Timeline of Hubble’s works

1920

-Photographic Investigations of Faint Nebulae (Univ. of Chicago Press, Chicago). [Ph.D. dissertation]

-The Color of the Nebulous Stars (with Frederick H. Seares)

1922

-A General Study of Diffuse Galactic Nebulae

1925

-NGC 6822, a Remote Stellar System

-Cepheids in Spiral Nebulae

1926

-A Spiral Nebula as a Stellar System

-Extragalactic Nebulae

1929

-A Spiral Nebula as a Stellar System, Messier 31

-A Relation Between Distance and Radial Velocity Among  Extra-Galactic Nebulae

1930

-Distribution of Luminosity in Elliptical Nebulae

1931

-The Velocity-Distance Relation among Extra-Galactic Nebulae (with Milton L. Humason)

1932

-Nebulous Objects in Messier 31 Provisionally Identified as Globular Clusters

1934

-The Distribution of Extra-Galactic Nebulae

-Redshifts in the Spectra of Nebulae (Lecture)

1935

-Angular Rotations of Spiral Nebulae

-Two Methods of Investigating the Nature of the Nebular Redshifts (with Richard Tolman)

1936

-The Luminosity Function of Nebulae. I. The Luminosity Function of Resolved Nebulae as Indicated by Their Brightest Stars

-The Luminosity Function of Nebulae. II. The Luminosity Function as Indicated by Residuals in Velocity-Magnitude Relations

-Effects of Red Shifts on the Distribution of Nebulae

-The Realm of Nebulae.

1937

-Redshifts and the Distribution of Nebulae

-The Observational Approach to Cosmology (Rhodes Memorial Lectures delivered at Oxford in 1936)

1942

-The Problem of Expanding Universe

1943

-The Direction of Rotation in Spiral Nebulae

1953

-The Law of Red Shifts (Lecture)

-The Brightest Variable Stars in Extragalactic Nebulae. I. M31 and M33 (with Allan Sandage)

1954

The Nature of Science, and Other Lectures