Astronomy 3L, Section 4215 Spring 2011

05/19/11:
Today we took the last quiz at the beginning of class. Our activity for the week was a discussion-based examination of the possibility of life in the universe. Each student played the part of a scientific expert on a particular subject attending a conference on life in the universe. We tried to estimate the number of life-bearing worlds in our galaxy, and the number of intelligent civilizations that we could talk to within the Milky Way. After looking at some reasonable estimates and applying some probabilities based purely on speculation, we talked about the Drake Equation and then did some follow-up questions.

05/12/11:
I went over last week's quiz results (the average was 11.5 out of 15) at the beginning of class, and cleared up some confusion about the difference between an assumption, a calculation, and a conclusion in an argument. We did two activities today focused on the expansion of the universe. First, we measured the redshifts of five galaxies from their spectra, and used their distances from the Milky Way to plot the Hubble Law. We then used that plot to determine the age of the universe. In the second exercise we used two simulated images to visualize the expansion of the universe and, again, determine its age. We then looked at some statistics of our data and computed the standard deviation of our data sets.

05/05/11:
We took Quiz #6 at the beginning of class today, and I went over the most recent homework assignment and last week's lab. We had two activities today centered around measuring the properties of galaxies. In the first activity, we learned how to classify galaxies according to their shape (or "morphology"), and figured out how far away they were. In the second activity, we used an image called the Hubble Deep Field to estimate the total number of galaxies in the universe. We then used this number (along with some more estimates) to try and figure out the overall density of the visible universe.

04/29/11:
I went over last week's quiz at the beginning of class (average score was 10 out of 14), and talked about the main ideas from last week's lab. We did two activities this week, one about the life cycles of stars and one about black holes. In the first activity, everyone got a balloon of one of four colors: white, red, yellow, or blue. We simulated the evolution of a cluster of stars by blowing them up (as they turn into supergiants or giants) or popping them with thumbtacks (when they go supernova, if they have high enough mass). We looked at a compressed time scale to see the differences in the life spans of different masses of stars. In the second activity, we used more balloons and tin foil to simulate the collapse of a stellar core into a black hole, and measured how the density changes as it gets smaller and smaller in size. We also compared the density of our tin-foil stellar cores to the actual density of neutron stars and white dwarfs.

04/21/11:
Today we took Quiz #5 at the beginning of class, then I did a short intro about how filters work using the Hubble Color Toolbox. Our lab for this week involved looking at many different images of objects throughout the universe, and learning how filters are used to create and interpret those images. We also brushed up on how to use the star wheel.

04/14/11:
I went over last week's quiz at the beginning of class today (average was 12/16) and last week's lab before starting our activity. This week we studied HR diagrams by looking at a few different populations of stars. First, we compared the HR diagrams of the nearest stars and the brightest stars, and saw that for main sequence stars there's a relationship between the size, temperature, and luminosity. For the second half of lab, we plotted HR diagrams of two different star clusters and used the diagrams to determine the relative ages of the two clusters and their relative distances from Earth.

04/07/11:
I went over last week's lab at the beginning of class, and then we took Quiz #4 before starting our activity. For our lab this week we built two scale models using styrafoam balls, string, and thumbtacks. Using the styrafoam balls to represent stars, we hung them from the ceiling to make a scale model of the 20 nearest stars to the Sun. We also made a second model, this time representing the 20 brightest stars as seen from Earth. We looked at the properties of these two groups of stars using their spectral types (OBAFGKM) and luminosities, and answered some questions about the differences between apparent and absolute magnitude.

03/31/11:
Today we began class by looking at the Sun. We observed several sunspots using two different methods: we projected an image of the Sun onto a sheet of paper using a smaller telescope, and viewed the Sun directly using a larger telescope and solar filter. The rest of our activities involved measuring the speed of a solar prominence and the Sun's rotation period using images of the Sun. We learned how to determine the scale of an image in today's lab, which will be an important technique on the quiz next week. If you'd like to keep track of the Sun's activity, the website spaceweather.com is a particularly good site to use.

