Show Notes
When accurately recorded historical observations do not agree with what we what we see today it is often very rewarding to find out why. In modern telescopes we see Theta Eridani to a be pair separated by about 425 times our distance from the Sun orbiting a common center of gravity. Detailed observations of the spectrum of one of these show it to be itself a pair of stars orbiting each other every 4.1 days. One of this very close pair, as it is aging, dumps matter onto its companion causing it to brightened significantly. In the past this mass transfer rate was much higher than it is today and the naked eye brightness of Theta Eridani is fainter to us than it was long ago.
More from Travelers In The Night
The Vera C. Rubin Observatory, also known as LSST, with its 8.4 m mirror, the width of a tennis court, and the worlds largest 3.2 gigapixel camera, roughly the size of a small car, will image the entire sky every 3 or 4 nights in such a way as to detect objects that change in position and/or brightness. It is estimated the LSST will discover one or two new impacting small asteroids per year and provide several days of lead time for follow up telescopes to track an impactor into the atmosphere to find meteorites whose chemical composition will tell us about where they originated.
My Catalina Sky Survey teammate Greg Leonard's discovery of, 2018 FO5, a three football field diameter asteroid that can come closer than our Moon is a reminder that we need to keep searching for the many thousands of Potentially Hazardous asteroids larger than 500 feet in diameter which are likely to exist.
After completing a sample and return mission to the asteroid Ryugu (ree-oo-goo) and a fly by of asteroid Torifune (toh-ree-foo-neh), the Japanese asteroid exploring spacecraft Hayabusa2 (high-yah-BOO-sah-too )is on its way to fly by the rapidly spinning tiny asteroid 1998 KY2 .
My Catalina Sky Survey teammate Jess Johnson was very surprised when the large comet with a long stringy tail, which he has just imaged with our 60 inch telescope on Mt. Lemmon, Arizona, was an unknown object. Jess quickly emailed his discovery observations along with a description of the comet's coma and tail to the Minor Planet Center. Over the next eight days astronomers at 11 different observatories around the world tracked Jess's new comet. Scientists at the Minor Planet used these data to calculate it's path around the Sun, verify it to be a comet, and give it the name C/2018 F3 (Johnson). We now know that Comet C/2018 F3 (Johnson) had crossed the orbit of Pluto in 1997 and had reached it's closest point to the Sun 217 days previous to Jess's discovery observations. Further, about two weeks before Jess spotted it , moving through the constellation of Leo, Comet 2018 F3 (Johnson) had streaked unnoticed past the Earth. Unfortunately Jess's comet is likely to be visible only in electronic camera images and in 2037 will once again cross Pluto's average distance from the Sun on a path which will take it into truly deep space. Until a few years ago all of the comets human astronomers had observed originated in the distant regions of our solar system, the Kuiper Belt or the Oort Cloud . Perhaps C/2018 F3 (Johnson) is an interstellar visiting Comet and is thus a sample of a place currently beyond our reach.
Viewed in a telescope an asteroid appears as a moving star like point of light while a comet often appears to be a fuzzy point of light with a tail. The orbit of an asteroid is governed force of gravity exerted by the Sun, planets, and in some cases our moon. In addition the Yarkovsky Effect can cause the orbit of a spinning asteroid to shift slightly over millions of years as the heat it absorbs from the Sun radiates back into space. Comets on the other hand can have orbits which change erratically as its nucleus emits small rocket like bursts when frozen gases trapped within it are heated by the Sun.