The Sun Flashcards
How is the mass of the sun determined?
Keplers laws
How is the astronomical unit found?
Keplers laws
How is the solar radius found?
Trig
How is the solar luminosity found?
flux and au
How is the age of the sun found?
Using the rocks on the Earth ie using uraniums half life to find the age of the Earth which is approximately the age of the sun
What conditions are needed for nuclear fusion?
10^7 K and 10^9 atmospheres. They are needed to overcome the energy barrier
Where does the energy released by fusion come from?
Mass lost in the nuclear reaction
What percentage of mass is lost?
0.7%
What percentage of mass of the sun is available for fusion?
10% of the mass of the sun is in the core
How is energy transported in the sun from the core?
Initially by photons then on the outer third by convection
Why does the sun have a granular appearance?
The top convective cells - the cooler gas dropping is darker, and the hotter parts are brighter
What is the photosphere?
The visible surface of the sun, where the visible light of the sun originates from.
What is the surface of the sun?
There isn’t a surface - the gas increases with density and temperature as you get further into the sun
What is corona?
The very hot and low density outer atmosphere of the sun, which extends several solar radii. It emits in UV and xrays
How is the suns rotation revealed?
Sunspots reveal the differential rotation of the sun, where the parts closest to the equator travel faster than at higher latitudes.
What is a sunspot?
It is a physically lower spot where vertical field lines go through it, which stop heat transfer form the gas as the charged particles cannot cross the field lines. Therefore they are cooler, so darker in appearance.
They come in bipolar pairs, linked by a loop made of hot magnetic plasma - corona gas. The N leads in one hemisphere and the other it is S.
What is the solar cycle?
Every 11 years, magnetic activity reaches a maximum. The sunspots start at high latitude and move closer to the equator. The polarity of the sunspots changes, so it is actually a 22 year cycle.
What is the model for solar activity?
It is a combination of differential rotation and convection that generates a strong magnetic field around the equatorial regions. It becomes wound up and twisted, eventually forming a circle which has kinks that extend outside of the surface of the sun, which form the sunspots, and giving their polarity. When the magnetic field unravels it flips so the polarity changes. The high energy activity can break off and come at the Earth, interacting with its magnetic field giving the aurora.
What is the continuum spectrum?
When light from the sun is split, it gives radiation at all wavelengths, with a peak of intensity at 500nm. It falls off rapidly towards the blue and slowly towards the red. It is approximately the curve of a blackbody with temperature T=5800K. Most of the starlight is in the visible spectrum, because of electronic transitions that give energy in visible photons.
Why is the effective temperature of the sun, the surface temperature?
The effective temperature is the temperature of a blackbody that emits and absorbs all the energy. The surface is the part that provides the luminosity- emits the energy.
What is monochromatic flux?
The amount of energy per unit area per unit time per unit wavelength interval.
What is total flux?
The amount of energy per unit area per unit time. It is the total of the monochromatic fluxes.
