Which revolutionary retail innovation, introduced by Celestron in 1970, fundamentally changed how amateur astronomers purchased telescopes?

The exploration of space has led to many consumer product innovations that we use in our daily lives. From memory foam to freeze-dried foods, NASA's research has transformed into commercial products. But one particular retail innovation stands out in astronomy history as changing how enthusiasts shop for telescopes and other stargazing equipment. Test your knowledge of astronomy product history with this challenging question!

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The Schmidt-Cassegrain C8 telescope, the first mass-produced advanced telescope affordable enough for the consumer market
The AstroMall catalog, the first direct-to-consumer mail-order system for astronomy equipment
The Observatory Franchise model, allowing customers to test telescopes before purchasing
The Star Payment Plan, the first financing program specifically for amateur astronomy equipment