PHY 515: Astronomy Summary and Experiment List
Note: Following a re-evaluation of the laboratory courses, the following is
in effect as of the fall 2008 semester:
- The astronomy labs are available only to graduate students enrolled in
Undergraduates who wish to learn astronomical observing techniques should
enroll in AST 443.
- Only two labs will be offered in PHY 515 in 2008. Thse are the Hubble Law
and the Cepheid Period-Luminosity relation.
- We expect to offer more labs in 2009, following the refurbishment
of the telescope on the roof of the ESS building.
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.
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
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
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
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
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
at Cerro Tololo. The USB
participation is summarized
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
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