Apollo 11 astronauts planted a flag on the moon on July 20, 1969. NASA In the market for a helium tank from an Apollo-era spacecraft? How about a bag to collect lunar soil samples? Or an authentic training checklist for launching to the moon?

Welcome to the spectacle that is Sotheby's first "Space Exploration" live auction, which is being hosted on eBay.

The event kicks off at 11 a.m. EDT on Thursday, July 20 — the 48th anniversary of the Apollo 11 moon landing. It features 173 lots of space artifacts and memorabilia, which are collectively worth between an estimated $2.9 million and $5.3 million.

Some sellers hope to fetch a premium on rare toys and signed photographs from the Space Race, while others are hawking near-priceless artifacts that could fetch millions of dollars.

One lot that may garner $4 million alone: a dusty bag that Apollo 11 astronauts dumped the first samples of lunar soil, grit, and rocks into in 1969. (The bag was "lost" for decades until the US Marshals Service confiscated it during a raid and later auctioned off — for $995.)

NASA and other groups (including "For All Moon Kind") admonish the sale of such one-of-a-kind spaceflight objects. "This artifact, we believe, belongs to the American people and should be on display for the public," NASA said in a statement shortly after a court granted the buyer ownership of the bag.

That said, here are some of the more notable items in Sotheby's and eBay's live auction and how much they might sell for.