October 22, 2017

27.07.9: What Ails Jupiter?

Something has slapped the largest planet in our solar system as of late. A large black spot has emerged in Jupiter’s southern polar region, reminiscent of the Shoemaker-Levy 9 collision of 15 years ago. Initially discovered by Anthony Wesley of Australia utilizing a 14.5” reflector early last week, the discovery was backed up mid-week by NASA’s Infrared Telescope Facility in Mauna Kea, Hawaii. Looking similar to a Galilean satellite shadow, it has all the hallmarks of an impact. Will it evolve and develop over the coming weeks and months? By the time this goes to (word)press, we hope to get a glimpse of it here at Florida Astroguyz HQ. Leading theories are; 1. a comet; 2. an asteroid; 3. The monolith from 2010 compressing Jupiter into a star. The “Great black spot” of 09′ leads the more pedestrian Great Red Spot by about 2 hours of longitudinal rotation, as Jupiter spins once an amazing 11 hour day. Rising around 10 PM local, the planet is well placed for observation from midnight onward. And don’t forget to check your observations against any potentially confusing moon shadow transits! Word has even come to us of a “white spot” on Venus… its nice to see folks looking at, and making discoveries in our solar backyard again. Will the whole solar system (or at least the Internet) break out in spots?

This week’s astro-word of the week is the Roemer Hypothesis. I love the quote from the Hitchhiker’s Guide where Douglas Adams states “light travels so fast that it takes most civilizations millennia to discover that it travels at all.” Danish astronomer Ole Romer was the first one in our civilization to figure this out, and he used Jupiter to do it. In 1676, he discovered a curious fact; that transits and occultations of Jupiter’s four large moons consistently occurred later than predicted when the Earth was on the opposite side of its orbit and consistently earlier when it was on the same side as the gas giant. Rather than dismissing this as simply a product of the “crappiness” of the almanacs of the day (as most astronomers did) he correctly deduced that the light was being “retarded” in some manner, hence taking time to transit. Not that he was searching for the speed of light; like many of the great discoveries in science, his was purely serendipitous. Many astronomers of the day sought to use the transits of Galilean satellites to solve the longitude dilemma. Just how navigators were supposed to fix on the tiny moons from the deck of a pitching ship was another problem entirely! From Roemer’s meticulous observations, Christian Huygens calculated that light travels about 130,000 miles per second, about 70% of today’s accepted value of 186,282 miles per second. Had he not misinterpreted Roemer’s value of 22 minutes for light to cross the diameter of the Earth’s orbit, he would have got it almost right. (It actually takes 998 seconds, or about 16 minutes and 38 seconds, according to Astroguyz’ calculations).

Incidentally, this is an experiment that you can do from your back yard as you are “black spot hunting…” just remember that modern day tables account for this deviation. Do I smell a “home experiment” blog post in the offing?


  1. [...] Belt that it’s embedded in pulls a “disappearing act” every decade or so, as it last did in 2009. Along with the Great Red Spot, the northern and southern belts are the first features noticeable [...]

Speak Your Mind