December 2006

Farewell Mars Global Surveyor

Ten years ago, on November 7 1996, a new mission to the planet Mars was launched: the Mars Global Surveyor (MGS). Hopes were very high for this mission and so were the stakes for NASA, because a previous high profile mission (Mars Observer) had failed. But on September 11, 1997 MGS successfully arrived at Mars.

Artist Impression of Mars Global Surveyor

MGS was the first spacecraft to use a technique called 'aero breaking' to slow the craft down using the drag of the Martian atmosphere. This was done in April 1999 and MGS started its primary mapping phase of the Martian surface. Many thousands of images were beamed back in unsurpassed detail. At the same time, MGS was working as a relay station for missions on the ground, like the Mars Sojourner Rover and the currently still active Mars rovers Spirit and Opportunity. It also surveyed landing sites for future missions.

Originally MGS was scheduled to work for two years. But seen the recent failures of other Mars missions, NASA was nervous whether the craft would last that long. Needless to say, MGS outperformed NASA's wildest expectations lasting ten years instead of its designed two! It looks like MGS has finally reached the end of its rope. Since November 2nd nothing has been heard from the satellite and NASA has been unable to reesteblish contact. Even the newest mission, the Mars Reconnaissance Orbitor has tried to help, but was unable to locate MGS. NASA has not given up completely yet on locating and communicating with the MGS, but the outlook is grim.

A few of MGS' many important discoveries about Mars include:
(taken from NASA news release 2006-139)

• The spacecraft's camera found gullies cut into many slopes that have few, if any, impact craters. This indicates the gullies are geologically young. Scientists interpret this as evidence of action by liquid water, essentially in modern times.
  
  
• The mineral-mapping infrared spectrometer found concentrations of a mineral that often forms under wet conditions, fine-grained hematite. This discovery led to selection of a hematite-rich region as the landing site for NASA's Mars Exploration Rover Opportunity.
  
  
• Laser altimeter measurements have produced an unprecedented global topographic map of Mars. The instrument revealed a multitude of highly eroded or buried craters too subtle for previous observation, and mapped canyons within the polar ice caps.
  
  
• The magnetometer found localized remnant magnetic fields, indicating that Mars once had a global magnetic field like Earth's, shielding the surface from deadly cosmic rays.
  
  
• The camera found a fan-shaped area of interweaving, curved ridges interpreted as evidence of an ancient river delta resulting from persistent flow of water over an extended period in the planet's ancient past.
  
  
• A long life allowed Global Surveyor to track changes through repeated annual cycles. For three Martian summers in a row, deposits of carbon-dioxide ice near Mars' South Pole shrunk from the previous year's size, suggesting a climate change in progress.

Special Event

Tight grouping of Three Planets

On the morning of December 10th, the planets Mercury, Mars and Jupiter will be clustered together in a tight grouping. This will be the closest three planets will appear together for us in over 50 years.

Conjuntion of planets on the morning of Dec. 10

At the beginning of the month, Mercury is actually the highest of the three, rising less than an hour before the Sun. By the morning of the 10th, Jupiter and Mars have climbed closer to the fleet-footed wanderer. All three rise only one hour and fifteen minutes before the Sun on that morning. You will need a clear eastern horizon. This wonderful conjunction should be at its best around 40 minutes before sunrise. Viewing with a pair of binoculars will definitely enhance your experience.

If your sky is relatively dark, you might even be able to make out a double star just above and to the left of Mercury. This is Beta Scorpii, a twin-star system that represents the front part of the creature in the constellation Scorpius. By month's end, Mercury will have fallen from view while Mars and Jupiter climb higher each day.

Shuttle Discovery is a go for NightTime Launch

Space Shuttle Discovery is cleared for lift-off on the evening of December 7th (now delayed until Dec. 9th). This is the 20th mission to the International Space Station (ISS). The remaining missions to complete the ISS will be the most difficult and complicated for those crews.

Nighttime launch of Discovery October 11, 2000

The main task of this mission is to entirely rewire the electrical system for the ISS. The ISS has been running on a temporary electrical system since it went into orbit in 1998. So, finally after eight years, the ISS will get its permanent wiring done. This is no small task for the astronauts. They have two scheduled space walks as well as a multitude of tasks to perform from within the ISS. There are temporary solar panels that need to be folded up to make room for the permanent solar panels to rotate into their correct orientation.

The crew of this mission has been training for their tasks for the past six years. With the installation of two new electricity-generating solar array panels in September, all the pieces are now in place to switch to the permanent system. Lead Space Station Flight Director John Curry compared this to the way you might build a house on the ground - until your electricity is hooked up, you probably plug your saws into a generator. That's basically what the astronauts building and living on the station have been doing for the past eight years.

