Posted on by Jason Major

If You Could See in Radio These Are the Crazy Shapes You’d See in the Sky

"Color" radio image of galactic cluster Abell 2256. Credit: Owen et al., NRAO/AUI/NSF.

Even though it’s said that the average human eye can discern from seven to ten million different values and hues of colors, in reality our eyes are sensitive to only a very small section of the entire electromagnetic spectrum, corresponding to wavelengths in the range of 400 to 700 nanometers. Above and below those ranges lie enormously diverse segments of the EM spectrum, from minuscule yet powerful gamma rays to incredibly long, low-frequency radio waves.

Astronomers observe the Universe in all wavelengths because many objects and phenomena can only be detected in EM ranges other than visible light (which itself can easily be blocked by clouds of dense gas and dust.) But if we could see in radio waves the same way we do in visible light waves – that is with longer wavelengths being perceived as “red” and shorter wavelengths seen as “violet,” with all the blues, greens, and yellows in between – our world would look quite different… especially the night sky, which would be filled with fantastic shapes like those seen above!

View of the VLA in New Mexico. Image courtesy of NRAO/AUI.
View of the VLA in New Mexico. Image courtesy of NRAO/AUI.

Created from observations made at the Very Large Array in New Mexico, the image above shows a cluster of over 500 colliding galaxies located 800 million light-years away called Abell 2256. An intriguing target of study across the entire electromagnetic spectrum, here Abell 2256 (A2256 for short) has had its radio emissions mapped to the corresponding colors our eyes can see.

Within an area about the same width as the full Moon a space battle between magical cosmic creatures seems to be taking place! (In reality A2256 spans about 4 million light-years.)

See a visible-light image of A2256 by amateur astronomer Rick Johnson here.

The VLA radio observations will help researchers determine what’s happening within A2256, where multiple groups of galaxy clusters are interacting.

“The image reveals details of the interactions between the two merging clusters and suggests that previously unexpected physical processes are at work in such encounters,” said Frazer Owen of the National Radio Astronomy Observatory (NRAO).

Radio image of the night sky. (Credit: Max Planck Institute for Radio Astronomy, generated by Glyn Haslam.)
Radio image of the night sky. (Credit: Max Planck Institute for Radio Astronomy, generated by Glyn Haslam.)

Learn more about NRAO and radio astronomy here, and you can get an idea of what our view of the Milky Way would look like in radio wavelengths on the Square Kilometer Array’s website.

Source: NRAO

Posted on by Jerry Coffey

What Is Light Energy

Lighting Up the Night
Lighting Up the Night

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Just asking ‘what is light energy’ opens you up to a flood of other questions trying to narrow down the context that you are asking the question in. In photometry, luminous energy is the perceived energy of light. It can also be defined as the electromagnetic radiation of visible light. Since light itself is energy, then another definition is relevant: light is nature’s way of transferring energy through space.

The speed of light is about 300,000 km/s. To put that in perspective, when you watch the sun set, it has actually been 10 minutes since that light left the Sun. Light energy is measured with two main sets of units: radiometry measures light power at all wavelengths and photometry measures light with wavelength weighted with respect to a standardized model of human brightness perception. Photometry is useful when measuring light intended for human use. The photometry units are different from most units because they take into account how the human eye responds to light. Based on this, two light sources which produce the same intensity of visible light do not necessarily appear equally bright.

Light exerts a physical pressure on objects in its path. This is explained by the particle nature of light in which photons strike and transfer their momentum. Light pressure is equal to the power of the light beam divided by the speed of light. The effect of light pressure is negligible for everyday objects. For example, you can lift a coin with laser pointers, but it would take 1 billion of them to do it. Light pressure can cause asteroids to spin faster by working on them like wind pushing a windmill. That is why some scientist are researching solar sails to propel intersteller flight.

Light is all around us. It has the ability to tan or burn our skins, it can be harnessed to melt metals, or heat our food. Light energy posed a huge challenge for scientist up to the 1950’s. Hopefully, in the future, we will be able to use light energy and solar wind to travel among the stars.

We have written many articles about light energy for Universe Today. Here’s an article about the prescription for light pollution, and here’s an article about where visible light come from.

If you’d like more info on Light Energy, check out NASA’s Page on Atoms and Light Energy. And here’s a link to an article about How Photovoltaics Work.

We’ve also recorded an episode of Astronomy Cast all about Energy Levels and Spectra. Listen here, Episode 139: Energy Levels and Spectra.

Sources:
Johns Hopkins University
Wikipedia

Posted on by John Carl Villanueva

Radiation from the Sun

Extreme Ultraviolet Sun
Extreme Ultraviolet Sun

[/caption]Radiation from the Sun, which is more popularly known as sunlight, is a mixture of electromagnetic waves ranging from infrared (IR) to ultraviolet rays (UV). It of course includes visible light, which is in between IR and UV in the electromagnetic spectrum.

