Download 2009 Assessment Schedule (90764)

NCEA Level 2 Science (90764) 2009 — page 1 of 3
Assessment Schedule – 2009
Science: Describe the nature and life cycle of stars (90764)
Evidence Statement
Achievement
Achievement with Merit
Achievement with Excellence
ONE
(a)
Two star types described with
TWO out of three
characteristics (luminosity,
temperature and spectral type)
correctly described. (a)
Eg: Supergiants
Luminosity 10 000 – 1 000 000
Temperature 20 000 – 2 500°K
Spectral Type B – M
(b)
Gives a description of another
type of star and compares those
characteristics to Sun’s
characteristics, eg white dwarfs
are around 10 000K, 1  10–4 so
less luminous than the sun, and
spectral type of B – F.
(The Sun is a main sequence
star / other stars are not main
sequence stars so are at different
stages in their life cycles) (a)
Explains TWO differences
between the star’s
characteristics and the Sun’s
characteristics, eg white dwarfs
are less luminous than the sun
but are hotter than the sun. (m)
(c)
Describes luminosity: (a)
OR
Relates luminosity to both the
size AND temperature of a star.
Explains EITHER a small hot
star or a large cool star (m), eg:
A small hot object has same
luminosity with smaller surface
area, so higher surface
temperature – gives idea of
smaller surface area (or size)
therefore higher temperature.
OR
A large cool object has same
luminosity with larger surface
area, so lower surface
temperature – gives idea of
larger surface area (or size)
therefore lower temperature.
Discusses BOTH a small hot star
and a large cool star (m), eg:
A small hot object has same
luminosity with smaller surface
area, so higher surface
temperature – gives idea of
smaller surface area therefore
higher temperature.
AND
A large cool object has same
luminosity with larger surface
area, so lower surface temperature
– gives idea of larger surface area
therefore lower temperature.
1a=A
1m=M
1e=E
Luminosity is the amount of
energy emitted by the star (over
a second).
NCEA Level 2 Science (90764) 2009 — page 2 of 3
TWO
Describes how a massive star
collapses into a very dense
neutron star. (a)
Describes how a massive star
ends up as a neutron star, via a
supergiant and a supernova.
After Massive stars (mass > 4 –
8 times that of our sun) have
finished burning their nuclear
fuel, they expand to become
supergiants then undergo a
supernova explosion. (m)
Discusses how the supernova
explosion ends up a neutron star
linking two points.
eg
The core of the star then
collapses, combining protons and
electrons to form neutrons. Hence
the name “neutron star”.
AND
If the star is too massive, the
gravitational force of the collapse
is so powerful, a black hole is
created instead of a neutron star.
TWO points linked. (e)
1a=A
THREE
(a)
(b)
1m=M
State that astronomers analyse
the spectra of light and / or
using spectroscopes. (a)
Explains that spectra are
directly related to atomic
structures. Thus hydrogen and
helium will show the spectral
characteristics unique to
hydrogen and helium. (m)
Giant molecular cloud (GMC),
cloud of dust and gas, or stellar
nursery collapses / condenses by
gravity. (a)
As the temperatures and
pressures increase, the
fragments condense into
rotating spheres of superhot gas
known as protostars. (m)
1e=E
When the mass of the protostar is
sufficiently high it enables the
nuclear fusion of hydrogen into
helium and becomes a main
sequence star.
AND
Gravitational collapse explained
using one or more causes stated
below.
Gravitational collapse can be
caused by:
• giant molecular clouds
colliding,
• passing through dense matter
regions,
• nearby supernovae explosions
send matter into the giant
molecular cloud,
• galactic collisions provide high
energy particles to the giant
molecular cloud.
BOTH ideas linked. (e)
1a=A
1m=M
1e=E
NCEA Level 2 Science (90764) 2009 — page 3 of 3
Judgement Statement
Achievement
Achievement with Merit
Achievement with Excellence
2 A or above
2M
1M
PLUS
1E
Lower case a, m, e may be used throughout the paper to indicate contributing evidence for overall grades for
questions.
Only the circled upper case A, M and E grades shown at the end of each full question are used to make the final
judgement.