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Special Topic: The K-T Event

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Special Topic: Large Ground Meteorites

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Special Topic: Close Cometary Encounters

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Special Topic: Occultations by Asteroids

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For many people, one of the most fascinating periods of Earth’s natural history is the Mesozoic Era, which spanned from roughly 252 million years ago to 66 million years ago. This period of time is often called the “Age of Dinosaurs,” and indeed these large reptiles were the dominant animals on Earth for well over …

The general topic of meteorites was discussed as a “Special Topics” presentation four weeks ago. The large majority of meteorites that are known are not especially large, being of the order of a few kg in mass; with only a handful of exceptions, even the larger ones tend to have a mass of no more …

One of the most spectacular and awe-inspiring celestial sights is that of a bright, long-tailed comet – a “Great Comet,” the subject of a previous “Special Topics” presentation. On average, these appear about once a decade, and I have been privileged to have witnessed four of them during the half-century I have been observing comets …

The “Comet of the Week” this week is Comet IRAS-Araki-Alcock 1983d, which passed just 0.031 AU (4.68 million km, or 12.2 lunar distances) from Earth on May 11, 1983 – the closest confirmed cometary approach to Earth during the 20th Century, and the fifth-closest confirmed such approach in all of recorded history. Within this context, …

In astronomy, an occultation – which comes from Latin words meaning “to hide” – occurs when one body passes in front of, and thus for a time hides, another body. (In this context, a solar eclipse can be considered as a kind of occultation.) In its most common usage, an occultation usually refers to the …

Interplanetary space in the vicinity of Earth’s orbit – and, presumably, elsewhere as well – is littered with debris. Dust ejected from comets, bits and pieces of asteroids, rocks from various bodies . . . Meanwhile, Earth during its annual orbits around the sun is constantly sweeping up this debris. From the standpoint of terminology, …