Astronomy 162: Introduction to Stellar, Galactic, and Extragalactic Astronomy

Fall 2001

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    Roof and Planetarium Nights: Find opportunities that you will have during the quarter to observe through the telescope, attend planetarium shows, and hear some star talks.


    The Hubble Deep Field

    The faintest sources of light ever detected by human beings are the galaxies in the Hubble Deep Field. Some of these galaxies are seen when the universe was only 10% or 20% of its present age. This is our view of the universe that is our home: we see galaxies into the past, being born and evolving to their present form.

    The Hubble Deep Field

    Click here to see a movie where you start with a wide-angle view of the sky toward the constellation of Ursa Major (the Big Dipper), then you zoom in and see a smaller and smaller region of the sky until you end up in the Hubble Deep Field. All the sky around you is filled with similar images of faint galaxies as they were forming and evolving throughout the history of the universe!
    COBE Picture of the Milky Way Our view of the Milky Way Galaxy is hindered in visual light by dust obscuration. Absorption by dust is greatly reduced in the wavelengths of the far-infrared (much longer wavelength than visual light). Observations in the far-infrared must be done from space, because the Earth atmosphere is opaque to light at these wavelengths. The COBE satellite has given to us the best unobscured pictures of the Galaxy we live in. The picture shows many individual stars, the dust lane in the disk, and the bulge. Notice the asymmetry of the bulge, appearing slightly larger on the left side; this is an indication of the presence of a small bar in the inner parts of the Milky Way.

    COBE Picture of the Milky Way


    The Cluster of Galaxies and Gravitational Lens Abell 2218

    This picture of the core of a massive cluster of galaxies, containing hundreds of galaxies of the size of the Milky Way, reveals also some highly distorted images of background galaxies, whose light has been deflected by the gravity of the intervening cluster. The gravitationally lensed galaxies appear as little arcs of light, and for a few of them multiple images are produced. The amount of mass that is present in the cluster, as inferred from the angle by which light is deflected, is far too large to be accounted only by the observed stars in the cluster galaxies. The cluster must also contain a lot of dark matter, a mysterious type of matter about which we know nothing about.
    Movie of Stars orbiting around Black Hole in the Center of the Milky Way

    Movie

    A supermassive black hole has been discovered in the center of the Milky Way, at a distance of about 25000 light years. Supermassive black holes have been found in the centers of many other galaxies and are believed to be responsible for quasars, which are extremely luminous sources in the universe. Our own black hole (named Sagittarius A*) has a mass of 3 million solar masses, and at present it seems to be dormant because little matter is in its vicinity and moving down the throat of the monster. In the movie, you see images of stars taken in infrared light within the central light year. The gravitational attraction of the black hole on these stars is so large that they move faster than any other stars in the Galaxy. While stars appear almost stationary in other images of the sky, in this one you can see how stars move along their orbits around the center over a time of only several years.


    VLA Radio image of the Virgo galaxy M87 Giant galaxies in the centers of clusters harbor massive black holes in their cores, which eject jets of matter at relativistic speeds. Over millions of years, these jets energize the halo of hot gas surrounding the galaxy. Relativistic electrons produced in the jet slowly lose their energy spiraling in the magnetic fields of the energized cloud, creating these beautiful images in the radio part of the electromagnetic spectrum.

    The Radio Image around the M87 Galaxy observed with the Very Large Array


    Cosmology in a Computer

    The NCSA has put together a fascinating exposition Cosmos in a Computer featuring some of the latest state-of-the-art simulations of our Universe. Be sure to try the exhibit map to navigate the site.


    What is astronomy about? Since ancient times, astronomy has been about watching the sky. At present, precisely when scientists are rapidly advancing in the understanding of astronomy, most people are being deprived of the magnificence of the sky because of pollution and city lights. But thanks to the internet, we can watch pictures of celestial objects by using the resources in a multitude of websites. Explore the links provided here, which will bring you to images of star clusters (open and globular), gaseous nebulae, galaxies, etc. As part of learning astronomy, you simply need to have a good idea of what all these objects really look like.

    Among many other links below, you can try the Astronomy Picture of the Day, where every day a different picture of some interesting object in the sky is displayed. If you then go to the index, you can click on any class of objects you wish, to access the archive of all images that have been displayed in the past. You should try also the Messier and NGC catalogues, the Ohio State University Astronomical Picture Gallery, and the Hubble Space Telescope Image Archive. The astronomical society of the pacific and other links listed here will provide you with resources for writing a paper and learning more on astronomy.


    Where to find me:

    Astronomy 162 Fall Quarter 2001
    MWF 11:30am-12:48pm, Evans Lab 1008