Messier's Catalogue and Shapley-Curtis Debate

Messier's Catalogue and the Shapley-Curtis Debate

• Charles Messier, a French comet hunter, created a catalogue of astronomical objects, including fuzzy objects later identified as spiral nebulae.
• Messier numbers are still used to refer to these objects.
• The nature of our galaxy and the nature of spiral nebulae were key questions in the Shapley-Curtis debate.

Shapley's Arguments

• Shapley estimated the Milky Way (MW) was much larger than previously thought, placing the solar system thousands of light-years from the galactic centre.
• He argued spiral nebulae were within the MW based on three main arguments:
  • Relative size: If spiral nebulae were similar in size to the MW, they would need to be millions of light-years away, which Shapley considered unlikely.
  • Relative brightness of novae: A nova in Andromeda (M31) briefly outshone the nebula, implying, according to Shapley, excessive energy output if it were a distant galaxy.
  • Maanen's observations: Observations of spiral nebulae rotating over a few years suggested velocities exceeding light speed if they were outside the MW, which was considered impossible.

Curtis's Arguments

• Curtis supported the "island universes" theory, suggesting spiral nebulae are distant galaxies like the MW.
• He used scientific publications to support his arguments, including:
  • Dark paths: Photographs of spiral nebulae showed dark paths similar to those observed within the MW, implying they could be distant galaxies.
  • Nova occurrences: A higher rate of nova occurrences in M31 compared to the MW suggested it was a distinct astronomical object rather than a small section of the MW.

Shapley and Curtis's Contributions

• Shapley significantly altered our understanding of the MW's size and the solar system's position within it.
• Curtis established that our galaxy is one of many in a vast universe.

Cosmic Distance Ladder

• Measuring cosmic distances requires various methods, not a single universal method.
• The cosmic distance ladder consists of a series of methods that build on each other, to get progressively longer distances, because methods can't be directly used on all ranges.
• Methods often relate to standard candles or standard rulers:
  • Standard candle: objects with known intrinsic luminosity used to measure distance from apparent brightness.
  • Standard ruler: objects with known size used to measure distance from apparent size.
• Fundamental distance measurement methods don't rely on the object's nature.

Explore the pivotal arguments of the Shapley-Curtis debate about the size and nature of our galaxy. Delve into Charles Messier's contributions to astronomy and how his catalogue influenced perceptions of spiral nebulae. Understand the dynamics between the Milky Way and these celestial objects through key observations.