Monday, August 4, 2008

Dwarfs Hiding in the Sky

Welcome back to What's Up?

Last month the Phoenix Mars Lander found water ice on Mars. This is the first time that any form of water has been observed directly on the surface of Mars up close. As of writing this the Lander has just found that the soil is not toxic in any way and that it is similar to soil that would be found in a garden (minus the organic substances). It also found the soil is somewhat salty, not acidic, and has interacted with liquid water at some point in its past.

Looking at the sky, Mars is barely above the western horizon at the start of this month, and it will be sinking even lower along with Spring's constellations. Let's look at the stars within these constellations. More specifically, let's look at the hidden stars that actually make up the vast majority of stars in our galaxy.

The stars being referred to are called red dwarfs and brown dwarfs. And yes, they are very small stars like their name suggests. Let's look at the red dwarf stars first.

Red dwarfs are the most common type of star that we know of by far. Out of the nearest thirty stars to our sun, twenty-one of them are red dwarfs!These small stars are less than one half of our sun's mass (our sun is called a yellow dwarf) but more than 0.08 solar masses (80 Jupiter masses). Any objects smaller than this are called brown dwarfs.

Since red dwarfs are so small they don't give off very much light - the smallest of these stars give off 10,000 times less light than the sun!Considering their minute size, most people would think at first thought that these little stars would burn out quickly since they have less fuel (hydrogen).

In reality, they actually burn their supply of hydrogen so slow that they can keep burning for over a trillion years! Normal stars can only burn for billions of years and the largest of stars may only last a few million!Even smaller than the dim little red dwarfs are the brown dwarfs. These are the smallest and dimmest type of star. They mainly give off infrared light so they can only be seen with special telescopes.

It is difficult to tell where the dividing line can be drawn as to what is a planet and what is a brown dwarf. It's usually somewhere around 0.013 solar masses (about 13 Jupiter masses).The main difference between planets and brown dwarfs is how they form. Brown dwarfs form in the same way as regular stars, in a collapsing cloud of dust and gas with them at the center. Planets form when that cloud of dust and gas collapses into a rotating pancake shape and the planets form within this disk around the star at the center.

Brown dwarfs generate light and heat in two ways: deuterium (heavy form of hydrogen) fusion and through the slow contraction of all the material within these objects due to their gravity trying to pull everything inwards. Their deuterium supply usually runs out after ten million years and the gravitational contraction mainly creates heat so it can be nearly impossible to see these objects against the darkness of space.

The first brown dwarf was discovered in 1995 and is called Gliese 229B. Many others have been discovered since.

Since these are so difficult to see and detect, let's look for something which we can see with a little more ease.

This month there was a full moon on July 3rd and the moon will reach its full phase by the 18th.Jupiter is at opposition on July 9th. This would be the best time to view or photograph the planet since this is when the planet is closest to the Earth for this year, but Jupiter is favoring the southern latitudes this year so we won't get a good view since it's low on the horizon. By naked eye, it will be a fine sight. Just look towards the Southern sky this month. It will be by far the brightest object in the sky.

Until next month, just look up!

Hey Kids...
If you can't get out to see the skies due to those annoying clouds, you can explore the sky on the web at . Click and drag around to move around, double-click to zoom or use the middle scroll wheel on your mouse. There are buttons at the bottom to help you find certain objects like planets, constellations, or images taken by the famous Hubble space telescope. Also, at the top left hand corner of the page are three links: Sky, Moon, and Mars. Click on "Moon" to view the Moon or click on "Mars" to view Mars in high detail. Don't forget about the search box at the top, it can really be a help. Enjoy!


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