For satellites that are millions of miles away, NASA uses huge dish antennas up to 230 feet (70 meters) in diameter. The antenna can be anything from a long, stiff wire (as in the AM/FM radio antennas on cars) to something as bizarre as a satellite dish. Take another piece of wire, 10 to 20 feet (3 to 6 meters) long, and connect one end of it to the other end of the diode. You might have noticed that the AM radio antenna in your car is not 300 feet (91 meters) long – it is only a couple of feet long. The antenna will receive thousands of sine waves. The DJ’s voice is modulated onto that carrier wave by varying the amplitude of the transmitter’s sine wave. Now the radio has to extract the DJ’s voice out of that sine wave. The job of a tuner is to separate one sine wave from the thousands of radio signals that the antenna receives. Radio transmitters also use extremely tall antenna towers to transmit their signals. In the U.S. over-the-air television has moved entirely over to digital transmission, and many terrestrial radio stations operate on digital antennas in addition to their analog signals.

This is why cell phones can have such short antennas. Why can radio waves travel millions of miles? The nearby signal overwhelms everything else by a factor of millions. In this case, the tuner is tuned to receive the 680,000-hertz signal. The tuner causes the radio to receive just one sine wave frequency (in this case, 680,000 hertz). Once you modulate a sine wave with information, you can transmit the information. When you listen to an AM radio broadcast, your radio is tuning in to a sine wave with a frequency of around 1,000,000 cycles per second (cycles per second is also known as hertz). It is transmitting a sine wave with a frequency of 680,000 hertz. In other words, the electrons will change direction four times during one cycle of the sine wave. In one cycle of the sine wave, the transmitter is going to move electrons in the antenna in one direction, switch and pull them back, switch and push them out and switch and move them back again. A space collision is just what it sounds like — one body, whether it’s a star, an asteroid or a comet, crashes into another body.

NASA Astronaut Group 2 (nicknamed the “Next Nine” and the “New Nine”) was the second group of astronauts selected by the National Aeronautics and Space Administration (NASA). As an editor with over 10 years of experience in science journalism she has previously written for Scholastic Classroom Magazines, MedPage Today and The Joint Institute for Computational Sciences at Oak Ridge National Laboratory. Related to modern horseshoe crabs, the trilobites vanished 248 million years ago at the end of the Permian Period. Attach the diode to the other end of the ground wire. An AM antenna is simply a wire or a metal stick that increases the amount of metal the transmitter’s waves can interact with. For a cell phone working at 900,000,000 (900 MHz), on the other hand, the optimum antenna size is about 3 inches or 8.3 centimeters. This wire is your antenna. This is the ground wire. Strip the insulation off the end of a 10-foot (3-meter) piece of wire and wrap it around the stake/post five or 10 times to get a good solid connection. As the sunlight has passed through all this air, the air molecules have scattered and rescattered the blue light many times in many directions.

Even if we are able to fill up flying cars with regular unleaded gasoline, if you start running low on fuel in the air it’s not like you can just pull into a station and fill up. That is, tuners resonate at, and amplify, one particular frequency and ignore all the other frequencies in the air. One simple way to think about it is this: When current enters the antenna, it does create a magnetic field around the antenna. If you made the antenna longer it would receive better, but AM stations are so strong in cities that it doesn’t really matter if your antenna is the optimal length. Because you are so close to the transmitter, the antenna is also receiving lots of energy – enough to drive an earphone! What kind of foam are Nerf darts made of? As we start to find out more about the conditions both inside our Solar System and on exoplanets, Rothschild and her colleagues are presented with a new problem: what if we find conditions for life that are just outside the extremes studied on Earth? Such is the new era of American spaceflight, in which the federal government seeks cheaper, safer and more reliable access to orbit not by directly building and operating fleets of spaceships and rockets but rather by spending tax dollars on launch services provided by private companies.