All electromagnetic waves (EM) travel at a speed of approximately 3.0 x 10 8 m/s in vacuum. Although space is not a perfect vacuum, as it is really composed of low-density particles, EM waves, neutrinos, and magnetic fields, it can certainly be approximated as such.

Now, since the average distance between the Earth and the Sun over one Earth orbit is one AU (about 150,000,000,000 m), then it will take about 8 minutes for radiation from the Sun to get to Earth.

Actually, the Sun does not only produce IR, visible light, and UV. Fusion in the core actually gives off high energy gamma rays. However, as the gamma ray photons make their arduous journey to the surface of the Sun, they are continuously absorbed by the solar plasma and re-emitted to lower frequencies. By the time they get to the surface, their frequencies are mostly only within the IR/visible light/UV spectrum.

During solar flares, the Sun also emits X-rays. X-ray radiation from the Sun was first observed by T. Burnight during a V-2 rocket flight. This was later confirmed by Japan’s Yohkoh, a satellite launched in 1991.

When electromagnetic radiation from the Sun strikes the Earth’s atmosphere, some of it is absorbed while the rest proceed to the Earth’s surface. In particular, UV is absorbed by the ozone layer and re-emitted as heat, eventually heating up the stratosphere. Some of this heat is re-radiated to outer space while some is sent to the Earth’s surface.

In the meantime, the electromagnetic radiation that wasn’t absorbed by the atmosphere proceeds to the Earth’s surface and heats it up. Some of this heat stays there while the rest is re-emitted. Upon reaching the atmosphere, part of it gets absorbed and part of it passes through. Naturally, the ones that get absorbed add to the heat already there.

The presence of greenhouse gases make the atmosphere absorb more heat, reducing the fraction of outbound EM waves that pass through. Known as the greenhouse effect, this is the reason why heat can build up some more.

The Earth is not the only planet that experiences the greenhouse effect. Read about the greenhouse effect taking place in Venus here in Universe Today. We’ve also got an interesting article that talks about a real greenhouse on the Moon by 2014.

Here’s a simplified explanation of the greenhouse effect on the EPA’s website. There’s also NASA’s Climate Change page.

Relax and listen to some interesting episodes at Astronomy Cast. Want to know more aboutUltraviolet Astronomy? How different is it from Optical Astronomy?

References:
NASA Science: The Electromagnetic Spectrum
NASA Earth Observatory

Posted on by John Carl Villanueva

Visible Light

Sunlight passing through a prism. Image credit: NASA

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Of all the wavelengths in the electromagnetic spectrum, those that lie between 400 nm to 700 nm are the ones most familiar to us. That’s because these are the waves that comprise what we call visible light. 

When we see objects, it’s because they’re being illuminated by visible light. When we see that the sky is blue, or the grass is green, or hair black, or that an apple is red, that’s because we’re seeing different wavelengths within the 400nm-700nm band. Because of the waves in this band, a lot has been learned about the properties of electromagnetic waves.

Through visible light, reflection & refraction are easily observed. So are interference and diffraction. Mirrors, lenses, prisms, diffraction gratings, and spectrometers have all been put to use to understand and manifest the qualities of the light that we see through our naked eyes.

Galileo’s telescope, which was composed of a simple set of lenses, made use of the refractive properties of light to magnify distant objects. Today’s  binoculars and periscopes capitalize on the optical phenomenon called Total Internal Reflection by using prisms to improve on what early refractive telescopes were capable of achieving.

As mentioned earlier, visible light is made up of the wavelengths that range from 400 nm to 700 nm. Each wavelength is characterized by a unique color, with violet on one end (adjacent to ultraviolet light) and red on the other (adjacent to infrared light). When all these wavelengths are combined together, they make up what is known as white light. 

You can separate these wavelengths (and the corresponding colors) by letting them pass through either a prism or a diffraction grating. The magnificent array of colors that we see in a rainbow, on a diamond, or even a peacock’s tail are examples of this separation.

All phenomena of visible light such as reflection, refraction, interference, and diffraction are also exhibited by non-visible wavelengths. Hence, by understanding these phenomena, and applying them to the non-visible wavelengths, scientists were able to unearth many of nature’s secrets. In fact, if we trace back the roots of modern physics, particularly the wave-particle duality of matter, we will be led back to its manifestation in visible light. 

The study of visible light falls under the realm of optics. Among the scientists who have contributed substantially to the development of optics are Christiaan Huygens for his wavelets and a wave theory of light, Isaac Newton for his contributions on reflection and refraction, James Clerk Maxwell for the propagation of electromagnetic waves as explained in a series of equations, and Heinrich Hertz for verifying the truth of those equations through experiments.

You can read more about visible light here in Universe Today. Want to know where visible light comes from? How about a visible light image of a distant galaxy?

There’s more about it at NASA and Physics World:
Visible Light Waves
The special effect of physics

Here are two episodes at Astronomy Cast that you might want to check out as well:
Optical Astronomy
Interferometry

Sources:
Windows to Universe
NASA: Visible Light
Wikipedia: Christiaan Huygens
NASA: Maxwell and Hertz