only those galaxies we can, in principal, see with our telescopes. There may be trillions beyond the reach of our current equipment. In fact, many astronomers suspect the universe, and the number of galaxies, is infinite.

It's the Hair, Not the Humidity - I have a thermometer hanging on the wall that also has a humidity gauge. The humidity gauge is just a round strip of metal. How can a strip of metal tell how much humidity is in the air? - John

Humidity is a measure of water vapor in the air. We usually refer to it as relative humidity as it is measured as a percentage of the maximum amount of vapor the air can hold. If the humidity reaches 100 percent, it is sure to start raining as the water in the air will condense into droplets.

The device you have there is probably a mechanical hygrometer. It's not really the metal that is doing the work, but a small bundle of human hair (chemically treated to remove any oil). Hair, being organic in nature absorbs water in the air and stretches (That's why bad hair days are usually those with high humidity).

If your mechanical hygrometer is like others I've seen there is a needle that points to the level of humidity. On the shaft that turns the needle there is one spring that is spiraled around it pulling he needle back toward zero. The shaft also has a chain (or possibly some inorganic thread) wrapped around it that goes from the shaft to the center of the hair bundle. Attached to the other side of the center of the hair bundle is another, more powerful spring. The two springs pull the mechanism in opposite directions. What actually controls the position of the needle is the length of the hair. As the hair lengthens a tiny bit, it deflects under the pull of the powerful spring, and this, in turn, pulls the chain to move the needle more toward 100%

This is hard to describe, so hopefully the attached diagram will help.

Moon's Strange Orbit - Does the moon revolve the Earth directly above equator? If yes, does it mean that people in upper northern hemisphere will be see it on the horizon? - Anonymous

Our moon, unlike most moons in our solar system, does not follow a path directly above its planet's equator. Instead, our moon follows an orbital path very much closer to Earth's ecliptic plane. Earth's ecliptic is the path Earth follows as it orbits the Sun.

The earth's equator is tilted off its ecliptic by a little more than 23 degrees. This angle is what gives us the seasons as the northern hemisphere is more tilted toward the sun during the summer and away from the sun in the winter (The opposite is true for the southern hemisphere where the seasons there are reversed).

This tilt also explains why the moon traces a different path across the sky depending on the season. Like the sun, during the winter it is closer to the horizon. In fact, further north than the Arctic Circle the moon will not be visible for 14 days at a time as it passes out of sight behind the tilt of our planet for half of its orbit. Or course when it does re-emerge it rises and stays up for fourteen days (The same is true at the Antarctic Circle).

The fact that the moon orbits close to the Earth's ecliptic plane has been used as evidence against the theory that the moon was created at the same time the Earth. In this theory, most of the spinning material in the region of Earth was pulled together by gravity to form our planet, but some of pulled together to form the moon. If that was the case, however, we would expect out moon to be orbiting along the equator. The current leading theory as to the creation of the moon is that a body the size of Mars hit Earth throwing massive amounts of material into orbit. Over the course of the next century this material was drawn together by gravity to form our moon.

Please how old is the Earth? Biblically it is accurately about 6042 to 7000 years and scientifically it counts on millions. Should we believe in God's wisdom or mere knowledge of man? - Cheta A

There has been a dispute going on in some circles between some biblical fundamentalists, who argue that science is wrong about the age of the planet because the Bible says that the Earth is only 10,000 years old; and some scientists who claim that the Bible must be inaccurate because clearly the Earth is millions of years old. There are, however, a number of people who hold the views that these differences are not irreconcilable. Though I am not a theologian, I will endeavor to give you the highlights of some of these ideas.

Age/Day View - One of the major reasons that science doesn't seem to match up with the Bible is the creation story in Genesis that seems make the universe and the earth appear in only 6 literal days. This view says that the days mentioned in Genesis are not 24 hour days, but "ages." These "ages" might have lasted millions of years or even billions of years and may have also overlapped. Though some critics argue that a "day" in this context in the Bible must only be 24-hours long, others argue that this alternate interpretation is not really inconsistent with some Biblical understandings of the word "day."

