Which innovative retail strategy did Celestron use in the 1970s that revolutionized telescope sales and dramatically expanded the amateur astronomy market?

In the competitive world of astronomy retail, telescope manufacturers and retailers have had to adapt their marketing strategies to reach both amateur stargazers and serious astronomers. This poll tests your knowledge about how one of astronomy's most significant product innovations was brought to market and changed consumer behavior in the field of astronomy forever.

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The introduction of 'Star Parties' - free nighttime demonstrations where potential customers could test telescopes before purchasing
The 'Celestial Subscription' program that allowed customers to pay for premium telescopes in monthly installments
Their 'Trade-Up Guarantee' allowing customers to upgrade to more advanced models within 3 years at 50% of the price difference
The first astronomy retail catalogs featuring detailed star charts that showed what specific objects would look like through each telescope model