In their short but fascinating book, Extraterrestrials: A Field Guide for Earthlings, science writer Terence Dickinson and artist Adolf Schaller offer some educated conjectures about living beings elsewhere in the cosmos.

Dickinson starts off with the reminder that as yet there is no evidence of any life beyond Earth, yet with the enormity of the cosmos, he thinks it is almost inconceivable that we are alone. If only one star in a billion had a planet with life, the universe would still contain a trillion or more homes for ETs, a hundred or so of which could be in our own Milky Way galaxy.

After presenting some popular conceptions of aliens in science fiction, he identifies the kinds of environments that might support life as we understand it, and where such places might be found. Then with Schaller’s marvelous depictions, they pose some ideas of how alien beings might appear.

Finally, Dickinson offers some plausible responses to questions begged by the rest of the book, like “Where are they?” and “If they’re out there, why haven’t we been contacted?”

Perhaps we are the most advanced life form in our sector, and we’ll have to find our less-advanced neighbors. Then again, maybe highly advanced beings are trying to contact us right now, but we’re not advanced enough to receive their signals.

Possibly other intelligent beings know we exist but we’re so primitive they have no interest in contacting us, or they have chosen only to monitor us and not intervene in our life. And, of course, there remains the unlikely prospect that we are alone.

Assuming extraterrestrials exist, Dickinson suggests four ways contact could occur. Aliens might visit us as they did in Steven Spielberg’s 1977 movie Close Encounters of the Third Kind.

Or maybe we’ll receive a signal from afar such as the Message received from the star Vega and discovered by radio astronomer Dr. Ellie Arroway in Carl Sagan’s 1985 novel Contact, later made into a movie starring Jody Foster as Ellie.

Perhaps we’ll discover something left behind by intelligent beings like the signaling device left on one of Jupiter’s moons in Arthur C. Clarke’s and Stanley Kubrick’s classic 1968 movie 2001: A Space Odyssey.

Or we may just have to wait until we have the resolve and sophistication to venture out and discover other life as did Captain Kirk, Mr. Spock, and their intrepid crew of explorers in Star Trek, the highly popular 1960s television series — and countless other science fiction books and movies.

If it’s not in your local bookstore, Extraterrestrials is available via the Internet.

Paul Derrick is an amateur astronomer who lives in Waco. Contact him at 918 N. 30th, Waco, 76707, (254) 753-6920 or paulderrickwaco@aol.com. See the Stargazer Web site at stargazerpaul.com.