SYRACUSE — Why have sightings of unidentified flying objects around the nation more than tripled since 2001? Why is July the busiest month for U.F.O. sightings? Why did they spike in Texas in 2008, or in New Mexico in September 2015?

And how in the world, or out of it, has Manhattan racked up New York State’s second-highest tally of U.F.O. sightings in this century?

These questions and many others emerge from the first comprehensive statistical summary of so-called close encounters: 121,036 eyewitness accounts, organized county by county in each state and the District of Columbia, from 2001 to 2015.

The unlikely compendium, “U.F.O. Sightings Desk Reference,” is the work of a couple in Syracuse, who crunched unruly data on U.F.O. reports collected by two volunteer organizations: the Mutual U.F.O. Network, or Mufon, and the National U.F.O. Reporting Center, or Nuforc.