Feb 18: 80th Anniversary of Tombaugh’s Encounter with Pluto

Posted by Lydia on February 18th, 2010

Portrait of Clyde TombaughIf you click to read more, you will find an interesting essay by Mr. Justin McCollum, member of Houston and Fort Bend Astronomy clubs. We salute the late Mr. Tombaugh and remember his accomplishments with awe and admiration. (He once replied when asked about his political views: “I am not a Republican or a Democrat … for several years now, I have been a Plutocrat.”)


(Mr. McCollum’s article is reposted from the Houston Astronomical Society mailing list and has been slightly edited and condensed.)

Hello Everyone,

It is on this day 80 years ago that Clyde Tombaugh, a staff Astronomer working at the Lowell observatory in Flagstaff, AZ, discovered the planet Pluto. At the time the big thing in Planetary Astronomy was the search for a ninth planet in the solar system as an explanation to the gravitational distortions in the orbit of the Planet Neptune. Mr. Tombaugh was hired by the observatory for his ability to build his own telescope and make detailed maps from his observations of the planets Jupiter and Mars.

He used the old 13 inch f/5.3 Astrograph, 3 element lenses telescope to make photographic plates in scanning certain sections of the night sky over several nights to observe the movement of any new potential planet against the background stars using a blank comparator.

I had the pleasure of seeing the Astrograph telescope back in 2003 during my visit to the observatory [and] touring and talking to professional Astronomers who worked there at the time [and paid] homage to Percival Lowell’s mausoleum which is there. I even saw the 24 inch ‘Alvan Clark’ refractor which Lowell used in his observations and mapping of the planet Mars along with the museum there which had his ..original maps and drawings of Lowell’s observations of Mars. A globe of the planet Mars made during the early 20th century based on his observations [is] also located there [along with] the original plates and the blank comparator that Clyde used to discover the planet Pluto!

[The public is able to] use a similar blank comparator to watch the faint white dot move against the background stars to see the first observations of Pluto. In those days there were [not] any exact methods available to determine the size of Pluto at that distance from the Sun, but estimations varied from the size of Neptune to [a planet the size of] Earth as a means of believing it had to be the cause and massive enough to affect Neptune’s orbit. Today though we now know a lot more about Pluto from when it was discovered back on this day [Feb 18, 1930] and that Pluto is much smaller than the Earth’s Moon.

Tombaugh worked at the observatory from 1929 until 1945 and then worked for White Sands Missile Test Range in the 1950s. [He] then taught Astronomy at New Mexico State University from 1955 until his retirement in 1973 and passed away in Las Cruces, NM in 1997.

The Asteriod 1604 Tombaugh [discovered in 1931] is named after him. One of the byproducts of his research in the search for ‘Planet X’ was the discovery of some 14 asteriods starting with 2839 Annette. He received the Jackson – Gwilt medal from the Royal Astronomical Society in 1931 and one ounce of his ashes from his cremated remains were placed in the New Horizons Probe on its 2015 redezvous flyby with Pluto.

The Jackson – Gwilt medal is awarded [by the Royal Astronomical Society] to those who have contributed in improvements, inventions, and new techniques and instrumentation in observational Astronomy or research into the history of Astronomy.

Today that Astrograph telescope is now known as the ‘Discovery Pluto Telescope’.

So Remember that today Feb 18, 2010 is the 80th Anniversary of the discovery of Pluto by Clyde Tombaugh!

Justin McCollum
HAS Novice Meeting Coordinator

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