I don't understand the meaning of "will have to do" in the following paragraph. What does it mean?
"However, whatever significant portion of Earth's satellite will be visible Sunday, July 21, will have to do for everyone joining in at the Hamptons Full Moon Fest shindig starting at 6 p.m."
-- Article "Hamptons Full Moon Fest at Gurney’s Inn", newsday.com (July 21 2013)