My Stepmother Is an Alien  (1988)

Theatrical Release Information:
My Stepmother Is an Alien

An astrophysicist falls in love with a beautiful woman who is actually a disguised extraterrestrial in this high-concept comedy. Dan Aykroyd plays Steven Mills, a dedicated and harmlessly odd scientist researching ways to send radio signals to deep space. Unbeknownst to him, one of his experiments works better than expected, attracting the attention of an alien in need of help. She travels to Earth and poses as a human, assuming the name Celeste and the body of Kim Basinger. Celeste's lack of knowledge about humanity causes her to act bizarrely at times, but her odd behavior unexpectedly causes Mills to fall in love with her. The confused Celeste decides to play along for her planet's sake, but she finds her plan threatened by Mills' teenage daughter Jessie (Alyson Hannigan), who has become suspicious of Celeste after witnessing some odd behavior. The culture clash between Celeste's planet and Earth serves as an excuse for broad slapstick and sitcom-style humor, such as Celeste's fumbling efforts to enact the human ritual of "kissing." ~ Judd Blaise, All Movie Guide