Stars and Cosmology
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Define planet.
An object in orbit around a star with: • A large enough mass to have its only gravity (round). • No fusion reactions. • Cleared orbit of most objects.
What is the difference between a planet and a dwarf planet?
Dwarf planets have not cleared their orbit of other objects.
Define planetary satellites.
A body in orbit around a planet (eg moon, satellite).
Define comet.
• Small, irregular bodies of dust, ice and rock. - Elliptical orbit around Sun.
Define solar system.
Planetary system with a star and at least one planet in orbit around it.
Define galaxy.
A collection of stars and interstellar dust and gas bound together by gravitational force.
What are the stages when forming a main-sequence star?
• Nebula • Protostar • Main sequence
What are the stages when forming a neutron star?
• Red giant • White dwarf • Neutron star
What are the stages when forming a black hole?
• Red supergiant • Supernova • Black hole
How is a nebula formed?
Tiny gravitational attraction between dust and gas pull particles together, forming vast clouds.
How is a protostar formed?
• Gravitational collapse accelerates as dust and gas get closer together. • Denser regions form and pull in dust and gas -> gains mass and is denser. • Hotter because GPE is transferred to thermal energy.
How is a star formed?
• Extremely high pressures and temperature in the core to overcome electrostatic repulsion between H nuclei. • Nuclear fusion takes place (H nuclei forced together to make He nuclei)
Explain why nuclear fusion in the core of a star prevents further gravitational collapse.
Gas and radiation pressure released pushes against gravitation collapse.
Explain why nuclear fusion in the core of a star prevents further gravitational collapse.
• Fusion produces gas and radiation pressure - Pressure pushes outwards against gravitation collapse.
Describe the similarities and differences between planets and comets.
Similarities: • In orbit of a star • Elliptical orbit Differences: • P: regular and C: irregular • Comets cannot clear their orbit of most objects
How does a main-sequence star remain in stable equilibrium?
• Fusion produces gas and radiation pressure • Pressure pushes outwards against gravitation collapse. • Forces balance, maintaining equilibrium.
Explain why larger stars spend less time in their main-sequence phase.
• Greater rate of fusion - Depletes Hydrogen in a shorter time period
Name two factors that affect the stability of a star.
• Size - Mass
What is the astronomical unit (AU)?
Average distance from the Earth to the Sun. 1.50 X 10^11 m
What is a light-year (ly)?
Distance travelled by light in a vacuum in one year
How many arcminutes and arcseconds are there in 1°?
60 arcminutes 3600 arcseconds
Define parsec (pc).
The distance at which a radius of 1AU subtends an angle of 1 arcsecond.
How can you determine the value of 1pc with tan?
tan (1 arcsecond) = 1 AU / 1 pc
What is stellar parallax?
• Technique used to determine the distance to stars less than 100pc from the Earth. • Relies on the apparent shift in position of nearby stars against the fixed background of distant stars.