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.

It is the reference “U.F.O. researchers dreamed of having,” Gordon G. Spear, emeritus professor of physics and astronomy at Sonoma State University in California, writes in the foreword.

The book contains no narrative or anecdotal accounts, just 371 pages of charts and graphs that slice and dice the geography and timing of the incidents and the various shapes that witnesses reported: flying circles, spheres, triangles, discs, ovals, cigars.

Many of the sightings turn out to be explainable, the authors say, but a small percentage defy resolution.

The authors are Cheryl Costa, 65, a former military technician and aerospace analyst, and her wife, Linda Miller Costa, 62, a librarian at Le Moyne College and a former librarian at the National Academy of Sciences, NASA and the Environmental Protection Agency.

Working on PCs amid sewing tables in the upstairs parlor — the warmest room in their hundred-year-old house — the two spent weekends for the last 16 months extrapolating figures from sightings reports and laying out the graphics.

Cheryl Costa was writing New York Skies, a U.F.O. blog for The Syracuse New Times, when the Costas decided to expand their tallies of U.F.O. sightings nationwide. “We wanted to do our bit for disclosure,” she said. “It’s something the government should have been doing.”

The Costas realize some might find this a strange way to spend weekends. But both say they have spotted U.F.O.s themselves and want to detoxify the subject.

“We’re doing scientific research,” Cheryl Costa said. “What’s crazy is not being willing to look at research.”

She came to the collaboration roundabout, having served as a cable lineman in the Air Force in Vietnam, and afterward in the Navy’s submarine service, as a man before undergoing gender-reassignment surgery in the 1980s. Ordained as a Buddhist nun, she was running a theater group in Maryland when she met Linda. They wed in 2011.

U.F.O. trackers welcomed their publication.

“With this compendium, Cheryl and Linda Costa have reminded the public and the media the extraterrestrial phenomenon continues unabated,” said Stephen Bassett, founder and executive director of the Paradigm Research Group, which lobbies for disclosure of official U.F.O. records.

 

Rebutting a common perception that U.F.O. sightings are on the wane, the Costas’ book shows that sightings have risen in waves, to 11,868 nationwide in 2015 from 3,479 in 2001. Only a small fraction of sightings are actually reported to Mufon or Nuforc.

Their labor of love is about the numbers, just the numbers, and the Costas refrain from speculating on what exactly is happening. “We really don’t know,” Linda Costa said. “But all these people are seeing these things.”

The government officially quit the U.F.O. business in 1968, with the finding in the Condon report from the University of Colorado that there was nothing significant to investigate, although some 30 percent of the incidents were unexplained.