International Year of Astronomy

By Riddle, Bob | Science Scope, January 2009 | Go to article overview
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International Year of Astronomy

Riddle, Bob, Science Scope

During the year 1608, Hans Lippershey, a Dutch spectacle maker, applied for a patent describing an instrument that could be used to make distant objects appear closer. At about the same time, several others either filed for patents or claimed the rights for inventing what we now know as a telescope. Due to the many disputes, no patent was ever issued for the invention and it did not take much time before others started making their own telescopes, including Galileo Galilei, a mathematics professor at the University of Padua in Italy. In 1609, Galileo apparently became the first to aim a telescope skyward and, among other observations, viewed craters on our Moon, sunspots, the phases of Venus, and moons orbiting Jupiter. With observations such as these, Galileo helped to dispel the belief in a geocentric universe by providing evidence that proved otherwise.


This year marks the 400th anniversary of when a telescope was used for astronomical observations, and 2009 has also been designated the International Year of Astronomy--a yearlong celebration of astronomy through various events and activities both online and in the real world. These include the GLOBE at Night star count program; 100 Hours of Astronomy; Astronomy Day; and Space Week (see Resources).

The ride of your life

On January 4, 2009, the earth reaches perihelion, the closest our planet comes to the Sun. At perihelion the earth is approximately 0.98 AU from the Sun as compared to July 3rd, when at aphelion the earth is 1.02 AU distant. While it may seem counterintuitive to be closest to the Sun while you are shivering during the chill of winter, it is the nature of having an elliptical rather than a circular orbit. And keep in mind that it is only winter for us north of the equator. Folks in the Southern Hemisphere are enjoying their summer season.

While you are reading this column and passing closest to the Sun, you are also moving through space in other ways than simply orbiting the nearest star. The obvious ways are the ones we teach our students--rotating with the earth as it spins on its axis and revolving with the earth around the Sun. However, our Sun is also moving with the other stars, dust, and gases making up the Perseus Arm of the Milky Way Galaxy as we revolve around the galactic center at a distance of around 28,000 light years. As it revolves around the galactic center, the Sun also oscillates (moves up and down) relative to the galactic plane by about 1% of the galaxy's diameter, or about 1,000 light years. our Sun, as a disk star (stars in the disk-shaped part of a galaxy), also has its own proper motion that is taking us and the rest of the solar system across the orion Spur, a short branch off of the main Perseus Arm, in the direction of the star Vega in the constellation Lyra, the Harp.

The orbital motion of the Sun is a result of the gravitational attraction of the mass at the galaxy's center, but this does not mean that distance from the center influences the orbital speed. In other words, stars in the spiral arms closer to the galactic center do not orbit faster than more distant stars. We know this because if the closer stars did move faster, the spiral arms would wrap and twist around the center. Instead, the stars all move at about the same orbital speed around the galactic center.

The oscillations, or bobbing motion, of a disk star result from its initial position above or below the galactic plane and the gravitational attraction of the galaxy's disk. A star not on the plane is attracted toward the plane, but the density of the disk is not enough to stop the star, and so the star keeps on moving, passing through the disk. However, the gravitational attraction of the disk will slow down the star and pull it back toward the disk, where the star will again pass through the disk. This is repeated several times during a revolution around the galactic center, a galactic year of approximately 200 million years.

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