A thousand years ago the Vikings, or Norsemen, lived in northern Europe. They were adventurous sailors who traveled to Iceland and Greenland and may even have reached the New World. The Norsemen told many stories about their gods.

You’ve probably heard of some of the Norse divinities. One was Odin, the wise father of the gods. Another was Thor, god of thunder and lightning. Freya the beautiful was the goddess of love. And then there was Loki, the foster-brother of the gods. He was handsome, but dishonest, full of mischief and trickery.

One day, Loki found himself in real trouble. He, Odin, and another god named Honir were roasting a steer for supper, when a big eagle swooped down and grabbed the best pieces of meat. Loki hit the bird with a stick. The stick stuck to the eagle and to Loki’s hands. The eagle flew away, dragging Loki behind him.

The eagle was really a giant named Thiazi in disguise. He wouldn’t release Loki until Loki promised to bring the goddess Idun and her basket of golden apples to him. Now, Idun’s apples were not just regular fruit – they were the magic apples of youth. As long as the golds and goddesses ate Idun’s apples, they never grew old.

Loki returned to Asgard, the home of the goods. He asked Idun to take a walk with him. He led her across the rainbow bridge that separates the land of the gods from the land of humans.

As soon as Idun crossed the bridge, the eagle swooped down, snatched her up in his talons, and carried her off to his home in the snow-covered mountains.

Without Idun and her apples, the gods began to grow old. Thor’s red hair turned white. He couldn’t throw his magic hammer as far or as accurately. Odin got a little deaf. Freya, the goddess of love and beauty, found silver streaks in her golden hair. Worst of all, cold and frost spread from the north and began to cover the Earth.

"This is your fault," Odin said to Loki. "You’d better fix it – or else!"

So Loki disguised himself as a falcon, or small hawk, and flew off to the land of the giants to see what he could do.

When Loki reached Thiazi’s castle, the giant was not at home. Loki flew in a window and found Idun crying in a small room. He changed her into a nut, grasped it in his claws, and flew out of the window.

But long before Loki reached Asgard, Thiazi returned to his castle and saw than Idun was gone. He changed into an eagle again and flew angrily after the falcon.

While the two birds were far in the distance, the gods saw them coming. The eagle was gaining on Loki, and had almost caught up to him. The gods piled a lot of brush and kindling wood by the walls of Asgard. Just as Loki flew over the wall, they set the wood on fire.

The eagle swooped down in pursuit. Flames rushed up to meet him. Unable to stop in time, Thiazi the eagle was caught in the fire. He fell inside the walls, and the gods killed him.

Idun and her apples were safe at home again.

It may be hard to believe, but even giants have relatives who love them. When Thiazi’s daughter heard of her father’s death, she came to Asgard demanding justice. To comfort her, Odin placed Thiazi in the night sky, where people could see him forever. Some say the giant is Sirius, the brightest star in the heavens.

Finding Sirius on a February evening is easy. Face south and look for the brightest start you can see. Don’t be confused by the planet Jupiter, which is brighter than Sirius and lies northeast of it. Sirius is much closer to the southern horizon.

How good is your knowledge of mythology? What are the names of some of the gods in the article in Greek and Roman mythology? What is Asgard?

The different faces of Mars as seen through a simple, inverting telescope. South is up. (Daniel Troiani of the Association of Lunar and Planetary Observers International Mars Patrol)

Mars is high in the sky right now in the southeast after sunset, shining with an orange light and enticing amateur astronomers around the world to come and look at it.  Mars is called the Red Planet because of the way it appears to the naked eye when it is far from the Earth, so don’t be fooled into looking for a bright red star.  Right now, to the eye and through a telescope, Mars appears more yellow than red.

Any size telescope will show the planets disk. And, if you gaze long enough at it through a telescope, you may see some interesting features, such as dark surface markings and bright hazes or clouds. You may even be lucky enough to see a raging yellow dust storm! If you do not own a telescope, call your local planetarium, observatory, or astronomy club to find when they have public Mars viewing through a telescope.

To see the most detail on Mars, plan to spend an evening with it. Once you center the planet in the eyepiece, you will have to wait for the atmosphere to become very still, because that’s when tiny dark and bright markings look their best. The atmosphere is in constant change, and is sometimes very turbulent. The longer you look, however, the more you will see. The details will pop in and out of view so you have to be patient. It is a skill that all great planetary observers have.

