The first U.S. astronauts were selected in 1959, before human spaceflight operations began. NASA asked the military services to provide a list of personnel who met specific qualifications. After stringent screening, NASA announced its selection of seven men, all pilots, as the first American astronauts. NASA has selected 18 more groups of astronauts since the “Original Seven.” The backgrounds of NASA’s latest group of Astronaut Candidates include schoolteachers, doctors, scientist, and engineers.

NASA selects astronauts from a diverse pool of applicants with a wide variety of backgrounds. From the thousands of applications received, only a few are chosen for the intensive Astronaut Candidate training program. Including the “Original Seven”, only 321 astronauts have been selected to date.

The astronauts of the 21 st century will help lead NASA through the next steps of its Vision for Space Exploration as we explore the Moon, Mars, and beyond.

A ceremony marking the opening of a new $3.2 million addition and renovation to the Physics and Astronomy Building will take place on Tuesday beginning at 2 p.m.

The new and renovated space, which is on the north end of the 50-year-old building, will include a new home for UGA's Center for Simulational Physics, a conference room that will double as classroom space and much-needed additional space for graduate student offices, among many improvements.

"The completion of this important project significantly enhances research and teaching in our department of physics and astronomy," said Garnett S. Stokes, dean of the Franklin College of Arts and Sciences. "The new extension provides a very nice facility for our faculty, staff and students, and it will impress the many international researchers who come to Athens regularly to collaborate with our distinguished faculty in the department."

Bill Dennis, head of the department of physics and astronomy, agreed.

"This project has been in the planning stages for a decade and has added some 10,400 square feet of new space," he said. "We think this is tremendous step forward for us and are grateful to the dean's office and the central administration at UGA for their long-term support in making this happen."

Originally constructed as part of the burgeoning science complex on UGA's South Campus in the late 1950s, the building on Cedar Street has long been in need of additional space. In special need of new quarters was the internationally known Center for Simulational Physics, which uses computers to develop techniques for solving problems that are intractable to current analytical theory and to gain insight into physical phenomena where the accuracy and scope of experimental results is limited.

Scheduled to be present for the ceremonies will be University of Georgia President Michael F. Adams, Provost Arnett C. Mace Jr., Vice President for Research David C. Lee, Dean Stokes of the Franklin College, David Landau, director of the Center for Simulational Physics, and faculty members and departmental alumni.

Included in the new space will be state-of-the-art research labs that will aid in recruiting new high-quality faculty to the department.

"The renovated space also includes a lab for Physics 1112/1212 and will accommodate 40 students per lab section," Dennis added, "so the area will also add great value to what we are able to offer undergraduates in the department."

In particular, the upgraded facilities for graduate students will help the department in recruiting top students to continue their studies here. There will also be added space for the annual Computer Simulation Studies in Condensed Matter Physics Workshop that draws participants from all over the world.

- UGA News Service

Карафелов Александр Миронович адвокат

The Heart Of NGC 4261
Credit: H. Ford and L. Ferrarese, (Johns Hopkins), W. Jaffe, (Leiden), NASA

Explanation: What evil lurks in the hearts of galaxies? This Hubble Space Telescope picture of the center of the nearby elliptical galaxy NGC 4261 tells one dramatic tale. The gas and dust in this disk are swirling into what is almost certainly a massive black hole. The disk is probably what remains of a smaller galaxy that fell in hundreds of millions of years ago. Collisions like this may be a common way of creating such active galactic nuclei as quasars. Strangely, the center of this fiery whirlpool is offset from the exact center of the galaxy - for a reason that for now remains an astronomical mystery.

Karafelov Aleksandr Mironovich (Карафелов Александр Миронович)

Much of the early stages of the Main-Sequence Turnoff for a high mass star is the same as a low mass star.

(Science Cartoons Plus)

It is important to state that while the fusing of hydrogen to helium is being performed in both low and high mass stars, high mass stars primarily burn hydrogen through the CNO cycle (Carbon, Nitrogen, Oxygen). Carbon acts as the catalyst in the fusion of hydrogen and nitrogen and oxygen absorb the protons to create helium.

