ASTRONOMY 102: LAB 4
- How Big is Our Galaxy?
NOVEMBER 2nd 2023.
Objective:
This lab project “How Big is Our Galaxy?” is an introduction to methods of
measurement astronomers use to get exact assessments of distance. By measuring the widths
of globular clusters and comparing estimated sizes of the RR Lyrae within them, this lab
allows for a beginner’s guide to measurement through observation.
Introduction:
The milky way, while very similar to millions of other galaxies, is special for the
reason that it is home to humankind. Earth is located on the outer edge of one of the arms, yet
still central to the galaxy so stars are observable from anywhere on Earth. By observing
globular clusters such as M15 and the RR Lyrae within, accurate estimations can be made
about distances and sizes of very far away entities. RR Lyrae are variable stars that are used
as standard candles, and therefore act as a way to track and measure other distances due to
their period-luminosity.
Knowing how RR Lyrae present their temperature and luminosity means other stars can be
compared and estimated. Since all the RR Lyrae studied are in M15 they are the same
apparent magnitude, and have the same absolute magnitude for this lab. By studying these
stars using multiple pictures and observed dates, the variable nature of the RR Lyrae will
, produce a mean. This mean will be used to estimate the distance to the cluster M15. In much
the same way, ten clusters will be measured in diameter to provide an accurate measurement
to the center of the galaxy.
Procedure:
For the first section of this lab, eight photographs were analyzed using a small
magnifying glass. In each photograph was the M15 globular cluster and several RR Lyrae
demarked by their apparent magnitudes. Once given a specific, unlabeled star, I used the
magnifying glass to compare other labeled stars to estimate and apparent magnitude. By
observing the apparent brightness of the RR Lyrae and my unlabeled star, I was able to
ascertain a close guess of apparent magnitude.
The second section of the lab required the application “Center of Galaxy”. On the
right- hand side of the program there were a list of ten different globular clusters, and each
was chosen in turn. Each cluster was measured for their diameter based on the general
circular outline the stars made, due to their dense relationship. By dragging the mouse from
one edge of the cluster to the opposite side, the program could calculate the apparent
diameter of the cluster, therefore measuring the distance to it. Once all measurements for the
clusters had been taken and volume- corrected by the program, a distance to the galactic
center is displayed at the bottom of the measurements.
Observations:
Cluster ID Diameter (parsecs)
M15 245.9
NGC 6625 32.3
NGC 6626 54.9
NGC 6637 35.8
NGC 6638 31.4
NGC 6652 25.6
NGC 6656 102.2
- How Big is Our Galaxy?
NOVEMBER 2nd 2023.
Objective:
This lab project “How Big is Our Galaxy?” is an introduction to methods of
measurement astronomers use to get exact assessments of distance. By measuring the widths
of globular clusters and comparing estimated sizes of the RR Lyrae within them, this lab
allows for a beginner’s guide to measurement through observation.
Introduction:
The milky way, while very similar to millions of other galaxies, is special for the
reason that it is home to humankind. Earth is located on the outer edge of one of the arms, yet
still central to the galaxy so stars are observable from anywhere on Earth. By observing
globular clusters such as M15 and the RR Lyrae within, accurate estimations can be made
about distances and sizes of very far away entities. RR Lyrae are variable stars that are used
as standard candles, and therefore act as a way to track and measure other distances due to
their period-luminosity.
Knowing how RR Lyrae present their temperature and luminosity means other stars can be
compared and estimated. Since all the RR Lyrae studied are in M15 they are the same
apparent magnitude, and have the same absolute magnitude for this lab. By studying these
stars using multiple pictures and observed dates, the variable nature of the RR Lyrae will
, produce a mean. This mean will be used to estimate the distance to the cluster M15. In much
the same way, ten clusters will be measured in diameter to provide an accurate measurement
to the center of the galaxy.
Procedure:
For the first section of this lab, eight photographs were analyzed using a small
magnifying glass. In each photograph was the M15 globular cluster and several RR Lyrae
demarked by their apparent magnitudes. Once given a specific, unlabeled star, I used the
magnifying glass to compare other labeled stars to estimate and apparent magnitude. By
observing the apparent brightness of the RR Lyrae and my unlabeled star, I was able to
ascertain a close guess of apparent magnitude.
The second section of the lab required the application “Center of Galaxy”. On the
right- hand side of the program there were a list of ten different globular clusters, and each
was chosen in turn. Each cluster was measured for their diameter based on the general
circular outline the stars made, due to their dense relationship. By dragging the mouse from
one edge of the cluster to the opposite side, the program could calculate the apparent
diameter of the cluster, therefore measuring the distance to it. Once all measurements for the
clusters had been taken and volume- corrected by the program, a distance to the galactic
center is displayed at the bottom of the measurements.
Observations:
Cluster ID Diameter (parsecs)
M15 245.9
NGC 6625 32.3
NGC 6626 54.9
NGC 6637 35.8
NGC 6638 31.4
NGC 6652 25.6
NGC 6656 102.2
