Cetus
What is Cetus?
Constellations· Autumn evenings (N) · a sprawling figure south of Pisces, home of Mira. The sea monster sent for Andromeda — fourth-largest constellation, holding Mira, the "wonderful" star that appears and vanishes on an 11-month cycle, and Tau Ceti, a nearby Sun-like star. With few bright stars it needs a dark sky.
📍 Visible from where you are right now — computed in your browser
bearing · altitude · rise time · best time tonight
Where Cetus is in your sky right now: https://nowsky.org/solar/sky?sel=con:Cetus — location and time set automatically, no login.
Stars of the figure
| Star | Magnitude |
|---|---|
| Mira | 3.0 |
The 1 brightest of the 8 stars used in the figure (8 lines). Lower magnitude means brighter.
Deep-sky objects near this constellation
Constellation basics
| Season | autumn evenings, October–December |
|---|---|
| Brightest star | Diphda (2.0) |
| How to find | the wide, faint polygon south of the Great Square and east of Fomalhaut |
| Area rank | 4th of 88 |
Figures are representative approximations. Source: compiled from NASA and IAU public data.
Frequently asked
- When can I see Cetus?
- autumn evenings, October–December.
- How do I find Cetus?
- the wide, faint polygon south of the Great Square and east of Fomalhaut.
- What is the brightest star in Cetus?
- Mira, magnitude 3.
- Where is Cetus in the sky right now?
- Open the sky view for your location and time and it shows the position in the sky right now.
Mira's tail — a star trailing 13 light-years
When the ultraviolet satellite GALEX imaged Mira in Cetus in 2007, a tail 13 light-years long appeared behind the star. Mira moves fast relative to its neighbours, at 130 km/s, and the gas it sheds as it pulsates collides with the interstellar medium and streams behind it like a comet's tail. Material at the tail's end left the star 30,000 years ago.
The tail is invisible in ordinary light and glows only in ultraviolet, so despite four centuries of watching the star no one had known. The discovery is cited as a single picture of how an old star returns material to the galaxy, showing that the carbon and oxygen made by stars like Mira become the stuff of the next generation of stars and planets. The Wonderful Star that appears and vanishes every eleven months is passing through the sky leaving a long wake.
The constellation in depth
Cetus is the sea monster Poseidon sent to punish Cassiopeia's vanity; Perseus turned it to stone with Medusa's head and saved Andromeda. Though called the Whale, old charts drew it as a toothed beast, and it lies in the sky's "Sea" region between Pisces and Eridanus. It is the largest of the watery constellations and one of the 48 listed by Ptolemy.
Mira, discovered by David Fabricius in 1596, was the first periodic variable star known: every 332 days it climbs to second magnitude, then fades below naked-eye visibility as a red giant 400 Suns wide pulsates. Ultraviolet images show it trailing a comet-like tail 13 light-years long. Tau Ceti, 12 light-years away, is a Sun-like star with several candidate planets and a favourite target of SETI searches.
On autumn evenings scan the wide region south of the Great Square and east of Fomalhaut for Diphda at the tail and Menkar at the head; the body lies between them. When Mira is near maximum an extra reddish star appears at the neck. Set the Sky view to a November night to see the whole figure in the south, with deep-sky objects on to mark Mira.
Related
Figures are representative approximations. Simulated positions use J2000 mean elements.