Understanding Our Place in Space and Universe

Our Place in Space

• The Moon is not a star because it does not produce its own light; it reflects light from the Sun.
• The Earth is not a moon because it orbits the Sun, has its own gravity, spherical shape, and clear orbit without nearby similar-sized objects. Moons orbit planets or other objects, but never stars.

Our Place in the Universe

• You could put a return address on a capsule traveling beyond our galaxy for a hypothetical intelligent life form. Example: Planet Earth, The Solar System, Orion Arm, Milky Way galaxy, Local Group, Virgo.

Measuring Distances in Space

• A light-year is the distance light travels in one year and is used to measure distances in space. Light is the fastest known energy form and its speed is constant in space.

The Sun

• The Sun is stable because two opposing forces balance each other: the outwards push of nuclear fusion and the inwards pull of gravity.

The Life Cycle of Stars

• Nebulas are giant clouds of dust and gas where pockets of denser material clump together increasing density and gravity. This ultimately leads to the collapsing of the nebula onto itself, increasing the temperature to 13 million degrees. This is hot enough to allow hydrogen gas to fuse, creating a protostar and eventually a star.

Life Cycles of Stars (Small and Large)

• Small stars become red giants, then planetary nebulae, and finally white dwarfs that turn to black dwarfs.
• Large stars become red supergiants, then supernovae, and either neutron stars or black holes.

The Big Bang

• Observations like redshifted galaxies moving away from Earth (the further away, the faster they move) suggest that the universe is expanding.
• The Big Bang theory explains the universe's formation starting from an infinitesimally small point that quickly expanded, forming particles, atoms, then stars and galaxies over 13.7 billion years.