Dwindling in success, popularity, or relevance. (Typically used in slightly more formal language.) Sure, that author was big 10 years ago, but her career is in eclipse now, and I doubt her new book will be a big seller.
If something is in eclipse, it is much less successful and important than it used to be. The Socialist party, which has spent most of the past 21 years in government, is now in eclipse. Since then, his career has been mostly in eclipse. Note: An eclipse of the sun is an occasion when the moon is between the earth and the sun, so that for a short time you cannot see part or all of the sun. An eclipse of the moon is an occasion when the earth is between the sun and the moon, so that for a short time you cannot see part or all of the moon because it is covered by the shadow of the earth.
in eclipse1 (of a celestial object) obscured by another or the shadow of another. 2 losing or having lost significance, power, or prominence.
2 1991 Atlantic Within a decade of his death…he was in eclipse: not written about, undiscussed, forgotten in architecture schools.