25 Jul 2011
This week the Moon will be on the other side of the planet for most of the night, allowing our skies to be a little more dark, despite all our local light pollution. That's a good time to scan the skies. So let's take a look at a constellation, one that actually looks like what it is named for.
In the southern skies, in the lower half of those skies, is a giant swirl of stars shaped like the letter "J." In fact, it does not take too much imagination to see a giant scorpion in that J. That, of course, is the constellation Scorpius.
It is a sight to behold in and of itself but let's look more closely at a couple of its gems.
The bright red star near the top of the "J" is named Antares. Most people believe the name comes from a contraction of the Greek word for rival - "anti" - and Ares, the Greek name for Mars. The reason here is obvious: Antares, like Mars, is a bright reddish object in the sky. Hence, a rival of Mars.
It is red because it is a red giant, a star in the latter stages of life. And being a giant, it is, well... gigantic. Antares is 2700 times bigger than our sun. Put it where the sun is and it would swallow planets out to beyond Mars!
Free trivia! Antares is the big star in the lower right constellation of the Brazilian flag, representing the state of Piauí.
Now follow the long, curled tail of the scorpion until you get to the two bright stars on the very end. They are Shaula and Lesath. Seeing them, it takes little imagination to understand why they are also called the Cat's Eyes.
Our last stop on our whirlwind tour through the scorpion involves two objects called open clusters. Christened M6 and M7, they are collections of hundreds of young stars all born together but now starting to leave home.
M6 and M7 are both a little to the "left" of the Cat's Eyes. A challenge would be to try to spot the two naked eye. If the sky is dark enough you can, but use binoculars to see them in their full glory. M6 is the one "above" M7, and slightly less spectacular.
That's how easy it is to observe the skies for various objects like beautiful stars, red giants and open clusters! It won't take long - but will last with you forever.
Until next time, clear skies.
11 Jul 2011
Watching the fireworks light up the skies last Monday reminded me of how much those blazing colors play a role in discovering nothing less that what a star is made of.
Fireworks are not merely explosives in a package. The guts of the firework are sprinkled with what chemists call metal salts. The metals in these compounds give off certain wavelengths of light when they get excited. For example, strontium and lithium salts give off a combination of wavelengths which add up in our eyes to look reddish. Copper salts bleed a bluish-green. Sodium salts blaze a bright yellow.
You can see this for yourself by carefully sprinkling a pinch of table salt, sodium chloride, into a flame. Watch how yellow flares pop off as the crystals hit the flame.
Notice though that the compounds have to be excited with a jolt of electricity or fire or with the energy in an explosion to give off those special wavelengths.
Because of some heavy-duty physics beyond the scope of this article, those elements give off just certain wavelengths - no more, no less. For example the yellow of our table salt is really just two wavelengths of light, at 589.0 and 589.6 nanometers. That is it. Those are sodium’s signature wavelengths.
Now let’s weave this into astronomy.
Those elements will not only give off wavelengths if excited, they will also steal those same wavelengths right out of thin air, as it were.
A star’s guts pour out all the wavelengths of light, the entire rainbow. The elements in the atmosphere of that star will steal their own personal wavelengths before they can get to our eyeballs.
You might now see how this can help us figure out what is in a star.
When a star’s full spectrum hits us, our eyes see the star as a single twinkling light source. But special instruments like spectroscopes can spread the light out into the entire rainbow of colors.
When we look at this rainbow laid out before us - behold! - some wavelengths are missing! By matching the missing wavelengths with our earthly library of elemental wavelengths we see in that star’s atmosphere gaseous sodium or hydrogen or iron or helium or calcium.
That’s how we can tell what a star is made of without ever going there. And we can also tell what is in those giant glowing clouds which surround some star nurseries or envelop old, dying stars. That’s also how we can tell that supernovae are exploding out the entire periodic table of the elements.
Lights and colors and energy, those things that make fireworks so mystically attractive and beautiful, are what astronomy is all about. Next time you witness a fireworks display, remember you are seeing a key that unlocks one of the mysteries of this great universe.