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For his 65th birthday, Stephen Hawking took a ride in zero gravity. Photo: Associated Press

On January 8, 2007, scientist Stephen Hawking did something special for his 65th birthday—he took a trip up into zero gravity. He rode in the Zero Gravity Corporation’s modified Boeing 727 jet, which traveled up to 24,000 feet over the Atlantic Ocean off the coast of Florida and performed a series of dips that let Hawking experience a total of about four minutes of weightlesness. Because Hawking suffers from a degenerative nerve disease related to amyotrophic lateral sclerosis, a medical support team was on hand to monitor his blood pressure and cardiac readings. But the renowned physicist held up even better than expected, negotiating for two additional 30-second rounds of weightlessness while in flight.

NASA has been using aircraft to simulate the zero-gravity environment of orbit for decades, and in 2004 the Zero Gravity Corporation became the first company to offer the experience to the general public. The sensation occurs as the plane climbs upward with a very steep pitch and then levels out—a little like the feeling you get at the top of a roller coaster—and lasts about 30 seconds at a time. The price tag: $4,950 plus tax.

Hawking took the flight in order to publicize the possibility of commercial space travel. “I believe that life on Earth is at an ever-increasing risk of being wiped out by a disaster such as sudden nuclear war, a genetically engineered virus, or other dangers. I think the human race has no future if it doesn’t go into space,” he said before the flight. Using the force of commerce, he believes, is the most practical way to eventually make mass space travel a real possibility.

After the flight, Hawking was exuberant, and discussed his hopes to someday fully enter earth’s orbit (Richard Branson, owner of the company Virgin Galactic, has said he will waive the $200,000 fee). “It was amazing. The zero-G part was wonderful, and the high-G part was no problem,” Hawking said. “I could have gone on and on. Space, here I come.”

Opinions vary on what caused the Hindenburg to explode so suddenly.

On May 6, 1937—75 years ago this week—the Hindenburg airship was about the complete its 35th trip across the Atlantic, having departed from Frankfurt, Germany and nearly arrived at Lakehurst, New Jersey. Then, suddenly, after thousands of miles of uneventful travel, the great zeppelin caught fire while less than 300 feet from the ground. Within a minute of the first signs of trouble, the entire ship was incinerated, and the burning wreckage crashed to the ground. Thirty-five of the 97 people on board perished in the disaster.

Then the finger-pointing began. From the very start, observers disagreed about what exactly sparked the explosion and what caused it to burn so quickly. In the years since, scientists, engineers and others have used science to weigh in on the debate and attempt to solve the mystery of the Hindenburg.

During an era of tension between the United States and Germany’s new Nazi government, suspicious minds quickly alighted on the idea that a crew member or passenger had sabotaged the airship, intentionally starting a fire. However, nothing more than circumstantial evidence was ever put forth to support the idea. Realistic alternatives for the cause of the explosion include a buildup of static electricity, a bolt of lightning or a backfiring engine, but at this point it’s impossible to determine what exactly caused the spark.

A different question is what provided the fuel for the explosion—and this is where the science really gets interesting. Initially, observers assumed that some of the lighter-than-air hydrogen that kept the ship aloft somehow leaked from its enclosed cells, mixing with the oxygen in the air to create an incredibly flammable substance. Photographs taken right after the initial explosion show lines of fire along boundaries between the fuel cells, and crew members stationed in the stern reported seeing the actual cells burn, supporting the idea that leaking hydrogen caused the craft to explode so violently. Many have theorized that, during one of the sharp turns the ship took just before exploding, one of the bracing wires inside snapped, puncturing one of the cells.

Then, in 1996, retired NASA scientist Addison Bain, who had years of experience working with hydrogen, presented a new idea: the incendiary paint hypothesis. As part of his argument that hydrogen can be safely used for transportation and other purposes, Bain claimed that the fire was initially fueled by a special paint used on the zeppelin’s skin. The varnish compound included chemicals such iron oxide, which can be used as rocket fuel.

Bain also pointed out that the hydrogen inside the cells had been given a garlic scent, to help crew members detect a leak, but no one reported smelling garlic at the time of the explosion. He also said that a fire fueled by hydrogen would produce a blue flame, but the fire was a bright red. In his scenario, the mystery spark would have ignited the varnish rather than leaking hydrogen—meaning that a design flaw, rather than the inherent risks of hydrogen, had caused the disaster.

