Introduction to Science in the Galactic Plane
Lesson 2: Image Analysis
This is the first in a series of exercises that allows a student to
perform analysis of real radio-astronomical data. During the course
of this and the following exercises, the student-experimenter will
analyze images taken by the Green Bank Earth Station. The Green Bank
Earth station uses a 45 foot parabolic antenna connected to a very
sensitive radio receiver operating in the microwave part of the
electromagnetic spectrum. The frequencies of the receiver are
8.35 GHz (wavelength of 3.6 cm) and
14.35 GHz (wavelength of 2.1 cm).
This activity is usable for high school physical science, astronomy,
and physics classes
The planet Earth orbits a star that resides in a spiral arm of the
Milky Way galaxy. Our planet is about 26,000 light years distant
from the center of the galaxy. As we observe the galaxy, we see it
as an 'edge-on' view. Think of looking at the edge of a pancake
rather than at the top of the pancake. As a result of the clouds of
dust and hydrogen gas, visible light tends not to penetrate well
throughout the galaxy. Radio waves pass through these regions with
greater ease; therefore, radio astronomers are capable of viewing
parts of the galaxy that are invisible to visible-light astronomers.
In this exercise, you will be viewing the galaxy as a radio
astronomer views the galaxy. Think of this as having a different pair
In this project, you will use image processing software to load and
analyze sets of images taken during the GPA survey. The analysis is
based on a careful measurement of the intensity of the same object at
the two survey frequencies. Those objects that yield a reasonably
constant intensity will be classified as thermal objects. Those
objects that yield a decreasing intensity as frequency increases will
be classified as supernova remnants. Positional data for each
identified object will then be obtained. Comparison between your
measured position and the true position from astronomical tables will
confirm your hypothesis.
A supernova remnant catalog is
available on the World-Wide-Web at
DESCRIPTION OF THE DATA
This CDROM contains calibrated radio wavelength images of the Milky Way
(our galaxy). These images are obtained by the Green Bank Earth
Station, a 45 foot diameter parabolic reflector and radio receiver
operating in the microwave part of the radio spectrum. The receiver
frequencies are 8.35 GHz and 14.35 GHz. The CDROM contains FITS
images as well as software to analyze the images. FITS stands for
Flexible Image Transport System. It is the standard format for
recording and transmitting astronomical images and data. The images
contain information on what part of the sky has been
observed and what is the intensity of the radio signal from that part
of the sky.
To get the most out of this activity, students should have a basic
understanding of the following concepts:
loading image processing software
loading FITS images
IMAGE PROCESSING INSTRUCTIONS
Recommendation: students work in groups of NO MORE than 3/group;
therefore, students are more individually involved in the research.
Navigate to the SIP icon on the CDROM and open the program.
Read the opening paragraph titled:
'How to process images with SIP'
Skip down and read the paragraph titled:
Choose 'back to SIP homepage'. Open SIP program using button.
Choose FILE OPEN;
IMAGE FILE FROM USER'S MACHINE|
Choose 'gpa' and filter; filter lists available files.
Choose VIEW; change IMAGE DISPLAY PARAMETERS|
SET:||minimum display value= 0;|
|maximum display value = 5;|
|colors= false color|
ANALYSIS TO BE PERFORMED BY STUDENTS
Galactic Plane Science
Choose ANALYZE and Determine Centroid or Instrumental Magnitude of
Object. Take readings of x- and y-position, object instrumental
magnitude, and object flux for the 10 brightest objects. Record
this data in your data table.
Which object is brightest and which object is least bright at
How does the brightness of radio sources compare with the same
objects at visible wavelengths?