5. The Sun Flashcards
The Sun’s characteristics (mass, radius, luminosity, rotation period)
Mass 1.98910^30kg
Radius 696,340km
Luminosity 1 L☉ (3.84610^26 watts)
Rotational period 24.47 days at equator, 38 days at poles
The Sun is made of…
The same elements we find on the Earth but in different proportions: the Sun is mostly hydrogen and helium.
How do we determine the Sun’s composition?
we can use a star’s absorption line spectrum to determine what elements are present
What is the Sun’s structure?
Core
Radiative Zone
Convection Zone
Chromosphere
Corona
The Sun’s core
Innermost 20–25% of the Sun’s radius
Temperature and pressure allow nuclear fusion
Hydrogen fuses into helium
Fusion process releases energy, and the core gradually becomes enriched in helium.
The Radiative Zone
Between about 20–25% to 70% of the radius
Energy transfer occurs by means of radiation (photons) rather than by convection.
The Convection Zone
Between about 70% of the Sun’s radius and a point close to the visible surface.
Sun is cool and diffuse enough for convection to occur
Primary means of outward heat transfer
The Chromosphere
Thin layer of the Sun
Sculpted by magnetic field lines that restrain electrically charged solar plasma.
Occasionally prominences form and extend far into corona
Sometimes ejecting material away from the Sun.
The Corona
Outermost part of suns atmosphere
The ionized elements within corona glow in x-ray and ultraviolet wavelengths
NASA instruments can image the Sun’s corona at these higher energies since the photosphere is quite dim in these wavelength.
Coronal Streamers - The outward flowing plasma of the corona is shaped by magnetic field lines into tapered forms called coronal streamers, which extend millions of miles into space.
What are the different layers in the Sun’s atmosphere?
Photosphere - the deepest part of the Sun which we can directly observe with visible light.
Chromosphere
Transition Region - Very narrow (100 km) layer between the chromosphere and the corona where the temperature rises abruptly from about 8000 to about 500,000 K
Corona
What are sunspots and where do they form?
Sunspots are areas that appear dark on the surface of
the Sun. They appear dark because they are cooler than
other parts of the Sun’s surface.
What is the solar wind?
The solar wind is a stream of charged particles released from the upper
atmosphere of the Sun, called the corona. This plasma mostly consists of
electrons, protons and alpha particles
What causes solar activity?
Electrically charged gases on surface that generate areas of powerful magnetic forces (magnetic fields).
The gases are constantly moving, which tangles, stretches and twists the magnetic fields. This motion creates a lot of activity on the Sun’s
surface, called solar activity
What are coronal mass ejections and how are they connected to solar
flares?
CMEs are giant clouds of particles from the Sun hurled out into space, while flares are flashes of light—occurring in various wavelengths—on the Sun
How does solar activity affect humans?
Solar flares and CMEs send enormous amounts of energy and charged particles hurtling into collision with the Earth’s upper atmosphere, where they can cause geomagnetic storms. Charged particles during geomagnetic storms cause disturbances in the Earth’s magnetic field, generating effects on electrical systems
How does solar activity vary with time?
Every 11 years or so, the Sun’s magnetic field completely flips. This means that the Sun’s north and south poles switch places. Then it takes about another 11 years for the Sun’s north and south poles to flip back again.
How does the Sun work?
The surface of the Sun is a dense layer of plasma that is continually in motion through the action of convective motions driven by heating from below. This constant motion of high-temperature causes a nuclear reaction. In the core of the Sun, hydrogen turns into helium and causes a fusion – which moves to the surface of the Sun, escaping into space as electromagnetic radiation, a blinding light, and incredible levels of solar heat
What keeps the Sun shining?
The Sun shines by turning hydrogen into helium in its core. This process is called nuclear fusion. Fusion happens when lighter elements are forced together to become heavier elements. When this happens, a tremendous amount of energy is created.
What possible sources of energy are there?
Gravitational contraction and fusion
How long could gravitational contraction keep the Sun shining at its
current luminosity?
Since the solar luminosity is 4 × 10^26 watts (joules/second) or about 10^34 joules per year, contraction could keep the Sun shining at its present rate for roughly 100 million years.
How does nuclear fusion occur in the Sun?
The Sun gets its energy when hydrogen nuclei are fused together to form helium nuclei within the solar core. This hydrogen burning is described by a sequence of nuclear fusion reactions called the proton-proton chain
Why are neutrinos important for understanding what is happening inside
the Sun?
The Gamma rays produced by fusion takes thousands of years to reach the surface of Sun. But neutrinos travel at the speed of light and reach us. So the light is telling us about the fusion which took place millions of years back. But the neutrinos tells us the current status.
What causes gas pressure?
The pressure a gas exerts comes from the motion of its molecules. When the molecules of a gas bounce off the walls of their container, they exert a force. Gas pressure is defined as the force per unit area produced by the gas.
What is hydrostatic equilibrium?
Balance between thermal pressure and gravity
Heat transfer in stars
radiation and convection zone.
How we know what is happening inside the Sun?
Theoretical models
How do we know that the theoretical models are accurate?
solar oscillations, detecting neutrinos
How do we know the temperature of the Sun’s photosphere?
The Sun’s color provides a rough measure of where the Sun’s thermal radiation spectrum peaks, and this peak depends on temperature. Studying spectral lines gives us an even better indication of the Sun’s temperature, because different lines form more easily at different temperatures.
What two forces are balanced in what we call gravitational equilibrium in the Sun?
Outward pressure from thermonuclear reactions and gravity from mass of the stellar core.