Gravity Probe B

9 05 2011

Last week, while my attention was elsewhere (no one can prove I was watching KLF videos on YouTube), NASA announced the results of an EPIC space-time experiment. The World of Warcraft language is all theirs, but I have to admit that EPIC is an appropriate descriptor in this case. According to analyses of data returned by Gravity Probe B (GP-B), Einstein was correct.  The earth exists within a 4-dimensional space-time fabric that behaves precisely as predicted:  the mass of the earth dimples space-time and the movement of the earth distorts the dimple, creating a vortex or swirl in space-time.

GP-B is a nifty little instrument. As the graphic below shows, the orbiting spacecraft encapsulates a 9′-tall, 650-gallon dewar flask (thermos)  filled with cooled liquid helium. Before launch, the cigar-shaped probe was inserted into the helium along the central axis of the flask.  The instrumental component of the probe is the Science Instrument Assembly (SIA), which is composed of a telescope and a quartz block housing four gyroscopes.

Gravity Probe B Payload Components. Image courtesy of NASA.

In 2004, the spacecraft, complete with SIA, was launched into a polar orbit 642 km (400 mi) above the Earth.  After the satellite reached orbit, the telescope and the spin axes of the four gyroscopes were aligned with a pre-designated star. The goal was to keep the telescope aligned with the star for a year without making similar axial corrections to the gyroscopes.  After a year, the (postulated) precession change of the spin axis alignment of the gyros would be measured in respect to the plane of orbit (the geodetic precession) and the plane of the Earth’s rotation (frame-dragging precession).

Scientists are interested in the geodetic effect because it is an effective measure of how far the Earth is warping its local space-time.  The axial drift is incredibly small (0.041 arcseconds over a year, with one arcsecond equalling 1/3600th of a degree), but the fact that it was measured at all indicates that the axis was tracing the curves introduced into the fabric of space-time by the mass of the earth.  Most simply, the measure of geodetic precession reflects the “dimple” in space-time.

Scientists are even more interested in  the frame-dragging effect, however.  The idea that massive celestial bodies drag their local space-time around with them as they rotate was proposed about ninety years ago, almost immediately after Einstein gave us his theory of general relativity. If it’s true that space-time is dragged a bit during rotation, we would expect to see evidence not of a perfect dimple, but more of a twist, like a small tornado.  It works on paper, anyway, but we’ve lacked the ability to measure the drag.

Until Gravity Probe B, that is.  This is actually the spectacular part:  the design team managed to encapsulate the probe in a drag-free satellite that protected the gyroscopes from disturbance as it moved through the planet’s outer atmosphere. Moreover, they designed a device that measured the spin of the gyroscope without actually touching the them (which would have disturbed their motion and made the results useless).  While the results might indeed be EPIC, I have to admire the design process even more. Sometimes it can be difficult to get three people in the same room working collaboratively. Gravity Probe B comes to you courtesy of teamwork between NASA, Lockheed Martin, Stanford University, and King Abdulaziz City for Science and Technology in Saudi Arabia. That is EPIC, indeed.

Read more on the Gravity Probe B technology here and here.  Check out the GP-B in a Nutshell posters for explanatory graphics

Cincinnati Observatory Center

7 05 2011

Cincinnati Observatory (Herget) Building. Photo courtesy of Cincinnati Observatory Center.

My partner and I stopped by the Cincinnati Observatory Center the last time we were in town, even though overcast skies meant conditions weren’t ideal for viewing. Sometimes observatories cancel their public programs on cloudy nights, but the Cincinnati group tries to find something interesting to substitute for a viewing session.  So, if you show up to find clouds, you won’t get to use the Merz und Mahler 11″ refractor, but you might hear a good presentation by one of the undergraduate students on her research, look at some of the new images from the observatory’s astrophotography program, or take a historical tour of the main building. The historical tour is also offered every other Sunday afternoon (or so). [Side note:  there’s a 16″ refractor, built by the same company that built the 40-inch refractor at Yerkes Observatory, Alvan Clark and Sons, but public education programs usually use the Merz und Mahler telescope.]

Going on that tour is a good idea since Cincinnati is the oldest professional observatory in the U.S. and houses the oldest telescope still in use nightly by the public.

That brings me to my real interest in the site–the Herget building. If you walk around the outside of the main building (the Herget building), you may notice this cornerstone:

Original Cornerstone of Cincinnati Observatory. Photo courtesy of Cincinnati Observatory Center.

Cool, huh? Laid by John Quincy Adams in May, 1843 CE. The only problem is, this is the stone from the original observatory building that was constructed on Mt. Ida (renamed Mt. Adams).  The observatory existed at that location until a few years after the end of the Civil War, when the University of Cincinnati took responsibility for the observatory and its existing instruments. Over a period of two years, beginning in 1871 CE, the observatory was moved to its present location on Mt. Lookout, where the old cornerstone was incorporated into a new structure.

