Announcements
•Don’t forget the second project.
Presentations are less than two weeks
away.
•Exam 3 is Tuesday May 3 at 4:00pm.
Will cover Chapters 8 & 9. Sample
questions are posted.
The First Astronomical
Photograph
John William Draper took the first successful astronomical
image of the Moon in 1840. It’s debatable if his very first
was “successful” but his second attempt definitely was
The earliest wide-field
astrophotography was by David Gill
Gill’s photo ushered
in a new era in
astronomy
By the 1890’s E. E. Barnard
was making wide-field images
The first stellar spectrum was made
by Henry Draper in 1872
Henry Draper was John
William Draper’s son and
much of his equipment was
developed by his father
Draper put a prism between
the photographic plate and
the telescope. It recorded
Vega and other nearby stars.
The image was black &
white and uncalibrated.
William
Huggins was
doing similar
spectrum
photography at
the Greenwich
Observatory in
England
Starting in 1863, Angelo Secchi
examines hundreds of stellar spectra
and devised a scheme to classify them
Secchi classified stars into four
types based on the complexity of
the spectrum
Karl Friedrich
Zollner
suggested the
differences
were due to
temperature
In addition to stellar spectra,
Huggins looked at selected nebulae
Huggins spectrum of the Cat’s Eye
nebula proved its true nebulosity
He could identify the hydrogen lines but didn’t know
what the other lines were
After examining the spectra of
dozens of nebulae he deduced
different types
Some spectra were
continuous with
absorption lines. We
now know they are
galaxies
Emission
nebulae were
similar to
planetary
nebulae
Christian Doppler thought his
Doppler Effect would apply to
starlight, changing the color of stars
The Doppler effect isn’t large
enough to change a stars color
The change in wavelength of a typical star due to the
Doppler Effect is small enough to be influenced by
temperature changes in the camera over the course of a
night and loading differences as the orientation of the
camera changes during an exposure
Hermann Vogel and Julius Scheiner
were the first to successfully measure
stellar Doppler shift
The Doppler Effect did explain the
splitting of lines in binary systems
Edward Pickering and Antonia Maury at the Harvard
Observatory had observed a double line spectrum in the star
Mizar. The Doppler Effect proved it was actually two stars
orbiting a common center of mass. They became known as
spectroscopic binaries
The sweat-shop of Harvard
Observatory
In the late 1800’s the Harvard Observatory was one of the
only places that allowed women to work as astronomers.
Stellar classification became
assembly line at the Harvard
Observatory in the 1890’s
Annie Jump Cannon led the way in
coming up with a new stellar
classification scheme
The original scheme of Secchi had been expanded but it
was still alphabetical by complexity
Cannon’s classification system is
still used: OBAFGKM
Cannon realized the temperature dependence of the
spectra and re-organized the Secchi scheme
The nature of stars
Annie Jump Cannon had developed a stellar classification
system based on temperature and the women of Harvard
Observatory had classified hundreds of thousands of stars
but the lifecycle, energy source and evolution of stars was
still not understood
With enough
data on the
distance to
nearby stars,
Henry Norris
Russell made a
plot of absolute
magnitude
versus spectral
type in 1910
Ejnar Hertzsprung had made similar
plots of the Hyades and Pleiades
We now call them Hertzsprung –
Russell Diagrams
At the time they only identified two
“bands”: the Main Sequence and
the Giant Branch
W. S. Adams and Arnold Kohlschutter
figured out how to tell main sequence
from giant in the spectra
W.W. Morgan developed the
technique of Spectroscopic Parallax
Determine the luminosity class and spectral
class from the spectrum, plot it on the H-R
diagram and then read off the luminosity
Advances in atomic physics led to a
better understanding of stellar spectra
Max Planck, Ernest Rutherford and Niels Bohr pioneered
the new theory of quantum mechanics which explained
existing lines seen in spectra which had not been identified
Meghnad Saha used the new
quantum theory to explain the
differences in main sequence and
giant spectra