A10 - Solar astronomy

Question 1

Describe 2 methods of observing the Sun safely:

Excluding the pinhole method

Answer 1

telescopic projection - point telescope at Sun and use the eyepiece to project an image of the Sun onto some card

H-alpha filter - attach to telescope to filter out all wavelengths except hydrogen-alpha, allowing you to observe the Sun’s surface

Question 2

Describe the internal structure of the Sun:

Answer 2

-core
-radiative zone (super dense, photons have to bounce around a lot before escaping, transferring light/heat outwards)
-convective zone (convection cells bring heat from R-zone to surface)
-photosphere (visible outer layer, where granules and sunspots form on)

Question 3

What are solar granules?

Answer 3

the top of a convection cell from the convective zone, visible on the photosphere

Question 4

Explain the processes that occur at the core of the Sun:

Answer 4

proton-proton cycle/chain

-2 protons fuse together, but one of them turns into a neutron by also releasing a positron and a neutrino - this forms deuteron

-deuteron and another proton fuse into a He-3 nucleus (2 protons, 1 neutron) and release gamma radiation

-2 deuterons fuse forming a standard helium nucleus (2 protons, 2 neutrons) and release 2 protons

Deuteron is just the nucleus of deuterium (1 proton, 1 neutron).
Overall, 6 new protons are used to make 1 helium nucleus, plus 2 leftover protons

Question 5

Summarise the proton-proton chain/cycle:

Answer 5

4 hydrogen nuclei produce 1 helium nucleus

Question 6

Give some detail about the 2 external layers of the Sun:

Answer 6

chromosphere - thin layer of plasma between photosphere and corona
corona - outermost part of the Sun’s atmosphere that stretches for millions of kilometres

Question 7

Give the temperatures of the Sun in Kelvin at each of its layers, both internal and external:

Answer 7

core - 15 million
radiative zone - 2 million
convective zone - 5800
photosphere - 5800

chromosphere - 100,000
corona - 2 million

Question 8

What are sunspots? Describe their structure:

Answer 8

-regions found on the photosphere that are cooler (~4000K) than its surroundings, so they appear darker

-umbra is the central dark spot, and is surrounded by a slightly lighter penumbra (same terms used for shadows)

Question 9

How do sunspots form?

Answer 9

-the convection currents that bring protons and electrons up to the photosphere interact with the stronger regions of the Sun’s magnetic field
-magnetic fields exerts a force on moving charges (motor effect), so the convectional flow of the protons and electrons are redirected outwards
-this means that the region where the magnetic field is strongest has less heat being expelled from it, and so it appears darker

The wiggly bright parts around it are granules, the top of convection cells

Question 10

Explain the causes of the solar sunspot cycle:

Answer 10

-differential rotation of the Sun between different latitudes

-the Sun rotates faster near the equator and slower at higher latitudes, and its magnetic field lines slowly get twisted

-they then return to their original position after an 11 year cycle

Its magnetic poles also flip every 11 years

Question 11

How do the position and number of sunspots change throughout the sunspot cycle?

Answer 11

solar minimum - fewer sunspots appear at latitudes of ~30° N/S

solar maximum - more sunspots appear nearer to the equator

This is the butterfly diagram, showing how the latitude of observed sunspots change over time, showing a clear cycle

Question 12

Describe how a group of sunspots changes its appearance over a period of 1 month:

Answer 12

-appears in pairs (leaders and followers)
-breaks up and disperses

Question 13

Why do we observe the Sun in different wavelengths?

Answer 13

different parts of the Sun are more clearly visible in different wavelengths (eg H-alpha to see its surface)

Question 14

What is the solar wind, and what are some extreme causes of it?

Answer 14

-a constant flow of charged protons and electrons flowing outwards from the Sun at velocities of ~400 km per second

-coronal mass ejections which release lots of these particles

Question 15

What is the magnetosphere? Describe some of its special features:

Answer 15

-the Earth’s magnetic field which deflects the particles in the solar wind

-it has Van Allen Belts
-the outer Belt (~5000km up) traps electrons from the Sun
-the inner Belt (~2000km up) traps protons from the Sun

Named after Dr James Van Allen who discovered them in 1958

Question 16

Name 4 effects of the solar wind:

Answer 16

-comet’s ion tails
-disruption of satellites/aircraft/manned missions
-geomagnetic storms
-aurorae

Ion tails are discussed in chapter A11

Question 17

Explain how we can see aurorae:

Answer 17

-particles caught in the Van Allen Belts move along the Earth’s magnetic field lines toward the magnetic North/South poles
-they collide with the gases in the upper atmosphere, creating colourful flashes

-observers near those regions can witness aurorae (Borealis in the North, Australis in the South)

Question 18

What are geomagnetic storms?

Answer 18

the disturbance of the magnetosphere due to an increase of plasma hitting it after a violent coronal mass ejection (CME)

Question 19

How does the solar wind affect satellites?

Answer 19

increased solar wind on Earth’s atmosphere can heat up the upper atmosphere, affecting satellite orbits (GPS is at risk)

Question 20

How are aircraft affected by the solar wind?

Answer 20

-affects the ionosphere

-used for communicating with radio waves, meaning an aircraft’s primary communication method is disrupted