The launch window for Discovery extends until the 17th. NASA wants to have the shuttle and crew back down on Earth before New Years, because they are not certain the computer systems in the shuttle can handle the switchover from one year to the next. In all the years the shuttle has flown, there has never been a mission that has gone up one year and come down the next.

November 2006

Did you see the large fireball over Austin on October 22, around 10:20 pm? Or maybe you heard it: a loud rolling thunder sound? There have been many reports of exactly that! That Sunday evening, at 10:20 pm, just after the end of the concert of the Rolling Stones, a meteorite burned up over Austin and made its own spectacular fireworks. It traveled from East to West, and most sightings were in or around West Austin. The sound, which brought a lot of people outside, was described as thunder, and was loud enough to be heard inside. The thunderous noise was likely the sonic boom from the meteorite, because it travels much faster than the speed of sound. In addition to the sound, it left a trail in the sky, and apparently broke up in several segments; several people described seeing many trails. One person in Jonestown described seeing a large green ball. He was surprised this event was not widely covered in the media.

Events like this are relatively common, but definitely not a daily occurence. The Earth is bombarded by many thousands of meteorites each day. Most of them are the size of sand grains, or smaller, but sometimes they are substantially bigger. This meteorite was probably an inch or so when it entered the atmosphere. The larger the meteorite, the rarer they are. This is a good thing for us, of course, because if they get really large, they can reach the ground and potentially do a lot of damage. Meteor Crater in Arizona was formed by a meteorite of about 50 yards across. Impacts like that are, thankfully, exceedingly rare.

Victoria Crater on Mars.

Special Event

As you have read in the notes above about the planets, Jupiter, Mars, and Venus are all on the opposite side of the Sun. But, on November 8th, Mercury will be on the exact opposite side of the Sun from those planets, right between the Sun and the Earth. Mercury's orbit is relatively short compared to the Earth; a year on Mercury is just less than 89 days. So, Mercury passes between the Sun and Earth fairly frequently. This time however, Mercury will actually cross in front of the Sun, and we will be able to see a small black dot slowly transverse across the face of the Sun.

The reason that this does not happen every time, is that the orbit of all the planets are a little tilted. Some orbits more so than others, but just enough so that most of the time Mercury (or Venus) will cross just below or above the Sun - but not so this month. By the way, only three bodies exist that can pass in front of the Sun from our perspective: Mercury, Venus, and the Moon. The other planets are further away from the Sun than the Earth and cannot do the same 'trick'. Of course, if you happened to be on Mars, the Earth can cross in front of the Sun.

So what will be visible? Let's first start with a warning:

Never look directly into the Sun! NEVER, NEVER, EVER use a telescope or binoculars to look at the Sun. You will damage your eyes severely. Also, do not use a smoked piece of glass, or a CD to look at the Sun. It may feel like it is OK, but the Sun transmits other radiation (like UltraViolet rays) that will not be stopped, and will damage your eyes.

The only safe ways to observe the Sun is when it is projected, or to view it on TV.

Composite image 2003 Mercury transit

These days, transits like this one, are not terribly important. But in the seventeenth and eighteenth centuries, they were regarded as one of the most important scientific occurrences. You probably have heard about James Cook and his famous travels around the Earth. One of his main missions was observing a transit of Venus. The reason this was so important was because it presented a rare opportunity to measure the distance between the planets, and also measure the size of the Earth. Very precise measurements were needed, from different places on the Earth. So, they would observe the same transit from Europe, America, and Indonesia etc. Can you imagine traveling for six months or more, only to find the day of the transit it is cloudy? What a disappointment that would be.

October 2006

Pluto is not the first object in our Solar System to be down-graded from 'planet' status.

Last month, in this column, we talked a little about the recent reclassification of Pluto as a dwarf planet. In August, the International Astronomical Union (IAU) convened and decided on a new definition for a planet. One result of this change is that Pluto is no longer considered a major planet (please see last month's column for more details on Pluto and the new definition of a planet).

Johann Elert Bode (1747 - 1826)

Giuseppe Piazzi (1746 - 1826)

For the next few months, Ceres was heralded as the missing planet.

Then, in March 1802, another object was found. It was at about the same orbital distance from the Sun as Ceres. This came as a complete surprise to many people. They had just assumed that Ceres was the eighth planet - and that was that! However, they learned as we know, that that is not the case. For awhile, these objects were called small planets, but the number of the ones known grew large rapidly. In fact, at least one of these objects, now known as asteroids, has been discovered each year since 1801. As a result, Ceres was stripped of her 'planet' title within a few years of discovery. Even though Ceres is the largest asteroid, thousands of asteroids exist in the space between Mars and Jupiter - a region now termed the asteroid belt. Some of their orbits even go beyond Jupiter, almost to Saturn.

