Astronomy 3L, Section 0201 Fall 2009

I will use this space to post announcements about the class, scheduling, homework assignments, exam results, etc. If you miss class, check here first to see if you missed anything!

Final Exam is next week!

12/10/09:
I handed back the last quiz at the beginning of class (average score was 11 out of 15), and went over the correct answers. I also brought a grade update so everyone can see where they stand before the final exam. We did a large-group discussion-based activity designed to get everyone thinking about the question: "Is there life elsewhere in the universe?" We looked at the different definitions of life, possible mechanisms for contacting other civiliztions, and the probabilities of life arising on a random world. Next week we will be taking the final exam in our regular classoom from 5-6:45 PM. The review sheets for the final and the previous quizzes are up on the website.

12/03/09:
Today we took our last quiz at the beginning of class, and I will bring those back next week along with a current grade update. Our activities for today involved studying Hubble's Law and 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 and learn how it can tell us the age of the universe. In the second exercise we examined some simulated images of many many galaxies, one representing the universe now, and one representing the universe a long time ago. Using these two images, we were able to measure the distance and time that galaxies have appeared to have moved since the universe began expanding (i.e., since the Big Bang). We then looked at some statistics of our data, computing the average age of the universe and the standard deviation in our data sets. I also talked a bit about standard deviation, what it means in terms of a data set, and how scientists use it to compare relative agreement between different measurements.

11/19/09:
This week I returned Quiz #6 (average score was 12 out of 16), then reviewed the main ideas from last week's exercise. Our last quiz will be in two weeks on 12/3, and the review sheet is posted above. We had two activities today, one of which involved classifying galaxy images according to the Hubble Tuning Fork and determining their distances using the Hubble Law. In the second activity, we used the Hubble Deep Field image to determine the number of galaxies in the universe. Next, we used some estimates to determine the approximate mass, size, and density of the universe and compared these results to what we think will happen to the universe in the distant future.

11/12/09:
We took Quiz #6 today at the beginning of class, then went over the first half of our activity as a group. Using balloons, we collectively simulated the evolution of a cluster of stars. We compressed time so that 1 second represented 1 million years, and were able to compare the length of time it takes stars of different masses to pass through their evolutionary stages. Next, we used balloons and tin foil to simulate the collapse of a black hole, and compared the density of everyday objects to the densities found in black holes and other objects in the universe.

11/05/09:
Today I handed back Quiz #5 (average out of ) and went over the answers, and collected the Images homework assignment. Our activity today had us investigating colored filters and how they are used to create and interpret astronomical images. We saw how a composite picture is formed from several tinted pictures taken with different colored filters, which may or may not approximate true color. We looked at images of star clusters, nebulae, and galaxies using blue and red filters in 3D glasses and were able to analyze the physical properties of the objects based on their overall color. We also got a refresher on how to use the star wheel to look up objects' locations and rise and set times. I also showed some information about how the Hubble Space Telescope uses filters to process images from this website.

10/29/09:
We took Quiz #5 at the beginning of class today, and went over the some points from last week's exercise. Our activities for this week focused on plotting HR diagrams. We investigated the different properties of the group of stars nearest to the Sun, and the group of brightest stars as seen from Earth. We learned how to determine a star's radius from its luminosity and temperature, then plotted color-magnitude diagrams for two star clusters. We used these diagrams to compare the distances and ages of the clusters.

10/22/09:
I began class this week by going over Quiz #4 (average was 9 out of 15) and going over last week's exercise on distance measurement methods. Next I went over the requirements for the Images homework assignment, which will be due in two weeks. Our exercise gave us some insight about the population of stars around us in space. We made two scale models showing the locations of two groups of stars: one showing the 20 nearest to the Sun, and another showing the 20 brightest stars as seen from Earth. We looked at the general properties of each group, and how these properties are related to the selection criteria (i.e., closeness or brightness). Finally, we also learned a bit more about magnitudes and how they can tell us about the luminosity and appearance of stars.

10/15/09:
Today we took Quiz #4 at the beginning of class, then I went over some of the sticky points from last week's exercise on spectral classification. We also handed in our News Article homework. I'll post the next homework here and bring in hard copies next week, along with a grade update of everyone's progress in the class so far. The update will be ordered by the last four digits of student ID number, so you will need to have or know your number to look up your grade. Our activities focused on different methods astronomers use to measure distances within the universe. We learned how radar pulses are used to measure the distances to objects in the solar system, how parallax works for relatively nearby stars, and how standard candles work for distances in our galaxy and beyond. Later in the semester we will also learn one more distance measurement method: the Hubble Law.

