Milton Humason : Humason was a colleague of Edwin Hubble’s at Mt. Wilson and Palomar Mtn. who was
galaxy is rotating, and calculated the sirance of the sun from the centre of the galaxy and the period of its
Harlow Shapley : Shapley deduced that the Sun lies near the central plane of the Galaxy some 30,000 light-
years away from the centre.
Cepheid variables cannot be star pairs that eclipse each other. He was the first to propose that they are
In the Mount Wilson Observatory, Pasadena Calif., in 1914, he made a study of the distribution of
the globular clusters in the Galaxy; these clusters are immense, densely packed groups of stars, some
containing as many as 1,000,000 members. He found that of the 100 clusters known at the time, one-third
lay within the boundary of the constellation Sagittarius. Utilizing the newly developed concept that variable
stars accurately reveal their distance by their period of variation and apparent brightness, he found that the
clusters were distributed roughly in a sphere whose centre lay in Sagittarius. Since the clusters assumed a
spherical arrangement, it was logical to conclude that they would cluster around the centre of the Galaxy;
from this conclusion and his other distance data Shapley deduced that the Sun lies at a distance of 50,000
light-years from the centre of the Galaxy; the number was later corrected to 30,000 light-years. Before
Shapley, the Sun was believed to lie ne!
ar the centre of the Galaxy. His work, which led to the first realistic estimate for the actual size of the
Galaxy, thus was a milestone in galactic astronomy.
brightest stars in various globular clusters indicate that the clusters can be arranged in order according to
identified the first of many such objects Sandage later discovered that some of the remote, starlike objects
with similar characteristics are not radio sources. He also found that the light from a number of the sources
varies rapidly and irregularly in intensity.
Cerro Tololo Interamerican Observatory
This is called the Cerro Tololo Interamerican Observatory or CTIO. It was founded in 1965 in Chile as the
50 miles inland from the coastal city of La Serena. The European Southern Observatory and the Carnegie
Institution of Washington also operate major astronomical observatories nearby. It’s coordinates are : W
70d48m52.7s S 30d09m55.5s
CTIO’s facilities are available for use for approved projects by all qualified astronomers in the
Optical Astronomy Observatories, which also operates Kitt Peak National Observatory in Tucson Arizona
and is the operating agency for the US portion of the International Gemini Project.
The CTIO houses several telescopes and auxiliary instruments, the most significant of which is a
reflecting telescope with a 4-metre mirror. On site are six optical telescopes, and one radio telescope:
4.0 Meter Blanco Telescope.
1.5 Meter Ritchey-Chretien Telescope.
Yale 1.0 Meter Ritchey-Chretien Telescope f/10 (19.5 arcsec/mm).
0.9 Meter Telescope f/13.5 (16.5 arcsec/mm).
Curtis/Schmidt Telescope (0.6/0.9 Meter) f/3.5 (96.6 arcsec/mm).
Lowell (0.6m) Telescope f/13.5, f/75 (25.0, 4.5 arcsec/mm)
1.2m Radio Telescope (SCMT, Universidad de Chile).
Magellanic Clouds, and high-energy cosmic radio and X-ray sources.
How Galaxies Evolve :
there has not been much data to work with, and many models of galaxy formation and evolution have been
constructed on the basis of presumptions about conditions in the early universe, which are in turn based on
models of the expansion of the Cosmos after the “big bang”–the explosion from which the Universe is
eventually form galaxies. At the time when the mass of such a stable perturbation in the cloud was
approximately 10 solar masses, the galaxies formed. It is still not known whether the clusters of galaxies
emerged first or whether they resulted as accumulations of already formed galaxies. Following the
separation of mass into individual galaxies, the next step probably depe!
nded on the characteristics of the particular clump of matter involved, especially on its mass and angular
momentum. The latter quantity was the most likely determinant of the form of the galaxy that eventually
rapidly rotating system (a spiral galaxy), whereas one with very little angular momentum developed into a
more nearly spherical system (an elliptical galaxy.)
Calculations show that a galaxy very gradually becomes dimmer and redder as time progresses
and its constituent stars evolve. There is some evidence from very distant galaxies–those whose light was
emitted billions of years ago when they were younger–that the effects of this kind of slow evolution can
actually be seen.
Based on my readings I believe that the following scientist have all made valuable contributions
to astronomy :
Copernicus (1473-1543) : Nicolas Copernicus is often considered the founder of modern astronomy. His
The Copernican theory was contrary to the Ptolemaic theory then generally accepted. In 1530 he
published for 13 years. Copernicus apparently received the first copy as he was dying, on May 24, 1543.
The book opened the way to a truly scientific approach to astronomy. Such men as Galileo and Kepler were
profoundly influenced by it.
Galilieo (1564-1642) : Modern physics owes its beginning to Galileo, who was the first astronomer to use a
Copernican theory. Galileo thus helped disprove much of the medieval thinking in science.
cathedral at Pisa. He timed it with his pulse and found that, whether it swung in a wide or a narrow arc, it
In about 1609, after word from Holland of Hans Lippershey’s newly invented telescope reached
him, he built his own version of the instrument. He developed magnifying power until on Jan. 7, 1610, he
to be a dense collection of stars.
happens to light when it enters a telescope. In addition, he designed an instrument that serves as the basis of
the modern refractive telescope.
Kepler’s great work on planetary motion is summed up in three principles, which have become
known as “Kepler’s laws”: (1) The path of every planet in its motion about the sun forms an ellipse, with
the sun at one focus. (2) The speed of a planet in its orbit varies so that a line joining it with the sun sweeps
cubes of the planets’ mean distances from the sun. These laws removed all doubt that the Earth and planets