NCEA Level 2 Science (90764) 2011 — page 1 of 3
Evidence Achievement
Question One
• Within the nebulae gas cloud, gravitational forces cause dust and gas particles to come together.
• Protostars are formed.
• Gravitational forces cause the hydrogen in the star to begin to fuse. (4 hydrogen atoms to form one helium atom.)
• Fusion process causes the star to begin to release energy in the form of electromagnetic radiation across the spectra.
• The star has sufficient mass to become a main sequence star.
• Brown dwarf has insufficient mass and therefore insufficient gravitational forces to begin the fusion process.
• Brown dwarfs emit only infra-red radiation and have no luminosity.
Describes aspects of a brown dwarf
OR describes aspects of star formation.
Eg:
•
Gravitational forces cause dust and gas to join together.
• Main sequence star has sufficient mass that enables fusion to take place.
• Hydrogen nuclei fuse to give helium.
• Brown dwarf has insufficient mass
• Insufficient gravitational forces to begin the fusion process.
•
Brown dwarf has no luminosity.
• Sun is luminescent.
• Description of fusion (increased pressure leading to an increase in temperature).
Evidence can be obtained from a labelled diagram.
Achievement with Merit
Describes the sequence of brown dwarf formation
OR
The sun formation.
OR
Partial description of a brown dwarf and the sun formation.
Eg:
(Protostars) form within nebulae gas and dust clouds under influence of gravity.
Main sequence star has sufficient mass that gravitational forces cause the hydrogen nuclei to fuse and release energy (electromagnetic radiation). The Sun is luminescent.
Eg:
Protostars form within nebulae gas clouds under influence of gravity.
• Brown dwarf has insufficient mass and therefore insufficient gravitational forces to begin the fusion process. Brown dwarf does not release same energy/ no luminosity as main sequence star.
Evidence can be obtained from a labelled diagram.
Achievement with Excellence
Discusses formation of Sun and brown dwarf and explains why brown dwarf has not developed into a star like our sun.
(Protostars) form within nebulae gas clouds under influence of gravity.
Main sequence star has sufficient mass that gravitational forces cause the hydrogen nuclei to fuse and release energy and luminance like the
Sun (electromagnetic radiation). On the other hand a brown dwarf has insufficient mass to start fusion process of hydrogen nuclei. Brown dwarfs are small in comparison to the sun and (emit only infra-red radiation). No luminosity.
Evidence can be obtained from a labelled diagram.

NCEA Level 2 Science (90764) 2011 — page 2 of 3
Question Two:
• Sirius A is a blue / white star in the main sequence.
•
Sirius B is a white dwarf.
• Sirius A is much hotter star, burning fuel more rapidly.
• Sirius A is more luminous due to the faster fuel burning rate and size.
• Luminosity is the amount of light being given off by the star.
• White dwarf is greater in mass than the main sequence star, but smaller in size.
• White dwarf has no fuel to burn. Seen as result of radiation release.
• Mass of a white dwarf is very dense causing a change in spin of the larger star.
Describes the properties of two stars:
Evidence may come from Sirius A
OR
Sirius B
OR
Wobble
Sirius A
• luminous
• hotter star as result of more rapid fuel use.
• large in size
• lower gravitational force
• smaller in density.
Sirius B
• not luminous.
• smaller star in size.
• no fuel
• high gravitational field
• higher in density.
Wobble
Sirius B has a higher gravitational force, which causes Sirius A to wobble as Sirius B orbits Sirius A.
Evidence may be obtained from a labelled diagram
Contrasts properties of Sirius A and B
OR
Wobble and mass
Eg:
Hydrogen use in Sirius A is more rapid hence the luminosity and higher star temperature.
Sirius B has no fuel to burn hence lower luminosity.
OR
Higher mass of Sirius B (higher gravitational force) causes Sirius A to wobble as Sirius B orbits Sirius A.
Evidence can be obtained from a labelled diagram.
Contrasts properties and explains why
Sirius A wobbles.
Eg:
Hydrogen use in Sirius A is more rapid hence the luminosity and higher star temperature. Sirius B has no fuel to burn hence lower luminosity
As the mass of Sirius B is denser thus higher gravitational force causes
Sirius A to wobble as Sirius B orbits
Sirius A.
Star types required
Evidence can be obtained from a labelled diagram

NCEA Level 2 Science (90764) 2011 — page 3 of 3
Question Three:
• Supernova originates from a large red giant / super giant.
•
Hydrogen runs out.
• When it cannot fuse iron, the core will collapse and then explode.
• Star core collapses due to gravity and the outer layers of the star are exploded out.
• A very dense neutron star or a black hole remains.
• The variability in brightness caused by the gases and plasma exploding off the surface.
Describes origin and outcome of a supernova.
• originates from an exploding large red giant
• partial explanation of the cause of a supernova
• a black hole or neutron star is left.
OR
Describes the origin OR outcome and the steps that form a supernova.
Evidence may be obtained from a labelled diagram.
Explanation of the origin and outcome and the steps that form a supernova
OR
Describes the origin or outcome and the steps that form a supernova.
AND
Explains the appearance of a supernova.
OR
Explains gas clouds are the birthplaces for new stars.
Evidence may be obtained from a labelled diagram.
Discusses the formation and outcome of a supernova and explains the appearance of a supernova.
OR
Explains gas clouds are the birth places for new stars.
Supernova gives out clouds of gases and plasma exploding off its surface.
AND
These gas clouds are the birth places for new stars.
AND
After this process ceases, a black hole or a dense neutron star remains (detail provided about the formation).
Eg:
The core of the star then collapses, combining protons and electrons to form neutrons. Hence the name
“neutron star”.
If the star is too massive, the gravitational force of the collapse is so powerful, a black hole is created.
Evidence may be obtained from a labelled diagram.
Achievement
2 A
Achievement with Merit
2 M
OR
1 E + 1 A
Achievement with Excellence
2 E
OR
1 E + 2 M