Tuesday, August 21, 2007
The Stellarium software is describe further down
Sunday, August 19, 2007
Already I have received some feedback explaining the twin comet tails in more detail, or rather correcting the way I had written it in the Comet Facts article.
One tail is neutral particles (dust) and the other consists of electrically charged gas (plasma). The charged particles (the "ion tail") are affected by the magnetic field of the sun, which is typically directed across the path of the comet, whereas the neutral particles simply show where the comet has been.
It's like a long steam train. The carriages behind the loco simply follow the track, whereas the smoke from the engine will be carried sideways by the wind as well.
Saturday, August 18, 2007
Additionally, if you spotted a mistake in my writing, or an incorrect fact, there's not a lot you can do about it. You could point it out by leaving a comment as above, or you could email me, but it may well be something reasonably trivial and you decide it's simply not worth the bother. The moment passes.
So I've started up an Astronomy for beginners wiki over at wikispaces. This is not meant to replace or detract from the blog, it's just a complementary addition.
On the wiki you can just click the "edit page" button and change the text right there and then. You can also create new articles of your own, and link pages together using wikitext links. That's enough about it for now. If you have any queries you know how to ask.
I've gathered a few comet facts to publish here on astronomy for beginners. Of course comets are often only visible for a short number of days in a normal year, but when a particularly important comet passes by then it makes for quite an astronomical occasion.
Fact1: A comet is a conglomerate of particles bound together by ice (not necessarily H2O water ice, it could be dry ice (CO2), for example)
Fact2: When a comet approaches the sun the ice melts and releases the particles from the main body.
Fact3: The tail of a comet always points away from the sun.
As the picture below shows, there are in fact two tails, both curved, and they are 30 MILLION kilometres long. That's a lot of fine particles. The theory is that the solar wind is responsible for the blue gas and gravity alone for the larger particles.
You still need a planisphere for when you're outdoors looking at the real sky but now you can also study the heavens at any time of day or night, winter or summer no matter what the weather by running awesome computer simulation software. There are lots of packages available which cost anything from $19 to thousands, but now I'm going to let you in to the secret of open source software. Open source software is written by people who are happy to release the code whoich makes it work out into the public domain. That means it's completely free and legal for you to download it and run it for nothing. And often it works even better than the commercial software.
Stellarium is a free open source planetarium for your computer. It shows a realistic night sky in three dimensions, just like what can be seen with the naked eye, binoculars or a telescope but without any danger of cloud cover obscuring the stars. Another amazing thing about Stellarium is that all the documentation, questions and answers are available on a great Wiki with community support. To get started, all you have to do is download Stellarium for Windows, Linux or Mac, set your location from the map in the configuration window, (the default is Paris) then use your mouse or arrow keys to look around. Use the page up and page down keys to zoom in and out. Zooming on nebulas or planets is very interesting!
This is the first post to Astronomy for beginners and it's not about buying a telescope! The great thing about astronomy for beginners is that all you really need to get started is a pair of eyes. Without a telescope or even a pair of binoculars it is easily possible to begin a hobby which will provide a lifetime of fascination and maybe even a career. I'll show you how.
Start close to home
The nearest astronomical body to the earth is of course the moon. Get used to noticing the phases of the moon because that's going to be important later on. Recognise Venus the 'Evening Star' (which is of course a planet), and the basic star constellations like the Plough and Casseopeia (the “W”). Contrary to popular belief, beginners can go a long way with amateur astronomy before buying any expensive equipment at all.
Buy a planisphere.
There's only one item of equipment which is vital to amateur astronomy for beginners, and that is a thing called a 'planisphere'. You may know that better as a map of the stars, an atlas of the heavens or a constellation guide but the proper name is planisphere. It's made of overlapping sheets which are circular in shape, and you rotate them according to the date, time and location in order to see a map of what should be visible in the night sky.
You can buy a planisphere for only about ten dollars but my advice is to make sure you buy a plastic one and not one made out of paper or card. There's a good reason for this and it's because of the conditions in the night air. Often it's cool and a little moist. Dew forms. If your paper planisphere gets wet then it's ruined, and in my experience they usually last about one day or a week at best. So really, one of the most important pieces of advice on astronomy for beginners is simply to buy a plastic planisphere. Here's one place you could buy a really good one - Deluxe Planishpere @ telescopes.com