At least one author, Israeli physicist and Genesis scholar Gerald L. Schroeder, argues that depending how you define "time" these days could be both 24 hours and millions or billions of years long. For more information on this idea check out his book The Science of God: The Convergence of Scientific and Biblical Wisdom.

Mature Creation - Another view is that the Earth and Universe were created in seven days 10,000 years ago, but they have been given a whole consistent history of billions of years. This idea isn't really inconsistent with other parts of the Bible. For example, Adam is created as an adult man without the usual 20 years or so need to grow from baby to mature human under the usual laws of nature. Perhaps the earth and universe were also created in a relatively short amount of time without the 15 billion years that might normally be needed for such a process.

If you accept this view then for theological reasons the world is 10,000 years old, but for purposes of science the world is some 4.5 billion years.

Some argue that this seems somewhat disingenuous of God to create a false history. However, it isn't any more dishonest then creating Atom, calling him a man, though he never went through the normal human creation process. Indeed in our own poor attempts to create worlds and universes inside computers (i.e. video games like "The Sims") we always apply this method and it never seems dishonest to us within that context.

This isn't meant to be a complete discussion on the subject - just a starting point. Debates over this subject have already filled thousands of web pages, so I recommend you take a look at what has already been written about these ideas across the internet.

Vital Vitamins - What is a "vitamin", and how can sunlight make vitamin D? - John

A vitamin is an organic compound needed by a human or animal in tiny amounts in order to stay healthy. Usually a compound is only called a vitamin when the animal is unable to make it by itself, but must get it by eating it. This means that some compounds are vitamins for some animals but not really for others. For example, vitamin D is not really a vitamin in the human diet because we create it ourselves when sunlight hits our skin. It is a vitamin for most fish, however, who must get it by eating algae (Or by eating other fish who have eaten algae). The algae in turn create when they float in shallow waters under the sun.

For many years scientists suspected that certain foods contained tiny amounts of some substances needed for health, but they didn't know what those substances were. For example, in 1749, the Scottish surgeon James Lind discovered that citrus foods helped prevent scurvy, a particularly deadly disease often suffered by sailors who did not get fresh fruit in their diet. As it turns out the sailors were not getting vitamin C - otherwise known as ascorbic acid - which is found in the fruits. Though Lind didn't exactly know what the missing ingredient was, he recommended eating lemons and limes to avoid scurvy, an idea which was adopted by the British Royal Navy and led to their nickname "Limies".

In 1881, Russian doctor Nikolai Lunin did an experiment where he gave one group of mice milk and the other group an artificial mixture of all the separate parts of milk known at that time: proteins, fats, carbohydrates, and salts. The mice that got the regular milk were fine, but those which got just the parts got sick and died. This told Lunin that there was something in the milk that science was unaware of that was needed for the mice to stay healthy. The first scientist to extract one of these micronutrients was Japanese researcher Umetaro Suzuki in 1910. He named his discovery aberic acid. It would later become known as vitamin B1.

A couple more facts about vitamins:

-The world "vitamin" is a blend of the words "vital" and "amine" where amine is a specific sort of organic compound. However, as other vitamins were found, not all turned out to be amines, but the name stuck.

-Often an animals will have to eat the vitamins they need every day because their bodies will not store the vitamins for any length of time.

Vitamin D is produced photo-chemically when ultra-violet light interacts with the substance 7-dehydrocholesterol. In the case of humans the creation of the Vitamin D takes place in the epidermis, the top layer of our skin, when light from the sun penetrates it and hits the 7-dehydrocholesterol our bodies put there. How much and how quickly you make your Vitamin D depends on how much sun light you get and the color of your skin. People with darker skin produce it more slowly than people with lighter skin.

