A Visual Observation of Eta Carinae on 1st May 2000 – by Albert Lim
I) High Power Drawing of Eta Carinae (η)
This drawing was made from observations on the 1st of May 2000 (Monday night).
Observational details to follow.
North
South
Figure 01 : Drawing of Eta Carina at high power (1,083X) covering a field of view of
about 4.5 arcminutes as above. Star positions are recorded as precisely as visual judgement
will allow without any aid (i.e. grids or micrometers). At such high powers, turbulence
are a problem and observations had to made and confirmed part by part at moments when
the air stayed still. The above is a refined drawing made from combined information from
several sketches at the telescope. North is at the top
II) Observational Information
Observer : Albert
Lim ( TASOS )
Main Instrument : 40cm
Cassegrain, F13.5, 5200mm FL
Oculars / Powers : TeleVue
4.8 mm Nagler (1,083X), 7 mm Nagler (743X),
13
mm Nagler (400X)
NB
- Naglers have 82 deg apparent field
Sec Instrument : 15cm
Refractor, F12, 1800mm FL w 15 mm ocular (120X)
Location : Singapore
Science Centre Observatory, Singapore
Longitude : 103
degrees 44 minutes 14.4 seconds - East
Latitude : 001
degree 20 minutes 3.2 seconds - North
Obv Date / Time : 1st
May 2000 (Monday) - 12:15 UT to 14:00 UT
Techniques : Visual
- no filters used
Antoniadi’s scale : 4
- good - partly cloudy and slightly tremulous
with approximately 5 seconds steady intervals
Pg 1 of 2.
III) Subject Information
Subject : Eta
Carina (η) - Homunculus ejecta-nebula
Circumstance : No
moon interference - moonrise after 4.00am
Distance : > 10,000
ly
Rise / Transit / Set : 07:15
UT / 13:10 UT / 19:08 UT
App. Angular Dia. : Homunculus
nebula estimated ~ 8 x 16 arc seconds
Appearance : Bright
orangish centre with yellowish and whitish surroundings
App Magnitude : ~
8th magnitude ?
Azimuth : From
172d 15m to 187d 6m Az
Altitude : From 27d
51m to 28d 0m N
IV) Notes about Eta Carinae
Eta-Carinae is an unusual star that lies in the huge Eta Carina nebula. The star, Eta
Carinae, has a mass of 150 suns and a luminosity of approximately 4 million suns and
is one of the most luminous stars known in our Milky Way galaxy. Eta-Carinae is well
known for its erratic and violent eruptions. In 1841 for example, it erupted and became
the second brightest star in the night sky and by 1843, it shone at a magnitude of -1.
The star itself is embedded within the Homunculus (named by Gaviola) - an ejecta
nebula that is gradually growing in size - at about an average of 7 arcseconds per century.
For over a century, astronomers have been unable to see through the Homunculus because
it was opaque - an although it is gradually becoming more transparent, astronomers can
now see through the homunculus nebula through multiwavelength techniques. Because the
nebula has gas and dust mixed in it, it is not possible to understand the geometry of
the homunculus through optical alone. There is a need to combine optical and Infrared
observations at selected lines to achieve this. Visible light from the homunculus is
due to reflection of light from the star and intrinsic emission from the ionised gas.
Since dust grain cannot be radiating more energy than it receives from the star itself,
accessing the present luminosity of Eta Carinae must therefore necessarily take into
account the IR component. Indeed, with IR taken into account, astronomers are finding
that Eta Carinae have hardly faded in the last 140 years - the formation of grains of
dust in the Homunculus is in effect causing the visible light to be dimmed.
Pg 2 of 2.
