Johannesburg Centre, Astronomical Society of Southern Africa


Variable of the Month: Eta Carinae
( Plus a bonus - S Carinae. )

This enigmatic object (It is not a star in the accepted sense of the word) has featured in this column before, I think, but very recent developments have brought it back into the limelight.

Last month, professional astronomers noticed that the Hubble Space Telescope data showed an increase in its brightness and asked some of us for our long term visual observations.

Eta has indeed shown an increase in brightness, albeit a small one. It is now at about magnitude 5 1/2 (I do not quote my estimate for fear of influencing other observers) so it should be visible to the naked eye. As it is embedded in nebulosity, it is best observed with a small aperture and fairly high magnification. An aperture of only 10mm should be sufficient but I routinely use 30mm.

Burnham devotes over two pages to Eta Car, mentioning that in April 1843 it outshone every star in the sky except Sirius.

S Carinae. is one of the best-known variable stars in the Southern Hemisphere, and is a favourite with beginners because it can be located quite easily, has a large amplitude of variation and short period compared with other Mira type stars.

Please note that the chart including these two objects is oriented with South to the Top.

Enjoy observing them, using the comparison stars 45, 54 and 65.

Danie Overbeek.


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