For mammals with fur, who can't get sunlight to their skin at all, the Vitamin D is synthesized in oily secretions that are deposited onto the fur. As those oils sit on the fur and are exposed to the sun, the vitamin D is created. The animal then must lick the oils off and swallow them to get the Vitamin D into their systems.

Glowing Arthropods - Why do scorpions fluoresce under a UV light? - Warren

This is a subject that scientists don't know a great deal about, but let's start with some basic facts. Some materials when hit by a light with a wave-length shorter than humans can see will absorb that light energy and then radiate back light within the visible spectrum so when a person looks at the object, it seems to glow. This process is called fluorescence.

There is a substance in the epicuticle (sometimes called the hyaline layer) of the scorpion's exoskeleton that fluoresces when exposed to ultra-violet light. Nobody knows exactly what this stuff is but some scientists speculate it is a complex of mucosaccharides (a simple form of sugar) and proteins. Also ß-Carboline, a trytophan derivative, is known to play an important part.

Nobody really knows how the fluorescence gets there either. Baby scorpions aren't born with it and scorpions that have just molted don't have it. This has leads some people to suggest that it is either secreted by the scorpion over time, a side effect of the animal's exoskeleton as it is tanned by the sun or the result of chemical reactions as the new exoskeleton hardens. The fact that some scorpions that live their entire lives in dark caves and still fluoresce, however, leads some people to think that it unlikely to be the tanning process.

Finally we also don't know what advantage this gives the scorpion. Some have speculated that this property somehow helps the scorpion with their ultra-violet light sensitivity, but studies have shown that different levels of UV light seem to have little effect on the animal's behavior.

We do know that scorpions have had this characteristic for a very long time. This kind of fluorescence has even been seen in some of the fossils of ancient scorpions. We also know it is not unique to scorpions as some sow bugs, millipedes, centipedes, solfugids and a few beetles also will glow in ultra-violet light. We also know that with each molting the effect grows stronger so that older scorpions glow brighter than young ones. The amount a scorpion glows is also connected the particular species. Some glow brightly, others hardly at all.

Whatever it is, this characteristic has been a boon to scientists and scorpion enthusiasts. A small camping lamp can have its fluorescent bulb replaced with one that produces ultra-violet (or "black") light that will cause scorpions to glow a soft blue or green at a distance of one or two feet. This is a great aid in finding the small animals. Scientists can then easily use tongs to collect specimens and many new species have been found this way. A flashlight that produces UV light can also be useful when camping in scorpion habitats to check your sleeping back to make sure you are not crawling in with one of the tiny critters.

Air on the moon - Is it possible to channel a pipe from Earth to Moon and pump in some of earth's atmosphere so as to support free life? - Cheta A.

Construction of a pipeline from the Earth to the Moon would be a difficult and probably impossible construction problem. Though scientists think it might be feasible to build an elevator that would lift people and materials in earth orbit, the space station that the elevator would be connected to would rotate in sync with our planet so it would always be directly overhead. The moon orbits the earth once a month, however, while our planet spins every 24 hours, so a pipeline from earth to moon would quickly get twisted and tangled.

There would be little point in building one, anyway, in an attempt to pressurize the moon and give it a breathable atmosphere. The moon already has an atmosphere, (mostly created by out gassing from the underground chemical reactions) but the atmosphere is so thin it almost does not exist. The gravity of the moon, only one-sixth that of Earth is too weak to hold any significant amount of gas on the surface. Most of it drifts into space to be swept away by the solar wind.

Of course we still might have an interest in putting stations and maybe even cities on the moon. (These would probably be airtight and partly or completely underground. By putting a couple of meters of rock above the habitations you can protect life from the stray radiation that often bombards the lunar surface) If we do build underground cities we will need air for the inhabitants to breath. Rather than pipe it up, or even bring it up in large cargo spaceships, it would much more efficient to create it from materials already on the surface. There is plenty of oxygen and nitrogen (to major components of air) locked up in lunar rocks and soil. Getting these out of the rocks will require energy, but there is plenty of that on the moon. It gets lots of sunlight (no cloudy days) that can be turned into electrical power. For that reason NASA is thinking of locating the first lunar stations near the poles so they can get an almost continuous exposure to energy from the sun.

