Caldwell 92, NGC 3372
|Apparent size:||120 arc min.|
|Diameter:||349 light years.|
|Distance:||3,100 light years.|
Eta Carinae (The Nebula)
The Eta Carinae Nebula is a spectacular, emission nebula, embedded with several individual star clusters and lying within the Southern Milky Way. With an overall diameter of 120 arc minutes – equivalent to four Lunar diameters – it is too big to fit completely within the my f/7 refractor’s field of view.
It contains three main lanes of dark nebulosity, which might remind some of the Trifid Nebula in Sagittarius.
The nebula is circumpolar – never setting below the horizon from the privilege of my of 34° S latitude, although it’s best seen between about January to June each year, when I can watch it rise to an altitude of about 64°.
Eta Carinae is not visible north of about latitude 30° N.
Eta Carinae (The Star)
Not far from the centre of the nebula is the unusual variable star, Eta Carinae (yes it has the same name as the nebula), a highly luminous hypergiant star. Estimates of its mass range from 100 to 150 times the mass of the Sun. It is a prime supernova candidate and I can’t wait!
It is actually a double star system. Eta Carina A is quite faint by most standards (magnitude +6.2) but it is twelve times brighter than it’s companion Eta Carinae B (magnitude +11.1). However, when Eta Carina A erupted in the 1840s it briefly became the second brightest star in the sky, before fading.
The star emitted two massive lobe shaped ejections called the ‘Homunculus Nebula’, created by the eruption. Homunculus means a small depiction of a human, so I’ll leave you to work that one out. I can’t. 🥺
Where is the Star?
So where is Eta Carinae (the star), the ticking time-bomb that is causing such mayhem deep inside Eta Carinae (the nebula)? It’s technically a bright star but is partly hidden by the Homunculus nebulosity, so I admit I was never quite sure. I decided to find out.
One of its identifiers is HD93308 and I used the fantastic website nova.astrometry.net to show the exact location:
I’m glad I took the trouble to establish it’s true identity, because it is not the star I thought it was!
|Feature image date:||2021-01-23|
|Exposure:||63 minutes (16 x 236 sec)|
|Field of View:||1.57° x 1.04° (up is 241 degrees E of N)|
Where Was The Telescope Pointing?
While the telescope was collecting its data, I took this 2.5 second snap of the Carina constellation. The nebula, with its dark lanes, can be seen in the centre, with a hint of colour:
Where is Carinae?
Eta Carinae (the Nebula) is gigantic. It appears larger and brighter than the more popular M42 Orion Nebula – despite being more than twice the distance of M42.
|SkyWatcher Esprit 120 mm apochromatic 3-element refractor; 840 mm f/l @ f/7.|
|Field flattener; ZWO Duo-band Hα (656nm) and OIII (500nm) filter.|
|SkyWatcher EQ6-R Pro mount; ZWO ASI120 guide camera.|
|Imaging camera: ZWO ASI 071 MC Pro (CMOS 28.4mm 16 Mpx).|
|Software: EQMOD, PHD2, SharpCap, Gimp.|
|Observatory location: 34° South.|
Images © Roger Powell
I’m a founder member of Macarthur Astronomical Society