03/17/11:
I handed back last week's lab and went over some of the more confusing questions at the beginning of class. We turned in Homework #2, and then spent some time talking about what factors influence how many stars one can see in the night sky. For this week's activity, we used star charts of the constellation Orion to simulate different levels of light pollution typical of urban, suburban, and rural conditions. We used these charts to determine the limiting magnitude of each type of sky conditions, and then used the limiting magnitude to figure out how many stars would be visible in the sky. Our next homework assignment involves following the plan written out at the end of the lab to collect similar data for two different observing locations around Sonoma County. Unfortunately bad weather prevented us from practicing our star-counting technique outside, but we will go over the process as a class on the next time we have a clear sky.

03/10/11:
I handed back last week's lab on spectral classification at the beginning of class and went over the main ideas, then we took Quiz #3. Our lab for this week centered on how astronomers measure the distances to objects out in space. Our first activity focused on how astronomers measure the parallax of nearby stars from images of those stars. We also saw how radar pulses can be used to measure distances within the solar system, and how standard candles can help us measure larger distances across our galaxy. Later in the semester we will learn about Hubble's Law, another method used to measure distances within the universe. If you're interested, here is a link to a demo showing parallax of stars.

03/03/11:
I handed back Quiz #2 at the start of class and went over the answers (average was 12 out of 16), and went over the main ideas from last week's exercise on spectroscopy. Our activity for this week involved studying the spectra of six different stars, and determining their spectral class (OBAFGKM) using the stars' temperatures. We also measured the strength of the key hydrogen absorption line (the H-alpha line) to see an alternate method of determining a star's spectral class.

02/24/11:
We took Quiz #2 at the beginning of class, and turned in the observing homework. Our lab for the week focused on the study of spectra. We learned how to use diffraction gratings and spectrometers, and looked at examples of continuous, absorption, and emission spectra. Next, we spent some time in small groups learning how to identify elements based on their spectra, measuring the wavelengths of different visible colors, and understanding how an object's spectrum influences the overall color blend that our eyes detect.

02/10/11:
This week I began class by going over the first quiz (average score was about 12 out of 15) and last week's lab. This week we looked at the two fundamental properties of a lens (diameter and curvature) and how these affect the images produced by a lens. We characterized a set of six lenses and learned how a lens can produce a large or small image, and a bright or dim image. Next we built some simple two-lens refracting telescopes and learned about the relationship between a telescope's magnification and field of view.

02/03/11:
After handing back last week's lab, we took the first quiz at the beginning of class. Our lab for the week focused on how the force of gravity works. By dropping pennies and timing how long it took them to fall, we were able to measure the strength of the gravitational force due to the Earth. We also did some very basic error analysis with our data sets, and used our results to figure out the mass of the Earth using Newton's law of gravity.

Quiz #1 is next week at the beginning of class!

01/27/11:
At the beginning of class today I went over some of the more confusing questions from last week's lab, then we talked about the need for scientists to estimate their uncertainties whenever they make a measurement. We did a short exercise on measurements and errors, then talked a bit about the motions of the Earth and their time scales. Our main activity covered the motions of the night sky over one day, over one year, and over several thousand years. We also reviewed the ecliptic from last week, and talked briefly about how the Earth's axis wobbles slowly over 26,000 years due to precession. Next, we set up a model of the Sun, the Earth, and the constellations along the ecliptic in the lab room and used the model to determine what will be visible at different times of year. Next week we will take Quiz #1 at the beginning of class on the material from this week's and last week's lab; you can find a review sheet posted above.

01/20/11:
Welcome to Astronomy lab! Today I went over the syllabus and course structure, then we did an activity about the Celestial Sphere and how to look up the positions of stars in the sky using a star wheel. Here's a link to the Celestial Sphere Demo I was showing on the projector. We also went outside after it got dark and got some practice using the star wheel to orient ourselves in the night sky, and looked at the Big Dipper, Polaris, and the constellation Orion. Finally, I did a quick refresher on scientific notation and how to multiply and divide numbers using this shorthand. Don't forget to answer the prelab questions before class next week.