What makes for a fun gala? It’s a question I’m asked often, and it is almost impossible to answer, because so many factors go into a good night for a good cause.

But I do have an answer: The most fun galas are the ones at which an accomplished orchestra gets everyone onto the dance floor.

For proof, I offer the happy expressions on the faces of the couples pictured here at galas around town.

The bar is high: A band must be able to switch from Cole Porter to Aretha Franklin to Frank Sinatra to the Beatles, and know exactly when to do so.

“There is a give and take between an audience and an orchestra, they react to one another in real time. That’s the magic: We feed off the energy of the crowd and the crowd feeds off our energy,” band-leader Bob Hardwick said yesterday, speaking over the telephone from Palm Beach, Fla.

These days, most of the people attending the galas grew up with the Beatles, so pop rock, swing, and disco are the genres that get people moving. The best thing about that is everyone can join in.

Dancing is a highlight at several events this spring, including the Glimmerglass Opera gala in mid-April, where board member Peter Duchin will be on the bandstand; the season opening night of the New York City Ballet in late April (where a deejay will be playing), and the New York Botanical Garden Conservatory Ball in June, where Mr. Hardwick’s orchestra, the Bob Hardwick Sound, will be playing.

Dancing has plenty of benefits for gala guests. For instance, it burns calories; it allows people to mingle and mix instead of being trapped at a table, and it shows off to best effect the long designer gowns women usually wear to these events, not to mention their sparkling jewels and expensive coifs that stay perfectly in place in spite of all that movement.

In terms of the dance floor’s aesthetics, it also helps if there are some great dancers in the crowd. That’s why dance company galas have an advantage. Professional dancers tend to dance better than the rest of us (and look better doing so), and they also make everyone else look good. Alvin Ailey American Dance Theater’s fall gala is famous for the action on the dance floor. Before then, there’s the Jacob’s Pillow Dance Festival gala on June 14, which is so much fun it usually sells out more than a month in advance (this year tickets go on sale April 7).

Do people dance less at galas than at weddings? Not at all, Mr. Hardwick said. And that’s because the fact that a few hundred people have paid upward of $1,000 each to support a charity is as worthy of celebration as a wedding.

agordon@nysun.com