Equally challenging is trying to draw any markings you spy. You do not have to be a trained artist to draw Mars. Just sketch any features you see in a circle you prepare before you go out. Try also to match what you see through the telescope to what appears on the maps above. Remember that the details on the maps are greatly enhanced. Nothing is ever that clear when you are using a telescope (except on the Moon!). If you are not sure, then be sure to write down the time and date of your observation (you should do this anyway), because, someone at a local planetarium or astronomy club can help you identify the features you sketched.

Mars shows almost the same face from one night to the next. That’s because the Martian day is only about 40 minutes longer than the Earth’s. To see other parts of the planet, you must either view at a different hour of the night, or wait for a week or two to pass. If viewed at the same time every night, Mars takes somewhat over a month to complete one retrograde (backward) "rotation."

Of course, astronomers know what face of mars is visible at every hour of the night. So here’s a bit of help: On July 1st at 9:00 p.m. Eastern Standard Time, Mars will have an appearance similar to that of the seventh globe from the left (CM = 270 degrees). "CM" stands for Mars’s Central Meridian, or Martian longitude. Features near this part of the map are the ones that will be visible on Mars’s disk. Remember, if you go out at a different time of night, the face of mars will be slightly different. On July 15 at 9:00 p.m., Eastern Standard Time, Martian longitude 127 degrees will be near the center of the disk, so the face of Mars will appear something like that of the fourth globe from the left (CM=135 degrees). And on July 31, Martian longitude 334 degrees will be near the center of the disk, and will appear something like that of the first globe (CM = 360 degrees) or the eighth globe (CM = 315 degrees).

If you can immediately recognize the features on the actual planet that you see on the globes, well, then you’re doing extremely well! Congratulations! Next try memorizing some of the names of the features. You’ll certainly impress your friends with your new vocabulary!

Good luck. By the way, if you don’t want to look through a telescope, you can always check what’s going on with Mars by scanning the images being returned by NASA’s Mars Global Surveyor. These can be found at www.msss.com, along with much other information relating to the progress of the mission.

Does the night sky excite you? Astronomy can be a most fulfilling and rewarding pastime. There are boundless treasures to seek out for pleasure, and there is opportunity for discovery. In fact, some amateur astronomers have made outstanding discoveries with nothing more than their eyes or binoculars.

Beginners to astronomy should shy away from purchasing telescopes until they’ve explored the universe through binoculars. These simple instruments help novices get accustomed to views more powerful than the naked eye, but with fields of view wide enough to scan the skies without the confusion introduced by telescopes. In a telescope, not only are the images upside down, but they are usually greatly magnified. Thus, it’s best to test your skills first with binoculars.

A good pair of binoculars opens an entirely new world that is invisible to the naked eye. In our Solar System alone, binoculars can show craters on the Moon, the rings of Saturn, phases of Venus, four bright moons of Jupiter, all the planets except Pluto, asteroids, and comets with tails.

Double stars increase in number when using binoculars. There are hundreds of stars within binocular range that periodically change in brightness and are worth following. And many star clusters and galaxies can be seen.

Which Binoculars are Best?
Binoculars come in a variety of sizes. They will be labeled 7×35, 7×50, 8×30, 10×50, 11×80. The first number in each pair is the magnification; the second number is the size of the lens in millimeters. Thus 7×35 binoculars have lenses with diameters of 35 millimeters and eyepieces that magnify the image 7 times.

Large-diameter binoculars are heavy, and some even require a tripod. Consider this when selecting because when you’re observing you have to hold the binoculars for extended periods of time. Your arms will get tired. Most beginners select either 7×35 or 7×50 binoculars.

Never buy binoculars that you can’t return if they’re faulty. Look for these three warning signs: coma, vignetting, and chromatic aberration. All are artifacts of poorly ground lenses. Coma makes the stars appear butterfly shaped. The "butterflies" get progressively worse away from the center of the field. Many observers can tolerate some coma on the extreme edges of the field of view. Remember, stars should be pinpoints of light. Vignetting is a gradual darkening across the field, while chromatic aberration shows up as rings of color, especially red, around each star. If your binoculars suffer badly from any of these effects, return them and try another pair or brand.

The evidence is in — Earth’s atmosphere is warming, and many scientists would agree that if we dusted the global thermostat we’d find human fingerprints on it. One huge unknown remains, however: How much of this increasing heat can Earth’s oceans absorb? Since oceans cover 70 percent of Earth’s surface, their ability to absorb heat, to act as a "heat sink," is very great. Extra heat from the atmosphere may pour into this ocean sink, slowing the greenhouse effect and, perhaps, allowing the greenhouse gases to be removed from the atmosphere by global ecosystems. But will it be enough to keep global warming in check? Scientists sure hope so! And they’ve launched a study to find out.

