PHY 515: Astronomy Summary and Experiment List

(Fall 2008)

Note: Following a re-evaluation of the laboratory courses, the following is in effect as of the fall 2008 semester:

Purpose

The rigorous description of the Astronomy experiments is on on another page. This description is intended only to give you a flavor of the experiments, to help you choose which one, if any, you wish to try.

General

Development and use of detectors in Astronomy (mostly for photons, but also neutrinos, cosmic rays, gravity waves, and exotica) is a thoroughly experimental science, like the rest of physics. But the study of astronomical objects itself is not: unlike in labs, our subjects of study cannot be manipulated by turning knobs, nor can experimental circumstances be changed. As a result, we have to make do with whatever experiments Nature has decided to perform for us right now. In general, such experiments are much less clean than those in the lab: a typical Astronomy situation is `messy'. There are two ways in which astronomers try to counter this. First, by performing very large systematic surveys and keeping an eye open for little gems, we try to find at least the cleaner among the natural experiments. Second, we perform detailed analysis of large bodies of data on a given object to separate the systematic from the incidental.

The emphasis in Astronomy therefore often lies in automated and/or complex data analysis, with the help of computers. Each of the experiments in the Astronomy section of the lab bear this out by not only having you take data but also having you write a computer program, in IDL or C, to analyse the data.

Note on Scheduling

There are three computer stations available in the lab. Because these are generally computer-intensive labs not requiring specific hardware, students can work off hours from at the Math SINC site (where IDL is available), or from other location if they have access to the appropriate software.

Because we are dealing with software and not experimental equipment, there is nothing to prevent two or more groups from undertaking the same exercise, although there may be scheduling conflicts with use of the 14" telescope in some cases.

The Specific Experiments

Jupiter and Speed of Light Not available this semester.

In this classic experiment, whereby Ole Roemer was the first to measure the speed of light, eclipses of the moons of Jupiter are observed. You will use archival data plus an observation of your own. Since the Earth-Jupiter distance varies, the varying travel time of light from the eclipse moment causes variations in the apparent time at which we observe the eclipse. Knowing the orbit of Jupiter and Earth, this can be used to find the speed of light. The data in this experiment are relatively simple, and the analysis a bit more involved. Tell me more!

2. Eclipsing Binary Star Not available this semester.

One of the hardest measurements to make of a star is its mass and distance, yet these properties are essential to testing theories of stellar structure and evolution. The one place where these measurements can be made relatively free of assumptions is in binary stars, because the motion of one star measures the effect of the other's gravity (as we can weigh the Sun by measuring the orbital size and period of the Earth). In eclipsing binary stars, the regular dimming when one star occults the other also allows a measurement of the stellar radii. In this lab, you will use a CCD camera on the 14-inch telescope at Stony Brook to observe the eclipse of a binary star. You will also use archival satellite data to measure the orbital velocities of these same stars, and thus measure their masses and radii. This lab has most of its effort in the acquisition and reduction of the data, after which the analysis is relatively simple. Tell me more!

3. Solar Rotation Not available this semester.

Using daily changes in the pattern of sunspots or other features on the Sun, we can measure how fast it rotates around its axis, and how this rotation varies between the polar and equatorial regions of the Sun. You will measure sunspots using a telescope and other features using X-ray images taken daily by the Yohkoh satellite to perform this analysis. Data acquisition and analysis are both neither very simple not very complex in this experiment. Tell me more!

4. Radio Astronomy Lab Not available this semester.

This lab requires the facilities of the Haystack Observatory.

5. The Hubble Law

In the 1030's Edwin Hubble discovered and quantified a relationship between the distance of galaxies and their recessional velocity. This provided the first proof that the universe was expanding (and led Albert Einstein to renounce the Cosmological Constant". The slope of the relation is called the Hubble Constant, and its inverse is proportional to the age of the universe. Measuring the value of the Hubble Constant has not proved simple; the latest (and we hope definitive) value is about a factor of 7 smaller than Hubble's first estimate.

Your task is not so demanding as to derive the correct value of Hubble's constant, but rather to show that the universe is indeed expanding. To that end we have assembled images and spectra of 30 Sc galaxies. Your task is to estimate their distances, measure their recessional velocities, and verify that Hubble was on the right track. Tell me more!

6. The Cepheid Period-Luminosity relation

Distances are one of the most fundamental quantities we need to measure in astronomy: linear size scales with distance, luminosity scales with distance2. Close in we can use trigonometric parallax to estimate distances to stars, and main sequence fitting to estimate distances to star clusters. Aguably the most important rung in the cosmic distance ladder, that which ties the galaxies together, involves the Cepheid variables. The delta Cephei variables are supergiants (hence very luminous and visible to great distances) which pulse regularly. In 1908 Henrietta Leavitt noted that the longer period Cepheids tended to be more luminous than the shorter period systems. In a classic study, she determined the periods and brightnesses of a number of Cepheid variables in the Large Magellanic cloud, and demonstrated a linear relation between luminosity and period. This was later calibrated absolutely.

Your task is to find the Cepheid variables in two fields in the Large Magellanic Clouds, measure their periods, determine their relative brightnesses, and derive the p-L relation. Tell me more!

7. Create Your Own Project

If you have enough of an Astronomy background to judge projects for yourself, you may want to select from one of these choices:
  • a project involving planning and then analyzing observations using the SMARTS facilities at Cerro Tololo, Chile,
  • an analysis project involving archival data of your choice, or
  • an observing project using the 14-inch SBU is a member of the SMARTS consortium, which operates the small telescopes at Cerro Tololo. The USB participation is summarized here. Time has been set aside on the 1.3m telescope (ANDICAM dual channel imager) and the 1.5m telescope (RC spectrograph) for student projects. Or, if you wish to observe a northern hemisphere object, you can use our own 14" telescope In addition, there is a vast store of data available in archives via the Web, in case of ground-based observatories very eclectic, for satellite data quite systematic, of which you can make good use.

    Your project proposal has to be ready for approval by the Astronomy teacher of the lab at least one week prior to the start of the lab period in which you are scheduled to do this. You are encouraged to informally discuss your idea even sooner, so that the chances of finding a doable non-trivial project are maximized. Tell me more!

    Created by RAMJW; Last Updated: 31-Aug-2008 by FMW