Star Stars · In Cetus
Diphda
Diphda, β Ceti, is an orange giant in Cetus: the 53rd brightest star in the night sky.
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- Constellation
- Cetus
- Designation
- β Ceti
- Apparent magnitude
- 2.04 · 53rd brightest star in the night sky
- Spectral class
- K0III
- Distance
- 96.3 light-years
- Highest at midnight
- late September
- Position (J2000)
- RA 00h 44m · Dec −17° 59′
An orange giant, around 5,200 K, like Arcturus and Aldebaran. About 61× brighter than the faintest star the eye can see. Gives off about 110 times the Sun's visible light. The light you are seeing left around 1930.
When to see it
On the night of Wed 29 Sep 2027, when it is highest around midnight, on each city’s own clock:
| From | Rises | Highest | Sets |
|---|---|---|---|
| London GMT+1 | 20:47 | 01:11 · 21° | 05:35 |
| New York EDT | 20:11 | 01:06 · 31° | 06:01 |
| Singapore GMT+8 | 19:19 | 01:16 · 71° | 07:14 |
| Sydney GMT+10 | 17:18 | 00:07 · 74° | 06:56 |
Common questions
- Can I see it from 50° north?
- Yes. It rises and sets, and at its highest it stands 22° up in the south.
- Can I see it from 35° south?
- Yes. It rises and sets, and at its highest it stands 73° up in the north.
- When is the best time of year to see it?
- Around late September, when it stands opposite the Sun and is highest at midnight. It comes round about two hours earlier each month, so by late December it is highest in the early evening, and in late June not until the hours before dawn.
- How far away is it, and how bright?
- It is 96.3 light-years away, and shines at magnitude 2.04 in our sky. From that far, the Sun would be a star of magnitude 7.2: too faint for the eye, a target for binoculars.
- Naked eye, binoculars or telescope?
- The naked eye, even from a city: at magnitude 2.04 it is brighter than the faintest stars a city sky still shows, about magnitude 4.5.
Look for
Start from Fomalhaut: Diphda is 27° east of it, about three fists at arm’s length.
Look for
From 50° north it climbs to 22°; from 35° north it climbs to 37°; from the equator it climbs to 72°; from 35° south it climbs to 73°.
Science
Diphda’s surface is about 5,200 K, some 600 K cooler than the Sun’s 5,772 K, so its light is strongest at about 560 nm, where the Sun’s is strongest at 500 nm. Moved to 33 light-years, the distance astronomers compare stars at, it would shine at magnitude −0.3, about as bright as Rigil Kentaurus looks to us.
Did you know
Against Fomalhaut, the brighter star the hop starts from: Fomalhaut looks 2.2 times as bright as Diphda in our sky, but Fomalhaut is 25 light-years away and Diphda 96 light-years, so side by side Diphda would give off 6.6 times as much light as Fomalhaut.
Science
Diphda is the 51st nearest to us of the 156 stars on these pages with a measured distance. Its nearest neighbour among them in space is Ankaa, about 40 light-years from it; on our sky the two are 25° apart.
Look for
The Sun passes 21° north of Diphda around late March, when it is highest at noon, in daylight: the weeks either side are its worst time of year. From 50° north it is above the horizon for about 9 hours a day, from 35° north about 10 and from 35° south about 14. It is 81° from the plane of the Milky Way, well away from the band.