June 2008

A photon is a "light particle". Well, it is not a particle per se, but it will do for this article. When we look up in the night sky, photons emitted by stars thousands or tens of thousands of years ago will strike your eye and you can see the star. Of course the same goes during the day, but then the photons we mostly see are emitted by our Sun, but the principle is the same.

One thing you will have noticed is that not all stars have the same color. Especially through a telescope this is very visible, some stars are obviously red, while others are yellow or even almost blue. The difference is that the photons have a different energy. Photons with a lower energy are red, and photons that appear blue have a higher energy. But your eye can only see photons within a certain range of energies. If the energy becomes too low, it is called infrared. Infrared is invisible to the eye, but you can feel it because it is "warmth radiation". On the other end, when photons carry too much energy it becomes Ultra Violet, and once again your eye cannot detect this.

But even infrared through Ultra Violet is only a very small potion of energy range that a photon can have. The GLAST mission will be observing photons which are several billions more energetic then the photons that you can see with your eyes. In order to observe these photons you must be in space, because the atmosphere of our Earth shields us from those harmful rays. Take a look at the very informative image below (taken from WikiPedia) with a ton of information about the electro magnetic spectrum, i.e. the energy a photon can have.

May 2008

May will be an exciting month for the further exploration of Mars! On May 25 NASA will attempt to land another spacecraft onto the surface of mars: the Phoenix. Unlike the Mars rovers who landed using inflated airbags to soften the landing, the Phoenix will use a rocket to land on the surface, much like the Viking landers did back in the mid seventies. Landings like this are very risky and difficult, so we're sure that some NASA engineers will be holding their breath during the landing.

Just like the rovers however, the Phoenix mission is planned to last 3 months which may get extended if the mission is successful. Although the Phoenix does not have the ability to move and roam around the landscape like the Mars rovers, the lander does have a long arm to do its research. This arm can dig a hole up to 20 inches deep! Phoenix will land in an area much further to the poles as any of the previous missions (see image below), so we're sure to receive back exciting data and literally out-of-this-world images!

One of the mission goals is to research the possibility of microbial life, specifically whether Mars had ever favorite conditions to harbour life. But of course there is a small chance that the lander would discover something amazing. Be sure to check back to this AstroNews page as the mission progresses, we will keep it updated if anything exciting happens. For more information on this exciting mission please check out the Phoenix home site

April 2008

Four times a year, the Friends of the Austin Planetarium (FOTAP) sends out a free newsletter. This newsletter details our progress bringing a planetarium to Austin, details projects we participate in and also talkes about upcoming events that we are hosting or where we will be present.

If you are interested in astronomy, science education and/or FOTAP's efforts this newsletter is a must. Our latest Winter 2008 newlsterrer is available for download here (opens new window). Please use the form below to sign up for future releases of our newsletter and stay up to date!

Please note: FOTAP will never sell or give away your information to any other group, person or entity without your approval.

UPDATE: signing up for our newsletter can now be done by clicking here.

March 2008

Of course we all have seen the Moon. Probably you have seen our closest neighbor many hundreds of times. But did you know that sometimes the Moon can be of great help finding stars and planets? This month we get an especially wonderful helping hand from the Moon. The Moon is very bright. Of course not as bright as the Sun, but still much brighter then anything else we can see in the sky. So, most of the time the Moon is a distraction, and makes observing more difficult. A star party when there is a full Moon is often considered silly because the "light pollution" from the Moon interferes with observing other sky-wonders.

For this month our show starts on April 4th. This will be just before New Moon, and the Moon will be a very thin sliver. For this showing you will have to look in the Eastern sky just before Sunset and the Moon will be very close to Venus.

A couple of days later, on April 8, the Moon, which will be waxing (=growing) now because we are after New Moon, the Moon will come very close to the Pleiades. This is great, because the Moon is still very dim and its glare will not outshine the Pleiades. If you lived further up north you may even see the Moon covering a couple of the stars of the Pleiades, but here in the deep south we will not see that. But still a very lovely pairing, definitely worth your time. Look to the western sky just after Sunset to catch this show.

Next installment of our Moon-led show is on April 11 where the Moon will pay our red neighbor a visit: Mars. Of course the Moon is not really close to Mars, but it appears this way in our sky. If you look once an hour or so starting at 8 pm, you actually will be able to tell that the Moon is moving through the sky!

On April 14 and 15 the Moon will be pointing out Saturn and the bright star Regulus. And finally our Moon-led star show comes to an end on the early morning of April 27 when the Moon will be just below Jupiter. Have fun catching this month long show!

February 2008

In astronomical diagrams you often see the phrase: "This image is not drawn to Scale". You might wonder why we don't take the time and effort to do draw something to scale? Look for example at the image of the solar and lunar eclipse above. That image is not drawn to scale, but how would it look like if we had drawn it to scale?

Let us assume we will draw the same image to scale, with the Sun drawn the same size as above. Of course the Sun is a lot larger then the Earth, so in the image above we have exaggerated the size of the Earth. The Sun's diameter is 864938 miles, and the Earth is only 7941 miles. So the Sun is more then 100 times as large as the Earth. Taken the fact that the yellow circle is about 50 pixels wide, the earth should be about one half pixel, which is invisible!

