Sunlight and Stars

Sunlight and Stars

Team C

University of Phoenix

SCI350

Alex Bukreyev

July 9, 2006

Sunlight and Stars

Our Sun is the star in the center of our solar system and accounts for more than 90 percent of the solar system's mass. Our team will take a look into the different aspects of our Sun and how we study and learn from such a bright star that is basically nothing more than a ball of hot gasses.

The Sun is composed of six parts. From the inside working outward, the six parts are the core, the radiation zone, the convection zone, the photosphere, the chromosphere, and the corona. The core, which reaches temperatures of 15 million Kelvin, hydrogen atoms are transformed into helium through thermonuclear fusion. The heat drives pressure outward, while the gravity balances the force by pulling back inward. The photons from the nuclear reactions are absorbed and released into the radiation zone. The currents of gas are circulated and transferred to the surface in the convection zone. The photosphere, which provides 99% of the visible light, is the apparent surface of the Sun. The photosphere is approximately 300 miles thick, with temperatures reaching 5,800 Kelvin. There can be limb darkening visible in this layer, which can occur when the edge appears darker due to light being emitted from higher, cooler regions, creating an apparent shadow. The chromosphere reaches a few thousand miles above the surface and can vary in temperature from 6,000 Celsius to 50,000 Celsius. "It appears red because hydrogen atoms are in an excite state and emit radiation near the red part of the visible spectrum" (Enchanted Learning, 2006). The outermost part of the Sun is the corona. The corona extends millions of miles from the solar surface with temperatures of two million Kelvin, which is hot enough to emit X-rays. The coronal layer also emits dangerous coronal waves, which scientists are currently finalizing ways to study these layers.

Helioseismology is the studying of the internal structure of the Sun. This is accomplished by measuring its modes of oscillation on a five minute cycle. This cycle is used to view the characteristics of the sound waves trapped in the photosphere. The velocity amplitude modulation is less than one microsecond, and is non-repetitive, therefore must be monitored for several hours.

The now famous SOHO project was originally launched December 2, 1995, by NASA, along with other coordinating agencies. The mission has now been extended until March 2007. SOHO was originally designed to determine the structure and dynamics of the solar interior, determine if a solar corona exists and what their temperature is, and to determine where solar wind is produced and how it is accelerated. However, in its extended time SOHO has experienced numerous interesting finds, including:

* Revealing the first images of the convection zone and structure of sunspots.

* Providing the most detailed and precise measurements of the temperature structure, the interior rotation, and gas flows of the solar interior.

* Measuring the acceleration of the slow and fast solar wind.

* Identifying the source regions and acceleration mechanism of the fast solar wind in the magnetically 'open' regions of the Sun's poles.

* Discovering new dynamic solar phenomena such as coronal waves and solar tornados.

* Revolutionizing our ability to forecast space weather, by giving up to three days notice of Earth-directed disturbances and playing a lead role in the early warning system for space weather.

* Monitoring the total solar irradiance (the 'solar constant') as well as variations in the extreme ultra violet flux, both of which are important to understand the impact of solar variability on the Earth's climate." (NASA, 2006).

Due to the coronal flares discovered from SOHO, STEREO (Solar TErrestrial RElations Observatory) is set to launch no earlier than July 30, 2006. The two-year mission consists of "two nearly identical observatories - one ahead of the Earth in its orbit, and the other trailing behind - [which] will trace the flow of energy and matter from the Sun to Earth as well as reveal the 3D structure of coronal mass ejections (CME's) and help us understand why they happen" (NASA, 2006). The CME's can trigger geomagnetic storms, which can in turn destroy satellites, thereby affecting GPS to cell phone communication, and are hazardous to any astronaut outside of the Space Shuttle or the International Space Station. STEREO was designed by the Applied Physics Laboratory at Johns Hopkins. Some of the instruments on STEREO will actually capture data, which could be used to generate an audio counterpart to the images produced by STEREO.

The Sun, classified as a G2-type star. It provides the light and heat to make Earth an inhabitable planet. As stars go, our Sun is small in comparison, but supplies the needs for our entire solar system.

"The Sun is, at present, about 70% hydrogen and 28% helium by mass everything else ("metals") amounts to less than 2%. This changes slowly over time as the Sun converts hydrogen to helium in its core." (Arnett, 2006). Chemical interactions between the hydrogen and helium and the intense density within the core help to create the intense heat, resulting in nuclear fusion.

"Conditions at the Sun's core (approximately the inner 25% of its radius) are extreme. The temperature is 15.6 million Kelvin and the pressure is 250 billion atmospheres. At the center of the core the Sun's density is more than 150 times that of water. The Sun's energy output (3.86e33 ergs/second or 386 billion billion megawatts) is produced by nuclear fusion reactions. As it travels out toward the surface, the energy is continuously absorbed and re-emitted at lower and lower temperatures so that by the time it reaches the surface, it is primarily visible light. For the last 20% of the way to the surface the energy is carried more by convection than by radiation." (Arnett, 2006).

The top layer of the Sun is the chromasphere. As altitude increases, the heat takes a dramatic rise. Scientists, not understanding the cause, continue to study this dramatic temperature increase.

Above the chromasphere lies the corona, which is only visible during a total eclipse. It