What kind of star is Caph?
Caph, catalogued as Beta Cassiopeiae (β Cas), appears in the official constellation Cassiopeia. Its apparent visual magnitude is about 2.27; varies by a few hundredths, while its estimated distance is about 54.5 light-years. Astronomers classify the object as F2 III–IV Delta Scuti variable. These labels describe temperature, luminosity class or system components; they should not be read as a claim that every naked-eye point is a single isolated star.
Caph is crossing the instability strip, where pulsations can be driven in an evolving F-type star. It varies by only a few hundredths of a magnitude on a timescale of hours, placing it among Delta Scuti variables rather than dramatic naked-eye variables. Rapid rotation broadens its spectral lines and makes a simple spherical model inadequate; interferometric work has examined its oblateness and inclination. The star appears to be leaving the main sequence for the subgiant or giant phase. Its closeness permits relatively detailed constraints on radius, temperature and rotational geometry.
The coordinate pair RA 00h 09m 10.69s, Dec +59° 08′ 59.2″ fixes the object's direction on the celestial sphere for the J2000 reference epoch. Right ascension works like celestial longitude measured in hours, while declination works like latitude north or south of the celestial equator. Proper motion and improved measurements can refine catalogue positions, but these coordinates are sufficiently precise for a finder chart or planetarium search.
Caph data at a glance
| Proper name | Caph | Catalogue designation | Beta Cassiopeiae (β Cas) |
|---|---|---|---|
| Constellation | Cassiopeia | Apparent magnitude | about 2.27; varies by a few hundredths |
| Spectral or system type | F2 III–IV Delta Scuti variable | Estimated distance | about 54.5 light-years |
| Right ascension (J2000) | 00h 09m 10.69s | Declination (J2000) | +59° 08′ 59.2″ |
Values are rounded for an observer-friendly overview. Consult the linked SIMBAD record for component-level identifiers, bibliography, measurement provenance and newer catalogue values.
The name Caph
Caph derives from Arabic kaff al-khaḍīb, “the stained hand,” part of an older figure associated with the Pleiades. It now marks one end of Cassiopeia’s W.
The name’s Arabic source belonged to a sky picture different from the Greek queen Cassiopeia, illustrating how names can migrate between cultural maps. Bayer designated it Beta Cassiopeiae. Its proximity to the zero-hour meridian once made it useful in timekeeping and coordinate orientation, though precession continuously shifts stellar coordinates. Modern photometry identified its low-amplitude Delta Scuti pulsation, and the IAU standardized Caph in 2016.
Modern professional catalogues retain identifiers such as the Bayer designation alongside a proper name. The International Astronomical Union standardizes which name belongs to which component—an important distinction for systems whose combined light looks like one star from Earth.
How to find Caph
Find Cassiopeia’s bold W opposite the Big Dipper across Polaris. Caph is the western end star and the first of the five main points to rise. It lies close to zero hours right ascension, making it a useful landmark near the celestial coordinate system’s starting meridian.
Circumpolar from much of northern Europe and North America; best placed on northern autumn evenings. Visibility on a particular night still depends on latitude, season, time, horizon obstructions, weather and local light pollution. Use the interactive atlas below to check the surrounding field before observing.
Observation checklist
- Find the end of Cassiopeia’s W farthest from bright Schedar.
- Use Polaris to recognize how this circumpolar constellation rotates during the night.
- Do not expect to see Caph’s tiny pulsation casually; differential photometry is needed.
- A wide binocular view shows the Milky Way star fields surrounding the W.
Interesting facts about Caph
- Caph lies close to zero hours of right ascension.
- It is a low-amplitude Delta Scuti pulsating variable.
- Rapid rotation makes the star measurably non-spherical.
- Caph is evolving away from the main sequence.
- Its traditional name came from a cultural star figure distinct from Cassiopeia.
Continue from Caph into the night sky
Use the Cassiopeia constellation guide to place this star within its larger pattern. When you are ready to observe, compare dark-sky places, find a nearby observatory, or follow our practical guide to finding a star in the night sky. Symbolically registered names are kept separately in the searchable Star-Register catalogue.
Sources and further reading
Measurements are rounded for readability. Multiple systems, variable stars and distant supergiants can have component-specific or model-dependent values. Survey panels show photographic sky fields, not the physical surface of the star.