Hey! What is that Bright Star near Sunset?

Friday, February 9th, 2007 at 12:48 PM by Dave

This reminds me of that quote from the original Star Wars movie, “That’s no Moon, it’s a Space Station.” Well, this is no star but a planet called Venus.

The ancient Greeks called the wandering stars, planētēs, or wanderers. We now use the word planet for these denizens of our solar system.

Venus will be an evening star for most of the spring and summer. This means that is will be found in the west just at Sunset for an hour or so until it sets.

If you could look at Venus through a telescope right now you would see that it has a shape to it. We commonly call this shape a gibbous shape, similar to one of the phases of our Moon. As Venus moves around the Sun this shape will change to a quarter phase then eventually to a crescent phase. When Venus is closer to the Earth we will see the crescent phase. You can see the crescent phase during the summer months with binoculars or a small telescope.

Galileo was the first to discover that Venus went through phases, like the Moon. This was proof of the Heliocentric Theory proposed by Copernicus, that everything went around the Sun (Venus included). At the time of Galileo the Earth was thought to be the center of the Universe (the Geocentric Theory).

Perhaps we can wax philosophically about the Goddess of Love right around Valentines Day?

Enjoy this lovely apparition through the upcoming months!

Posted in Astronomy News | No Comments »

Dwarf Planet Names: Eris and Dysnomia!

Thursday, September 14th, 2006 at 11:38 AM by Dave

With all the hub-bub with Pluto’s demotion from a planet to a dwarf planet, it is interesting to note that the International Astronomical Union (IAU) has named the object that is slightly larger than Pluto. The dwarf planet’s name is Eris and its satellite is Dysnomia. It’s former designation was 2003 UB 313. The discoverers of Eris wanted the name of Xena. However, the IAU has naming rights to all solar system objects.

The discovery of Eris 3 years ago raised the question of a definition of a planet. Many astronomers have puzzled over the definition for years. Only after the discovery of an object larger than Pluto that the question came to the forefront of debate. The IAU recently gave precise definitions for a planet and dwarf planets (please see previous posts).

Eris’ orbit is highly incliined to the planets by 44 degrees. This does not fit the Solar Hypothesis Theory which states that planets would form along a plane (the traditional 8 planets do lie along this plane), which astronmers call the ecliptic. All objects beyond Neptune are called Trans Neptunian Objects (TNO).

I am sure that as time goes by that people will forget the furor of Pluto’s demotion. However, I have students in my class that are mad that Pluto is not a planet anymore. I am sure that Pluto doesn’t care that it was demoted. And neither do I.

Posted in Astronomy News | 1 Comment »

Stop the presses, there are now only 8 planets!

Thursday, August 24th, 2006 at 12:25 PM by Dave

Well, the IAU has changed their minds. We now have 8 Planets!

The International Astronomical Union (IAU) has changed their minds on the topic of planets. They initially proposed 12 planets but now have decided that there are 8 “Classical” Planets consisting of Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.

The IAU resolution 5A states, “Comtemporary observations are changing our understanding of planetary systems, and it is important that our nomenclature for objects reflect our current understanding. This applies, in particular, to the designation of “planet”. The word “planet” originally described “wanderers” that were known only as moving lights in the sky. Recent discoveries lead us to create a new definintion, which we can make using currently available scientific information.

“The IAU therefore resolves that “planets” and other bodies in our Solar System be defined into three distinct categoreis in the following way:

(1) A “planet” is a celestial body that
(a) is in orbit around the Sun,
(b) has suffiecient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape,
(c) has cleared the neighbourhood around its orbit.

(2) A “dwarf planet” is a celestial body that
(a) is in orbit around the Sun,
(b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape,
(c) has not cleared the neighbourhood around its orbit, and
(d) is not a satellite.

(3) All other objects except satellites orbiting the Sun shall be referred to collectively as “Small Solar-System Bodies”.”

