John Hartnett various secular physics and astrophysics journals have published Dr. The discoverer of gravity Isaac Newton rejected the nebula hypothesis that gravity could condense a gas cloud into our sun and its orbiting planets.
The Sun as a point of comparison Variations in stellar size With regard to mass, size, and intrinsic brightnessthe Sun is a typical star. Other stars often have their respective quantities measured in terms of those of the Sun. A massive loop-shaped eruptive prominence is visible at the lower left.
Nearly white areas are the hottest; deeper reds indicate cooler temperatures. NASA Many stars vary in the amount of light they radiate. Sirius A and Vegathough much brighter, also are dwarf stars; their higher temperatures yield a larger rate of emission per unit area.
Aldebaran AArcturusand Capella A are examples of giant starswhose dimensions are much larger than those of the Sun. Betelgeuse and Antares A are examples of supergiant stars. The latter has a radius some times that of the Sun, whereas the variable star Betelgeuse oscillates between roughly and solar radii.
Several of the stellar class of white dwarf starswhich have low luminosities and high densities, also are among the brightest stars. Sirius B is a prime example, having a radius one-thousandth that of the Sun, which is comparable to the size of Earth. Also among the brightest stars are Rigel A, a young supergiant in the constellation Orionand Canopusa bright beacon in the Southern Hemisphere often used for spacecraft navigation.
It has been found that stars of many types are active and have stellar winds analogous to the solar wind. The importance and ubiquity of strong stellar winds became apparent only through advances in spaceborne ultraviolet and X-ray astronomy as well as in radio and infrared surface-based astronomy.
X-ray observations that were made during the early s yielded some rather unexpected findings. They revealed that nearly all types of stars are surrounded by coronas having temperatures of one million kelvins K or more. Furthermore, all stars seemingly display active regions, including spots, flares, and prominences much like those of the Sun see sunspot ; solar flare ; solar prominence.
Some stars exhibit starspots so large that an entire face of the star is relatively dark, while others display flare activity thousands of times more intense than that on the Sun. Such powerful flares, called X-class flares, release intense radiation that can temporarily cause blackouts in radio communications all over Earth.
Observations of their ultraviolet spectra with telescopes on sounding rockets and spacecraft have shown that their wind speeds often reach 3, km roughly 2, miles per second, while losing mass at rates up to a billion times that of the solar wind. The corresponding mass-loss rates approach and sometimes exceed one hundred-thousandth of a solar mass per year, which means that one entire solar mass perhaps a tenth of the total mass of the star is carried away into space in a relatively short span ofyears.
Accordingly, the most luminous stars are thought to lose substantial fractions of their mass during their lifetimes, which are calculated to be only a few million years. Ultraviolet observations have proved that to produce such great winds the pressure of hot gases in a coronawhich drives the solar wind, is not enough.
Instead, the winds of the hot stars must be driven directly by the pressure of the energetic ultraviolet radiation emitted by these stars.
Aside from the simple realization that copious quantities of ultraviolet radiation flow from such hot stars, the details of the process are not well understood.
Whatever is going on, it is surely complex, for the ultraviolet spectra of the stars tend to vary with time, implying that the wind is not steady. In an effort to understand better the variations in the rate of flow, theorists are investigating possible kinds of instabilities that might be peculiar to luminous hot stars.
Observations made with radio and infrared telescopes as well as with optical instruments prove that luminous cool stars also have winds whose total mass-flow rates are comparable to those of the luminous hot stars, though their velocities are much lower—about 30 km 20 miles per second.
Because luminous red stars are inherently cool objects having a surface temperature of about 3, Kor half that of the Sunthey emit very little detectable ultraviolet or X-ray radiation; thus, the mechanism driving the winds must differ from that in luminous hot stars.
Winds from luminous cool stars, unlike those from hot stars, are rich in dust grains and molecules.The measurable quantities in stellar astrophysics include the externally observable features of the stars: distance, temperature, radiation spectrum and luminosity, composition (of the outer layers), diameter, mass, and variability in any of these.
Nucleosynthesis is the process by which atoms of lighter chemical elements fuse together, creating atoms of heavier elements.  Atoms are comprised of three elementary particles - protons and neutrons bound into a dense nucleus and .
Stellar nucleosynthesis is the nuclear process by which new nuclei are produced. Equally convincing evidence of the stellar origin of heavy elements is the large overabundances of specific stable elements found in stellar atmospheres of asymptotic giant branch stars.
Big Bang Nucleosynthesis The Universe's light-element abundance is another important criterion by which the Big Bang hypothesis is verified. It is now known that the elements observed in the Universe were created in either of two ways.
May 01, · Indirect evidence includes the geological history of Earth, which shows that the surface temperature has not changed dramatically in billions of years.
Stellar nucleosynthesis is the only theory we currently have that involves laboratory tested physics that could explain that. AET Internal Combustion Engine Theory and Servicing. This is a theory/laboratory course designed to introduce the student to basic heat engine types, their .