One of the truisms in amateur astronomy is that the minute something exciting is predicted to occur in the sky, the sky immediately clouds up. This is true especially if there’s an especially juicy coronal mass ejection inciting some space weather in Earth’s close neighborhood. Or, perhaps an occultation of a star by the Moon. As soon as the news gets out, the clouds start to gather.
This happened to me on October 8th, when the space weather forecast showed a good chance of seeing aurorae even at the mid-latitudes. I mentioned this as part of a talk I gave onboard a cruise ship that day (I do astronomy enrichment presentations for the Smithsonian and Celebrity Cruise Lines) and of course it clouded up that night. But, we persevered, and eventually a sucker hole did open in the clouds that revealed some of the sky, and we saw a gorgeous greenish display to the north, complete with spiky formations that came and went.
Another case in point has been the media hype for the Orionid Meteor shower that was supposed to deliver dozens or more meteors per hour. The news media picked up on this right away, and I saw at least one headline about “spotting a stunning meteor shower” from a news organization that used to have a qualified science writer on its staff but now just rewrites from a press release, spices it up, and then publishes hypey stuff that they think will grab people’s attention. (Yes, CNN, I’m talking about you…)
The press release I got from a reputable observatory mentioned that it might be possible to see up t0 25 meteors per hour. No promises, just a possibility. No flashy graphics about “dazzling” sights… And, reports I’ve seen from actual observers indicate that the counts have been a bit less than normal.
This is the sort of thing that really ought to give the media a bad name for over-hyping. A competent science writer would have been able express the story much more clearly for readers/viewers and given a more realistic view of what the shower might look like.
The reality of observational astronomy is that sometimes something can be quite spectacular, and sometimes it just isn’t. Astronomers’ models can only go so far in predicting how good a meteor shower, for example, will look. There are a lot of other factors that influence your observational experience… including clouds.
The best thing to do is get out there and observe… there are some gorgeous skies coming our way over the next few months, so be ready for them! Cherish each meteor, search out the planets, check out the nebulae, and never stop looking for the wonders to be seen in the night-time sky!
There’s an unstable star out there that’s on the brink of destruction. It lies some 7,500 light-years away, embedded in a star-forming region called the Carina Nebula. The star itself is called Eta Carinae (Eta Car, for short), and it’s actually a double star system. Some 170 years ago, observers noticed that it was growing very bright. Over time, it became the second-brightest star in the sky.
This unexpected brightening came to be known as the “Great Eruption”, and astronomers of the time watched it with great interest — but didn’t have much in the way of sophisticated instrumentation to really dig into the object to tell what was going on there. Today, modern telescopes are showing us what really happened during the Great Eruption.
The story goes like this: the more massive member of the duo — a type of star called a luminous blue variable — began blasting out huge amounts of its own mass. Over the period of 20 years that it was seen to be erupting (from 1837 to 1858), this heaving star lost more than 20 solar masses of material. Much of that “star stuff” can still be seen in a double-lobed cloud surrounding the system.
These images reveal light from a massive stellar outburst in the Carina Nebula reflecting off dust clouds surrounding a behemoth double-star system. The color image at left shows the Carina Nebula, a star-forming region located 7,500 light-years from Earth. The massive double-star system Eta Carinae resides near the top of the image. The star system, about 120 times more massive than the Sun, produced a spectacular outburst that was seen on Earth from 1837 to 1858. But some of the light from the eruption took an indirect path and is just now reaching our planet. The light bounced off dust clouds (the boxed region at the bottom of the image, indicating an area of space that lies about 100 light-years away ) and was rerouted to Earth, a phenomenon called a light echo. The image was taken in February 2000 by the U.S. National Optical Astronomy Observatory's Curtis Schmidt Telescope at the Cerro Tololo Inter-American Observatory (CTIO) in Chile. The three black-and-white images at right show light from the eruption illuminating dust clouds near the doomed star system as it moves through them. The effect is like shining a flashlight on different regions of a vast cavern. The images were taken over an eight-year span by the U.S. National Optical Astronomy Observatory's Blanco 4-meter telescope at the CTIO. Credit: NASA, NOAO, and A. Rest (Space Telescope Science Institute, Baltimore, Md.)
Eta Car (the LBV) is a massive dying star. Such stars do not make up the majority of stellar systems in our galaxy, so of course, astronomers are quite interested in what sort of death process Eta Car will go through. Unlike our Sun, which will sort of gently swell to become a red giant (and lose much of its mass in a less-explosive manner), Eta Car will likely go out in a huge cataclysm called a supernova. Some astronomers suggest it could be such a catastrophic event it would be termed a “hypernova.”
However it blows, Eta Car’s passing will afford astronomers with a ringside seat to stellar mass destruction. The first thing they’ll detect when it blows is a gamma-ray burst that could affect our communications satellites. After that, they’ll be busy cataloguing the process of the explosion and the ring of debris that will be rushing out to space. Some astronomers have suggested that this explosion could happen anytime from the next few years to a few million years from now. Regardless of when it blows, it’s not likely to hurt us much on Earth, since the rotational axis of the system is pointed away from us.
Hubble Space Telescope has been observing Eta Car for a couple of decades now, watching subtle changes in the cloud surrounding the stellar pair, and analyzing the mixes of gas and dust in that cloud. The most recent observations actually pinpoint an echo of the light from the Great Eruption bouncing off more distant parts of the clouds. The observations of the light echoes mark the first time astronomers have used spectroscopy to analyze a light echo from a star undergoing powerful recurring eruptions, though they have measured this unique phenomenon around exploding stars called supernovae. In spectroscopy, light from an object is captured by the telescope and sent to an instrument (called a spectrograph) that breaks that light into all its wavelengths. Each wavelength of light tells you something about the chemical makeup of the object, its speed through space, whether or not it is spinning, and gives a measure of its temperature. For the Hubble observations, the spectrograph captured Eta Car’s characteristic “fingerprints,” providing details about its behavior, including the temperature and speed of the ejected material.
The light echoes from Eta Car are telling astronomers that this restless, heaving old star system does not behave like other stars of its class. The temperature of the outflow from Eta Carinae’s central region, for example, is about 8,500 degrees Fahrenheit (5,000 Kelvin), which is much cooler than that of other erupting stars. So,this gives some important clues about what’s happening inside the star. There are other clues in the stream of light HST is studying, and light from the outburst is still on its way to Earth. Astronomers are expecting another brightening in about six months and that will give them more data to chew on as they seek to understand how this star is going through its death process. So, stay tuned. There’s more news on the way from Eta Car!
