The Sun

Question 1

How is the mass of the sun determined?

Answer 1

Keplers laws

Question 2

How is the astronomical unit found?

Answer 2

Keplers laws

Question 3

How is the solar radius found?

Answer 3

Trig

Question 4

How is the solar luminosity found?

Answer 4

flux and au

Question 5

How is the age of the sun found?

Answer 5

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

Question 6

What conditions are needed for nuclear fusion?

Answer 6

10^7 K and 10^9 atmospheres. They are needed to overcome the energy barrier

Question 7

Where does the energy released by fusion come from?

Answer 7

Mass lost in the nuclear reaction

Question 8

What percentage of mass is lost?

Answer 8

0.7%

Question 9

What percentage of mass of the sun is available for fusion?

Answer 9

10% of the mass of the sun is in the core

Question 10

How is energy transported in the sun from the core?

Answer 10

Initially by photons then on the outer third by convection

Question 11

Why does the sun have a granular appearance?

Answer 11

The top convective cells - the cooler gas dropping is darker, and the hotter parts are brighter

Question 12

What is the photosphere?

Answer 12

The visible surface of the sun, where the visible light of the sun originates from.

Question 13

What is the surface of the sun?

Answer 13

There isn’t a surface - the gas increases with density and temperature as you get further into the sun

Question 14

What is corona?

Answer 14

The very hot and low density outer atmosphere of the sun, which extends several solar radii. It emits in UV and xrays

Question 15

How is the suns rotation revealed?

Answer 15

Sunspots reveal the differential rotation of the sun, where the parts closest to the equator travel faster than at higher latitudes.

Question 16

What is a sunspot?

Answer 16

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.

Question 17

What is the solar cycle?

Answer 17

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.

Question 18

What is the model for solar activity?

Answer 18

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.

Question 19

What is the continuum spectrum?

Answer 19

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.

Question 20

Why is the effective temperature of the sun, the surface temperature?

Answer 20

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.

Question 21

What is monochromatic flux?

Answer 21

The amount of energy per unit area per unit time per unit wavelength interval.

Question 22

What is total flux?

Answer 22

The amount of energy per unit area per unit time. It is the total of the monochromatic fluxes.