You are relaxing with a book on a nice sunny day when a friend leans over your shoulder and the page goes dark. "Hey," you might say, "you're blocking my light!" It is a familiar experience - any time an object blocks the light from another source, it forms a shadow. But did you know all of the places that shadows occur?
We are most used to shadows of, say, people on a beach. As their bodies block the sunlight, this prevents the light from reaching the sand behind them and a darker region is formed.
But much larger objects such as the Earth and the Moon can also cast shadows. During what astronomers call a lunar eclipse, the alignment of the Earth, Moon, and Sun can result in the Earth briefly blocking most sunlight getting to the Moon. Some of the sunlight does make it to the lunar surface, but it is filtered by the Earth's atmosphere, and it is also slightly bent. This causes the sunlight reflected from the Moon during a lunar eclipse to often appear red. The exact color of the shadow across the Moon during a lunar eclipse can depend on the amount of dust and clouds in our atmosphere.
Have you ever watched a duck move quickly across a pond? You may have noticed that if the duck is paddling fast enough, the ripples of water in front of it will merge into a V-shaped wall of water. This structure called a bow wave.
Bow waves are not just found in duck ponds. Rather they can be anywhere in water, air, or even space where an object is moving quickly enough. Bow waves provide scientists with an important opportunity to study speed in many places.
Let's go back to the water for another example. As competitive swimmers move through the pool as fast they can, they push the water and a bow wave forms in the direction they are going. In fact, the best swimmers learn how to minimize the bow waves they produce so they can go even faster through the water.
Bow waves are also found in the air of Earth's atmosphere or even the very thin gas in between stars or across giant objects in space. An object moving through any of these environments creates a series of pressure or sound waves. If the object moves fast enough these waves merge into a 3-dimensional bow wave that is called a bow shock.
Our Sun is a star. In fact, it is the closest star we'll ever see. The Sun is about 5 billion years old and will live for about 5 billion more. But not all stars live this long. Some really big stars -- those that are about ten or twenty times bigger than the Sun -- live for only a few million years. Our Sun is too small to explode, but when these big stars run out of fuel, they go out with a bang!
What happens at the end of a big star's life? It has to do with how stars, which are essentially big balls of gas, shine. A star's energy is the result of gravity, which pulls all of its matter toward the center. This compresses the center of star and makes it so hot there that matter undergoes a process called nuclear fusion. Fusion is when atoms collide. When this happens, energy is released. This is what holds up the outside of the star against gravity. But when the center runs out of fuel, the outer layers come crashing down. A star like the Sun will get crushed down to the size of Earth when this process happens to it billions of years from now. For stars much larger than the Sun that we've talked about, they don't go so quietly. Instead when their outer layers collapse, it generates a massive explosion that astronomers call a supernova. These supernova explosions blow the star apart and, for several days, generate more light than a billion stars.
While astronomers know that Cassiopeia A, or Cas A for short, is the aftermath of a massive star that exploded, it is unclear exactly when the explosion took place.
Supernova explosions in the Milky Way are relatively rare - with one going off roughly every 50 years or so in our Galaxy. For those that exploded centuries ago, it is often difficult to identify their exact birthdate since, of course, there were no telescopes to record them. Getting a precise date is important because the age helps determine many other properties of the explosion.
There are many things around us that bend. Straws bend. Rivers bend. But did you know that light also bends? Actually, it's not light itself that bends, but rather the path that it takes. While this may sound strange, many of us witness this every day when we put on our eyeglasses or insert our contact lenses. These objects are especially shaped to bend incoming light so that it focuses properly on the retina of the eye, allowing those of us with poor vision to see more clearly.
It's possible to find examples of how light's path is bent at the end of the day as well. If you've ever looked at the horizon when the Sun is setting, you may have noticed that the Sun looks more oval than round. What you're witnessing is the Sun's image being distorted. With eyeglasses or contact lenses, it is a piece of glass or plastic that alters the path of light. However, in the case of the sunset, it's the Earth's atmosphere that acts as a lens. The thicker the atmosphere, the more the light from the Sun is bent. That's why the Sun looks more flattened as it gets closer and closer to the horizon, because the light has to travel through more of our atmosphere. The result is that the Sun can look like it's oval shaped, even though we know it always remains a sphere, as it sits some 93 million miles away from us in space.
Atoms are the building blocks of matter. They are also constantly in motion, moving at speeds of thousands of miles per hour at room temperature up to millions of miles per hour behind a supernova shockwave. When an atom collides with another atom at such tremendously high speeds, energy gets transferred. This extra energy has to go somewhere and it is often released in the form of a light wave.
You may not think you have seen this happen, but chances are you have. Most of us have seen the neon lights of a diner or maybe even the strip of Las Vegas. Those bright neon lights glow because of these atomic collisions. Here's how: These signs are made from glass tubes filled with atoms of neon, argon, mercury or other gases. When an electric field is run through the tube, this energizes the atoms inside, making them collide. Each type of atom will release different colors of light, which is how we see these kaleidoscope displays on signs everywhere.
Hurricanes are extreme weather events that can affect millions of people. Most of the concern surrounding hurricanes involves the experience of a hurricane from below - and for good reason given how much damage they can cause. But it is also very interesting to consider hurricanes from the other direction, that is, how they appear from the air. Looking at a hurricane from this point of view, we can see that the storm is, in fact, a giant spiral shape. And, it turns out, this spiral shape appears in many different objects of various sizes and scales across the Universe.
Let's compare hurricanes with two other spiral-shaped objects that are very different: water going down a drain and a spiral galaxy. The common thread for all of these three things is angular momentum, a physical principle that remains constant with time for a spinning object and applies over all scales.
We've all felt the wind - whether as a gentle breeze or the wrath of an angry storm. But what exactly is wind and what impact does it have?
Wind is an excellent example of a phenomenon that happens here, there, and everywhere. By studying wind wherever it occurs - here on Earth, somewhere in the Solar System, or across the vastness of galaxies - we are learning more about how science is connected no matter where it is found.