Comet Hale-Bopp is now very bright (around magnitude 0). As a consequence, it is becoming difficult to obtain images of it with the large telescopes on Mauna Kea: the detectors are saturated by this bright object, even when we are using the shortest possible exposure times (these telescopes are equipped to observe faint objects). Moreover, it is now so extended that it will not fit in the small field of view of our instruments! At this point, anybody with small telescopes and even binoculars can get a more dramatic view of the comet than we can!
That does not mean that we cannot do anything: while direct imaging at visible wavelengths is difficult, there are many other techniques that allow us to obtain some very interesting information on the comet. This infrared image of Hale-Bopp (obtained at a wavelength of 3.672 micron) was recorded with the NASA Infrared Telescope Facility (IRTF) at Mauna Kea Observatory, on March 8, 1997. The observations were done during DAYTIME when the comet was invisible to the human eye, but still could not hide from special IR detectors! During the day, the sunlight heats the ground and the air around the telescope, creating a lot of turbulence that tends to blur the observations, which is why this image appears less sharp than the ones obtained during the night - for example the one we obtained on February 17. However, the advantage is that the comet can be observed for a long time, high in the sky, while at night it is very low on the horizon and raises only shortly before sunrise.
This false color image depicts the heat emitted by the dust: the brighter the color the more dust is present. The field of view is extremely small. Each pixel of this image corresponds to roughly 45 miles at the distance of the comet's nucleus, which is a "dirty snow ball" approximately 25 miles in diameter. Because of the Sun's irradiation, the uppermost layers of the nucleus are sublimating (i.e., the ice is evaporating directly from solid to gas), dragging along large amounts of dust (tons per second) that hide the nucleus from our direct view. Ultimately, this dust spreads out and forms the visible (dust) tail of the comet. This image was used to center an infrared spectrograph on the comet.
(Observers: Alan Tokunaga and Roland Meier, IfA, UH)
Roland Meier & Olivier Hainaut
Creation: Tue Mar 11 19:01:31 1997
Creation: Tue Mar 11 19:01:31 1997 -- Hits: