An Astronomer 39;s View Of The Universe Question Answer

[Libano Parkes]

Ouruniverse is vast, mysterious, and ever expanding! Astronomers are constantly discovering and uncovering new secrets about space, which we know can lead to lots of questions. What is a black hole? When can you see the ISS? How old is the universe really? Well, you asked and our astronomers answered. Here are answers to some of the most frequently asked questions Adler Planetarium astronomers receive.

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Firstly, when maps are produced of stars and galaxies, are they just produced as we see them now from our viewpoint? Or are they based on the motion of those bodies? Eg Galaxy X is 1 million light years away and we know it's moving at Y speed, so it's real position now is actually 1 million years worth of movement along that trajectory.

Secondly, are those things taken into account when doing other studies of things like dark matter? Ie things are actually further apart than what we see because we're seeing them as they were Z million years ago. I would expect that would affect calculations for things like how much 'missing' matter there was.

To try to further clarify this second question, simplifying things to 3 points on a triangle... if we're at A and we observe points B and C which are X billion light years apart, then the effect of gravity on the speed of B and C moving apart would have been greater in the past when they were closer together and furthermore the effects of the current gravitational force will take more than X billion years to reach the other object. As far as I understand, dark matter is a way to account for observed gravitational effects that can't be accounted for in other ways. When astronomers do these calculations, can I assume that they have taken into account the time delay in the effects of gravity between galaxies? Or have I in my naivety, stumbled on some profound insight! (I doubt it.)

For the first part of your question, @userLTK has already provided a very good explanation, and I believe that by introducing redshift, the second part of your question is also partially answered. I will try to expand a little on it, hoping that I have understood your question correctly. To start off, I'm going to go ahead and quote my own thesis (not yet published);

This is why, when NASA earlier this year announced the Hubble Space Telescope having observed the most distant galaxy yet, the distance to the galaxy was never mentioned. The distance is not a direct observable, and has to be calculated based on certain assumptions. One direct observable we do have, is the line-of-sight velocity, which we express in terms of redshift. By describing objects in terms of redshift, we simultaneously have a "distance" measurement to the objects, as well as knowing how fast they move away from us.

When we make observations and try to learn more about things like the energy content of the universe (radiation, regular matter, dark matter, dark energy), the redshifts of the objects we observe are crucial. We consider various models of the universe, and see how they compare with what we observe on different redshifts. I very quickly found back to a paper written by my supervisor some years back; figure 7 in there shows you that kind of comparison.

Personally, I am working on something which I hope will lead to us being able to see whether dark energy evolves over time. In doing that, knowing the redshifts of the objects are crucial to my work, and I constantly need to keep in mind the implications of the distant objects' movement away from us. It is simply a factor I need to multiply or divide by in my calculations, to make sure I am comparing the correct things with each other.

For any local map of galaxies, the relative velocity is slow enough as to be irrelevant. Andromeda and the Milky way are roughly 2.5 million light years apart and they are moving towards each other currently at about 1 light year every 2,270 years (based on 402,000 km/h). In the 2.5 million years that it takes for Andromeda's light to reach us, it's moved less than 0.05% closer to us, so any adjustment on the maps to account for Andromeda's distance relative to our galaxy would be very small and not worth adjusting unless you're actually plotting it's movement in great detail. For most maps, what we see, even 2.5 million years old, is close enough and that's true for all local galaxies. That said, your intuition is correct, the light we see and the pictures made of Andromeda are where it was 2.5 million years ago. The more interesting movement is that it's rotated a handful of degrees in that time.

For maps over a billion light years across or of the known universe, then it's a little different because the relative movement is sufficient to measurably have changed the map in the time it took the light to reach us. That said, calculating where galaxies would be now vs where they were when the light left them is rather a lot of work. What's commonly done, rather than show distance for maps of that size is that they're usually coded with a redshift percentage instead of the more familiar distance ratio key.

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Retired businessman Fred Young '64, M.Eng. '66, MBA '66, has committed $11 million to CCAT, the Cerro Chajnantor Atacama Telescope, a proposed 25-meter aperture telescope that will be the largest, most precise and highest astronomical facility in the world.

The Department of Astronomy announced the gift Nov. 12 at a workshop for CCAT scientists. Vice Provost for Research Robert Buhrman called it "a beautiful day in Ithaca, a great day for astronomy and a great day for Cornell."

The telescope, to be built 18,400 feet above sea level on the Cerro Chajnantor mountain in Chile's Atacama desert, will give astronomers a new window into the epoch of star and galaxy formation to answer some of the most fundamental questions of cosmology.

With an extremely wide field of view, it will also enable large-scale surveys of the sky and complement the international Atacama Large Millimeter Array (ALMA), now under construction. As CCAT discovers new sources, ALMA will follow up with images of those sources in unprecedented detail.

Provost Kent Fuchs called Young's dedication to Cornell "spectacular" and expressed gratitude -- "not just on behalf of Cornell, but on behalf of CCAT, on behalf of astronomy worldwide and on behalf of the great science that's going to take place for many, many decades."

Young said he first heard about CCAT eight years ago, when he brought his daughter to Cornell for summer school. By "blind luck," he was invited to a meeting of the Friends of Astronomy, where he met Riccardo Giovanelli, professor of astronomy and CCAT director.

CCAT received a major boost earlier this year with strong endorsement from Astro2010, a national panel of scientists charged with determining priorities in astronomy and astrophysics for the next decade.

"With a broad scientific agenda, CCAT will enable studies of the evolution of galaxies across cosmic time, the formation of clusters of galaxies, the formation of stars in the Milky Way, the formation and evolution of planets, and the nature of objects in the outer solar system," the panel wrote.

"The carbon in our bodies, the silicon in our computers, the gold in gifts we give a girlfriend or boyfriend -- all these things were made with stuff being produced when our galaxies were born," he said. "Understanding that process is understanding how the universe became sophisticated enough in a chemical way to produce things we enjoy now, like black-and-white movies and the stuff we use to build telescopes."

Radiation at submillimeter wavelengths is normally difficult to detect from the ground because it is easily absorbed by water in the Earth's atmosphere. The Atacama desert's dry climate and high altitude make it a unique and ideal spot for ground-based far-infrared astronomy.

Young is a Foremost Benefactor of Cornell. His current commitment toward the Atacama telescope continues his support of the project over several years. He has also made gifts to Cornell to benefit the College of Engineering, the Johnson School, athletics and other areas. In addition to being a member of the Friends of Astronomy, he has served on Cornell University Council and is a former director of the Cornell Society of Engineers.

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On 18 June 1962, an 8-metre rocket carried three small X-ray detectors to the edge of space. They spent just under 6 minutes above the altitude of 80 kilometres, high enough for kiloelectronvolt-energy X-rays from space to reach them through the thinned atmosphere. The result of this brief flight by physicist Riccardo Giacconi and his colleagues revolutionized astronomers' view of what the Universe contains.

But it was the cosmic X-ray background that set the real programme for X-ray astronomy for the next 40 years. Was it caused by hot gas pervading intergalactic space, or by millions of faint and distant sources blending together? Early detectors could not answer this question, because they had to collect X-rays from a large chunk of the sky to detect a signal; discrete sources that might make up the background produced no more than one X-ray per square centimetre of detector each day. To see with greater precision, researchers needed more sensitive telescopes, which they built from nested cylindrical mirrors.

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