A recent post on Reddit* made me read up a bit more on Clyde Tombaugh. As things go on Reddit, there are many versions of this post and yet I would be surprised if many people could name him or say what he was known for. If at this point, you know all about him, you’re either spending more time on Reddit than I am or you’re just hot on your space knowledge! Good job.

*I won’t link to the post directly because I can’t be sure that what you find in the comments is appropriate to you!

So who was Clyde Tombaugh?

I’ll cut to the chase – he discovered everyone’s favourite not-quite-planet, Pluto. So, let’s start out by talking about why it was a big deal to discover Pluto.

This high-resolution image of Pluto was taken by New Horizons on July 14. Pluto’s surface sports a remarkable range of subtle colors, enhanced in this view to a rainbow of pale blues, yellows, oranges, and deep reds. Many landforms have their own distinct colors, telling a complex geological and climatological story that scientists have only just begun to decode. Image credit: NASA / Johns Hopkins University Applied Physics Laboratory / Southwest Research Institute.
Our best ever picture of Pluto.

Image credit: NASA / Johns Hopkins University Applied Physics Laboratory / Southwest Research Institute. 2015.

A model solar system…


Imagine that the earth was the size of a cherry tomato – about 3 cm across. As ever, I’m trying to think of examples that you could really find in your own home – the moon would be 0.8 cm across, or about the size of a peppercorn. Trying to get scaled objects for the solar system can be a bit crazy though, the sun in this example, would be 3.3 m across (most ceilings are only 2.4 m in the U.K. so it wouldn’t even fit in your kitchen, the world’s tallest man was only 2.7 m tall, an average African elephant has shoulders about 3 m from the ground). Our scale already has something as small as some single-celled organisms and as big as an elephant but the size of the objects is not the problem…


…the real issue is how far apart these things need to be.

The 0.8 cm moon, represented by our peppercorn, would be about 91 cm away from our cherry tomato Earth. That’s probably about the length from your eyes to the very tips of your fingers, so if you hold the peppercorn as far away as you possibly can, that’s about the right size and distance for the moon from Earth.

So, where is our sun going to be? 354 metres away – pretty much a quarter of a mile. You’d have to walk for three or four minutes just to get to the right place to put your 3.3 metre sun and when you get there, you’re trying to turn around and see a cherry tomato you left behind to represent Earth and a peppercorn-sized moon. The distances involved in our solar system alone are truly terrifying.

We can race through the solar system in this scale:


Size in our scale

Represented by:

Distance from Sun
in our scale

327 cmElephant
Mercury1.1 cmPea127 m
Venus2.8 cmCherry tomato256 m
Earth3.0 cmCherry tomato354 m
Mars1.6 cmA skittle539 m
Jupiter33 cmWatermelon1,840 m
Saturn27 cmGrapefruit3,387 m
Uranus12 cmApple6,789 m
Neptune12 cmApple10,643 m
Pluto0.6 cmPeppercorn14,002 m

So we need 14 kilometers (about 8 and a half miles) to fit our solar system in and the largest planet is the size of a watermelon in all this. There is a whole lot of empty space around. Trying to spot Pluto amongst all of this is like trying to see a peppercorn that’s 14 km away!

How did Clyde do it?

The planets we had discovered before Pluto were pretty well all in the same plane. If ever you see a planet in the night sky – a really bright, often slightly coloured object – it will probably be close to the horizon. You won’t need to tilt your head up too far to see Mars or Jupiter (there are some great guides out there for what you might see tonight) for example. The observatory that Clyde Tombaugh took lots of pictures of the region of the sky close to the horizon and then compared them night-by-night.

The moon, being so close to Earth, moves across the sky fairly quickly – and each night it will rise in a different place. The planets, further away, move more slowly. They will rise in a very slightly different place each night. The stars, really far away, will move very slowly and you will only notice the difference across one whole year. So in the pictures that Clyde had of the night sky, an object that moved faster than the stars was likely to be a planet in our own solar system. Sure enough, he found one in February 1930.

The impressive bit

For me, the impressive bit happened long before the discovery of Pluto.


Clyde worked on a farm with his family. He had saved up money to attend college and go down the traditional educational route.

A disaster struck when a hailstorm destroyed the family’s crops and they had to use the money from Clyde’s college fund to get through the season. This huge set-back would probably have stopped most of us. How do you fight back once something that you have saved for and looked forwards to for so long is just taken away from you that quickly and suddenly?


Clyde Tombaugh didn’t give up – he took his love for astronomy and actually built a telescope on his farm. This is the part where he really wins my respect because must have been so determined to pursue his interest and his hobby. It doesn’t matter what your circumstances or skills are, if you have that determination, passion and drive, you’ll certainly go places.

He used this home-made telescope to make really detailed observations of Mars and Jupiter – impressive enough – but then had the guts to send them out to an observatory to share his work. That move – to just go for it and show off how driven and determined he was – really paid off because the observatory that saw these drawings called him in and gave him a job.

At the time, Clyde was only 22. He was set to a task that many thought was either stupid or impossible. The person who had predicted that an extra planet beyond Neptune – Percival Lowell – had been ridiculed for a mistake he made while observing Mars (he believed that there were canals constructed by aliens while really he was observing the blood vessels in his own eyes reflected onto the image of Mars by his telescope) and his theory that an unknown ‘Planet X’ had not been proven during Lowell’s lifetime. Within a year of being hired by the observatory, the magic image was taken that showed this ‘Planet X’.

The Pluto Discovery Plates
Image credit: Lowell Observatory Archivesthis image was taken from The Planetary Society.

The tiny dot in those images marked with an arrow is the evidence that was needed to suggest that Planet X existed. The name Pluto was taken from a suggestion by a small girl (Venetia Burney) since Pluto was a god who could make himself invisible and the first two initials P and L were those of Percival Lowell who suggested the planet should be almost exactly where it ended up being found!


In the time since – nearly 90 years – Pluto has not completed an orbit around the sun. Clyde Tombaugh though, went on to do a great many things and you can read about them in one of the many articles written about his life. His lasting legacy is that, due to him, if you were born in around 1920, you probably would have known a solar system with 8 planets, then 9 in 1930 and then 8 again if you were lucky enough to survive until Pluto was classified as a dwarf planet instead in 2006.

Another piece of lasting legacy? He was asked by NASA whether they were allowed to send a probe to ‘his planet’ and many years later after his death his ashes were attached to the New Horizons probe and sent out to visit Pluto making his remains the furthest away part of a human! As of writing this piece, that’s about 6.5 billion km away from Earth – or in the scale we made earlier – about 15.5 km away from the cherry tomato Earth. Far away, basically.



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