Here are a few possibilities, depending on the context:
* A Star: This is a very common interpretation. Stars twinkle in the night sky and can be seen as jewels scattered across a dark canvas.
* The Moon: Especially a crescent moon, could resemble a delicate, shimmering jewel hanging in the night.
* City Lights: From a distance, a city lit up at night can resemble a collection of sparkling jewels.
* Fireflies/Lightning Bugs: These insects emit a bioluminescent glow, and their twinkling lights could be described as jewels.
* Dewdrops: On a dark night, dewdrops might reflect the light of the moon or stars, appearing like tiny jewels on plants or grass.
* A Specific Object: It could be a real jewel, a shiny ornament, or any object that glitters in the dark, depending on the story, poem, or situation where the phrase is used.
* Figurative/Metaphorical: It could be used metaphorically to describe something precious or valuable that stands out in a difficult or dark situation. For example, hope, love, or a moment of joy could be described as a "jewel at night."
To understand the exact meaning, you'd need to know the context in which the phrase is used.