EVENING ON THE MALL: It's relatively cool and uncrowded, there's a parking space or two and, for the first time in a budget-crunching while, the National Gallery, the Archives and the National Air and Space Museum are open till 9. It's the ideal time for those of us who live here to wander down and reclaim our turf.

To encourage families to come on down, the folks at Air and Space are offering free Fly-by-Night Family Nights through September 4. Every Friday from 6 to 9, there's a mix of fun and facts with a theme: special tours, games, lectures, costume parties, movies and exhibits you can actually get your hands on.

At the Space Touchables exhibit (August 14 and September 4) visitors can try on astronaut gloves and handle space-shuttle tiles, among other far-out objects. Other nights, families can build a space station tower with straws and straight pins; come dressed '40s-style for an Airmen of Note concert of World War II favorites; watch powered model airplanes fly and learn to build kites; and dress up as your favorite "Star Trek" characters for a night of star trekking.

This Friday, the focus is on "Astronomy From Your Own Backyard" with the National Capital Astronomers setting up a Telescope Fair, which includes some simple telescopes you can make at home. There'll be stargazing from the South Terrace, if it's not too hazy. A tour of the Planets Gallery starts at 7 and an expert with the right stuff from the NASA-Goddard Space Flight Center lectures on "Comets and Planets" at 8 in the Albert Einstein Planetarium. BUILDING IN SPACE --

August 14. Space Touchables, 6 to 9, Space Hall; build a space station tower and win prizes; watch a videotape of astronauts building in space; learn about space stations from an expert at 8.


August 21. The Airmen of Note perform in the Milestones of Flight Hall; members of the International Plastic Modelers Association demonstrate model airplanes; tour of the World War II Gallery at 7; prizes for the first 30 visitors dressed in '40s costume.


August 28. Powered model-airplane building demonstration by the Academy of Model Aeronautics; kite-building demonstration; "see-worthy" bonus for the first 2,000 visitors.


September 4. "Star Trek III: The Search for Spock" will be shown on large-screen monitors in Space Hall; Trekkie costume contest with prizes; Space Touchables and telescope viewing; a lecture "Trekking Through the Autumn Stars" in the Planetarium at 8.