The main reason for this is increased temperature and pressure at the core than a low mass star. The hydrogen burning shell and helium ash core also exist in the high mass star. One major difference between a high mass star and a low mass star at this point is the helium flash - there is no flash of helium fusion in a high mass star.

Here is a bit of a summary for high mass stars:

(Image credit: Brooks/Cole Thomson Learning)

The exact stages of evolutions are:

• Subgiant Branch (SGB) - hydrogen shell burning - outer layers swell
• Red Giant Branch - helium ash core compresses - increased hydrogen shell burning
• First Dredge Up - expanding atmosphere cools star - stirs carbon, nitrogen and oxygen upward - star heats up
• Core Helium Flash - continued compression with added helium ash ignites helium - lots of neutrinos
• Horizontal Branch - helium burning core - hydrogen burning shell
• Pre AGB (Asymptotic Giant Branch) - outer layers expand cooling the star - hydrogen shell becomes dormant
• AGB - re-ignited hydrogen shell burning (like a second Red Giant phase)
• Several stages of dredge up - nucleosynthesis creates numerous elements (F, Ne, Mg, Al, Li, Ne, Na)

Because a high mass star (> 4 Solar Masses) has considerably more gravity than low mass stars, several shell burning stages can occur:

(Image credit: Brooks/Cole Thomson Learning)

But there is a limit. Iron cannot fuse, and when it tries the end result is a highly compacted core and intense temperatures. The core density is 4 x 10¹⁷ kg/m³. This is very degenerate and cannot be compressed further. The intense heat generated by this compression (core bounce) blows the star apart in a type II supernova.

Click on the image to the left to view an animation of a supernova. In this video, two things happen: the core collapses, explodes and begins to expand while the star collapses (video care of Swinburne Astronomy Online).

(© 2005 Russell Croman, www.rc-astro.com)

The classic supernova remnant is the Crab nebula.

The end result of a supernova is three fold:

• Heavy elements created in the explosion

• Intense interstellar wind

• A neutron star (or black hole) stellar remnant

A white dwarf is the degenerate carbon core of a low mass star. As such, a neutron star is the degenerate iron core of a high mass star.

(Image credit: Brooks/Cole Thomson Learning)

Because if its composition (and energy at the time of compression), intense magnetic energy emanates from the neutron star, and it is spinning rapidly (several thousand times a second).

(Image credit: Brooks/Cole Thomson Learning)

This spinning neutron star is called a Pulsar. At the heart of the Crab nebula is its stellar remnant - a pulsar:

The image above demonstrates how fast a pulsar can spin. What is also interesting is that they are extremely accurate time keepers. A neutron star also emits strong in the X-ray spectrum. Also, just like a white dwarf, a neutron star can accrete material from a companion star, but superheats it to extreme temperature and spins faster.

If the high mass star is around 25 Solar masses, the stellar remnant can compress much further than a neutron star resulting in a Black Hole.

It's important to realize that a black hole is not a hole in space, its just an object with extremely high surface gravity - but since we have yet to "see" one (and we probably never will), we can only infer their existence by its effect on surrounding matter. A good friend and fellow class-mate wrote an excellent paper going into detail on the subject of Black Holes, and he has graciously allowed me to post it here. So for more information on Black Holes, click Black Holes.

Core Burning Stages in a 25 Solar Mass Star:

Fuel:	Products:	Temperature (K):	Minimum Mass:	Burning Period:
H	He	4 x 106	0.1	7 x 106 years
He	C, O	1.2 x 108	0.4	5 x 105 years
C	Ne, Na, Mg, O	6 x 108	4	600 years
Ne	O, Mg	1.2 x 109	~8	1 year
O	Si, S, P	1.5 x 109	~8	~0.5 years
Si	Ni - Fe	2.7 x 109	~8	~1 day

Classifications of Supernova:

Type:	Characteristics:	Mechanism:
1a	No H lines, strong Si II lines	Thermonuclear runaway on white dwarf
1b	No H lines, prominent He I lines	Core collapse of massive star stripped of hydrogen envelope
1c	No H, Si II or He I lines	Core collapse of massive star stripped of helium (and hydrogen) envelope
II-P	H lines - flat light curve	Core collapse of massive star
II-L	H lines - no flat light curve	Core collapse of massive star

Is the dissipation of energy in the form of tidal friction in the Earth-moon system causing global warming?

