General overview (astronomy)

How and why does weight and gravitational strength differ between Earth and other bodies/planets in space?

Weight is force caused by gravity due to a planet. The value of gravitational field strength depends on the mass of the object; objects with a larger mass have a higher value of gravitational field strength. Weight and gravitational field strength are directly proportional, so if gravitational field strength increases, weight also increases.

What does the solar system consist of?

The sun, eight planets, natural satellites, artificial satellites, dwarf planets, asteroids, comets

What are the planets in the solar system (in order)?

Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune

How have ideas about the solar system changed over time?

The Earth was once believed to be at the centre of the solar system (Geocentric model), with every other planet and the sun orbiting it - but now scientists agree that the sun is at the centre of the solar system (Heliocentric model)

Pluto was thought to be a normal planet, and was demoted to a dwarf planet in 2006

What orbit do moons use?

Elliptical orbits

What orbit type do planets have?

Elliptical

What is the orbit like for artificial satellites?

Polar orbits: they travel very close to the earth, at high speeds

Geostationary orbits: it takes 24 hours to orbit the earth as they travel slowly and at a higher distance away from the earth

How do circular orbits work?

The object is at a constant speed (but not velocity as the direction is always changing). The object is always accelerating, but due to gravity, the object stays in orbit

How does an object maintain a stable orbit if speed always changes?

The radius of the orbit changes

What does the steady state theory state?

The universe has always existed, it is expanding, new matter is constantly being created as the universe expands, so the density of the universe remains constant

What does the Big Bang theory state?

The universe and all of its matter started in a tiny point, from which it expanded and still is. Density is decreasing as new matter is not being created

What evidence is there for the Big Bang theory?

Red shift: the further away a galaxy is, the more red shifted its light is, which means that galaxies are moving further away from us, showing that the universe is expanding

Cosmic Microwave Background Radiation: radiation was predicted by the theory, so its presence provides the theory

Why is the Big Bang the accepted theory of how the universe started?

There is more evidence to support it

What happens when the source of a wave is moving relative to an observer?

There is a change in observed frequency and wavelength

How does red shift received change depending on distance?

Red shift happens if galaxies are moving away

Blue shift happens if galaxies are moving closer

What is the lifecycle for a star similar in mass to the sun?

Nebula: a massive cloud of dust and gas where the star forms. Gravity pulls the dust and gas together

Protostar: hot and glowing but not hot enough for nuclear fusion

Main sequence: nuclear fusion begins, fusing hydrogen into helium. The gravity holding the star together is balanced by higher pressure due to high temperatures. The star is stable

Red giant: when all hydrogen is used by fusion, the nuclei begins to form and the star may expand to form a red giant

White dwarf: when all nuclear reactions are over, the star may contract under gravity

Black dwarf: forms when the white dwarf has cooled down

How does the balance between thermal expansion and gravity affect the life cycle of stars?

When they are in balance, the star is in the main sequence. When they are imbalanced, the star collapses to form a red giant

What is the life cycle of stars with a mass larger than the sun?

Nebula: cloud of dust and gas. Gravity pulls the dust and gas together

Protostar: hot and glowing but with no nuclear fusion

Main sequence: nuclear fusion turns hydrogen into helium. Thermal expansion and gravity are in balance

Red supergiant: more fusion is possible - hotter temperatures allow all elements up to iron to be fused

Supernova: all other heavy elements are fused in an explosion

Black hole/neutron star: black holes form if they are too big to be able to stop them from collapsing in on themselves; neutron stars form if they are smaller, so collapse due to gravity and are very dense stars made of neutrons

How have methods of observing the universe changed over time?

Photography: allows for permanent records of observations (more accurate and faster to take than drawings used earlier in history)

Computers: increased the speed and analysis of details from telescopes. Telescopes are also much more powerful than earlier

Why are some telescopes outside of the atmosphere of the earth?

To detect radiation absorbed by the atmosphere, and give clearer images than ground-based telescopes