ASTR112Astrophysics: the Galaxy

Prof. John Hearnshaw 2003 semester 1

Room 804, Rutherford BuildingDepartment of Physics and Astronomy

email: john.hearnshaw@canterbury.ac.nz

ASTR112 The GalaxyLecture 1

Pro

f. J

ohn

Hea

rnsh

aw

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.

ASTR112 The GalaxyLecture 1

Pro

f. J

ohn

Hea

rnsh

aw

The Origin of the Milky Way by Jacopo Tintorettoc. 1575

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 upwardsto form the Milky Way

ASTR112 The GalaxyLecture 1

Pro

f. J

ohn

Hea

rnsh

aw

Historical introductionHistorical introductionto the Milky Way:to the Milky Way:

Some key landmarks Some key landmarks in galactic researchin galactic research

ASTR112 The GalaxyLecture 1

Pro

f. J

ohn

Hea

rnsh

aw

Historical introduction• William Herschel’s Galaxy of 1785

Herschel’s Galaxy cross-section was based on star counts.Fainter stars, he reasoned, indicated a greater distanceto the edge of the star system that comprised the Milky Way.

ASTR112 The GalaxyLecture 1

Pro

f. J

ohn

Hea

rnsh

aw

•Jacobus Kapteyn’s Galaxy, 1922 (Kapteyn’s universe)

The Sun is in the centre of Kapteyn’s universe, and thecontours show locations of equal star density

J. Kapteyn (1851-1922)

ASTR112 The GalaxyLecture 1

Pro

f. J

ohn

Hea

rnsh

aw

• Harlow Shapley and the distance to the centre of the Galaxy, 1918

ASTR112 The GalaxyLecture 1

Pro

f. J

ohn

Hea

rnsh

aw

The globular cluster47 Tucanae, one of the nearer ones to us.It contains over105 stars.

ASTR112 The GalaxyLecture 1

Pro

f. J

ohn

Hea

rnsh

aw

Harlow Shapley and globular clusters

ASTR112 The GalaxyLecture 1

Pro

f. J

ohn

Hea

rnsh

aw

• Dust clouds in the Galaxy (E.E.Barnard, M.Wolf), 1913-27

l: Barnard photo of Milky Waycentre: Dark cloud Barnard 86r: Edward Emerson Barnard (1857-1923)

ASTR112 The GalaxyLecture 1

Pro

f. J

ohn

Hea

rnsh

aw

• Work of Robert Trumpler on interstellar dust absorption, 1930

RobertTrumpler in1930 comparedthe distances of star clusters from angular size with those from photometry. He showed space cannot be transparentby the discrepancy found.

ASTR112 The GalaxyLecture 1

Pro

f. J

ohn

Hea

rnsh

aw

• Rotation of the Galaxy (Strömberg, 1924; Oort 1926)

Jan Oort (1900-92)Dutch astronomer

ASTR112 The GalaxyLecture 1

Pro

f. J

ohn

Hea

rnsh

aw

• Discovery of galactic spiral arms, 1951

ASTR112 The GalaxyLecture 1

Pro

f. J

ohn

Hea

rnsh

aw

Young open starclusters and OBassociations near the Sun show parts ofthree spiral arms, calledthe Perseus, Orionand Sagittarius arms(from outside inwards).

ASTR112 The GalaxyLecture 1

Pro

f. J

ohn

Hea

rnsh

aw

• Spectroscopic analysis of gaseous nebulae by William Huggins, 1864, who showed they are gas clouds of hot low density gas from their emission line spectrum

left: Orion nebularight: Sir William Huggins(1824-1910)

ASTR112 The GalaxyLecture 1

Pro

f. J

ohn

Hea

rnsh

aw

• 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 GalaxyLecture 1

Pro

f. J

ohn

Hea

rnsh

aw

• Discovery of spiral structure from HI 21-cm map of Galaxy (Oort et al. 1958)

ASTR112 The GalaxyLecture 1

Pro

f. J

ohn

Hea

rnsh

aw

• Discovery of interstellar organic molecules, especially in microwave region, from 1963. The molecules include OH, CO, H2O, H2CO and C2H5OH etc.

ASTR112 The GalaxyLecture 1

Pro

f. J

ohn

Hea

rnsh

aw

End of lecture 1