(Re)discovering Pluto in 2026

January, 1930. Young astronomer Clyde Tombaugh is hunched over a blink comparator - a device that allows him to rapidly flick between two photographic plates. He's been doing this for the better part of a year.

Clyde's task is to search for the mysterious body thought to exist beyond the orbit of Neptune. Night after night he photographs sections of the sky, then diligently compares the resulting plates. He's looking for something special.

He's looking for "Planet X". He doesn't even know whether it exists. Only by looking for movement - a change between frames - can such a discovery be made.

Blink comparison of the photographic plates used to discover Pluto — The photographic plates used to discover Pluto in 1930

And finally, there it is.

It's subtle: a small, dim object that almost blends into the faint background, noticeable only with the aid of the blink comparator. Two images, six nights apart. That tiny, misplaced dot is exactly what Clyde has been searching for. It becomes known as Pluto - then the ninth planet in our solar system.

And unlike Clyde Tombaugh in 1930, we know exactly where it is.

Stellarium showing Pluto and nearby guide star SAO 189319 — Stellarium showing Pluto and my guide star, SAO 189319

I wanted to recreate the blink-comparator method of Pluto's discovery, with the obvious advantage of knowing where to look.

The cool part is that, at least with my relatively wide-field smart scope, the method is actually useful. Without automated annotation I'd never pick Pluto out from the stars in a single frame. Just as in 1930, it's the object's motion relative to the background stars that reveals what it is.

Of course, you don't really want to centre the telescope on Pluto itself. You could, but comparing the frames becomes less intuitive: the stars would shift while Pluto remained near the same position.

Instead I locked onto a nearby star, catalogued as SAO 189319, close enough that Pluto would remain within the field of view over successive nights. My "plates" are only two nights apart, but that's enough to make the movement obvious, as you can see in the resulting GIF:

Blink comparison showing Pluto moving between two images taken two nights apart — Two images, two nights apart. Pluto moves near the centre of the frame.

There it is. Indistinguishable from the surrounding starfield until you introduce the dimension of time. A distant world gliding silently through the icy outer reaches of our solar system.

Imaging Pluto is no longer the impressive technical achievement it once was, but I still find it rather incredible that you can capture this distant world from a suburban backyard using consumer-grade equipment.

Ninety-six years separate Clyde's images from mine, but I'll confess that I still felt something of the thrill of (re)discovery tonight.