Pluto discovery plates
13-inch astrograph, Delta Geminorum field, and Tombaugh's blink-comparator search
At Lowell Observatory, Clyde Tombaugh photographed zodiacal fields near opposition, when an outer planet's westward (retrograde) motion is fastest, and blink-compared two plates of the Delta Geminorum field taken on 23 and 29 January 1930. A point of light had shifted between them; it was identified on 18 February and announced on 13 March 1930.
- Author
- Clyde W. Tombaugh
- Date
- plates 23 and 29 January 1930
- Original language
- English
- Kind
- Observation record
- Planets
- Pluto
Editions
One edition.
| Year | Edition | © |
|---|---|---|
| 1930 | Lowell Observatory Observation Circular, 13 March 1930 (discovery announcement) | ? |
Read it
One digitised copy.
- Scanned sections of the 23 and 29 January 1930 discovery platesLowell Observatory Archives©Open ↗Archived copy
Copies stay with their holders; every link opens their site. Licence: PD public domain · CC BY · CC BY-SA · © rights reserved · ? not stated.
Myths we don’t repeat
Checked, and left out.
- Myth 01
Not a logbook quote: 'Retrograde motion!' is a narrative rendering of Tombaugh's thought.
Checked against the ephemeris
Retrograde, day 95 of 162.
| Source date | Planet | Station R | Station D | Sign | Where it falls |
|---|---|---|---|---|---|
| 23 Jan 1930 | Pluto | 21 Oct 1929 | 31 Mar 1930 | Cancer | Retrograde, day 95 of 162 |
| 29 Jan 1930 | Pluto | 21 Oct 1929 | 31 Mar 1930 | Cancer | Retrograde, day 101 of 162 |
Recomputed with the site’s ephemeris (astronomy-engine 2.1.19). All times UTC.
References
Also on the Early modern and modern shelf
| Date | Source | Planets | Kind |
|---|---|---|---|
| 1632 | Dialogo sopra i due massimi sistemi del mondoGalileo GalileiTheory / model | Me Ve Ma Ju Sa | Theory / model |
| 1647 | Christian AstrologyWilliam LillyAstrological | Me Ve Ma Ju Sa | Astrological |
| presented 7 August 1709 | Cassini's apparent path of MercuryJ. D. CassiniMath. astronomy | Me Ju Sa | Math. astronomy |
| 1756 (1st edition); many later editions | Astronomy Explained upon Sir Isaac Newton's PrinciplesJames FergusonTheory / model | Me Ve | Theory / model |
| late 19th century | Late-19th-century British astrology periodicalsVariousAstrological | Me | Astrological |
| 1970s–present | 'Mercury retrograde' as a popular catch-allVariousPopular culture | Me | Popular culture |