Anatomy of an Electromagnetic Wave

Energy, a measure of the ability to do work, comes in many forms and can transform from one type to another. Examples of stored or potential energy include batteries and water behind a dam. Objects in motion are examples of kinetic energy. Charged particles—such as electrons and protons—create electromagnetic fields when they move, and these fields transport the type of energy we call electromagnetic radiation, or light.

WHAT ARE WAVES?

Mechanical waves and electromagnetic waves are two important ways that energy is transported in the world around us. Waves in water and sound waves in

Learn about UV Waves

ULTRAVIOLET LIGHT FROM OUR SUN

Bees, along with some birds, reptiles and other insects, can see near-ultraviolet light reflecting off of plants. Bug zappers attract insects with ultraviolet light to lure them to the trap.

Ultraviolet (UV) light has shorter wavelengths than visible light. Although UV waves are invisible to the human eye, some insects, such as bumblebees, can see them. This is similar to how a dog can hear the sound of a whistle just outside the hearing range of humans.

The Sun is a source of the full spectrum of ultraviolet radiation, which is commonly subdivided into UV-A, UV-B, and UV-C. These are the classifications most often used in Earth sciences. UV-C rays are the most harmful and are almost completely absorbed by our atmosphere. UV-B rays are the harmful rays that cause sunburn. Exposure to UV-B rays increases the risk of DNA and other cellular damage in living organisms. Fortunately, about 95 percent UV-B rays are absorbed by ozone in the Earth's atmosphere.

Learn about X-Rays

X-RAYS AND ENERGY

X-rays have much higher energy and much shorter wavelengths than ultraviolet light, and scientists usually refer to x-rays in terms of their energy rather than their wavelength. This is partially because x-rays have very small wavelengths, between 0.03 and 3 nanometers, so small that some x-rays are no bigger than a single atom of many elements.

This mosaic of several Chandra X-ray Observatory images of the central region of our Milky Way galaxy reveals hundreds of white dwarf stars, neutron stars, and black holes. Separately, the Solar and Heliophysics Observatory (SOHO) captured these images of the Sun representing an entire solar cycle from 1996 through 2006. Credit: NASA/UMass/D.Wang et al. Sun images from SOHO – EIT Consortium: NASA/ESA

DISCOVERY OF X-RAYS

X-rays were first observed and documented in 1895 by German scientist Wilhelm Conrad Roentgen. He discovered that

What are Gamma Rays ?

SOURCES OF GAMMA RAYS

Brighter colors in the Cygus region indicate greater numbers of gamma rays detected by the Fermi gamma-ray space telescope. Credit: NASA/DOE/International LAT Team

Gamma rays have the smallest wavelengths and the most energy of any wave in the electromagnetic spectrum. They are produced by the hottest and most energetic objects in the universe, such as neutron stars and pulsars, supernova explosions, and regions around black holes. On Earth, gamma waves are generated by nuclear explosions, lightning, and the less dramatic activity of radioactive decay.

DETECTING GAMMA RAYS

Unlike optical light and x-rays, gamma rays cannot be captured and reflected by mirrors. Gamma-ray wavelengths are

NASA International year of Chemistry

Chemistry is one of the main threads that tie together the grand tapestry of space exploration. Obviously, chemicals are, literally, the fuel that put our satellites into orbit around earth, and send our spacecraft to other planets. But chemistry also tells us the composition (and thus history) of stars, planets and moons, both in our Solar System, and far beyond. It also is playing a key role in the search for life.

It is our detailed understanding of chemical structures and the arrangement of electrons around atoms that allow us to detect molecules from orbit, both on Earth and other planets. For example, we can measure molecules like CO2 in our own atmosphere, frozen as dry ice in the polar cap on Mars, on icy moons of Saturn, and in the space between the stars. This technique, called spectroscopy, allows us to see something like a finger print of molecules and the atoms of which they are composed. Sometimes we are looking at visible light, such as the colors of stars which indicate temperature, age, and the presence of metal ions. But often we are looking at the many other wavelengths of the electromagnetic spectrum, which are "colors" of light not visible to the human eye. For example, while the Hubble images are mostly in visible light, the Spitzer Space Telescope sees the universe in the infrared, Galex in the Ultraviolet, Chandra in X-rays, etc.

This means that we can confidently identify elements in stars, ices and minerals on the surfaces of other planets (moons, etc.) and molecules light years away, floating in space. We can learn more than just what is out there: the speed of the rotation of the molecule is a thermometer that can tell us the temperature at a distance, and the type of ion (e.g., atoms or molecules with electrons stripped off) are a measure of how harsh is the radiation near distant stars.

Life is made of molecules, so chemistry is central to the search for life on other planets. We don't expect to be lucky enough to see a whale breaching in the oceans of Europa, its far more likely that when one of our probes detects life elsewhere it will be remains of microbes that died out long ago or live beneath the surface. In other words our first indications of life elsewhere in our Solar System will probably be chemistry. We call these molecules left over from life 'biomarkers' and much of our search strategy relies on developing chemistry to find them.