Investigators from California’s Scripps Institution of Oceanography and 10 other international research centers developed a study called ATOC. Short for Acoustic Thermometry of Ocean Climate, ATOC will measure the effects of changing water temperature on acoustic (sound) waves traveling through the ocean. Begun in December 1995 and continuing for four years, the Scripps team will broadcast very-low-frequency sound waves into ocean waters off the coasts of California  and Kauai, one of Hawaii’s islands. The sounds will travel 850 meters below the ocean’s surface. Underwater listening stations 5,000 to 10,000 kilometers away will pick up these faint sounds. The warmer the water the faster sound travels in it. If investigators find shorter-than-average travel times for the sound waves, occurring repeatedly over long periods of time, they’ll know that the oceans are warming. They’ll have a hint that the oceans are absorbing increasing atmospheric heat and possibly can reduce the greenhouse effect.

But detecting climatic trends by this approach will take at least a decade, according to the ATOC Program Manager Andrew Forbes at Scripps. "ATOC is initially trying to establish a baseline [temperature of the oceans] to measure against in the future," Forbes says. To do this, the ATOC study will focus on establishing how sound waves transmit in deep water. Future, longer-lasting studies — two decades would be ideal says Forbes — will be needed to determine whether the oceans really are warming.

The sound generated by the ATOC study will be in the frequency range of 60 to 90 hertz, the very edge of human hearing and below what many marine mammals can hear. Two large underwater speakers, each 2 meters tall and 1 meter across, will generate the sound waves. Signals will transmit for 20 minutes, six times a day — a total of 2 hours out of every 24. If we could hear them, these signals would sound like a distant rumble, like thunder. Similar sounds already meander through the oceans, coming from the engines of large freight and cruise ships. ATOC’s noise level will be less than 1/1,000 of 1 percent of existing ship noise. And after an initial test period of several months to judge the effects of tides on the sounds’ travel times, the number and power level of transmissions will decrease.

Still, it is well known that dolphins and whales use their keen sense of hearing to communicate and locate objects underwater. Some people are concerned that the ATOC sounds may affect marine animals, such as dolphins, seals, and whales. Researchers hope this won’t be the case. They’ll use a frequency range of sound waves that will not interfere with the creatures. While blue, finback, and humpback whales have sensitive hearing in the range of very-low-frequency sounds, they do not  dive deeply enough to come within range of the ATOC sounds. The deep swimmers — toothed whales, sea lions, turtles, and seals — seem to have poor hearing in the ATOC sound range.

However, information on the effects of low-frequency sounds on marine mammals is limited. To be safe, Forbes and his team are studying how marine mammals sense or react to these new sounds. The ATOC scientists will follow safety measures recommended by this study. If changes in animal behavior do occur after ATOC begins, the scientists will suspend their activities.

"ATOC won’t solve all our planet’s problems," Forbes cautions, "but it will provide a ‘snapshot’ of ocean temperatures, an early step in helping us understand what part oceans can play in reducing the effects of a warming planet."

When the nucleus of a large atom is split into two smaller nuclei, a very small amount of matter is changed to energy, but an enormous amount of energy is produced. The process is called nuclear fission. The atomic bombs used in World War II contained only a few pounds of uranium as the fissionable material, but when detonated released as much energy as 20,000 tons of TNT.

An even more powerful bomb than the ones used in World War II, the hydrogen bomb works by a different nuclear reaction, called fusion.  In this reaction, two atoms of deuterium (a type of hydrogen that is found in ordinary water) combine to make one atom of helium. In the reaction, about 0.5 percent of the  original mass is converted into energy — a vastly greater amount of energy than is created by the fission process! Because the fusion reaction can occur only at very high temperatures — over 50 million degrees Celsius — an atomic bomb is used to produce the heat to start the explosion of the hydrogen bomb.

In addition to the massive destruction that occurs when nuclear bombs reach their targets, radioactive elements, formed as byproducts of atomic fission, can also be extremely hazardous to living things, including people.  Released into the atmosphere by the explosion, they can travel thousands of kilometers before returning to the ground as radioactive fallout. To protect people around the world from this hazard, the Test Ban Treaty of 1963 was signed by 23 countries, including the United States. The agreement not to explode nuclear bombs in the atmosphere or in outer space remains in place today.