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Astronomers determine color of the Milky Way Galaxy
A team of astronomers in Pitt’s Kenneth P. Dietrich School of Arts and Sciences announced today the most accurate determination yet of the color of the (aptly named) Milky Way Galaxy: “a very pure white, almost mirroring a fresh spring snowfall.” Jeffrey Newman, Pitt professor of physics and astronomy, and Timothy Licquia, a PhD student in physics at Pitt, reported their findings during a presentation at the 219th American Astronomical Society (AAS) Meeting in Austin, Texas.
While color is one of the most important properties of galaxies that astronomers study, it has been difficult to make the measurement for the Milky Way, as our solar system is located well within the Galaxy. Because of this, clouds of gas and dust obscure all but the closest regions of the Galaxy from view, preventing researchers from getting the “big picture” (see http://home.arcor.de/AXEL.MELLINGER/ for a full-color view of the Milky Way, where the obscuration is visible).
“The problem is similar to determining the overall color of the Earth, when you’re only able to tell what Pennsylvania looks like,” Newman noted.
To circumvent this problem, Newman and Licquia set out to determine the Milky Way’s color by using images from other, more distant galaxies that can be viewed more clearly. These galaxies were observed by the Sloan Digital Sky Survey (SDSS), a project in which Pitt had an instrumental role that measured the detailed properties of nearly a million galaxies and has obtained color images of roughly a quarter of the sky. Without the large set of galaxies studied by SDSS to compare to, an accurate color determination was not possible. The new color measurement is allowing Pitt researchers to better understand the development of the Milky Way Galaxy and how it is related to other objects astronomers observe.
“The problem we faced was similar to determining the outside climate when you are in a room with no windows.” said Newman. “You can’t see what’s happening, but you can look online and find current weather conditions someplace where they should be about the samethe local airport, for example.”
The Pitt team identified galaxies similar to the Milky Way in properties that were able to be determinedspecifically, their total amount of stars and the rate at which they are creating new stars, which are both related to the brightness and color of a galaxy. The Milky Way Galaxy, the Pitt researchers realized, should then fall somewhere within the range of colors of these matching objects.
“Thanks to SDSS, the large, uniform sample needed to select Milky Way analogs already existed. We just needed to think of the idea for the project, and it was possible,” said Newman. “Although it is a relatively small telescope, only 2.5 meters (100 inches) in diameter, SDSS has been one of the most scientifically productive in history, enabling thousands of new projects like this one.”
Newman described the overall spectrum of light from the Milky Way as being very close to the light seen when looking at spring snow in the early morning, shortly after dawn. Michael Ramsey, Pitt associate professor of geology, notes that new spring snow is the whitest (natural) thing on Earth. Many cultures around the world have given the Milky Way names associated with milkhuman vision is not sensitive to colors seen in faint light, so the diffuse glow of the Galaxy at night appears white. That association has proven to be very appropriate, given the Milky Way’s true color.
Astronomers divide most galaxies into two broad categories based on their colors relatively red galaxies that rarely form new stars and blue galaxies where stars are still being born. (The brightest stars are generally blue, but they are very short-lived on cosmic scales and die out quickly.) The new measurements place the Milky Way near the division between the two classes.
This adds to the evidence that although the Milky Way is still producing stars, it is “on it’s way out,” according to Newman. “A few billion years from now, our Galaxy will be a much more boring place, full of middle-aged stars slowly using up their fuel and dying off, but without any new ones to take their place. It will be less interesting for astronomers in other galaxies to look at, too: The Milky Way’s spiral arms will fade into obscurity when there are no more blue stars left.”
The Milky Way’s color is exceedingly close to the “cosmic color” measured by Ivan Baldry, a professor of astrophysics at Liverpool John Moores University in England, and his collaborators in 2002; these researchers measured the average color of galaxies in the local universe.
“This close match shows that in many ways the Milky Way is a pretty typical galaxy,” said Newman. “This also agrees well with the ‘Copernican Principle’ embraced by the field of cosmologythat, just as the Earth is not in a special place in the solar system, we should not expect to live in an unusual place in the Universe.”
The light from the Milky Way closely matches the light from a D48.4 standard illuminant, or a light bulb with a color temperature of 4700-5000K. “It is well within the range our eye can perceive as whiteroughly halfway between the light from old-style incandescent light bulbs and the standard spectrum of white on a television,” said Newman.
