[OAB 83] Sirius, the brightest star in the night sky, is known from modern observation to be white in color. However, many texts from ancient astronomers (although not all) indicate that they saw Sirius as red. The "red Sirius" mystery has puzzled scientists for decades, and no completely satisfactory answer has yet been formulated. One answer that has been proposed is that Sirius' small companion star (known as Sirius-B), which is currently a white dwarf, may have been a red giant star when the ancients were observing 2,000 years ago. The main problem with this hypothesis is that the transition from red giant to white dwarf is thought to take about 10 million years. Some young-Earth advocates have latched onto the red-giant explanation of the "red Sirius" mystery as the correct one, and have then gone on to claim that it is evidence against established "evolutionary" theories of astronomy. The first problem with this claim is that it is not simply "evolutionary theories" but the laws of physics themselves that challenge the transition from red giant to white dwarf in only 2,000 years. The laws of thermal physics make it unlikely that the rapid change in temperature required could have taken place in such a large body in such a short period of time. Also, red giants, being much more massive than white dwarfs, would have to lose most of their mass in such a transition, and would have left behind large clouds of gas (known as "nebula") surrounding Sirius. No such clouds of gas exist. Recognizing the physical evidence against this claim, many young-Earth advocates no longer use it. In reality, the "red Sirius" mystery is just that: It is an Unexplained Mystery that continues to puzzle scientists, but it is not evidence for a young Universe. Incidentally, a good discussion of the various proposed explanations of the "red Sirius" mystery was recently published by D.C.B. Whittet (Monthly Notices of the Royal Astronomical Society, v.310, pp.355-359 (1999)).