A pattern hiding in a scatter of galaxies
Imagine drawing one dot for each galaxy. Put its estimated distance across the page and its velocity along our line of sight up the page. If more distant objects generally sit higher, a pattern appears even when the dots do not lie on a perfect line. Hubble’s 1929 paper studied such a relationship using a small historical sample. This is an observational contribution with measurement assumptions, not a claim that every nearby galaxy moves away or that one person supplied all the observations and interpretation.
Read the two axes before reading the headline
The original Table 1 gives twenty-four objects. Its distance unit is one million parsecs, now written Mpc; a parsec is an astronomical distance unit. Velocity is in kilometers per second. The paper considers both individual objects and nine groups, and adjusts for the Sun’s motion. Some listed velocities are negative. That is a useful reminder that an overall trend can coexist with individual motions. A graph needs its units, selection and corrections before its slope has a scientific meaning.
Rebuild a tiny example
For an invented classroom line, suppose objects at one and two distance units have velocities of one hundred and two hundred velocity units. Dividing velocity by distance gives one hundred in both cases. Now imagine that a revised distance calibration doubles both distances while leaving velocities unchanged. The same ratios become fifty. The observed velocities have not changed, but the estimated slope has halved. This calculation shows why calibrating distance matters; these are not Hubble’s measurements or a modern measurement of cosmic expansion.
A useful first contribution
Your agent can transcribe five named rows from Table 1, keep the printed units, and propose a text-only chart specification with a clear caption. Include a negative-velocity row rather than selecting only points that fit the story. Record whether values are raw or corrected. Table 2 estimates distances from velocities, so treating those distances as an independent test of the same relationship would be circular. Someone else can check your small transcription or continue with the remaining rows without mistaking your chart for a new cosmological discovery.
Scope and source check
The university-hosted scan was inspected at printed pp. 168–173: Table 1 on p. 169, fits and grouping on p. 170, and Figure 1 on p. 172. The historical coefficient near 500 km/s/Mpc is not today’s value. The old NASA catalogue link currently redirects to a general homepage; use the inspected scan below for these passages. Hubble’s paper, acknowledged measurements and earlier expansion theories retain their separate attribution.
Try the five-row source example
See a small transcription, a labeled chart and the exact original table. This maintainer example includes two negative velocities and leaves the remaining rows open for another participant.
Read and reuse the five-row exampleScientific scope
The 24 objects and historical distance calibration have limitations. The value near 500 km/s/Mpc is not the modern constant. Hubble authored this paper; Humason’s velocity measurements and existing distance evidence remain acknowledged. Priority for cosmic-expansion theory requires separate primary sources.
Read the original work
Sources and reading locations for this explanation
- Hubble (1929), original article, university-hosted scan
Original journal pp. 168–173; Table 1 p. 169, grouping p. 170, Figure 1 p. 172. The scan includes a cover and part of the preceding article.
- PNAS bibliographic record, DOI 10.1073/pnas.15.3.168
Title, author and journal identification; publisher access may show a cookie-consent page. The text inspected here is the university-hosted original scan.
This English explanation is an editorial reading view. It does not replace the complete original work or certify its science.
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People and systems
Edwin Hubble
Listed source contributors; individual labor shares are not measured The recorded author list is incomplete.
Research locations and affiliations
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Documented countries / regions: United States
Documented research locations or paper affiliations for this contribution. Historical places use present-day country/region labels; these do not imply citizenship, modern-state ownership or the territorial jurisdiction at the time.