Diphda (Beta Ceti)
Diphda (Beta Ceti) is a star in the constellation Cetus, magnitude 2.0.
The second frog — a “beta” star that outshines its constellation’s “alpha”.
Its Arabic name means “the second frog”. The first frog is Fomalhaut, and the two sit in a dark, sparse stretch of sky. Diphda has a second name, Deneb Kaitos, “the southern tail of the whale”, and despite its “beta” label it is the brightest star in Cetus — half a magnitude brighter than Menkar, the “alpha”.
Diphda was born as a hot blue-white star of about three and a half solar masses. It has since swollen into an orange giant some 18 times wider than the Sun and 150 times as luminous. Now it quietly fuses helium in its core, a stage that will last more than 100 million years.
It is not as calm as it looks. Diphda throws flares that brighten it for several days at a time — far longer than the Sun’s, which last hours. In 2005 the XMM-Newton observatory found it shining in X-rays about 2,000 times more strongly than the Sun, enough for Chandra to take its picture.
Diphda (Beta Ceti) is 96 light-years away: the light we see from it set off in 1930, around the time Pluto was discovered.
Did you know?
- Superintendent of Earthworks. Chinese astronomers called it Tǔsīkōng, the Master of Constructions — “Superintendent of Earthworks” in R. H. Allen’s rendering. It stands alone in its own asterism.
- A frog that named a star. The Latin form of its name, Rana Secunda (“second frog”), gave the name Rana to another star, Delta Eridani.
An orange 2nd-magnitude star alone in a dark, empty patch of sky — the brightest light in Cetus. Follow the eastern side of the Great Square of Pegasus south, from Alpheratz through Algenib, and keep going to reach it.
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 south of 72°N and never sets south of 72°S.
At its highest it stands 22° up from 50°N, 37° up from 35°N, 72° up from the equator, 73° up from 35°S.
Facts
- Type
- Star
- Constellation
- Cetus
- Designations
- Beta Ceti, β Cet, 16 Cet, HR 188, HD 4128, HIP 3419
- Magnitude
- 2.0
- Position
- RA 0h 43.6m, Dec −17° 59′ (J2000)
- Spectral type
- G9.5IIICH-1
- Colour
- orange (B−V 1.01)
- Distance
- 96 light-years
- Discovered
- Known since antiquity
Open AstroPilot to see when Diphda (Beta Ceti) is highest tonight from your location, how easy it is with your telescope or binoculars, and an eyepiece view.