Giant star of rare brilliance in our sky

Buried deep within a rich region of the southern Milky Way lies a monster star of intense interest to astronomers.

Known as Eta Carinae, it first blazed to prominence in the early 1840s when it brightened to become the second brightest star in the sky, outshining even the brilliant Canopus.

Over the period when the Treaty of Waitangi was being signed, Eta Carinae transformed the whole look of the southern sky.

After 1850, this enigmatic star faded steadily and eventually fell below naked-eye visibility. When I began observational astronomy in 1967, Eta Carinae was easily seen with binoculars but has since been steadily brightening until today, when it can again be glimpsed by the unaided eye.

In the early 1990s, the Hubble space telescope obtained stunning images that showed Eta Carinae was embedded inside a dense dumbbell-shaped shell of gas and dust, blocking our direct view of the star.

It is 7500 light years away and so luminous that it produces as much light in six seconds as our sun produces in a year.

It may well be the most massive in our galaxy, perhaps 100 times the mass of our sun, which is close to the maximum mass any single star can have.

New x-ray and ultraviolet light observations have enabled astronomers to penetrate its dusty cocoon and there is now compelling evidence that Eta Carinae may, in fact, be a double star with its companion an astounding 30 times the sun's mass.

Such huge stars are exceedingly rare, making it a challenge to understand their inner workings.

Of one thing we can be sure - Eta Carinae cannot continue its current frenetic output and will, possibly even within a few millennia, detonate as a hypernova, releasing up to 100 times the energy of a supernova. Even from our safe viewing distance it will produce the most spectacular celestial fireworks display humans have witnessed.

On a more comprehensible scale, our solar system is also putting on something of a show. Venus is the brilliant white object dominating our western sky after sunset.

Mars is also very bright, rising in Aries in the northeast at sunset - it is at present the closest it will be to us for another 13 years. The next month will offer the best opportunity to see Mars through a telescope and it will be the feature object at the Stardome until Earth starts to leave it behind.