Probing Sunsets

Like a pot of boiling water, where bubbles burst at the surface and are replaced by new ones, the Sun's surface rumbles in a constant turbulence of "granules." Astronomers suspect that the character of the granules changes over the course of the Sun's 11-year magnetic cycle. Texas astronomers Carlos Allende Prieto, David Lambert, and others are using the Hobby-Eberly Telescope (left) at McDonald Observatory to study the Sun's spectrum over the course of this cycle. Since pointing the giant telescope at the Sun would burn out its sensitive electronics, the astronomers are pointing it at the southern sky at sunset instead. Since the light in the daytime sky is simply sunlight, this provides a safe way to probe changes in the Sun's surface.

Laser to the Moon

Engineer Jerry Wiant has been shooting the Moon for more than three decades. Wiant runs the Laser Ranging Station (right) at McDonald Observatory. He and his crew aim a laser at special reflectors (inset, right) placed on the lunar surface by Apollo astronauts and unmanned Soviet landers. The laser light is reflected back to the station’s 30-inch (0.8-meter) telescope. The crew uses a computer to precisely measure the round-trip travel time for each laser pulse. The time tells scientists the distance to the Moon to within a few inches. Scientists use the readings to test Albert Einstein’s theory of General Relativity and to decipher the Moon’s structure. The laser ranging project is the only Apollo program still under way.

Tracking Danger

An asteroid might seem like a hard thing to lose. Yet astronomers sometimes lose track of these chunks of cosmic rock and metal. For the asteroids that approach Earth’s orbit, that could be dangerous, because these objects could someday slam into our planet. McDonald Observatory astronomer Judit Ries and her colleagues follow up the discoveries of near-Earth asteroids to plot their orbits more accurately. They also track down asteroids that have not been observed in months or years. When an asteroid is discovered, astronomers plot its orbit based on just a few observations. These plots can have large margins of error, though. As a result, an asteroid that no one has seen in several years might not appear where expected. So it is important to record an asteroid’s location many times over a period of several years. These observations help astronomers plot a precise orbit, so they know whether an asteroid will threaten Earth long in advance.

Tracking a Collision

When the Deep Impact probe slammed into Comet Tempel 1 in July 2005, Texas astronomer Anita Cochran was watching it with one of the giant Keck telescopes in Hawaii, continuing a series of observations that lasted for months. Cochran’s campaign also used both the Hobby-Eberly and Harlan J. Smith telescopes at McDonald Observatory. Observations before the impact, which blasted a cloud of gas into space, provided a look at the comet’s normal appearance and behavior. Observations during the impact provided a comparison to readings from the Deep Impact spacecraft, which photographed the collision and studied the composition of the material excavated by the impact. And follow-up observations provided a look at how the gas dispersed into space and how quickly Tempel 1 returned to its appearance before the collision. Combined with work by other astronomers around the world, Cochran’s campaign is providing the most detailed look ever recorded of a comet’s original composition (the material below its icy surface) and how it changes as the result of collisions with other objects.

See Also

Current and Ongoing Explorations

Explorations of the Inner Solar System

Explorations of Minor Bodies