Saturday, May 31, 2008

Tropical Storm Arthur (2008)

Storm Active: May 31-June 2

On May 31, the remnant of a tropical storm in the Pacific (Tropical Storm Alma) crossed over into the Gulf of Honduras.  A few miles off of the coast of Belize, it became Tropical Storm Arthur.  During the afternoon of May 31, Arthur slammed into Belize with winds at 40 mph and internal pressure at 1005 millibars. Somehow, coming in to early June 1, Arthur managed to maintain minimal tropical storm status, with the internal pressure rising to 1006 millibars. The system continued to track slowly west over the Yucatan. It finally weakened and dissipated on June 2 over Central America.

All times are in Eastern Standard Time.

Image of Tropical Storm Arthur near peak intensity over the Yucatan Peninsula.

Track map of Arthur.

Monday, May 26, 2008

Hurricane Names List

For the Atlantic in 2008, the name list is

Arthur (used)
Bertha (used)
Cristobal (used)
Dolly (used)
Edouard used)
Fay (used)
Gustav (used)
Hanna (used)
Ike (used)
Josephine (used)
Kyle (used)
Laura (used)
Marco (used)
Nana (used)
Omar (used)
Paloma (used)

This list is the same as the 2002 list except Isidore and Lili are replaced by Ike and Laura respectively.

Wednesday, May 21, 2008

Sizes and Structures of Black Holes

There are four main sizes of black holes: micro, stellar-mass, intermediate, and supermassive. Micro black holes can only weigh up to the mass of the moon, and all are less then a 1/10 of a millimeter in diameter. These are results of colliding cosmic waves or even bombardment of particles in particle accelerator. Stellar-mass holes are formed by collapsed giant stars (info on collapsed stars here, and giant stars here). These black holes are typically under 10 solar masses and are about 30 km across. The next type, intermediate black holes, are formed when one black hole is swallowed by another, enlarging it. These black holes weigh up to a thousand suns! Finally, supermassive black holes are found at the centers of galaxies. These black holes began as quasars and weigh from 100,000 to a billion suns. These black holes are so large that the largest, if placed in the sun's position, would extend out to the orbit of Earth!!!!

Black holes have three main parts to them. The first and outermost is called the ergosphere. This only exists if the black hole has angular momentum (see types of black holes) . In this zone, it is impossible for any object to stand still. The spin of the black hole causes a tidal force that acts upon the gravity well, shifting it. The ergosphere is in the shape of an elongated sphere that is tangent to the outer event horizon. The outer event horizon is the point of no return. Nothing, not even light can escape once beyond this point. Since no light is emitted from this part of the black hole, nothing inside can be seen. But it is believed that inside, at the very center, is the singularity. The singularity is the star's core crushed to a point (or the case of a spinning black hole, a ring) so small that it must be magnified over a trillion times to view any structure. More on black holes here and here.

Tuesday, May 20, 2008

Types of Black Holes

Black Holes are the result of collapsed stars that are more than approximately 4 solar masses. Although stars, planets, moons, galaxies etc. all have thousands of distinguishing characteristics, black holes only have three (this was a theory entitled "Black Holes Have No Hair" created by John Wheeler).

The three characteristics are: mass, charge and angular momentum (the last is related to spin). A Schwartzschild black hole is a black hole with only mass, and neither of the other two characteristics. These black holes have an even gravitational well and a gravitational singularity shaped as a dot. Also, these black holes are perfectly spherical, and have a fixed event horizon radius. However, these holes are rare, and usually black holes are much more complex. More info on black holes can be found here, here and here.

Thursday, May 15, 2008

Variable Stars

Variable stars are stars that undergo significant changes in magnitude. About 50,000 of these have been discovered, and they are separated into two main groups. One type only appears to change in luminosity because it is eclipsed by another star in a binary system. Even planets have created optical variables by passing in front of stars.

Real variable stars actually swell and shrink. Usually, variable stars have periods that repeat over and over. In a lot of cases, these periods are a few days or weeks. But some have periods that last years, and they may increase or decrease by over 10 magnitudes. Others don't even have a period at all. These stars are very unstable (like stars in the process of a nova) and some explode without warning. Yet other variable stars are eruptive. Many of these are giants and supergiants, which flare easily because of unstable outer layers. Flare stars like these may brighten by two magnitudes in seconds, and then be gone just as fast.

