Transcript Lecture 1: Historical introduction to the Galaxy

ASTR112
Astrophysics: the Galaxy
Prof. John Hearnshaw
2003 semester 1
Room 804, Rutherford Building
Department of Physics and Astronomy
email: [email protected]
Panorama of the Milky Way showing millions of faint
stars, star clusters, gaseous nebulae and dark clouds in a
great circle around the galactic equator. Galileo in 1610
first used a telescope to resolve the Milky Way into a
myriad of faint stars.
Prof. John Hearnshaw
ASTR112 The Galaxy
Lecture 1
ASTR112 The Galaxy
Lecture 1
Jupiter, wishing to
immortalize his infant
Hercules (whose mother
was the mortal Alcmene)
held him to the breasts of
the sleeping goddess Juno.
The milk spilt and spurted upwards
to form the Milky Way
Prof. John Hearnshaw
The Origin of the Milky
Way by Jacopo Tintoretto
c. 1575
ASTR112 The Galaxy
Lecture 1
Prof. John Hearnshaw
Historical introduction
to the Milky Way:
Some key landmarks
in galactic research
ASTR112 The Galaxy
Lecture 1
Herschel’s Galaxy cross-section was based on star counts.
Fainter stars, he reasoned, indicated a greater distance
to the edge of the star system that comprised the Milky Way.
Prof. John Hearnshaw
Historical introduction
• William Herschel’s Galaxy of 1785
ASTR112 The Galaxy
Lecture 1
•Jacobus Kapteyn’s Galaxy, 1922
(Kapteyn’s universe)
The Sun is in the centre of Kapteyn’s universe, and the
contours show locations of equal star density
Prof. John Hearnshaw
J. Kapteyn (1851-1922)
ASTR112 The Galaxy
Lecture 1
Harlow Shapley and the distance to the centre
of the Galaxy, 1918
Prof. John Hearnshaw
•
ASTR112 The Galaxy
Lecture 1
Prof. John Hearnshaw
The globular cluster
47 Tucanae, one of
the nearer ones to us.
It contains over
105 stars.
ASTR112 The Galaxy
Lecture 1
Prof. John Hearnshaw
Harlow Shapley and
globular clusters
ASTR112 The Galaxy
Lecture 1
Dust clouds in the Galaxy (E.E.Barnard,
M.Wolf), 1913-27
l: Barnard photo of Milky Way
centre: Dark cloud Barnard 86
r: Edward Emerson Barnard (1857-1923)
Prof. John Hearnshaw
•
ASTR112 The Galaxy
Lecture 1
Robert
Trumpler in
1930 compared
the distances of
star clusters from
angular size with those from
photometry. He showed
space cannot be transparent
by the discrepancy found.
Prof. John Hearnshaw
• Work of Robert Trumpler on interstellar dust
absorption, 1930
ASTR112 The Galaxy
Lecture 1
Jan Oort (1900-92)
Dutch astronomer
Prof. John Hearnshaw
• Rotation of the Galaxy (Strömberg, 1924;
Oort 1926)
ASTR112 The Galaxy
Lecture 1
Prof. John Hearnshaw
• Discovery of galactic spiral arms, 1951
Young open star
clusters and OB
associations near the
Sun show parts of
three spiral arms, called
the Perseus, Orion
and Sagittarius arms
(from outside inwards).
Prof. John Hearnshaw
ASTR112 The Galaxy
Lecture 1
ASTR112 The Galaxy
Lecture 1
• Spectroscopic analysis of gaseous nebulae by
left: Orion nebula
right: Sir William Huggins
(1824-1910)
Prof. John Hearnshaw
William Huggins, 1864, who showed they are
gas clouds of hot low density gas from their
emission line spectrum
ASTR112 The Galaxy
Lecture 1
Prof. John Hearnshaw
• Discovery of 21-cm radio radiation from cold
atomic hydrogen gas clouds in disk and spiral
arms of Galaxy, 1951 (21-cm radiation was
predicted theoretically in 1944).
ASTR112 The Galaxy
Lecture 1
Prof. John Hearnshaw
• Discovery of spiral structure from HI 21-cm map
of Galaxy (Oort et al. 1958)
• Discovery of interstellar
organic molecules,
especially in microwave
region, from 1963.
The molecules include
OH, CO, H2O, H2CO
and C2H5OH etc.
Prof. John Hearnshaw
ASTR112 The Galaxy
Lecture 1
ASTR112 The Galaxy
Lecture 1
Prof. John Hearnshaw
End of lecture 1