# Ruchbah (Delta Cassiopeiae)

Ruchbah (Delta Cassiopeiae) is a star in the constellation Cassiopeia, magnitude 2.7.

**The queen’s knee in Cassiopeia’s W — a star ringed by cold, distant dust.**

Ruchbah is a [star](https://astropilot.space/glossary/star) at a turning point. It has just used up the hydrogen in its core — astronomers reckon it is only about 4% past the end of its main-sequence life — and at around 600 million years old it is beginning to swell, already nearly four times the Sun’s width.

Something cold surrounds it. The star gives off extra infrared light, the glow of dust at about 85 K circling roughly 88 times farther out than the Earth is from the Sun — well beyond the reach of our own Kuiper belt. It suggests a debris disc.

It was once listed as an eclipsing binary, dipping slightly every 759 days, but modern measurements show no changes larger than a hundredth of a magnitude. Its name is Arabic for “knee” — the knee of Queen Cassiopeia.

Ruchbah (Delta Cassiopeiae) is 99 light-years away: the light we see from it set off in 1927, around the time Pluto was discovered.

## Did you know?

- **A mystery name.** A second name, Ksora, appeared in Antonín Bečvář’s 1951 star atlas. The star-name scholar Paul Kunitzsch could find no clue to where it came from.
- **The Flying Corridor.** Chinese astronomers made it the third star of Gé Dào, the Flying Corridor, a path of six stars through Cassiopeia.
- **Another Ruchbah.** Alpha Sagittarii also bore the name Ruchbah. The IAU kept Ruchbah for this star and gave Alpha Sagittarii the variant Rukbat.

A white star of magnitude 2.7, the second star from the eastern end of Cassiopeia’s W. Point a small telescope about one degree east-north-east of it to find the open cluster M 103.

## When and where to see it

It is best placed in the evening sky around November, when it crosses the meridian at about 10 pm local time (around midnight in October). It can be seen from everywhere north of 30°S and never sets north of 30°N.

At its highest it stands 80° up from 50°N, 65° up from 35°N, 30° up from the equator, below the horizon from 35°S.

## Facts

- Type: Star
- Constellation: Cassiopeia
- Designations: Delta Cassiopeiae, δ Cas, 37 Cas, HR 403, HD 8538, HIP 6686
- Magnitude: 2.7
- Position: RA 1h 25.8m, Dec +60° 14′ (J2000)
- Spectral type: A5IV
- Colour: white (B−V 0.13)
- Distance: 99 light-years
- Discovered: Known since antiquity

Open AstroPilot to see when Ruchbah (Delta Cassiopeiae) is highest tonight from your location, how easy it is with your telescope or binoculars, and an eyepiece view. https://astropilot.space/object/ruchbah