Using Magnets for Traveling Through Space - I'm wondering if it's possible to use the principles of magnetism for travel (besides Maglev). For example, could a ship with a highly focused electromagnet aim and pull itself to a planet's magnetic field, or to the heavy metal core of an asteroid? Could this same idea be used to create a flying car, by pushing or pulling off more than one point at the same time? Thanks - Maxwell

While magnets and magnetic forces are very important in present and future transportation designs, the type of arrangement you suggest - focusing a magnetic field toward a distant object to pull yourself toward it seems an unlikely mechanism to be used. The problem is that magnetic fields lose their strength very quickly over long distances. So if you attempted to build a ship using this principal to pull yourself toward to a distant object you would need an impractically large magnetic field requiring a tremendous amount of energy. You would also have the problem that your engine would be attracting every piece of ferrite material (those attracted to a magnet) within miles -the wrenches in you tool kit, you belt buckle, other ships near you etc... You vessel would soon be covered with loose ferrite objects.

A train using Maglev does not have this same difficulty. The train uses magnetism to float just above its rails (often less than an inch) so that distance is not a problem. By changing the poles on the magnets involved the train can be not only pushed upward by the magnetic field but also down the track to give the vehicle forward speed.

A magnetic flying car might be workable, but only if it was levitating above a special magnetic road. Like the Maglev train it would be limited to "flying" just a few inches above the ground.

Of course many engines used in transportation now use magnets to operate. Almost every electric motor uses magnetic fields to generate movement and some advanced space probes use magnetic fields to shoot particles out the of the back of the probe at high speeds to push the device forward.

The only example of a magnetic transportation system that I could find that was similar to your design was a satellite engine being developed in conjunction with NASA. While details of the design are limited, the engine would interact with Earth magnetic field to allow satellites to maneuver while in orbit. Last year a model of the engine exploded during testing, but the inventors of the engine think they have worked out the bugs and are hopeful that they will be able to try a test in space in the next few years.

Geostationary Satellites - Is it true that for a satellite to hold the same position over the earth it can only be over the equator? - John

The type of satellite you are talking about is called a geostationary satellite and the idea for it was first proposed by Herman Potonik, a Slovenen rocket engineer, in 1928. Most people connect the idea, however, with famed science fiction writer Arthur C. Clarke. Clarke wrote an article about the idea for Wireless World in 1945.

The speed with which a satellite in orbit circles the Earth is dependent upon how high above the Earth's surface it is. Objects in low Earth orbit circle the globe much faster than those in higher orbits. For example, the space shuttle orbits the earth at a height of between 115 and 380 miles and will circle the Earth about 16 times in a 24 hour period. If an object is placed in orbit at a much higher level, say 22,300 miles, it will circle the globe only once in a 24 hour period. This makes it the object a geosynchronous satellite orbiting at the same rate the planet turns.

However, unless the satellite is also in an orbit over the Earth's equator, it will appear to move back and forth in the sky along a north to south line during the course of the day. To be a geostationary satellite the object needs to be in a circular orbit directly over the equator at the height of 22,300 miles (This is sometimes refered to as the "Clarke orbit"). Only then will it appear to be fixed in a single location in the sky.

There are many uses for geostationary satellites including communications (for example, the dish television broadcast satillite I get my TV on) and weather observation. Since they do not move in the sky, geostationary satellites allow receivers on the ground to use a simple fixed antennal to point to them and pickup broadcasts. Because the satellites are over Earth's equator, however, any northern hemisphere location wishing to point an antenna at them must have a clear view of the southern sky. The opposite is true in the southern hemisphere.

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