So, for over 200 years, we have known Ceres as an asteroid - until a few weeks ago. Two other objects were grouped with Pluto as dwarf planets with the recent redefinitions by the IAU. While Pluto's status was lessened, Ceres' was raised higher. No longer is Ceres just as asteroid. She is a mighty planet once again - albeit a dwarf planet.

In addition to the eight major planets, three dwarf planets are known in our Solar System at this point. Along with Ceres and Pluto, a third dwarf planet exists. This object was discovered in 2003 and initially named UB313, but also known popularly as Xena. This object has a new official name: Eris. Eris is slightly larger than Pluto and also has a moon, named Dysnomia. In Greek mythology, Dysnomia was the daughter of Eris, the goddess of discord.

Special Event

The Orionid meteor shower.

The Orionids should be at their best on the morning of the 20th, but will put on a good show through the 24th. You will need to stay up well past midnight of the 19th for good viewing. The Orionids seem to emanate from just north of the constellation of Orion.

An Orionid meteor

The Orionids, like their cousins the Eta Aquarids in May, come from a well-known source. Both of these meteor showers are a result of the Earth passing through the orbit of debris cast off long ago by Halley's Comet.

September 2006

Of course everyone has looked up to the stars in the night sky. Most of us can even name some constellations. But did you know you can also listen to the stars? That is the subject of this month's Did You Know.

Now, please do not run outside to see if you can hear a star making noise, because you will not hear anything. But stars are definitely noisy, and not just the stars. The whole sky is making a ruckus! If only you would have the right tool to change this noise into audible sound. The tool that we are talking about is a Radio Telescope.

The Compact Array, Australia Image © Friends of the Austin Planetarium

Next to light, the Universe is shining in all kinds of wavelengths, and one of those wavelengths is radio. So yes, if you can pick up this signal and plug it into an amplifier and loudspeaker, you can really hear noise. This will sound like static though, no pretty music or something. But sometimes, if you point the radio telescope right, you can truly hear some spectacular sounds. For example if you point it at a (Radio) Pulsar, you can clearly hear tick-tick-tick-tick.

But most of the time researchers are using radio telescopes to map an object to create pictures. There are some great benefits of a radio telescope over a normal telescope. The first one is that you do not have to wait until it is dark, because radio works during the day as well as during the night. Also, radio waves travel through interstellar clouds. For example, if you would like to 'see' what is behind the Orion Nebula, you can look through the nebula with Radio and see what is there.

As you can see from the picture above, radio telescopes are often working together. Because the wavelength of radio is so much longer then light, it is easier to combine signals from several radio telescopes making for all practical purpose a much larger telescope. Although radio astronomy does not produce beautiful pictures like the Hubble telescope does, it is an absolute essential cornerstone for astronomical research.

Special Event

As you have undoubtedly heard in the media, there have been made some changes to what is considered a planet, and Pluto is no longer considered a major planet, but a dwarf planet. But don't worry, Pluto is still there, and it is still a planet. FOTAP director Torvald Hessel was interviewed by News 8 Austin about this event. That video can be seen here.

So what happened? Why is Pluto no longer considered a planet? The thing is that for centuries we have struggled with the question, "what is a planet?". We have always known about the 5 naked eye planets (Mercury, Venus, Mars, Jupiter and Saturn), and for the longest time people just assumed that 5 was all there was.

Pluto & Charon Image courtesy of M. W. Buie (Lowell Observatory), D. J. Tholen (U. Hawaii), and K. Horne (St. Andrews)

Then in 1781 William Herschel discovered Uranus. At that time that meant a culture shock, because people were not even wondering if there were more planets, everyone knows there are only 5 right?

The result was of course that people started to study the Solar System in much more detail; if we missed one whole planet what else is out there? The result was the discovery of Neptune but also objects of the asteroid belt between Mars and Jupiter. First they were considered equal to the other planets, but when more and more objects were discovered, people started to call them 'Small Planets'. A book was published in 1898, and that has a list 434 'Small Planets'!

Soon after that, it was realized we cannot reasonably call them 'planets', and it was called the asteroid belt. So all was calm until 1930 when Pluto was discovered, and again the Solar System changed. Soon after the discovery we found that although Pluto was larger than anything in the asteroid belt, it was different than the other planets. But what to call it other than a planet, especially when in 1978 Pluto was discovered to have a moon (Charon)? We all thought the discussion was over; Pluto was a planet.

But the discussion started anew when new objects were found even further away than Pluto. And what's more, these objects shared characteristics with Pluto much more then with the other planets. This discussion finally culminated in the decision taken last month by the International Astronomical Union that defines a planet as follows:

• It must be in orbit around the Sun
• It must be heavy and large enough, so the shape is spherical
• It must have cleared it's orbit from other objects

The last statement disqualifies Pluto as a (major) planet, because it crosses Neptune's orbit. So, now we have 8 Major Planets, and three Dwarf Planets. Can you name them already? They are Ceres, Pluto and UB313 (or unofficially Xena).