In 2005, a team of researchers led by A.J. Dessler, a physicist at Texas A&M, published a detailed study in which they attempted to determine whether the chemicals in the varnish could possibly account for the fire. Their answer: no way. Their calculations indicate that, if fueled by the paint alone, the airship would have taken roughly 40 hours to burn completely, rather than the 34 seconds it took for it to be consumed. In the lab, they burned replica pieces of the Hindenburg‘s outer covering, which confirmed their theoretical calculations—and indicated that the paint alone could not have fueled the fire.

So, more than 75 years later, we’re still not quite sure what to believe about the Hindenburg disaster. Can the use of hydrogen gas in transportation be safe? Or is a vehicle filled with flammable gas simply an accident waiting to happen? However it was caused, the terrible explosion had one long-lasting effect: It permanently put airship travel on the back burner.

Read about a new exhibit at the Smithsonian’s National Postal Museum about the Hindenburg and read an eyewitness account of the disaster from a grounds crew member.

Acanthaspis petax, a type of assassin bug, stacks dead ant bodies on its back to confuse predators. Photo by Mohd Rizal Ismail

Imagine you’re wandering in the forests near Lake Victoria, in Kenya or Tanzania, when you spot something strange crawling on a leaf. It looks like a dozen or so ants, stuck together in a ball. But look more closely and you’ll see the ants are dead. And there’s a nasty-looking insect underneath, hauling these ants corpses along like a miniature backpack.

This is Acanthaspis petax, a member of the Reduviidae family, which is found in East Africa and Malaysia. Like other assassin bugs, it hunts its prey by piercing it with its proboscis, injecting paralysis-inducing saliva and an enzyme that dissolves tissue, then sucking out the innards. But unlike other bugs, it then fashions empty ant exoskeletons into protective outerwear. The insect can carry as many as 20 dead ants at a time, and binds them together with a sticky excretion into a cluster that may be larger than its own body.

For years, scientists debated why Acanthaspis petax engaged in this unusual behavior. It hunts several different types of prey, but appears to exclusively stack ant bodies on its back. Some suggested that the ant corpses may provide olfactory camouflage when hunting, while others thought the mound of bodies may be used as a visual distraction for larger creatures that are hunting the assassin bug.

Photo by Mohd Rizal Ismail

In 2007, a team of researchers from New Zealand carried out an experiment to test whether the insect’s corpse-carrying strategy truly helped protect it from predation. In the study, they left assassin bugs alone in glass cages with several species of jumping spiders, which are their natural predators. Some of the insects were carrying balls of ant carcasses on their backs (the researchers called these “masked” bugs) while others were left naked. Since the jumping spiders have excellent vision but a poor sense of smell—they hunt by using their acute sense of sight to make a precisely gauged leap and land on their prey—the experiment would indicate if the ant bodies served as visual camouflage or not.

The result: the spiders attacked the naked bugs roughly ten times more often than the masked ones. The researchers even repeated the experiment with dead, preserved assassin bugs, to control for the effects of movement and behavior, and the results remained the same. Carrying that ball of dead ants, it turns out, is a great strategy for the assassin bug to use in trying to survive for its next meal.

The scientists speculate that the large mound of corpses changes the visual form of the insect to the point where the spiders can’t recognize it as prey.

But why do the assassin bugs refrain from using other insects in the same way? The researchers suggest that Acanthaspis petax may actually be relying on the spiders’ inherent reluctance to attack ants. Because ants have a tendency to swarm and may secrete chemical weapons, the spiders don’t typically hunt them.

Good strategy for Acanthaspis petax. Raw deal for the ants.

Scientists calculated how to make a force field big enough to fit the Millennium Falcon. Photo courtesy of Mary Evans / Lucas Film / Ronald Grant / Everett Collection (10336353)

Today, if you aren’t already aware, is something of an intergalactic holiday. In recent years, May 4th has become an unofficial day to honor the iconic film series Star Wars, because the date is a rhyming pun of the signature line, “May the Force Fourth Be With You.” All around the world, Star Wars fans are celebrating Luke, Leia, Boba Fett and (maybe even) the Ewoks.