Resolution 6A states, “The IAU further resolves: Pluto is a “dwarf planet” by the above definition and is recognized as the prototype of a new category of trans-Neptunian objects (TNO).”

(I always thought there were 8 planets! - Read my previous posts.)

Kids, have fun learning the planets (and the other newly defined objects)!

Posted in Astronomy News | No Comments »

A New Solar System - 12 Planets!

Thursday, August 17th, 2006 at 10:43 AM by Dave

Wow! The International Astronomical Union (IAU) has submitted to its membership a new set of definitions for planets and smaller solar system bodies. They are now called “Planets” and “Plutons”, or pluto-like bodies. Please see the IAU text, http://www.iau2006.org/mirror/www.iau.org/iau0601/iau0601_release.html

Planets are defined as “a large and round body”. This implies that the planet Pluto and its moon, Charon, fit in this category. The asteroid, Ceres, also fits the definition of a planet. The new object UB313 also fits this new definition of a planet. This gives us 12 planets with this new definition.

The roundness of a planet comes from a sufficient enough gravity to cause it to overcome its natural rigidity. This would imply that our Moon (Luna) might also be classified as a planet. However, the center of gravity between the Moon and Earth lies beneath the Earth’s surface. This makes the Moon a satellite of the Earth. The center of gravity between Pluto and Charon lies between the two of them in space, making a double planet system.

If you want to find out where I stand on this issue, read my previous post and read between the lines (I think there are only 8 planets). I think that objects beyond the orbit of Neptune are Kuiper Belt objects and are not planets. However, I don’t have a vote in the matter.

The IAU has to vote on these definitions later this month. Watch for a further update.

Posted in Astronomy News | No Comments »

Pluto’s Moons and Planetary Status

Wednesday, June 28th, 2006 at 01:26 PM by Dave

(Click on image for full-size version.) The Plutonian planetary system on February 15, 2006 as imaged by the HST. (Courtesy: Hubblesite.org)

For years people have debated the planetary status of Pluto. Some have said it is a planet whereas others have said it doesn’t fit the characteristics of a solar system planet. Word is expected soon to clarify this question.
The International Astronomical Union (IAU) is the internationally recognized authority for assigning designations to celestial bodies. Recently, the IAU named the 2005 discovery of two additional moons of Pluto, Hydra and Nix.

Pluto was discovered in 1930 by Clyde Tombaugh. 48 years later, Charon (Pluto’s first moon) was discovered. 27 years later, Nix and Hydra were observed. Nix and Hydra are about 5,000 times fainter than Pluto, thus the reason for the long stretch in time for their discovery. They are not easily seen.

In mythology, Nix is the goddess of darkness, a good description of such a faint object. Hydra is the terrifying monster with the body of a serpent and nine heads, befitting the outermost moon of Pluto.

Now, do you think Pluto is a planet? Historically, Pluto has been called a planet since its discovery. So history is on its side. However, astronomers have observed that Pluto does not fit the same orbital characteristics of the other planets. It has a highly elliptical orbit, whereas the other planet’s orbits are nearly circular. All of the 8 other planets fall on a narrow plane called the ecliptic. The accepted solar hypothesis theory, the theory which describes the formation of the solar system, suggests that planets will form along a disk or plane around the Sun. Pluto’s orbit is inclined to this plane by 17 degrees. Pluto is made of frozen gases and rock. The other planets are either gaseous or rocky. The composition of Pluto is similar to those of comets, which lie outside of Neptune’s orbit.

The object 2003 UB313, or also known as Xena, will also be looked at closely to be determined if it is a planet or not. 2003 UB 313 is slightly larger than Pluto, is further out than Pluto, and has a greater inclination to the ecliptic (44 degrees).

In August this summer, the IAU will give a definition of a planet and will decide if Pluto or Xena fit the definition. If they don’t we’ll have only 8 planets. If they do, we’ll have 10 planets.

What do you think?

Posted in Astronomy News | No Comments »