Provided by University of Pittsburgh
Citation: Astronomers determine color of the Milky Way Galaxy (2012, January 11) retrieved 10 November 2023 from https://phys.org/news/2012-01-astronomers-milky-galaxy.html
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The cosmic spectrum
Stars and galaxies emit waves of electromagnetic radiation, which is separated into different groups based on the length of the waves emitted. From shortest to longest wavelength, the groups include gamma-rays, X-rays, ultraviolet light, visible light, infrared radiation, microwaves and radio waves.
Visible light makes up a tiny portion of the electromagnetic spectrum in terms of the range of wavelengths, but it is the only part the naked eye can see. What we perceive as colors are actually just different wavelengths of visible light; reds and oranges have longer wavelengths, and blues and purples have shorter wavelengths.
The visible spectrum of a star or a galaxy is a measure of the brightness and wavelengths of light that the star or galaxy emits, which, in turn, can be used to determine the average color of the star or galaxy, Baldry said.
In 2002, Australia’s 2dF Galaxy Redshift Survey — which was the largest survey of galaxies ever carried out at the time — captured the visible spectra of more than 200,000 galaxies from across the observable universe. By combining the spectra of all these galaxies, Baldry and Glazebrook’s team was able to create a visible light spectrum that accurately represented the entire universe, known as the cosmic spectrum.
The comic spectrum “represents the sum of all the energy in the universe emitted at different optical wavelengths of light,” Baldry and Glazebrook wrote in a separate non-peer-reviewed online paper in 2002 based on their discovery. The cosmic spectrum, in turn, allowed them to determine the average color of the universe.
Color conversion
The researchers used a color-matching computer program to convert the cosmic spectrum into a single color visible to humans, Baldry said.
Our eyes have three types of light-sensitive cones, each of which helps us perceive a different range of visible light wavelengths. This means that we have certain blind spots where we cannot properly register certain colors of wavelengths between these ranges, Baldry and Glazebrook wrote in their online paper. The colors we see also depend on what our reference for white light is as we are observing an object. For instance, the color of an object may appear different in a brightly lit room compared with the outdoors on an overcast day.
However, the CIE color spaces, created by the International Commission on Illumination in 1931, compensate for our visual limitations by attributing a color to different wavelength combinations as seen by a standardized human observer, which is what the team’s computer models used.
The team determined that the average color of the universe is a beige shade not too far off from white. Although this is a rather boring finding, it is not a surprising one, considering that white light is the result of combining all the different wavelengths of visible light and the cosmic spectrum includes such a wide range of wavelengths.
The new color was eventually named “cosmic latte,” based on the Italian word for milk, after a poll of the whole research team. Other suggestions included cappuccino cosmico, Big Bang beige and primordial clam chowder.
Unshifting the red
A key concept of the cosmic spectrum is that it represents the light of the universe “as originally envisaged,” Balrdy and Glazebrook wrote in their online paper. This means that it represents the light as it was emitted throughout the universe, not just as it appears to us on Earth today.
Like all waves, light gets stretched over vast distances because of the Doppler effect. As light gets stretched, its wavelength increases and its color moves toward the red end of the spectrum, known by astronomers as redshift. This means that the light we see is not the same color it was when it was first emitted.
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“We removed the effect of redshift from the spectra of the galaxies,” Baldry said. “So, it is the spectra of the galaxies when they emitted the light.”
Cosmic latte is, therefore, the color you would see if you could look down on the universe from above and see all the light coming from every galaxy, star and gas clouds all at once, Baldry said.
Originally published on Live Science.
The Colors of the Cosmos
Looking up to the skies? There’s a universe of inspiration to pull from, so it’s no surprise that the cosmos are finding their way into our homes. We’ve pulled a few ideas so you can create your own cosmic haven on Earth.
Deep Space
Saturating an entire room with dark colors like Endless Sea can make a space feel larger by adding depth that feels unending. Painting trim the same color as the walls can heighten a room even further by blending all of the color together. This optical illusion keeps the eye from registering any borders, so space feels like it continues on – just like the universe. When choosing decor to ground the infinite feeling of blue, mirrored and metallic accents create a futuristic vibe that brings a lighter touch to this design trend.
Star Light, Star Bright
Cosmos are bursting with energy and light. Capture that brightness in your home when you use Extra White to paint walls with reflective color. Creating a tone-on-tone backdrop of white walls and cream trim allows celestial-inspired accents, like Moravian star pendant lights, to be the center of attention in your room’s universe. Adding a splash of color to your door with Blue Sky is the perfect way to ground this look.
