Titan Occults Two Stars - Central Flash Observed
Titan occulted two stars November 14, 2003. The data received from occultations can tell scientists much about the atmosphere of Titan. These were the last occultations of relatively bright stars by Titan before the Huygens probe floats to the surface of Saturn's largest moon in January 2005.

On 14 November 2003 the star TYC 1343-1615-1 was occulted by Saturn's moon Titan. This is the light curve of the event as observed by the 1 meter telescope at the South African Astronomical Observatory in Sutherland, South Africa.

Teams of observers traveled around the world to observe Titan occult two stars on November 14, 2003. Observers in South Africa viewed the first occultation of magnitude 8.6 TYC 1343-1615-1 at 0h 11m U.T. This star, in the constellation Gemini, is nearly the same magnitude as Titan itself. Eight hours later, observers in Western Europe attempted to view Titan occult the fainter magnitude 10.7 star TYC 1343-1865-1 just before dawn. And a day later, amateur astronomers aimed their telescopes at Saturn to watch one of these stars occulted by the rings of Saturn. TYC stands for the Tycho star catalogue, the standard classification system for 3.5 million stars.

Occultations are like eclipses. They both involve the passage of one celestial object in front of another. Astronomers study occultations of moons and planets to learn more about their atmosphere. When these occultations are visible from earth, scientists can take photometric measurements of the star and create a light curve. A light curve is the brightness or intensity of light plotted against time on a graph. As Titan passed in front of the star, the light seen from the two objects decreased in intensity. If the center of Titan passes close enough to the line of sight from the star to the observer, just at the midpoint of the occultation, a small peak of light called a central flash is observed. The central flash is starlight refracted by Titan's atmosphere. The atmosphere of Titan acts as a lens. This central flash helps astronomers measure the shape of Titan's atmosphere and winds in a narrow band of its atmosphere.

One intriguing light curveshows evidence of gravity waves in the atmosphere of Titan. We see gravity waves on earth, in the wake of a motorboat and in bands of clouds. These waves should not be confused with gravitational waves -- ripples in the fabric of space and time. The gravity waves on Titan are just part of the atmospheric fluctuations scientists hope to understand as the Cassini-Huygens mission nears its destination.

The Huygens Probe, supplied by the European Space Agency, has six complex instruments aboard. The data from these instruments will be received by the Cassini spacecraft and relayed to Earth after the probe descends into Titan's mysterious atmosphere in early 2005.

GOOD REFERENCES:

Definition: Light curve. Brightness or intensity of light plotted against time on a graph. Astronomers discover dark stellar companions using the light curve of the star. As a dark orbiting object eclipses the star, the brightness falls, producing a dip on the light curve. Careful analysis of the light curve reveals the masses of the star and dark companion plus the distance to this eclipsing binary system.
http://www.cyprusastronomy.com/Astronomical%20Glossary.html

Titan November 14, 2003 occultation light curves and explanation.
http://despa.obspm.fr/%7Esicardy/titan/results.html

November 14 original light curve. This is the source of the light curve showing evidence of gravity waves referenced above
http://despa.obspm.fr/~sicardy/titan/SAAO_1m_gen.gif

European Space Agency Huygens Home Page:
http://sci.esa.int/science-e/www/area/index.cfm?fareaid=12

European Space Agency Stellar Occultations page:
http://www.rssd.esa.int/Huygens/Observations/Occultation.html

IOTA International Occultation Timing Association:
http://www.lunar-occultations.com/iota/iotandx.htm

Contact:
Jane Houston Jones
jane.h.jones@ jpl.nasa.gov
phone 818 393-6435