Globular and Open Clusters

Along with multiple star systems, there are also larger groups of stars called star clusters. Star clusters are divided into two main groups: globular clusters and open clusters. Globular clusters form in the halos of galaxies (areas outside the visible parts of galaxies), and consist of very old stars compared to the ones near the center. They may have hundreds of thousands of stars, all of which are gravitationally bound together, and orbiting the galaxy as a single satellite. Globular clusters are also very dense, and most of their mass usually is packed tightly in the center of the cluster.

Open clusters, however, are totally different. They don't form in all galaxies, and consist of very young stars. They are formed by a giant molecular cloud (see the formation of the solar system) that is way too big for one star. The upper limit of members in these clusters is only a few thousand. Unlike globular clusters, open clusters are very loosely gravitationally bound. They orbit near the center of a galaxy, and any interactions between them and other objects may scramble them. But even if they aren't disturbed, they always break up after a few hundred million years.

Friday, May 9, 2008

Types of Stars: Giants and Dwarfs

Stars come in a variety of sizes, temperatures and luminosities. The biggest stars are supergiants and hypergiants. These heavy stars fuse heavier elements than the ordinary Hydrogen and Helium. Although these stars have the hottest cores, their outer edges are very cool (the lowest only about 2000 K), and they also are the least luminous. The largest star on record is the star VY Canis Majoris. It is a hypergiant has a diameter 1800 times that of the Sun! In comparison, if the Sun was replaced with VY Canis Majoris, its outer edges would extend past the orbit of Saturn. Giants are always red or orange. These stars burn their fusion supply so quickly, that they only live for about 10 million years sometimes.

Other stars of this faint luminosity include: white dwarfs, brown dwarfs and black dwarfs (same as white dwarfs but totally cooled off). A brown dwarf is a special case of star where the temperature doesn't get high enough to start Hydrogen fusion, but high enough to do either deuterium (Hydrogen with a neutron and a proton) fusion (lower limit for this fusion is 13 Jupiter masses), or Lithium fusion (lower limit 65 Jupiter masses). These stars also have extremely long lives. They can live for trillions (not billions, trillions) of years!!!!!

Monday, May 5, 2008

Multiple Star Systems

As everyone knows, moons orbit around planets, and planets orbit around stars. But what if, in a developing solar system two clumps of matter form instead of one (information on formation of planetary systems shown here)? When two or more stars begin Hydrogen fusion close enough to each other to have a gravitational link, a multiple star system is born. Being near the Sun, most humans would think that binary or larger star systems are a rare occurrence. But in reality, most stars have a partner. Star systems are separated into two main categories, optical star systems, and physical star systems. An optical star system is present when two stars are right next to each other in the sky, but in distance, they may as well be thousands of light-years apart.

Physical star systems are when stars are actually orbiting one another. However, a star system is only truly binary if the center of gravity lies between the two stars. An example of a binary system (but not star system), is the relation between Pluto and Charon. Since Charon is about half the mass of Pluto, they both orbit around a point just outside Pluto's surface. Otherwise, in these systems are planet-moon systems. But sometimes three or more stars orbit each other. Most large star systems consist of a close binary relationship and a lighter single or binary pair orbiting farther out. The record for physical star systems is six stars. Three pairs of binaries make up this system. Sometimes, one star turns into a black hole (here, here, here and here) and the other loses gas to it, resulting in a nova.

Friday, May 2, 2008

Solar Wind

The Sun gives of waves of charged particles, called plasma.  These waves begin at incredible speeds, causing a "ring" to form around the solar system.  The Galactic Cosmic Rays generated by the magnetic field of the Milky Way itself, cannot cross into this ring because the output of the Sun's solar wind is so strong.  Galactic Cosmic Rays consist of interstellar medium (the particles that simply float freely in space, mostly Hydrogen and Helium).  The border between where solar wind stops is called the Heliopause.  Inside this boundary is called the Heliosphere.  The point where the solar wind slows to subsonic (under the speed of sound) speeds is called the Termination Shock.  On the other end, the place where Galactic Rays fall below sonic speeds is called the Bow Shock.  Relative to other solar system objects, the Kuiper Belt lies on the edge of the Heliosphere, while the Oort Cloud lies outside it.  The Heliopause is at about 100 AU from the sun (see map below).  No spacecraft has ever passed outside of the Heliosphere to date.

Image from Wikipedia showing a log scale plot of the solar system. For more info on parts of solar system, see Oort Cloud and Kuiper Belt