Lois & Clark Forums Forums General Discussion Off Topic Australia's flag and the Southern Cross

Well, I seem to be on an Off Topic roll right now. Hopefully this isn't going to be controversial....

Today Swedish televison has been reporting that there has been an election in Australia (and apparently there will be a new Prime Minister, Kevin Rudd). Anyway, the Asutralian flag has been very visible in the TV coverage of the election. So I just wanted to point out that the Australian national flag shows one of the most famous constellations in the sky, the Southern Cross:



This is the Australian flag, though maybe it's getting a new design?

Anyway, as you can see the Australian flag displays six stars in a prominent pattern. The five stars on the right are the Southern Cross. The bright star on the left is, probably, Alpha Centauri. Alpha Centauri is the nearest of all stars except our own Sun. Interestingly, Alpha Centauri is very like our own Sun, too, but most stars are really quite unlike the Sun!

This is a picture of the Southern Cross on the right and Alpha and Beta Centauri on the left:



In the picture, please note a few details. Much of the picture is grainy-looking, as if it was strewn with millions of fine grains of sand. Each of those "grains" is actually a star. Most of them are very distant, many of them thousands of light-years away. (A light-year, as you know, is the distance that light travels in a year. And since light travels 300,000 kilometer per second - that would be around 200,000 miles per second - you can image that the distance it travels in a year is pretty awesome!)

There are really very many grains of light in this picture. Other constellations, or parts of constellations, aren't surrounded by nearly as many background stars. The Big Dipper is an example:



The reason for the difference is that the Southern Cross in seen superimposed on the Milky Way, which is the disk of our own galaxy seen sideways. The Big Dipper, on the other hand, is far away from the band of the Milky Way. (Most of the background stars you can see in the Big Dipper picture belong to our more or less local neighbourhood and are not more than a couple of hundred light years away.)

Let's return to the Southern Cross picture. Can you see that black "blob" just below and left of the Southern Cross? That is the aptly named "Coal Sack". Interestingly, it's partly made up of miniature particles of coal! When stars produce energy, they do so by first fusing hydrogen into helium, and then by fusing helium into coal and oxygen. Later the stars get old and bloated, and they start shedding much of their gas into space. But that gas is now enriched with coal and oxygen. The oxygen reacts with hydrogen, forming miniature ice particles, which often stick to the coal. Voila - we have just created space "dust", from which new stars can form, if the dust is sufficiently concentrated (and if it contains hydrogen, too, of course - but it always does). Well, the Coal Sack isn't very concentrated, and unless it starts contracting in the future, it may never form new stars. Nevertheless, the dust of the Coal Sack is a reminder of previous generations of stars, which have huffed and puffed and deposited precious loads of elements into space, elements which these stars have created in their interiors, and which are a prerequisite for planets like the Earth - and for life.



Some stars are huffing and puffing....

Like I said, most of the very faint-looking stars are very distant, and most of the bright-looking stars are moderately nearby. But brightness alone does not clearly indicate distance, since stars are intrinsically of very different brightness. The brightest-looking star in the picture, the whitish star on the far left, is Alpha Centauri, which is the nearest of all stars except the Sun. The distance to Alpha Centauri is a little more than four light-years, and Alpha Centauri itself is very like the Sun. It's temperature is very like the temperature of the Sun, around 6000 degrees Celsius, and it shines about one and a half times as brightly as the Sun. Alpha Centauri's apparent "neighbour", the blue star to the upper right of it, is actually 77 times as far away from us as Alpha Centauri and thousands of times more luminous! Ah, but somewhere to the lower right of Alpha Centauri is a "grain of sand" which is so faint that you can't spot it in this picture. That is Proxima Centauri, a miniature star which orbits Alpha Centauri, and right now it's actually Proxima Centauri which is the nearest of all stars! But it is so faint - its luminosity is about 0.000055 times that of the Sun - that it's impossible to see it unless you have a good telescope!



Okay, here is Proxima Centauri! I apologize for the too-red color balance of the picture, which makes Alpha Centauri, the brightest star in the picture, look red. It isn't red, I assure you. But you can see how faint Proxima is, at least! And you can also see where Proxima is. It's inside the small yellow box on the left, which has been enlarged on the right to help you spot Proxima.

Please note, too, that the stars are of different colors. If you look closely, you can see that most stars look blue. The blue stars are all hotter than the Sun. They are blue because the light they emit is more energetic than the light emitted by the Sun, and the more energy light contains, the bluer it is. By contrast, the less energy it contains, the redder it is. The bottom star in the Southern Cross consists of two almost identical stars whose temperatures are about 28,000 degrees Celsius, almost five times as hot as the Sun. (Together these two stars emit almost 40,000 times as much light as the Sun, though most of it is invisible ultraviolet light.)

The top star of the Southern Cross, however, is noticably yellow. It is much cooler than the Sun with a temperature of about 3700 degrees Celsius. It is a giant star, with a radius more than a hundred times that of the Sun, and it emits about 1500 times as much light as the Sun, much of it invisible infrared light. (And by the way, since the radius of this star is more than a hundred times larger than the Sun's radius, that means that the volume of this star is more than a million times bigger than the volume of the Sun!!!)

Only one star in the picture is neither blue nor yellow, but white instead. That is Alpha Centauri, because that star is so like our Sun, and the light that the Sun emits is white to the human eye!

But most of the myriad stars that make up our galaxy are neither blue, like the hot stars, or big and bloated, like the red giants, or even white like the Sun and Alpha Centauri. Most of the stars in our galaxy are little red midgets and runts like Proxima Centauri instead!



The typical star, a runt!

Anyway, Australia, I'm envious of your gorgeous southern skies! And hey... your flag looks good, too. Don't do away with the Southern Cross if you change the design of your flag, okay?

Ann

I had heard that our flag was getting a do-over, but that's been a rumour for the last decade with nothing to show for it.

Oh, and...

Actually, that's the Federation Star - it has seven points, one representing each of the six states at the time of Federation and one for all of the internal and external territories. Nothing as glamorous as Alpha Centauri, I'm afraid.

Dave

Ann, the New Zealand flag is almost exactly the same as the Australian flag, except we don't have the larger (Federation) star off to the left. We just have the Southern Cross. It looks like this:



~Anna.

Thanks for enlightening me, Dave and Anna!

Ann

Hi Ann,

Yes we had the election yesterday. The Labour party was preferred and won the majority of seats in the Lower House of Representatives in Parliament so their leader Kevin Rudd will be the new Prime Minister. Labour has not held office in 11.5 years so it is a historic occasion. Our former PM John Howard will not be Opposition Leader or leader of the Liberal party because he lost his seat of Bennelong to the Labour candidate. If he loses his seat he cannot sit in Parliament and they can only choose a leader from those who are eligible to sit in Parliament.

It was a bit sad because though I don't support Howard - he was obviously upset at losing. And it's scary because Rudd will be responsible for changes and govt decisions that will affect the way my generation will live in the future. Whether I voted for him or not, not knowing what the future will hold is a scary thing.

Cheers, The Little Tornado.

I know what you mean. But, as a wise man(?) once said, "To prophesy is hard, especially about the future."

*ducks and runs*

Ann