When Yana Oselkin turned 28 in September, a brother bought her an unusual birthday gift."He got me an acre on the moon, with an Earth-facing view," the Manhattan-based dentist recalled recently. "I thought he was kidding."Oselkin now says she is a "proud moon owner" but views her property mostly as a novelty. She has no imminent plans to leave New York, let alone planet Earth.However, others take the lunar real estate business seriously. Dennis Hope, a Nevada-based entrepreneur who sells lunar property through his company, the Lunar Embassy, claims to own the entire moon and eight other celestial bodies in the solar system. He says he has sold 410 million acres on the moon and properties on Mars, Venus and one of the moons of Jupiter to nearly 2.5 million people. Hope recently formed a "galactic government," naming himself interim president. He expects the lunar property owners to ratify a newly drafted constitution. Hope has six "ambassadors," who sell property on his behalf, and 27 additional "realty agents" scattered around the world.He claims that they make 1,500 sales a day, selling individual plots over the Internet for $19.99 an acre, not including the $1.50 lunar tax."I take this as seriously as any other company," said Hope, who calls himself "the head cheese." "Our claim is as valid as any other claim of land."Hope says he claimed the moon in 1980 as an uninhabited land with an "intent to occupy." His legal team supports his ownership claim under a loophole in the 1967 U.N. Outer Space Treaty, drafted during the Cold War space race. Article II of the treaty states that "outer space, including the moon and other celestial bodies, is not subject to national appropriation by claim of sovereignty." Hope said the treaty says nothing about individual ownership.