10/08/09:
Today I handed back Quiz #3 and went over the answers (average was about 12.5 out of 17), then did a quick review of the differences between absorption spectra and emission spectra. Next, we went over the results of last week's exercise, and I talked a bit about what to expect for Quiz #4. We are going to cover only one lab in next week's quiz so the class has enough time to absorb all the material before being quizzed on it. Our activities for the week involved using observations of the Sun to analyze its features. We used images of the Sun rather than taking our own images, because class starts after sunset and the Sun is not very active at this time. We used the locations of sunspots to determine how long it takes the Sun to spin once on its axis, and then used images of a solar prominence to figure out how fast the material in the prominence is moving away from the surface of the Sun. Next week we will take Quiz #4 and hand in the news article homework. At the end of class, we took a telescope out into the Bech parking lot to look at Jupiter and three of its moons to make up for not being able to observe the Sun.

10/01/09:
We took the third quiz at the beginning of class today, and our activity centered on the system that astronomers use to classify stars, according to their spectra. We re-created the spectral classification system in alphabetical order by measuring the strength of the H-alpha line in the spectra of six diferent stars. Next, we used the underlying blackbody curve in each spectrum to measure the temperatrues of the stars and understand why the spectral classes are listedin an odd order: OBAFGKM. At the end of class I showed this demo of the hydrogen atom that might be helpful in visualizing how the electrons absorb and emit light.

09/24/09:
This week I handed back Quiz #2 at the beginning of class and went over the correct answers. The average score was about 11 out of 14. I also did some review from last week's lenses and telescopes activity in preparation for the third quiz. The review sheet for the quiz is posted above, along with the new homework assignment. Our activities for the week all centered on spectroscopy, the study of spectra. In the first exercise, we familiarized ourselves with the diffraction gratings and handheld spectrometers, and got some practice using them. In the second exercise, we saw several examples of different kinds of spectra given off by gas tubes, light bulbs, fluourescent lights, and the Sun.

09/17/09:
We took the second quiz at the beginning of class today, and I collected the observing homework. Our first activity for the week involved characterizing a set of convex lenses. We measured the diameters and focal lengths of the lenses, and were able to determine how these properties influence the image size, intensity, and light-gathering ability of each of the lenses. In the second activity we used these lenses to create simple refracting telescopes and investigate the relationship between a telescope's magnifying power and the size of its field of view.

09/10/09:
I handed back the first quiz at the beginning of class today and went over the correct answers. The class average was about 12 out of 15. Our activity involved measuring the strength of Earth's gravitational pull on objects. We measured how long it took pennies to drop from a certain height, then used that data to calculate how massive the Earth is using Newton's law of gravity. We also did some very simple error analysis on our data. At the end of class I also talked a bit more about error and uncertainty. Next week we will be taking the second quiz at the beginning of class, so a review sheet has been posted in the above section. I will also be collecting the observing homework next week.

09/03/09:
Today we took the first quiz at the start of class. I will have those graded and returned to you all next week. Our activities today focused on verifying Kepler's three law of planetary motion to the orbit of the Explorer 35 spacecraft. We saw that it follows an ellipse with the Moon at one focus, sweeps out equal areas in equal times, and used Kepler's third law to determine the period of its orbit. It was a nice clear night, so we had a chance to go out and do some naked-eye observing. I showed the class how to find Polaris using the pointer stars in the Big Dipper, and pointed out the planet Jupiter to everyone in the southeast.

08/27/09:
I have posted the first homework assignment and a review sheet for next week's quiz in the section above. Our quiz will cover material from today's lab and last week's lab. This week's activities involved studying the motions of the night sky over one day, over one year, and over many years. I showed this demo displaying two different viewpoints of the night sky's daily motion. 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, Earth, and zodiac constellations in the lab room and used the model to determine which constellations are visible at different times of the year. This demo might also be useful for demonstrating the constellations of the zodiac.

08/20/09:
Welcome to Astronomy Lab! This week I spent some time going over the syllabus and how class will be structured. Our activities included learning how to use the Star Wheel, a refresher on using scientific notation. We also did an exercise on scientific measurement, uncertainty, accuracy, and precision. The weather was slightly cooperative, and we were able to do a little parking lot observing of the Summer Triangle. If you're reviewing for lab next week, we will be covering the motions of the night sky over a year and the constellations along the ecliptic.