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.

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].

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

Comet Schwassmann Wachmann 3 passes the Ring Nebula

A fragmenting comet passed the Ring Nebula yesterday:

Animation from Horace Smith

Color image from Stefan Seip / Steffen Brückner.

Spaceweather has many images of the conjunction.

EDIT: This one by Johannes Schedler is great.

SECOND UPDATE: Even Better.

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.

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

Epimetheus, Saturn, and Titan from Cassini

Epimetheus glides in front of Saturn's rings with Titan far in the background.

Phil Plait's Bad Astronomy has pointed out another beautiful Cassini raw image. Think Titan is out of focus? Nope, it's just a thick atmosphere of nitrogen with a touch of methane.

Browse the Cassini's mission raw image archive here.

I made an animation out of another set of Cassini images here.

Aurora from space

Check out this awesome movie of the aurora as seen from the ISS: Movie

Also see Astronaut Don Pettit's longer science movie with real-time looks at the aurora. Don't miss the Manicouagan, Quebec impact crater visible by moonlight about 3/4 the way into the movie.

You can see how restricted the aurorae are to a particular height in the atmosphere (starting at about 100km in the ionosphere and extending up to 300-500km) and the color variation with height (the red emission of oxygen requires an excited atom to remain unjostled by other atoms for a time period before it will emit a particular wavelength).

Astronaut Don Pettit discusses the aurora from space further in this article.

http://eol.jsc.nasa.gov/EarthObservatory/PhotographsofAurorasfromSpace.htm

Robins singing at night and street lights: the light pollution problem

This weekend I traveled to Yerkes Observatory in Williams Bay, Wisconsin, on a trip organized by the Ryerson Astronomical Society. It was fantastically clear all night long. And quiet.

Oddly, at least to my city ears, I heard no birds all night long. The first birds I heard chirping occurred well after the start of nautical twilight at 4:52AM--in fact, it wasn't until the start of civil twilight thirty minutes later that I really began to hear a lot of robins and other birds.

Now, in Chicago, I have heard from friends time and time again, that if they stay up too late, they begin to hear robins singing late at night and can't get to sleep. We are talking 2 or 3 AM, not the expected nautical or civil twilight. What's going on?

I imagine, although haven't studied it, that birds are primed to begin singing by having a biochemical reaction when exposed to a dark period of a certain length followed by light. Plants use this method to produce flowers during certain seasons, and biologically it's easier to have a too-long cycle that is reset daily than to accurately time the cycle. So, for robins, during the night their cycle is reset by the first light they encounter. Normally, this is the dawn. But in many cities, it is unshielded streetlights. And they chirp away.

This is a direct result of light pollution caused by unshielded streetlights in the city of Chicago. Fully shielded lights (also known as full-cutoff) do not emit any light above horizontal--as a result they don't light trees above the streets and keep the birds from singing. You can't say the results from Yerkes are a result of no lights: Yerkes isn't completely isolated--it's in the town of Williams Bay, which has streetlights. Fully shielded streetlights.

When someone asks me if light pollution has a real effect on people other than astronomers, I believe I will mention my friends that can't get to sleep because of the robins.

Messenger departing Earth

The Messenger spacecraft on its way to Mercury flew back past Earth on August 2nd, 2005, and produced this wonderful movie while departing Earth. In 24 hours it moved from about 5 Earth diameters distance to past the Moon's orbit (which is about 30 Earth diameters away). You can see the spacecraft's long low-energy trajectory here. Click on the image above to get the movie.
Why I am posting this? Phil Plait's probably going to mention it, and the movie has been sitting on my "post about" pile for a while.

P.S. Here's the original source for the movie: http://messenger.jhuapl.edu/the_mission/images/flyby_images/mdis_depart.mpeg

The Sodium doublet

Steven previously mentioned his favorite absorption line in the sun's spectrum as sodium. And what's not to like: Strong, conspicuous, identical to the emission you see from low-pressure sodium lights, the sodium doublet is to the Fraunhofer lines like a hot dog is to ballpark food.

With this image I experimented with a vertical blur to remove the variations in intensity along the length of the slit due to dust, irregular coatings, and a small piece of crud in the digital camera. The spectrum is also sharpened, so you can't use this image to find astrophysical data.

