[Suzy]

Originally Posted by jjjnettie

You did have a great night Ron.
So...is Eta Carina brightening because the dust cloud is moving out of the way? Or is it physically brightening?

The star is indeed brightening.

HST/STIS observations confirm this. The possibility of a binary star, combined with the outbursts makes it a complex star to study.
However, with spectroscopy equipment we have the technology these days to penetrate the gas and take measurements of it’s brightness variations.

More information available here http://etacar.umn.edu/etainfo/history/

It is important to realize that the groundbased magnitudes shown since the great eruption refer to the integrated light over the nebula and not the central star. So why did it brighten so quickly? Most astronomers assume that the rapid brightening was caused by the destruction of dust. That may be correct, but why were at least two magnitudes of circumstellar extinction by dust removed so quickly? During the past 50 years the Homunculus has continued to brighten much more slowly possibly due to expansion of the nebula with small oscillations observed in both the visible and near-infrared until very recently when HST/STIS observations showed that the central star itself brightened significantly between 1997 and 2001 and is continuing to brighten after its recent (2003.5) "event" (Figure 4, below).

http:////en.wikipedia.org/wiki/Eta_Carinae
From Wiki

Brightness variations

One remarkable aspect of Eta Carinae is its changing brightness. It is currently classified as a luminous blue variable (LBV) binary star due to peculiarities in its pattern of brightening and dimming.
When Eta Carinae was first catalogued in 1677 by Edmond Halley, it was of the 4th magnitude, but by 1730, observers noticed it had brightened considerably and was, at that point, one of the brightest stars in Carina. Subsequently it dimmed again and by 1782 it appeared to have reverted to its former obscurity. In 1820, it was observed growing in brightness again. By 1827, it had brightened more than tenfold and reached its greatest apparent brightness in April 1843. With a magnitude of −0.8, it was the second brightest star in the night-time sky (after Sirius at 8.6 light years away), despite its enormous distance of 7,000–8,000 light-years. (To put the relationship in perspective, the relative brightness would be like comparing a candle (representing Sirius) at 14.5 meters (48 feet) to another light source (Eta Carinae) about 10 kilometers (6 mi) away, which would appear almost as bright as the candle.)
Eta Carinae sometimes has large outbursts, the last of which appeared in 1841, at around the time of its maximum brightness. The reason for these outbursts is not yet known. The most likely possibility is believed to be that they are caused by built-up radiation pressure from the star's enormous luminosity. After 1843, Eta Carinae's appearance faded away and between about 1900 and 1940 it was only of the 8th magnitude, invisible to the naked eye.[16] Eta Carinae's sudden and unexpected doubled brightness was seen in 1998–1999. In 2007, its light could easily be seen with the naked eye at brighter than magnitude 5.[2]
In 2008, the formerly clockwork regularity of the dimming was upset.[17] Following its 5.52-year cycle, the star would normally have started its next dimming appearance in January 2009, but the pattern was noticed starting early in July 2008 by the southern Gemini Observatory in La Serena, Chile. Spectrographic measurements showed an increase in blue light from superheated helium, which was formerly assumed to occur with the wind shock. However, if the cause is a binary star, it would be located too far away at this point in time for the wind to interact in so significant a fashion. There is some debate about the cause of the recent event.[17]
In 2010, Duane Hamacher and David Frew from Macquarie University in Sydney showed that the Boorong Aboriginal people of northwestern Victoria, Australia witnessed the outburst of Eta Carinae in the 1840s and incorporated it into their oral traditions as Collowgulloric War, the wife of War (the Crow, pronounced "Waah", denoted by the star Canopus)[18]. This is the only definitive indigenous record of Eta Carinae's outburst identified in the literature to date.

Since 1990 it has been on a steady increase, and then in 1999 had a sudden spike. In 2009 there was yet another sudden spike. It is actually the brightest now - sitting at a v.mag of 4.47, current as of February 2011 - than even during the second outburst in 1890, Though the extent of the brightness of the 1890 outburst was hidden by the gas of the previous 1840 outburst.

A current chart can be seen here. http://etacar.fcaglp.unlp.edu.ar/ This chart is current as of February 11, 2011.
If you keep scrolling down past the charts, you will come across one more chart detailing the historic brightening going back to 1820 (that one's a goodie).

We also discussed this on the forum early last year when some of us (myself included) had noticed that it had gotten noticeably brighter. www.iceinspace.com.au/forum/showthread.php?t=60184

I apologise for my lack of science "lingo" talk and that it's very simple, (at least it's easy to understand ), as I am not an astronomer, but a mere person with special interest in this star. Hope the info helps anyway- I went digging through my Eta Carina Scrapbook which I made, to find all the links & info. It was good to re-visit all this information again.