Monday, May 29, 2006

Noctilucent clouds: A volcanic ash cloud from Mt. Pinatubo

I have never seen a noctilucent cloud.

I've been far enough north before, roughly the arctic circle, but I
was up there in September and the clouds are entirely summer events, lit up by sunlight streaming over the pole.

I believe though, that I've seen what they would look like. In late
June of 1991 I was living in Las Vegas with my parents (that's what being in high school will do for you) and was in complete harmony with celestial cycles. Sunrise, sunset, moon phases, etc. There is room for another post in that, but the point I am trying to make was that I was very sensitive to the timing of the sunset and the fading of the daylight.

Mount Pinatubo in the Phillipines blew itself apart in one of the largest eruptions of the 20th century on June 15th. The explosion sent cubic kilometers of material high into the atmosphere, breaking into the stratosphere. Once material is in the stratosphere, the only way of removing it is by gravity or ultraviolet light destruction. Small particles fall really slowly, yah? I didn't think an explosion located literally on the other side of the globe would be so evident.

The sun had just set and I was in my bedroom reading with the fading twilight that was still coming through the windows. After about fifteen minutes, I noticed that instead of getting darker, it had suddenly brightened outside. I went out and was shocked to see a broad glowing cirrus cloud covering the western horizon up to about thirty degrees above the Spring Mountains. The cloud was glowing eerie white-yellow against the deepening blue. I was shocked enough to get my father and showed him
the cloud. It was like a spiderweb of cirrus. The color deepened into fluorescent pink and then faded away nearly an hour after sunset. For a few weeks details in the cloud could still be seen--although it spread and faded away. The nights were not as clear for a year afterward, as the ash slowly fell out of the stratosphere.

The Cocteau Twins "Heaven or Las Vegas" album art reminds me of this period and of the glowing cloud in the west that night.

P.S. This entry was originally written two years ago. I finally found an image I took of it and Venus.

Tuesday, May 23, 2006

Geiger counter for Regenstein back up

The live radiation readings from the Reg is back up and running. I took it down to use it for the Scavenger Hunt this year. The item was:

89. Find the most radioactive place you can get on campus without breaking any rules, laws, or safety regulations. Record the radioactivity level in μrad/h. [5 points. -100 points if we have to call radiation safety].

Saturday, May 20, 2006

My apologies--I've been visiting an ailing family member, but am back in Chicago.

Saturday, May 06, 2006

The old telescope maintenance routine -- a Carl Bamberg transit

I spent today trying to do all of the maintenance work at the Ryerson Observatory that has been long-delayed by lack of time. We generally hold these "work days" once an academic quarter.

One of things we decided to do was to move our Carl Bamberg transit telescope down to the office to decide on cleaning and to see if we can put it out on display somewhere. It's a historical instrument, being the first transit at Yerkes Observatory and on campus here at the University of Chicago for over a hundred years. It's not in use and suffers a harsh life in a box on the roof.

Transit telescopes are meticulously aligned to the meridian (a line running north-south) and are designed to measure the exact moment a known star crosses that line. When that happens, the stellar time is exactly the Right Ascension coordinate of that star. Once you have the stellar (or sidereal) time, it's easy to convert into solar time. This was the premier method of accurate time measurements until atomic clocks appeared. The one we have is called a broken transit because the light is bent 90 degrees in the middle of the instrument. It is also known as a geodetic transit.

Inscribed on the brass objective lens assembly is "Carl Bamberg Friedenau No. 1300."

Also noted, after hearing falcon cries for two days in a row, was I discovered that we are hosting a peregrine falcon's nest just below our office windows. They didn't pick the best of sites: it's in a rain gutter. I wonder if I can get a non-obtrusive webcam pointed at them.

I see the Smithsonian also has a Bamberg transit.

Somebody in Germany has one too (slow link).

Instructions on running University of Washington's transit is here.

And let it be known, any proper Scientific Instrument should be made of brass and green felt.

UPDATE: After looking a NMAH Geodetic Transit, I think the filar micrometer floating around the office could be originally from the transit. Look at the right side of the transit in the image.

Monday, May 01, 2006

Oligarchic Growth of the large planets: from systemic

Wonderously descriptive imagery of the earliest moments of the gas giants by Greg Laughlin at systemic:

The atmosphere bulks up fast. Liberated hydrogen and helium gas bubbles up from the layers of denser materials in the interior. The oligarch passes several Earth masses in size, and grows massive enough to grab gas directly from the disk. Meanwhile, new planetesimals are arriving all the time. Kilometer-sized projectiles streak through the exosphere, exploding as they slam into the atmosphere. The unsettled skies are continuously ablaze with meteors. The temperature rises, becoming so warm that the atmosphere glows a dull coal-red in the darkness of the nebula.

When the growing oligarch, now a full-fledged protoplanet, reaches seven or ten times the mass of the Earth, it is pulling in gas as fast as it can. The atmosphere has swelled and bloated to a thickness of literally hundreds of thousands of kilometers. The gas glows fire-engine orange, and pours infrared light out into space. This radiation is accompanied by slow settling of the lower layers, providing room at the top for more gas to flow in.

Oligarchic Growth