Recent global warming has occurred in the geologically instantaneous period of about a hundred years at a rate much higher than is typical over much of Earth’s history. In contrast, the Moon has been receding constantly since its origin ~4.5Ga ago and its rate of recession has increased only over geologic time scales, not over intervals as brief as 100a. Furthermore, Earth has gone through climate cycles in the past as marked by ice ages. This lack of coherence between the constantly increasing Earth-Moon distance and climate cycles on Earth is evidence that the recession of the moon is not a direct factor in modern global warming.

However, the recession of the moon, presently about 4 cm/a, is estimated to transfer about 3TW to Earth primarily in the form of energy dissipation by the friction between ocean tides and rest of Earth. Observations suggest that nearly 30% of the tidal energy budget may actually be distributed in the deep oceans and help sustain deep ocean currents. Since both deep and near-surface ocean currents are key moderators of global climate change, the recession of the Moon may be an important factor in the stability of the climate, even though it does not contribute to global warming.

I've read that the final core collapse of a star happens within less than a second. It seems to me that the outer layers of particles would have to go faster than the speed of light for this to occur so quickly. Is this actually true? Have I misread? Miscalculated? Or else, how can it occur so quickly?

At the time of the final core collapse of a star, the core itself is only about the size of Earth, and it contracts to something approximately 16 kilometers across (diameter). So if the star core has a radius of about 6378 kilometers when it begins to collapse, then it has to contract to something with a radius of about 8 kilometers. So the outer particles have to travel 6370 kilometers in less than one second, but the speed of light is 300,000 kilometers per second, so they actually have plenty of time to collapse.

The 'core' of the star is much smaller than the whole star.

Mars lost most of its atmosphere long ago to the solar wind due to a lack of a meaningful electromagnetic field. Saturn's Titan has an atmosphere denser than Earth's, yet Titan is a smaller body than Mars. Why hasn't the solar wind carried Titan's atmosphere away?

Roughly speaking, at the distance of Saturn, the solar electromagnetic power per unit area and solar wind flux are sufficiently low that elements and compounds that are volatile on the terrestrial planets tend to accumulate in all three phases. Titan’s surface temperature is also quite low, about 90 K. Therefore, the mass fractions of substances that can become atmospheric constituents are much larger on Titan than on Earth.

In fact, current interpretations suggest that only about 70% of Titan’s mass is silicates, with the rest consisting primarily of various H2O ices and NH3-H2O (ammonia hydrates). NH3, which may be the original source of Titan’s atmospheric N2, may constitute as much as 8% of the NH3-H2O mass.

Much of the original atmosphere appears to have been lost over geologic time. But since Titan began with a proportionally greater volatile budget than Earth or Mars, atmospheric pressure on its surface remains nearly 1.5 times that of Earth’s. It is possible that most of the atmospheric loss was within 50 Ma of accretion, from a highly energetic escape of light atoms carrying away a large portion of the atmosphere (hydrodynamic blow off event). Such an event could be driven by heating and photolysis effects of the early Sun’s higher output of X-ray and ultraviolet (XUV) photons.

We don't really know why only Titan has a thick atmosphere, while the structurally similar Ganymede and Callisto don’t. Temperatures may have been too high (well above ~40K) in the Jovian subnebula due to the greater gravitational potential energy release, mass, and proximity to the Sun, greatly reducing the NH3-hydrate inventory accreted by Callisto and Ganymede. The resulting N2 atmospheres may have been too thin to survive the atmospheric erosion effects that Titan has withstood.

Alternatively, cometary impacts may release more energy on Callisto and Ganymede than they do at Titan due to the higher gravitational field of Jupiter. The higher energies could erode the atmospheres of Callisto and Ganymede, while the cometary material would build Titan’s atmosphere. Nevertheless, D/H ratios suggest that cometary input is unlikely to be the major contributor to Titan’s atmosphere.

As with Mars, Titan’s internal magnetic field is negligible, and perhaps even nonexistent. Furthermore, relative speed between Saturn's magnetic field and Titan actually accelerate reactions within Titan’s atmosphere, instead of guarding the atmosphere from the solar wind.