MYP Physics The Solar System Notes

The Solar System Is A Gravitational System With Distinct Types Of Objects

1. The solar system is the collection of objects bound together by the Sun's gravity.
2. It includes the Sun (a star), planets, dwarf planets, moons, asteroids, comets, and clouds of small icy bodies beyond Neptune.
3. At the center is the Sun, which contains most of the solar system's mass and therefore dominates the motion of everything else.
4. The further an object is from the Sun, the weaker the Sun's gravitational pull, and the longer its orbital period.

Observing the Sky: Early Ideas About the Solar System

1. Humans have observed the sky long before modern science developed.
2. Early observers noticed regular patterns in the motion of the Sun, Moon, and stars.
3. The Sun appears to rise in the east and set in the west every day.
4. Stars appear fixed relative to one another over short timescales.
5. These repeated observations encouraged early models to explain the structure of the solar system.

What is a Star?

1. A star is a massive, spherical ball of hot gases, mainly hydrogen and helium.
2. Stars emit their own light and energy, unlike planets, which reflect light.
3. Stars are not all the same.
4. They vary in several important ways:
   1. Temperature
   2. Colour
   3. Mass
   4. Size
   5. Brightness (luminosity)
5. These properties are related:
   1. More massive stars are usually hotter and brighter
   2. Smaller stars tend to be cooler and dimmer

Star Colour and Temperature

1. Blue stars
   1. Hottest stars
   2. Surface temperature above 10,000 K
2. Yellow stars
   1. Medium temperature
   2. Example: The Sun (~5800 K)
3. Red stars
   1. Coolest stars
   2. Surface temperature around 3000 K

Constellations and Patterns in the Night Sky

1. Constellations helped people organize what they saw in the sky.
2. Constellations are patterns of stars that appear close together when viewed from Earth.
3. The stars in a constellation are not necessarily close together in space.
4. Constellations are used as reference patterns to describe locations in the sky.
5. Different cultures created different constellations using the same stars.

Fixed Stars and Wandering Objects

1. Not all objects in the sky behave in the same way.
2. Most stars appear fixed relative to each other.
3. Some bright objects change position against the background stars over time.
4. These moving objects were historically called wanderers.
5. Their motion led scientists to question how the solar system is arranged.

Models Of The Solar System Changed As Evidence Improved

There are different main models of the solar system.

The Geocentric Model: Earth at the Centre

1. Early models reflected everyday experience.
2. The geocentric model placed Earth at the centre of the universe.
3. All other objects were thought to move in circular paths around Earth.
4. This model explained why the sky appeared to rotate once every day.
5. It was widely accepted because it matched what people observed directly.

Retrograde Motion: A Challenge to Early Models

1. Some objects appeared to slow down, stop, and move backward temporarily.
2. This effect is called retrograde motion.
3. Simple circular orbits around Earth could not explain this motion accurately.
4. This suggested the model was incomplete.

Epicycles: Increasing Model Complexity

1. Astronomers modified the geocentric model to match observations.
2. Epicycles were small circular paths added to larger orbits.
3. They improved predictions of object positions.
4. However, the model became increasingly complicated.

The Heliocentric Model: A Simpler Explanation

1. In 1543, Nicolaus Copernicus proposed a heliocentric (Sun-centered) model.
2. The heliocentric model placed the Sun near the centre of the system.
3. Earth and other objects moved around the Sun.
4. Retrograde motion could be explained as an effect of relative motion.
5. This model required fewer assumptions.

Space and Space-Time: A Modern Perspective

1. Modern physics changed how space is understood.
2. Space is not empty; it is part of a combined structure with time.
3. Space-time describes space and time as linked dimensions.
4. Massive objects affect space-time, influencing motion.
5. Motion in space can be understood as movement through space-time.

Galaxies: Large-Scale Structure of the Universe

1. The solar system is part of a much larger structure.
2. A galaxy is a huge collection of stars, gas, and dust held together by gravity.
3. Galaxies contain billions of stars.
4. Our solar system is located in one galaxy.
5. Galaxies come in different shapes and sizes.