adjective

sidereal

sy-DEER-ee-ul

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Sidereal (adjective) means relating to or connected with the stars. Example: “The observatory tracks sidereal positions to aim its telescope accurately.”

adjective

Relating to or connected with the stars.

"The observatory tracks sidereal positions to aim its telescope accurately."

"Ancient navigators relied on sidereal patterns to find their way at sea."

technical In astronomy, describing time measured against the position of the stars rather than the sun.

"A sidereal day is slightly shorter than a solar day."

"Astronomers use a sidereal clock to keep telescopes aligned with distant objects."

How to use sidereal

Learner’s notes

In plain EnglishSidereal just means measured by or relating to the stars, rather than the sun.

When to use it

It is a specialist astronomical term rather than everyday vocabulary.

Memory tip

If you see sidereal next to time, day or year, it means the measurement is based on the stars, not the sun.

Trace the full origin ↓

Common pairings

sidereal time sidereal day sidereal year sidereal period

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C2 · Advanced serendipity Fortunate discoveries made entirely by accident.

Gen Z slang rizz Charm — the ability to attract a romantic interest.

B2 · Intermediate empathy The capacity to share another person’s feelings.

C1 · Advanced nonchalant Casually calm and relaxed; unconcerned.

Internet slang delulu Delusional — believing something against the odds.

Etymology nostalgia Greek nostos “return home” + algos “pain”.

C2 · Advanced serendipity Fortunate discoveries made entirely by accident.

Gen Z slang rizz Charm — the ability to attract a romantic interest.

B2 · Intermediate empathy The capacity to share another person’s feelings.

C1 · Advanced nonchalant Casually calm and relaxed; unconcerned.

Internet slang delulu Delusional — believing something against the odds.

Etymology nostalgia Greek nostos “return home” + algos “pain”.

Test yourself on “sidereal” A quick quiz — meaning, synonyms & usage →

Fill the gap

Can you complete this real example?

The observatory tracks _____ positions to aim its telescope accurately.

Etymology

Sidereal comes from the Latin adjective sidereus with the suffix -al added. Sidereus itself derives from sidus, the Latin word for a star or constellation, whose own origin further back is uncertain.

Origin: Latin

Rhymes for sidereal

deal zeal teal real meal seal heal peal veal Neal beal ideal

See all rhymes for sidereal →

Frequently asked questions

What does sidereal mean?

It means relating to the stars, and in astronomy it describes time or measurements based on the stars' positions rather than the sun.

What is a sidereal day?

A sidereal day is the time it takes the Earth to complete one rotation relative to distant stars, and it is slightly shorter than an ordinary 24-hour solar day.

Is sidereal only used in astronomy?

It is mainly a technical astronomical term, most often seen in phrases like sidereal time, sidereal day and sidereal year.

What is the meaning of sidereal?

"sidereal" (adjective) means relating to or connected with the stars.