We decided to channel our inner Jedi by checking out the contributions science has made towards a better understanding of the Star Wars universe. Last year, it turns out, a team of physicists from the University of Leicester in Britain took a closer look at many fans’ favorite spacecraft: Han Solo and Chewbacca’s hyperspace-traveling Millennium Falcon (which made the Kessel Run in less than 12 parsecs!)

The scientists noted that force fields are often employed in the Star Wars universe to provide a barrier between the hangars of spaceships and outer space, preventing the ship’s atmosphere from being sucked outwards (think of spacecraft flying inside the Death Star‘s massive hangar bay, with no mechanical airlock). The physicists noted that a real-life innovation, the plasma window, could theoretically serve to create such force fields. Plasma windows, invented by Brookhaven Lab physicist Ady Hershcovitch in 1995, use magnetic fields to create bounded areas filled with plasma (superheated, viscous ionized gas), which have the special property of blocking air from entering a vacuum while allowing radiation and physical objects to freely pass through.

With this knowledge in hand, the research team decided to try calculating the amount of energy that would be necessary to create a docking force field large enough to accommodate the Millennium Falcon, which they estimate is roughly 100 by 40 by 6 feet. Their conclusion? Theoretically possible with current technology—but generating sufficient amounts of energy to continuously sustain a force field that size is unlikely to be feasible.

But, in a galaxy far, far away, anything is possible.

The supermoon of March 2011, rising behind the Lincoln Memorial In Washington, DC. Photo by NASA/Bill Ingalls

This Saturday evening, take a look at the night sky and you might see something special. The moon will make its largest, most stunning appearance of the year—an event known to scientists as “the perigee-syzygy of the Earth-Moon-Sun system” and to the popular skywatching public simply as the “supermoon.” As one of the most spectacular supermoons in years, the moon will appear 14 percent bigger and 30 percent brighter than when it is on the far side of its orbit.

Why does the moon sometimes appear larger, and sometimes smaller? The answer lies in the fact that its orbit around Earth is elliptical, so its distance from us varies—it ranges from roughly 222,000 to 252,000 miles away each month. On Saturday, the moon will reach what is known as the perigee, coming as close as it ever does to the Earth, just 221,802 miles away. At the same time, it will be a full moon, with the entirety of its Earth-facing surface illuminated by the light of the sun.

This supermoon will appear especially large because the exact moment of perigee will neatly coincide with the appearance of a perfectly full moon. The full moon will occur at 11:34 p.m. EST, and the perigee will occur at 11:35. During last year’s supermoon on March 19, 2011, for comparison, the perigee and full moon were 50 minutes apart.

A comparison of last year's March supermoon (right) with an average moon from December 2010. Photo by Wikimedia Commons user Marcoaliaslama

“The timing is almost perfect,” says NASA, according to the Washington Post. AccuWeather’s astronomy blogger Daniel Vogler notes that a look through recent data reveals no more closely-timed (and therefore bigger) supermoons.

Apart from providing a sight to behold in the night sky, the moon’s perigee also has a tangible effect on Earth: It causes higher than normal tides. Because tides are driven by the moon’s gravitational effects, a closer moon means that the oceans will be pulled more than usual towards the satellite. In most places, this will mean a tide that is an inch or so higher than usual, but geographical factors can multiply the effect up to around six inches.

There has long been speculation that the moon’s gravitational effect during its perigee could be the cause of natural disasters, including earthquakes and volcanic activity. In particular, many suggested this link following the earthquake and subsequent tsunami off the coast of Japan in March of 2011. However, the devastating quake occurred over a week before the supermoon, and studies have shown no strong evidence for increased frequency of high-intensity seismic activity during the moon’s perigee.

There are more concrete examples, though, in which supermoons may cause problems. In particular, flooding during storms may be made more severe because of the higher tides. In 1962, the coincidental arrival of a powerful storm with the moon’s perigee inundated the entire Atlantic coast of Cape Cod, causing 40 deaths and $500 million in property damage.

On Saturday, assuming no damaging storms or floods are at your doorstep, just hope for a clear night and take a look outside. The moon will appear larger and brighter than usual all night, but for the most striking views, try to catch it just after it rises above the horizon, when an optical illusion causes it to look larger than it really is, and viewing it through the gases of the earth’s atmosphere can cause the moon to appear yellow, orange or red in color.