Monthly Archives: November 2014

Breaking the Wishbone - How to Win

The folks over at Michigan Engineering did some modeling, 3D scanning, and experimentation to tell us how to win at the age-old Thanksgiving game of breaking the wishbone. According to the folks over at, the tradition is much older than Thanksgiving, dating back over 2400 years to cultures that believed that birds were capable of telling us the future. There is even suggestion that the phrase "getting a lucky break" can be traced to this tradition.  If you want to win, watch the 76 second video below and remember: choke up, stay stationary, and pick the thick side.

We Are ... Seismic Noise

2014-10-28 13.27.05

Over the last few months construction crews have been hard a work tearing into the building adjacent to mine on the Penn State campus. Lots of demolition has been happening as the old building is completely cleaned out and being rebuilt. Some of the noise has been so strong that we could feel it next-door. As a data-nut, my first thought was "I'm going to look at this on our seismometer!"

At the base of Deike building (the geoscience building), we have a seismometer. The station, WRPS "We aRe Penn State", has been in operation on an isolated pier for some time, so we have lots of data to look at! For our purposes, I downloaded the entire month of October for 2013 and 2014. There are some hours/days that are missing, but we'll ignore those and work with what we have. This is a common problem in geoscience!

First let's just make a plot of this year's data. Each square represents one hour (24 squares in a row), and each row represents one day. Missing data is the lightest shade. The squares are colored by the strength of the seismic energy received during that hour; the darker the square, the more energy received.

WRPS_2014_HourlyYou'll immediately notice that there is always more noise starting about 11 UTC, which is the 7-8 AM hour locally. This is about when people are coming into work, vibrating the ground and buildings on campus as they do. The noise again seems to die off about 21 UTC or the 5-6 PM hour locally. This again makes sense with people leaving work and school. This isn't split finely enough to look for class change times on campus, but that could always be another project.

The other thing to point out is the dates of October 4-5,11-12,18-19,25-26. These are the weekends! You notice there is less of the normal daily noise traffic with fewer people on campus and construction halted. There is a repeating noise event at 11 UTC on the 1st, 12th, 20th, and 27th. I'm not sure what that is yet, but looking at more months of data may indicate if that event is associated with equipment starting up, or is really random.

While these daily life trends are interesting, they have been observed before. This whole discussion started with construction and how it was affecting the noise we saw on our local station. To examine this, I made a stacked power spectral density plot. Basically, this shows us how much energy is recorded at different frequencies. The higher frequencies would be human activity.


We can see that the curves from 2013 and 2014 are very similar, with the exception of the 11-16 Hz range. In that range, the energy is higher in 2014 than in 2013 without construction by about a factor of 10. That range makes sense with construction activity as well! The energy remains elevated even after the main bump out to 20 Hz.

You might be thinking that such a bump could be due to anything. That's not necessarily true considering that we have stacked a month's worth of data for each curve. To show how remarkably reproducible these curves are, I made the same plot for the same times with a station in Albuquerque, New Mexico.



In the Albuquerque plot, the two years are very similar, nothing like the full order of magnitude difference we saw in University Park. There are obviously some processing effects near 20Hz, but those are not actual signal differences, just artifacts of being near the corner frequency.

That's it for now! If there is interest, we can keep digging and look at signals resulting from touchdowns in football games, class changes, factories, etc. A big thank you to Professor Chuck Ammon as well for lots of discussion about these data and processing techniques.

315 Million Miles From Home, Cold, and Landing on a Ball of Ice


Image: Wikimedia

Tomorrow (November 12, 2014), the Philae robotic lander will detach from the parent spacecraft, Rosetta, and begin its short trip to the surface of comet 67P/Churyumov–Gerasimenko. This is a big step in technology and spaceflight! I'm sure we'll hear lots of fascinating new discoveries in the coming weeks, but before the lander detaches I wanted to point out how amazing this mission already is and a few things that it has already taught us.

First, let's talk about distance and speed. Space often confounds us with mind-boggling distances, sizes, and speeds. Rosetta was launched in 2004 and made a few loops in the inner solar-system to use gravitational acceleration to help it get out past Mars. As of this writing, Rosetta was about 315 million miles away from Earth, having actually travelled much further (map below). It is orbiting a small body (a comet) that is traveling at about 44,700 miles per hour (20 km/s). It is also orbiting very low to the comet, only about 19 miles (30 km) off the surface.

Image: ESA

Image: ESA


In the morning, at about 3:35 AM Eastern Time, the Philae probe will detach from the orbiter and begin the seven hour journey to a landing on the comet's surface. Not only is landing on a moving target far from home difficult, but it is made even more difficult by the small size of the comet. We know that small bodies exert less gravitational attraction on other objects (it's directly proportional to the mass if you remember the Law of Gravitation). Small masses are normally good, because it means that we don't have to be going as fast to escape the gravitational influence of the planet. For example, the escape velocity of Earth is about 25,000 miles per hour (11.2 km/s), while the escape velocity of the moon is only about 5,400 miles per hour (2.4 km/s). The escape velocity of the comet is only about 1.1 miles per hour (0.5 m/s)! Since the spacecraft is descending at about 1 m/s, this presents a problem: it would likely touch the comet, then bounce off, never to be seen again.

To solve the landing problem, Philae has legs with a strong suspension system that utilizes the impact energy to drive ice-screws into the surface. For additional security, two harpoons will be fired into the surface as well.

One of the ice drills securing the lander. Image: Wikimedia

One of the ice drills securing the lander. Image: Wikimedia


Once on the comet, the suite of 10 instruments will begin to collect data about the magnetic field, composition, and other parameters. I'm sure the team will have many fascinating discoveries to share, but in the interest of keeping this post short, I'd like to share one result we already have.

Rosetta has been, and will continue, to collect data from orbit with radar units, cameras, magnetometers, and spectrometers. As Rosetta began to get close, scientists noticed a periodic variation in the magnetic field around the comet. These variations are very low in frequency, about 40-50 milli-Hertz. We can't hear anything that low in frequency, but if you artificially bump up the frequency so we can listen to the data, you get the following:

What is most fascinating about this is that it was totally unexpected! Scientists are unsure of the cause. This is one of the many puzzles that Rosetta and Philae will reveal, along with a few of the answers. Best of luck to the team. We'll check in on the spacecraft again in the future and see what we've learned.

One last note: even traveling at the speed of light, the radio signal confirming the spacecraft status will take about 30 minutes to travel from Philae to us! Be sure to watch live tomorrow (here).