It turns out that finding biomarkers may be much more difficult than you might imagine, for at least two reasons. First, it turns out that the universe is filled with carbon compounds, some of which look quite like those in us, e.g., meteorites have been shown to contain amino acids, sugars, and nucleo bases. Second, we have no idea what alien chemistry might be like; our sophisticated biotechnology methods, which are specific to our biochemistry, may be blind to alien life.

Thus, from detecting molecules from Earth's atmosphere to other galaxies, to the search for life, chemistry is a unifying theme in NASA science.

How do matter, energy, space, and time behave under the extraordinarily diverse conditions of the cosmos?

How does the universe work? Understanding the Universe's birth and its ultimate fate are essential first steps to unveil the mechanisms of how it works. This, in turn, requires knowledge of its history, which started with the Big Bang.

Previous NASA investigations with the Cosmic Microwave Background Explorer (COBE) and the Wilkinson Microwave Anisotropy Probe (WMAP) have measured the radiation from the Universe when it was only 300,000 years old, confirming theoretical models of its early evolution. With its improved sensitivity and resolution, the Planck observatory is now probing the long wavelength sky to new depths in its 2-year sky survey, providing stringent new constraints on the physics of the first few moments of the Universe. Moreover, the possible detection and investigation of the so-called B-mode polarization pattern on the Cosmic Microwave Background (CMB) impressed by gravitational waves during those initial instants will provide clues for how the large-scale structures we observe today came to be.

Observations with the Hubble Space Telescope and other observatories showed that the Universe is expanding at an ever-increasing rate, implying that some day - in the very distant future - anyone looking at the night sky would see only our Galaxy and its stars. The billions of other galaxies will have receded beyond detection by these future observers. The origin of the force that is pushing the Universe apart is a mystery, and astronomers refer to it simply as "dark energy". This new, unknown component, which comprises ~75% of the matter-energy content of the Universe, will determine the ultimate fate of all. Determining the nature of dark energy, its possible history over cosmic time, is perhaps the most important quest of astronomy for the next decade and lies at the intersection of cosmology, astrophysics, and fundamental physics.

Knowing how the laws of physics behave at the extremes of space and time, near a black hole or a neutron star, is also an important piece of the puzzle we must obtain if we are to understand how the universe works. Current observatories operating at X-ray and gamma-ray energies, such as the Chandra X-ray Observatory, Fermi Gamma-ray Space Telescope, XMM-Newton, are producing a wealth of information on the conditions of matter near compact sources, in extreme gravity fields unattainable on Earth. Future missions such as LISA and the International X-ray Observatory, will push the frontier of knowledge of exotic astrophysical phenomena related to extreme regimes even further in space and time. For PCOS, the decade ahead holds the promise of exciting discoveries and new, bolder questions.

Trojan asteroid seen in Earth's orbit by Wise telescope

2010 TK7 traces a complex path at its orbital point, moving above and below the plane of the Earth's orbit

Astronomers have detected an asteroid not far from Earth, moving in the same orbit around the Sun.

The 200-300m-wide rock sits in front of our planet at a gravitational "sweet spot", and poses no danger.

Its position in the sky makes it a so-called Trojan asteroid - a type previously detected only at Jupiter, Neptune and Mars.

2010 TK7, as it is known, was found by Nasa's Wise telescope. The discovery is reported in this week's Nature journal.

It is a fascinating observation because the relative stability and proximity of Trojans would make possible targets for astronaut missions when we eventually go beyond the space station.

2010 TK7 is probably not the rock of choice, simply because it travels too far above and below the plane of Earth's orbit, which would require a lot of fuel to reach it.

Nonetheless, its detection means it is highly likely there are other, more 

suitable Trojans out there waiting to be found.

The difficulty is the viewing geometry that puts any Trojan, from the perspective of an Earth-based telescope, in bright skies.

It took an orbiting telescope sensitive to infrared light to pick up 2010 TK7.

Wise, the Wide-field Infrared Survey Explorer launched in 2009, examined more than 500 Near-Earth Objects (NEOs), 123 of which were new to science.

The authors of the Nature paper sifted through data on these rocks, looking for the candidates that might be Trojans.

Follow-up work on the Canada-France-Hawaii Telescope confirmed the status of 2010 TK7.

It traces quite a complex path at its orbital point. Currently, it is about 80 million km from Earth, and should come no closer than about 25 million km.

The team says its orbit appears stable at least for the next 10,000 years.

really be a surprise. Jupiter, Neptune and Mars all have collections of rocks sitting in the so-called Lagrange points 60 degrees ahead of or behind the planets in their orbits.

2010 TK7's existence should not 

In the case of Jupiter, the number of Trojans now tops 1,000 rocks.

"These objects are difficult to find from Earth, simply because they're not very big and they're pretty faint, and they're close to the Sun as seen from Earth," explained Christian Veillet from the Canada-France-Hawaii Telescope and a co-author on the Nature study.

"But we can find them from space, and future satellites will likely find some more. We think that there are others which will be very close to the Earth and have motions that make them relatively easy to reach. So, they could be potential targets to go to with spacecraft," he told.

                                Trojan asteroids are considered possible targets for astronaut missions

Source - BBC