Do you know which Harry Potter characters share their names with ancient constellations? What's the incantation for the levitating charm? Do you know your Bowtruckles from your Basilisks?

Because there will be a trivia test.

It has been 20 years since J.K. Rowling charmed readers of all ages with the publication of the first Harry Potter book, and it seems many of us are still spellbound.

To mark the anniversary, the British Library has swung open its doors for "Harry Potter: A History of Magic," a new exhibition that explores the history behind the wizarding world.

Others, too, are paying tribute. On June 26 — exactly 20 years to the day since the first book was published in the United Kingdom — Harry Potter was trending worldwide on social media. On Saturday evening, the BBC aired a documentary that includes a rare interview with Rowling. Before, during and after Halloween, millennials are slipping on robes and raising a celebratory pint to the boy wizard they grew up with at unofficial Harry Potter pub crawls (combining two of Britain's popular pastimes: drinking and dressing up in costumes.)

Not that it takes much to motivate Potter enthusiasts. Last month, for instance, thousands of Muggles descended on Platform 9¾ at King's Cross station to mark the day that Harry Potter's son Albus left for Hogwarts. For those truly potty about Potter, there is the "Making of Harry Potter" studio tour, next to the film studios where all eight films were made, which in the lead-up to Halloween is hosting feasts in the "Great Hall" with pumpkins and cauldrons full of lollipops.



A gallery at the preview of the “Harry Potter: A History of Magic” exhibition at the British Library on Oct. 18 in London. (John Phillips/Getty Images)

The latest draw is the exhibition at the British Library, which sold a record 30,000 tickets even before its opening last week.

The show delves into the historical links with the fantastical world dreamed up by Rowling — who studied classics and French at university — by exploring the wider cultural context in which the books are set. For those able to harness their inner Hermione, the library is hosting "quiz nights" to test visitors on their wizarding knowledge.

Perhaps the most exciting aspect for fans is the scores of items donated by Rowling herself, including original handwritten extracts from various Potter books with lines crossed out and annotations from the author.

There are also a number of intricate drawings (yes, she can draw). For instance, one is of Professor Sprout sketched on December 30, 1990. In the BBC documentary, Rowling said she can recall the exact date because it was the night her mother died 250 miles away. She also revealed that the film she was watching at the same time may have inspired the Deathly Hallows symbol.

"The Potter series is hugely about loss," Rowling told the broadcaster. "I've said this before — if my mother hadn't died, I think the stories would be utterly different."

Another drawing on display is a map of Hogwarts School of Witchcraft and Wizardry, complete with a Quidditch field and a lake with a giant squid.

Many of her items are dated from before she found a publisher — she was turned down eight times before Bloomsbury took a chance on her — and they illustrate just how vivid and richly imagined the Harry Potter-verse was from a very early stage, complete with its own consistent logic and rules.

The "first review" of her work is also on display. Alice Newton, the 8-year-old daughter of the founder of Bloomsbury, wrote on a piece of paper: "The excitement in this book made me feel warm inside. I think it is possibly one of the best books an 8/9 year old could read." The day after she penned the note, Bloomsbury agreed to publish "Harry Potter and the Philosopher's Stone."



A visitor takes a photo during the “Harry Potter: A History of Magic” exhibition at the British Library in London on Oct. 18. (Rain/Epa-Efe/Rex/Shutterstock)

The exhibit is lined with book wallpaper and is dimly lit. Cauldrons and tea cups "float" from the ceiling, and an invisibility cloak is, apparently, hanging from a hook. It's organized by the school curriculum at Hogwarts, so visitors explore rooms dedicated to subjects including potions, herbology, divination, astronomy and defense against the dark arts.

The potions room, for instance, features the Ripley Scroll, a 20-foot-long manuscript from the 1500s that is a kind of instruction guide on how to create a philosopher's stone, a substance that reputedly could turn base metals into gold and grant eternal life.

"It helps bring stories to life to see the real concepts behind them," said Alexander Lock, a mustachioed historian and one of the curators of the exhibit.

Leaning over the glass case containing the scroll, Lock pointed to an image depicting a black stone, a white stone and a red stone. He noted that Sirius's last name is Black, and that Albus [Dumbledore] is Latin for white and Rubeus [Hagrid] is Latin for red.

The scroll is displayed alongside the tombstone of Nicholas Flamel, a name shared by a character in the first Harry Potter book. On loan from the Musée de Cluny in Paris, the headstone was reportedly found in the 19th century at a Parisian grocery store where it was being used as a chopping board.

The real-life Flamel was a Parisian landlord and bookdealer who died in 1418. After his death, rumors surfaced that he was an alchemist — his work was referenced by Isaac Newton — who had unlocked the secret to creating a philosopher's stone.

"I heard when they extracted [Flamel's] tombstone, they didn't actually find a body, so it could well be true," said Lock, smiling.

In addition to borrowing artifacts from other museums, the library draws on its own rich collection to display ancient books like "Liber Medicinalis," which features the earliest recorded use of "abracadabra," a charm thought to have healing powers.



Artifacts and memorabilia are displayed during a preview of the “Harry Potter: A History of Magic” exhibition at the British Library in central London on Oct. 18, marking the 20th anniversary of the publication of “Harry Potter and the Philosopher's Stone.” (Niklas Halle'n/AFP/Getty Images)

In the herbology section, there are ancient manuscripts on mandrakes, plants with roots that look humanlike. In "Harry Potter and the Chamber of Secrets," Professor Sprout asks her students to wear earmuffs when replanting baby mandrakes because of their insanely loud cries.

Indeed, it was long believed that when the root of the plant was yanked from the ground, it would scream and kill anyone who heard it. According to a 15th century book on display, the recommended way of harvesting mandrakes included the use of a horn to drown out the shrieking.

In the astronomy room, which is dominated by a 400-year-old celestial globe, visitors discover the constellations that share names with characters in the book, including Bellatrix Lestrange and Sirius Black.

Keen stargazers will know that the brightest star in the night sky is called Sirius, also known as the Dog Star.

The reviews so far have been generally strong, with many critics noting the breadth of material on display. Some have said that it doesn't "hang together " as a whole or that younger children may become "fidgety " near the end — but most agree that Potter fans will gobble it up.

For her part, Rowling said it was "wonderful" and appeared to be particularly taken by the tombstone of one of her characters. She tweeted a picture of it with the caption: "Guess what this is? I've just seen it and was mesmerised . . ."

All of this is fair game for the Harry Potter quiz nights. If you do portkey over to London and find yourself participating in one, facts that may come in handy: Draco Malfoy and Remus Lupin also share their names with the constellations; Wing-gar-dium Levi-o-sa is the spell for levitation; and a Bowtruckle and a Basilisk are very different creatures.



A visitor views a sketch titled “The Boy who Lived” during a preview of the “Harry Potter: A History of Magic” exhibition at the British Library in central London on Oct. 18. (Niklas Halle'n/AFP/Getty Images)

"Harry Potter: A History of Magic" is at the British Library until the end of February 2018. It transfers to New York's Historical Society next October.