But that is not the only problem. If 864938 miles is 50 pixels in the image, then how far should we put the Earth in order to get the proper distance? The Earth is about 91 million miles away from the Sun. If 864938 miles is 50 pixels, then one pixel is 17,298 miles. Then 91 million is more then 5000 pixels. The image above right now is 550 pixels wide, so we need to make it 10 times as wide!

We hope that you now understand that in order to show the Sun and Earth in one picture, we almost always have to draw the image not to scale. Even if we made the image above 10 times as wide, the Earth would still be invisible because it is half a pixel big. Don't we live in an amazing universe?

Special Event

This month's special event is the Lunar Eclipse for February 20. Maybe not as special or as spectacular as a total solar eclipse, this event is definitely worth watching. The other good news is that we do not have to stay up late at all!

A total lunar eclipse takes place when the Moon slides through the shadow of the Earth. (See image below)

So gradually we will see the moon darkening, and on the20th, the Moon will actually almost move through the center of the Earth's shadow. This is not always the case,

Pictures of a total lunar eclipse sequence. Note the reddish color of the moon when totally eclipsed.

because most times the Moon will just graze the Earth's shadow, where one side of the Moon is significantly more eclipsed then the other. A good example is the image to the left: even at mid-totality the lower left is much darker, then the upper right. This time around we will not see such a large variation.

The reason for the red color is also interesting. When the Moon is in the shadow of the Earth, how can we see the moon at all? We can see the moon, even when it is in the center of the shadow, because the earth's atmosphere bends light around its rim. We see the same thing every day: it is already light even before the Sun has risen above the horizon. Somehow the light is bent through the atmosphere. And what color is the sky then? Indeed red! And that is the reason why the Moon appears red.

Unlike a Solar Eclipse, watching a lunar eclipse is completely safe, and does not require any aids like a telescope or binoculars. Just look up and enjoy the show! The moon will start touching the Earth's shadow at 7:05, but the eclipse really starts at 7:43. It will be totally eclipsed from 9:00 pm to 9:52 after which the moon will start slipping out the eclipse again. Have fun observing!

January 2008

The Earth is actually closer to the Sun during our Winter? Strange, but true! Let's look at why.

An elliptical orbit. The small dot in the sun is the actual center of the ellipse.

The Earth's orbit around the Sun is not circular - it is slightly elliptical (somewhat egg-shaped). The Sun is a little bit off of center of this ellipse (it actually lies at one of the two focal points). During January the Earth and the Sun are at their closest to each other. The Sun is actually brighter in the sky during January. This increased brightness goes unnoticed though. Since the Sun is lower in the winter sky, its rays pass through a greater thickness of atmosphere, easily canceling any brightening we might experience.

The earth's axis of rotation is tilted 23.5 degrees from the plane in which it revolves around the sun (see diagram below). Back in December, on the winter solstice, the North Pole reached its greatest tilt away from the Sun. Likewise, on the summer solstice in June, when the Earth is at the opposite side of her orbit, the North Pole will be leaning most directly toward the Sun. Correspondingly, the South Pole is tilted its greatest toward the Sun in December and has its maximum tilt away in June.

So, you might think that the southern hemisphere would endure hotter summers and colder, harsher winters compared with their northern counterparts. The combination of these two effects, being closer to the Sun and being tilted more directly at the Sun, should make for warmer summers and more frigid winters. In fact, the combined effect is not too noticeable. This is due to the large stretches of ocean that cover the southern hemisphere.

A representation of the tilt of the earth's axis in relation to the sun.

However, the current situation has not always been the way of things. These two factors may have combined to produce ice ages in the past. The ellipse that is Earth's orbit gradually rotates around the sun. Like a rubber band being twiddled between two fingers, it completes one total revolution in approximately 23,000 years. This means that over time, the North Pole will eventually be leaning away from the Sun at point in the Earth's orbit when it is furthest away. This could lead to increased glacial activity as in previous ice ages.

For right now, we are at a pretty even balance, so don't go buy a snow blower just yet.

Special Event

Mars is being visited by a number of spacecraft launched from Earth these days. But on January 30th, the Red Planet will be visited by an asteroid. In fact, this asteroid has a small chance of actually hitting Mars. The asteroid, known as asteroid 2007 WD5, actually passed close to Earth in November 2007. It's size is only about 160 feet across, so astronomers have not determined yet whether or not it will strike the surface of Mars.

If it does make a direct hit, it will produce an explosion equal to the detonation of roughly three megatons of TNT. Asteroid 2007 WD5 is travelling at 8.4 miles per second and would leave an impact crater over half a mile across. However, the chances of this asteroid making a direct hit on Mars on the 30th are only 1 in 28, or 3.6% (at the time this article is written). The mobile research vehicle Opportunity will be close, if an impact actually occurs. But, the Mars rover will be safely to the south of the potential target region.

Please visit the home page of the Near Earth Object Program to get updated details on the possible impact of 2007 WD5 on Mars.

An extra-terrestrial impact has happened in the not-too-distant past. In July 1994 Comet Shoemaker-Levy 9 actually impacted Jupiter. The comet had been torn apart by Jupiter's gravity, and 21 fragments of the comet succumbed to the giant planet.

Comet Shoemaker-Levy 9 and Jupiter image courtesy NASA