Do You Know What is the Aurora?

The aurora is a beautiful atmospheric phenomenon appearing as bands of coloured light sometimes visible in the night sky in the polar regions of the earth. In the northern region, it is known as the aurora borealis or the Northern Lights. In the southern region, it is known as the aurora australis or the Southern Lights.

Auroras take on different appearances. They can look like an orange or red glow on the horizon - much like a sunrise or sunset. They may also look like curtains or ribbons and move and undulate during the night.

Auroras can be green, red or blue. Often they will be a combination of colors, with each color visible at a different altitude in the atmosphere.

• Blue and violet: less than 120 kilometers (72 miles)
• Green: 120 to 180 km (72 to 108 miles)
• Red: more than 180 km (108 miles)

Aurora over Bear Lake, Alaska

Red aurora above Pioneer Peak, Alaska

How do auroras happen? The solar wind from the Sun can bring fast-moving particles towards the Earth. Some of them are then guided by the Earth's magnetic field towards the north and south magnetic poles. As they approach the Earth, the particles interact with the atmosphere making it glow in many different colours and causing the effect we call an aurora.

Illustration of how the aurora is formed

Auroras are like neon lights. Neon lights work by exciting gases inside of a tube with electricity. The resulting colors that you see are a result of the different gases used to make neon lights. In an aurora, the neon colors you see are the different wavelengths of light from gases high in the atmosphere.

A photograph of an aurora borealis taken aboard the International Space Station (ISS)

The following YouTube video shows the aurora australis captured by NASA's IMAGE satellite and overlaid onto NASA's satellite-based Blue Marble image.

For more information of the aurora, follow the links below:

• Wikipedia - Aurora (astronomy)
• Michigan Tech - The Aurora Page
• NASA - Aurora
• MSN Encarta - Aurora (phenomenon)
  

Do You Know Why Some Websites Have "www" in Their Address While Some Don't?

If you frequently surf the Internet, you may have realized by now that certain URLs have the "www" prefix in front of them, while certain others don't. For example http://www.google.com has it, while http://phfoong.googlepages.com doesn't. Why is this so, you may ask?

The reason for this happening is due to the usual practice of naming the Internet hosts according to the services they provide. For example:

• The host name of a Web server usually has the "www" prefix.
  
• The host name of an FTP server usually has the "ftp" prefix.
• The host name of a News server usually has the "nntp" or "news" prefix.

The use of the prefixes is in fact NOT required. That is why we can see many website today not having the "www" prefix in their URLs. The "www" is simply a choice in name, nothing more.

You can find out more from these articles:

• Wikipedia - World Wide Web
• Ask Leo! - Why do some website addresses have "www", and some don't? And why do some work with or without the "www"?
• HowStuffWorks - Why do some Web sites include www in the URL while others don't?