Preparing AstroBrain

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IC 2157

Set a site to see tonight's sky

When IC 2157 is up, how long it stays usable and when it is in season all depend on where you observe from. Set your site and this page adds tonight's answer and its year.

Set it on Tonight

The science

What you are looking at

In one sentence

Stars that formed together from one molecular cloud and are still loosely bound.

Class explainer for open cluster (SIMBAD classification).

The facts

IC 2157 is an open cluster in Gemini. SIMBAD gives its distance as 1,885 pc (−155 pc / +155 pc) — ≈ 6,148 ly, measured by parallax from 3 measurements. The light reaching us from it now left it about 6,148 years ago, around the end of the last ice age. SIMBAD measures it at 5.6′ × 5.6′ on the sky — 18% of the full Moon's width. At that distance, that angle means it is roughly 10 light-years across. Framing uses its catalogue size instead: 2.7′. It shines at magnitude 8.4.

Sources: AstroBrain catalogue; CDS/SIMBAD astronomical database, Strasbourg (SIMBAD record IC 2157 · distance from 2021MNRAS.504..356D). Contains information from SIMBAD, which is made available here under the Open Database License (ODbL). Download the SIMBAD-derived data.

For scale

Angular size, as it would sit on your sky.

10 ly

across — 2× the distance from the Sun to its nearest neighbour star (4.37 ly).

The same patch of sky in visible light

Sky image
Observatory photos and open-licence sky surveys.
Credits on each image.

Neighbours in the sky

Sky maths: apparent positions with refraction, one-minute steps; usable = full astronomical dark, at least 30° up and clear of your skyline. Survey images: CDS, Strasbourg (DSS2 and other surveys). Science: SIMBAD. The hours, heights and Moon on this page use no weather forecast; the rank is this target’s place in the Targets list, whose score also counts the cloud forecast when there is one.

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