August 2006

Astronomers of all kinds like to throw a party. This party doesn't involve bright lights or a bunch of noise. This party requires some telescopes (the more, the merrier), a group of people who appreciate the stars and planets and a nice, quiet dark sky (the darker, the better).

This kind of party is called a Star Party. People from all walks of life and all ages are welcome at this party. People who know just a little or nothing about astronomy are very welcome here. People who know a lot about astronomy are at the Star Party and are very willing to share the eyepiece of their telescopes and teach others about the fun and science of astronomy.

The Austin Astronomical Society and St. Stephen’s Episcopal School is throwing just such a party during the month of August. Please mark your calendar for August 12, a Saturday, for "Austin Under the Stars" at St. Stephen's School.

The Friends of the Austin Planetarium will be there with our StarBubble. The StarBubble is a portable planetarium that can hold 20-25 people. It will be set up inside a comfortable, air-conditioned room and even has its own air-conditioner attached directly to it. Every 20 to 30 minutes you can catch a free presentation. This will give you an idea of how wonderful it is to experience a planetarium. We will also have koozies and mugs available. Come by and find out how you can get one! We'll be glad to talk to you about what you can do to help bring a planetarium to Austin.

The event runs from 6:00 p.m. until midnight. Solar viewing and planetarium shows begin at 6:00 p.m. with the star party kicking into gear at about 8:00 p.m.

See ya there!

Special Event

There are three special events this month - two occurring on the same night!

The conjunction of planets in August, though low in the sky, should be quite spectacular.

On August 10th and 11th, looking east-northeast about an hour before sunrise, you should see Venus right above Mercury (see Mercury and Venus in the Planets section above).

The conjunction of Mercury, Venus, Saturn and the crescent Moon on the mornings of the 21st and 22nd should be a memorable sight (see image below). Also, Venus and Saturn are at conjunction on the mornings of the 26th and 27th. See Saturn in the Planets section above for more details on these events.

Conjunction of planets and moon on August 22nd

The other two events are the Austin Under the Stars (AUTS) star party (details in the Did You Know section below) and the Perseid Meteor Shower.

The peak of the Perseids occurs on the night of the 12th. The good news is that that date is also the date of the star party, so come out to AUTS and you might see a shooting star as you walk from one telescope to the next. The bad news is that the Moon is just three days past full on the 12th. That means he is still more than 90% full. The Moon will rise at 10:33 p.m. and not set until the following morning. The best times for viewing the Perseids is well after midnight, but you could see some before moonrise.

July 2006

In astronomy, and hence in this AstroNews column, we often talk about how bright something is. Venus is brighter than Mercury, and an Iridium flash can be many times brighter than Venus. To truly indicate how bright something is you need a term to describe this. In astronomy we use magnitude.

Hipparcos, CA 190 BC - 120 BC

The first person that we know of that made a list of stars and how bright they appeared was Hipparcos. Hipparcos lived from about 190 BC to 120 BC, and his list consisted out of 1080 stars. Taken the fact that the telescope had not been invented, these were all stars visible with the naked eye. Hipparcos separated the stars into 6 groups of different magnitude, where group number 1 contained the brightest stars and 6 the dimmest. So, the larger the number, the dimmer the star!

The basic idea of this scale we still use today. About a century ago, scientists discovered that these 6 groups followed a mathematical law. Without going into specifics here, it became possible to truly calculate magnitudes and to measure them electronically. Because Hipparcos did everything with the naked eye, when calculated some of the stars actually became magnitude zero, or even negative! For example, Sirius, the brightest star in the sky, shines at magnitude -1.6. We can also calculate that the Sun shines at magnitude -26.7. Do not make the mistake though, to think that the sun is -26.6 / -1.6 = 16.7 times as bright as Sirius. This scale is a logarithmic scale, the difference between magnitude -1.6 and -26.7 is more than 10 billion!

Another example is the Iridium flash from June; this flash had a magnitude of -7.4. The planet that can be the brightest is Venus. The maximum magnitude of Venus is about
-4. That means thatthe flash was about 40 times as bright as Venus ever can be. Quite a flash indeed!

Special Event

Iridium
Another interesting thing to look for are Iridium satellites. These satellites have very large solar panels, and if you are at the right spot at the right time, you can experience an Iridium 'flash'. The satellite will reflect the sunlight for a short time, so it's like a star that pop's up from nowhere, then becomes very bright, and then it disappears again, all in the matter of seconds.

Because the Iridium satellites are in regular orbits, you can also plan for an Iridium event. Check out this page to see if any will be visible. There was one on June 28 that was many times brighter then for example Venus ever can be. Drop us a line if you are flashed by Iridium!