Space Physics

What is the Solar System?

The Sun and all objects orbiting it, including planets, moons, asteroids, and comets

What is a planet?

A large object orbiting a star, clears its orbit, and nearly spherical

Name the eight planets of the Solar System.

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

What is a dwarf planet?

Objects that orbit the Sun but do not meet all criteria for planet status

Give two examples of dwarf planets.

Pluto, Eris, Ceres

What is a natural satellite?

Moon or object naturally orbiting a planet

What is an artificial satellite?

Man-made object placed in orbit (e.g. for communication, observation)

What is a moon?

A natural satellite orbiting a planet

What is a comet?

Small icy body orbiting the Sun, develops tails near the Sun

What is an asteroid?

Rocky object in orbit, mostly in asteroid belt between Mars and Jupiter

What holds the Solar System together?

Gravitational force from the Sun

How does gravity act in space?

Acts over long distances, always attractive

What is an orbit?

The path an object takes around another under gravity

Why do planets stay in orbit?

Forward motion balanced by gravity’s pull (centripetal force)

What is a geostationary satellite?

Orbits Earth once every 24 hours above equator, stays over same spot

What are geostationary satellites used for?

Telecommunications, TV signals

What are polar satellites used for?

Earth observation, weather, mapping

What shape are most orbits?

Elliptical (nearly circular for planets)

What is centripetal force?

Force acting towards the centre of a circular path

What is a star?

A massive, luminous ball of gas held together by gravity and undergoing nuclear fusion

What is nuclear fusion?

Joining of atomic nuclei to release energy (e.g. hydrogen to helium in stars)

What two elements are most stars mainly made of?

Hydrogen and helium

Briefly describe the life cycle of a small star like the Sun.

Nebula → protostar → main sequence → red giant → white dwarf → black dwarf

What is a nebula?

A cloud of dust and gas where stars begin

What is a protostar?

Early stage in star formation as gravity pulls gas together

What is the "main sequence" of a star?

Long, stable period of fusion balancing gravity and outward pressure

What happens when hydrogen in a small star runs out?

The star expands into a red giant, then sheds outer layers

What is a white dwarf?

Hot dense remnant after a red giant sheds its layers

What is a black dwarf?

Cooled white dwarf, no longer emitting significant heat or light (theoretical)

Describe the life cycle of a massive star.

Nebula → protostar → main sequence → red supergiant → supernova → neutron star or black hole

What is a supernova?

A huge explosion at end of a massive star’s life

What is a neutron star?

Extremely dense core left after supernova (if mass not enough for black hole)

What is a black hole?

Object with gravity so strong not even light can escape

What is the cosmic microwave background (CMB)?

Leftover radiation from the Big Bang, detected as microwave radiation

What is redshift?

Wavelength of light from distant galaxies is stretched – moving away

What does redshift tell us?

Universe is expanding, supporting the Big Bang theory

What is Hubble’s Law?

Galaxies farther away move faster from us (greater redshift)

What is the Big Bang theory?

Universe began as a tiny, hot, dense point and expanded rapidly

What two pieces of evidence support the Big Bang theory?

Redshift and cosmic microwave background

What is a galaxy?

Large collection of stars, gas, and dust bound by gravity

What galaxy is the Earth in?

The Milky Way

What is an exoplanet?

A planet orbiting a star outside our Solar System

How are exoplanets detected?

By changes in a star's brightness or dimming as planet passes in front

What is the universe?

All of space, time, matter, and energy

What is a light year?

Distance light travels in one year (about 9.5 trillion km)

Why are telescopes located in space?

To avoid atmospheric distortion, clearer images

What is escape velocity?

Minimum speed needed to escape gravitational attraction

What is the origin of elements heavier than iron?

Formed in supernovae explosions

How are elements distributed in the universe?

By explosion of stars (supernovae) spreading material

What does the colour of a star indicate?

Its temperature (blue = hotter, red = cooler)

How do astronomers determine a star’s composition?

By analysing spectrum of its light

What is stellar parallax?

Apparent shift in position of a star due to Earth's orbit (used to measure distance)

What is meant by equilibrium in a star?

Outward pressure from fusion balances gravity pulling in

What causes a star to become a red giant or supergiant?

Hydrogen runs out, fusion of heavier elements causes expansion

What does a supernova produce, besides neutron stars and black holes?

Heavy elements (iron, gold, etc.)

What types of nuclear reaction occur in stars?

Nuclear fusion (mostly hydrogen to helium in main sequence)

Why can’t nuclear fusion happen at low temperatures?

High temperature/pressure needed to overcome repulsion between nuclei

What is the fate of the Sun?

Become a red giant then white dwarf

What is the fate of a star much bigger than the Sun?

End as neutron star or black hole after supernova

How does a satellite stay in orbit at higher altitude?

Needs lower orbital speed

What happens to orbital speed as orbital radius increases?

Speed decreases

Describe one use of near-Earth satellites.

Weather observation, communications, navigation

What is a space probe?

Uncrewed spacecraft sent to explore the Solar System and beyond

What is gravitational field strength like on the Moon compared to Earth?

Weaker, as Moon has less mass

What is a quasar?

Extremely bright, distant star-like object believed to be massive black hole in galaxy centre

What is dark matter?

Unknown substance that exerts gravitational effects but emits no light

What is dark energy?

Mysterious force causing acceleration in expansion of universe

Why do astronauts feel weightless?

They are in free fall, accelerating with the spacecraft

What keeps the ISS in orbit?

Centripetal force due to gravity

How does a rocket work?

Newton’s 3rd law – exhaust gases out, equal force pushes rocket up

What was the first artificial satellite?

Sputnik 1 (1957)

What is the observable universe?

The part we can detect with telescopes

What causes craters on the Moon?

Meteoroid impacts

How have minerals on Earth been impacted by space?

Heavy elements produced in dying stars; spread by supernova

Why does the Moon have no atmosphere?

Low gravity, cannot retain gases

What is a meteor?

A small rock from space burning as it enters Earth's atmosphere ("shooting star")

What is a meteorite?

A meteor that survives the journey and hits Earth's surface

What is an asteroid belt?

Region between Mars and Jupiter where many asteroids orbit

What’s the main difference between a planet and a dwarf planet?

Dwarf planets have not cleared their orbital path

Why are tides on Earth caused?

Gravitational pull of the Moon (and Sun)

What is the name for Earth’s closest point to the Sun?

Perihelion

What is the Drake Equation?

Formula to estimate number of communicative alien civilisations

What is the Hubble Space Telescope?

Space-based telescope providing high-resolution images of objects in space

How do black holes affect light and time?

Light cannot escape; time slows down near event horizon

What are pulsars?

Spinning neutron stars emitting beams of radiation

What is a brown dwarf?

Failed star – not massive enough for fusion

What is the Kuiper Belt?

Band of icy bodies beyond Neptune

What is the Oort Cloud?

Hypothesised shell of icy objects far beyond Pluto

How do scientists know universe is still expanding?

Continued observations of redshift in distant galaxies

How are distances to nearby stars measured?

Parallax method (shift in position as Earth orbits)

What will likely happen to our galaxy in several billion years?

Collide and merge with Andromeda galaxy

What is meant by “our cosmic address”?

Earth, Solar System, Orion Arm, Milky Way, Local Group, Universe