Be humble, for you are made of dung. Chapter 30 – Stars. Be noble, for you are made of stars. SERBIAN PROVERB. 30.1 The Sun . OBJECTIVES Explore the structure of the Sun. Describe the solar activity cycle and how the Sun affects the Earth. Compare the different types of spectra. .
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The Sun contains 99 percent of the mass in the solar system, it controls the motion of the planets.
- The scale
The solar interior is not solid, but gaseous, because of its high temperature.
Other than the use of special instruments, the chromosphere is only visible during a solar eclipse when the photosphere is blocked.
In the convective zone of the solar interior, volumes of gas carry energy to the Sun’s surface.
The outermost layer of the Sun’s surface from which most of the light emitted by the Sun comes is the photosphere.
The photosphere is the Sun's visible surface, due to its high temperature, it glows yellow.
The top layer of the Sun’s atmosphere is the low-density corona.
The solar wind flows outward from the corona to the entire solar system.
In the 1600s, the solar activity cycle stopped, and there were no sunspots for nearly 50 years.
No sun spots equaled mini ice-age!
A prominence is an eruption of hot gas that can extend thousands of Km into space from the surface of the Sun before cooling and condensing and then rains back to the surface.
Earth is bombarded with particles and radiation after violent eruptions from the Sun’s surface called solar flares.
The energy that reaches our planet from the sun is 1354 J/m2/sec
That’s enough to operate ~10 - 100 Watt bulbs within each 1-m2 area.
The Spectrum is visible light arranged according to wavelengths.
A non-compressed gas produces a spectrum in which you see bright lines at certain wavelengths, this is called an emission spectrum.
The dark bands observed in a solar spectrum are caused by different chemical elements which absorb light at specific wavelengths.
With the help of TMBG! ,
A star that is gravitationally bound to another star can either be part of a star cluster or a binary star.
Astronomers can sometimes identify binary stars even if only one star is visible.
The speed of light is:
The Speed of Light:
It’s Not Just A Good Idea
It’s the Law.
Light-year (ly) Distance traveled by light in one year
9.461X 1012 Km
Parsec (pc) 3.26 ly, or . . .
3.086X 1013 Km
The apparent shift in a star’s position caused by the motion of the observer is called parallax.
Using the parallax technique, astronomers can accurately measure the distance of stars up to 500 pc away.
One of the most basic observable properties of a star is brightness, the classification was established by the ancient Greeks.
In the modern classification of apparent magnitude, a difference of 5 magnitudes corresponds to a factor of 100 in brightness.
Absolute magnitude takes distance into account when indicating the brightness of a star.
Both classify the brightness of stars.
takes into account differing distances and measures brightness at a distance of 10 parsecs.
The Hertzsprung-Russell diagram (H-R) diagram, first plotted in the twentieth century, demonstrates the relationship of luminosity and temperature.
O – B – A – F – G – K – M
Stars are assigned a spectral type, with M being the coolest stars.
The section of the H-R diagram into which about 90 percent of stars fall is called the main sequence.
Nebula is a cloud of interstellar gas and dust that collapses on itself to form a new star.
One principle used by astronomers to understand the basic structure of stars is hydrostatic equilibrium .
Fusion is combining of lightweight nuclei into heavier nuclei, such as four hydrogen nuclei combining to form a helium nucleus.
Stars on Main Sequence all produce energy by fusing
As a star ages, its internal composition changes as nuclear reactions in the star’s core convert one element into another.
Only 10% of a star's mass undergoes fusion because temperatures outside of the core never get hot enough for reactions to occur.
What happens next ? depends on the...
The main sequence lifetime of a low-mass star is much longer than the lifetime of the Sun.
The helium-reaction phase for a star the size of the Sun lasts only one-tenth as long as the hydrogen-burning phase. The result is a core made of carbon and it is a white dwarf.
Following the end of each reaction stage, a massive star becomes a red giant several times.
When the core of a star collapses forever, the extremely dense object that remains is called a black hole.
is a small, massive, dense object that has a gravity so immense that nothing—not even light—can escape it.