Main (Herget) Building, Cincinnati Observatory. Photo courtesy of Cincinnati Observatory Center.

The new building was designed by Samuel Hannaford and Sons, a local but prominent architecture firm. If nothing else, the observatory’s Greek Revival design demonstrates the firm’s incredible versatility.  Around the same time, Hannaford designed the Renaissance Revival (aka Italianate) Cuvier Press Club Building (1862), his own late Victorian house (1863), the Neo-Romanesque St. George Parish Church (1872), the Neo-Gothic Music Hall (1878), the Neo-Romanesque Nast Trinity Church (1881), the Second Empire Palace Hotel (1882), the god-knows-what-but-looks-vaguely-Pugin-esque Elsinore Arch (1883), and the Queen Anne style Balch House (1896).  Sure some of his aesthetic adaptability came from his early training at the firm of Edwin Anderson and William Tinsley (compare Hannaford’s work with Anderson and Tinsley’s Romanesque Revival buildings) and some came from a temporary partnership with Edwin Proctor. Most of his creativity seems to stem from his work with his own sons, though.

Note the original solution for the rotating “dome.”  The flat-sided/flat-roofed cupola rotated on bearings fashioned from cannon balls left over after the Civil War.  The cupola was replaced with a dome in 1895 CE. Today it rotates electronically, although the viewing door is still operated by rope and pulley.

Cincinnati Observatory Mitchel Building. Photo courtesy of Cincinnati Observatory Center.

There’s a second building on the observatory campus, the O. M. Mitchel building. When the 16″ Clark telescope was installed in the main building, the 11″ Merz und Mahler was moved into the Mitchel building. The conical roof on the Mitchel building opened to allow for comet hunting. Nifty, especially in the snow.

Wallpaper Wednesday

4 05 2011

Kokino Megalithic Observatory

Now for something different. Older. Cooler. Rockier.

In 2001 CE, archaeologist Jovica Stankovski discovered a site that dated to the Bronze Age (roughly 1800-1600 BCE for Central Europe) near the village of Kokino in the Republic of Macedonia.*  Near the top of the site, terracotta objects dating to 1800 BCE were discovered in a naturally formed stone “room.”  Even more interesting that those remnants, however,was the disposition of the volcanic rock around the site. As you can see from the wallpaper linked above, the site occupies multiple levels on a hilltop and consists of both natural and human-made rock formations.  In 2002 CE, physicist Gjore Cenev began conducting an archaeo-astronomical analysis of the stones and turned up some interesting results.

In the right-center of the photo, you can see the roughly quadrilateral shapes of stone seats, or “thrones,” that have been crafted and positioned so that they face east.  Not readily visible in the image are the stone sets that Cenev argues were used to mark particular days in the solar and lunar calendars.  The survey team located three stone markers that indicated the location of the sunrise at the summer and winter solstice, as well as at the vernal and autumn equinoxes.  They also located four stone markers that indicated the position of the rising moon on when it was at maximum and minimum declination.  Two more stone markers were meant to measure the length of the lunar month in winter and summer.

Across several publications, Cenev has provided a great deal of information about his team’s approach to measurement and analysis (they basically extrapolated from Gerald Hawkins’ work at Stonehenge in the 1960s).  That anyone is capable of looking at a pile of stone put together 3800 years ago and figure out what’s going in terms of astronomical observation is amazing enough; that they were able to postulate certain societal behavior from their study is even more so.

For example, Cenev notes that the position of the lunar markers suggests that the Macedonians were aware of the metonic (19-year) cycle of the moon. [Briefly, it takes 19 years before a full moon to appear in exactly the same place again.]  However, to gather enough data to determine the metonic cycle conclusively, astronomers would have needed make lunar observations for some 38-57 years.  Given a life expectancy of forty years for ancient Macedonians, that means the society assigned enough importance to the calendar to conduct observations for at least two, and probably three, generations.

There’s more to be read in Cenev’s work:  a single stone seems to mark the location of the sunrise on a day not obviously associated with the calendar, giving rise to the speculation that the day was important for some ritual or another, probably associated with harvest.  The geology of the site is interesting, as the inhabitants took advantage of the local andezite’s tendency to fracture along straight lines, providing them with natural building blocks.  At least some of the observation points can be occupied only by a single person.  So, while it’s interesting to read about the calendrical calculations and how they compared to those made at Stonehenge, it’s even more intriguing to use the (admittedly fragmented) evidence to try and build a picture of the people who built the observatory at Kokino.

*I used three papers by Gjore Cenev for this post:

Cenev, Gjore. “Archaeo-astronomical characteristicsof the Kokino archaeological site.” Bulgarian Astronomical Journal 9 (2007): 133-1.147

________. “Kokino Calendar.” Publications of the Astronomical Observatory of Belgrade No. 85 (2008): 87 – 94

________. “Megalithic Observatory Kokino.” Publications of the Astronomical Observatory of Belgrade No. 80 (2006): 313-317.