The color is weird--I am always surprised how redward the sodium doublet is from where I think it should be in the yellow, but in reality it's more orange than yellow. And yellow is visually such a small portion of the spectrum that there isn't much to it.

Other spectrum posts:
Blue-Violet
Terrestrial Oxygen
The Solar Spectrum: Magnesium Green

Airplane radiation graph with a geiger counter, MDW to LAX

A recent flight to Los Angeles had great results. Halfway through the flight the pilot announced he was dropping from the 38,000ft cruising altitude to 30,000ft to avoid persistent turbulence (in my notes I wrote 36,000ft but it can be difficult to hear what the guy was saying, and I think the data shows a better match to 30,000ft). The data were taken once a minute.



I also added to the graph a yellow line showing the background rate in my office which is 7.5 microrads/hr. So flying at 38,000ft gives you a rate about 40 times greater than here in my quiet little office in Chicago.

I've previously done this on trips to Los Angeles: Dean W. Armstrong: Geiger Counter

In the past I've also looked at potassium salt, Pentax Takumar lenses, dinosaur bones, and have a live report of radiation rates from my office.

Direct measurements of 2003 UB313

Mike Brown, Emily Schaller, Henry Roe, David Rabinowitz, and Chad Trujillo released their Hubble measurements of the disk of 2003 UB313 and found it to be just 34 milliarcseconds in diameter--that's roughly a millionth of a degree on the sky (the moon is half a degree in diameter). That makes it 2400km +-100km in actual size, and makes it a brightly reflective object with an albedo of 0.86+-0.07 (86% reflectivity). Freshly fallen snow on Earth is at most 90% reflective, so the surface of 2003 UB313 has got to be covered in new ice of some sort--Brown et al. suggest methane ice, like Pluto.
Previous measurements using infrared had it at 3000km+-400km.

Search this blog for previous posts about 2003 UB313.

a delay in posting

I had the good fortune of being quite busy over the weekend: I was a guest of Hugh M. Hefner at the occasion of his 80th birthday, and it was quite a bash, even by the standards I've associated with other Mansion events I've been to. But this meant I've haven't any blog posts to put up nor drafts to finish.

Tonight I gave a talk on interplanetary dust to the Ryerson Astronomical Society--a topic I had been interested in since seeing the zodiacal light again during my spring break geology field course, but didn't know much about. I believe the talk was well received. The material was compelling enough that I expect some posts to come from it.

P.S. Official publically-released videos and photos at http://www.playboy.com/worldofplayboy/events/birthday2006/
Peggy and I are in the last video with the Girls Next Door, halfway through the video.

The Moon in the northern sky

While on the couch in my apartment in the late-evening last night the light of the just-past First Quarter Moon fell upon my eyes. It told me a few things--that the Sun would be roughly where the Moon was now in a quarter-year (three months, or early July), and since my window faces northwest the moon was in the northern half of the sky. The "roughly" part had to be included because the Moon's orbit around the Earth is not precisely in the plane of the solar system (also known as the ecliptic). Instead it's tilted off about 5 degrees from the ecliptic, and it's why we don't have solar and lunar eclipses every month. Instead, we only get them roughly every six months: when the intersection of the plane of the moon's orbit and the ecliptic (also known as the nodes) line up with the line between the Earth and the Sun. We just had a solar eclipse just a week ago , so I know that the Moon should be nearly the full +5 or -5 degrees off the ecliptic.

I created a snapshot of the view from the couch with Stellarium and it shows the moon at +25 degrees declination, or a few degrees above the ecliptic, but not fully +5. Why? It's just past first-quarter, so it's heading back down to the ecliptic. When I plugged into Stellarium the previous night, you could see the Moon was at +27.5 declination, some +4 degrees above the ecliptic. Add the two weeks we are past the vernal equinox (where we'd expect the ecliptic to be near +23.5 declination), and it puts the Moon where we see it.

So, come early July, I can be lounging on my sofa in the late afternoon and the Sun should be streaming into my apartment and onto my face (apart from any leaves on the trees blocking it).