Isaac Newton 50p (2017)

Because the Isaac Newton 50p circulated, most examples show wear, and a crisp coin with sharp lines in the orbit diagram is worth more than a rubbed one. Brilliant uncirculated coins in the original Royal Mint pack sell above loose uncirculated coins and far above worn change. The 2018 strike-your-own coin from the Royal Mint Experience is the variety that commands a premium. Silver proof, piedfort and gold proof versions were also struck for collectors and are priced separately.

With 1,801,500 struck for circulation, the Isaac Newton 50p is the 23rd rarest of the 81 ranked 50p designs and has the 68th lowest mintage of all 194 circulating UK designs. That puts it in the Scarce band, for mintages 1,000,000 to 2,499,999.

The next rarer 50p is the Hockey 50p, with 1,773,500 struck, and the next more common is the Weightlifting 50p, with 1,879,500 struck.

Look for three elliptical orbits sharing a small stylised Sun at their focus, rather than a picture of Newton himself. The words SIR ISAAC NEWTON and FIFTY PENCE are on the reverse, with AW for Aaron West. Circulation coins are dated 2017 on the obverse. A version dated 2018 was struck by visitors at the Royal Mint Experience in Llantrisant; it was never issued for circulation, so a 2018 coin came from the Experience rather than from change.

Known varieties of the Isaac Newton 50p, all listed among the UK error coins and varieties:

• 2018 Royal Mint Experience strike: Dated 2018 and struck by visitors at the Royal Mint Experience in Llantrisant; 20,826 were made. Not issued for circulation.

Isaac Newton changed how the world understood mathematics and physics, but he also spent the last decades of his life at The Royal Mint, arriving as Warden during the Great Recoinage and serving as Master of the Mint until his death. He pursued counterfeiters, tightened the testing of coin quality and brought weights and measures to new standards of accuracy. The Royal Mint issued this 50p in 2017 to celebrate his legacy, in the year of the 375th anniversary of his birth. Aaron West designed the reverse around Proposition 11 in Book One of the Principia Mathematica, Newton's great work on physics. Instead of a portrait, the coin shows a geometric diagram: a stylised Sun sits at the shared focal point of the elliptical orbits of three planets. The lettering SIR ISAAC NEWTON and FIFTY PENCE completes the design, along with the designer's initials AW. Jody Clark's fifth portrait of Queen Elizabeth II is on the obverse.