Astrophysics mock nov y11

What is the Universe?

The Universe is a large collection of billions of galaxies and refers to all of space.

What is a galaxy?

A galaxy is a large collection of billions of stars.

What is a star?

A star is a large astronomical object, such as the Sun, that emits light and heat from nuclear fusion.

What is the Solar System?

The Solar System is a planetary system consisting of the Sun and the objects that orbit it, including planets, moons, and other bodies.

What is the hierarchy of the Solar System?

The hierarchy is: Universe → Galaxy → Solar System → Star → Planet → Moon.

Where is our Solar System located?

Our Solar System is located in the Milky Way galaxy, with the Sun at its center.

What is weight?

Weight is the force acting on an object due to gravitational attraction.

What is gravitational field strength (g)?

Gravitational field strength is the force per unit mass experienced by an object in a gravitational field, measured in N/kg.

What factors affect an object’s weight?

Weight depends on the object’s mass and the gravitational field strength of the planet or moon it is on.

How does gravitational field strength vary across planets?

Planets with greater mass have stronger gravitational field strengths.

What is the approximate value of g on Earth?

Approximately 10 N/kg.

How does weight differ on the Moon compared to Earth?

The Moon’s gravitational field strength is weaker, so an object weighs less there than on Earth.

How does weight differ on Jupiter compared to Earth?

Jupiter’s gravitational field strength is stronger, so an object weighs much more there than on Earth.

What causes orbital motion?

Orbital motion is caused by the gravitational force of attraction between two bodies, acting towards the center of the larger body.

Which bodies orbit the Sun?

Planets, comets, and asteroids orbit the Sun.

What do moons orbit?

Moons orbit planets.

What do artificial satellites orbit?

Artificial satellites orbit the Earth.

What shape are planetary orbits?

Slightly elliptical (stretched circles) with the Sun near one focus.

How do planets orbit relative to each other?

All planets orbit in the same plane and direction around the Sun but at different distances and speeds.

How does orbital speed change with distance from the Sun?

The further a planet is from the Sun, the slower it travels and the longer it takes to complete one orbit.

What type of orbits do comets have?

Comets have highly elliptical or hyperbolic orbits.

How does a comet’s speed change?

A comet’s speed increases as it approaches the Sun and decreases as it moves away.

What is the formula for orbital speed?

v = 2πr / T

In the formula v = 2πr / T, what do the symbols represent?

v = orbital speed (m/s), r = average orbital radius (m), T = orbital period (s).

What is the orbital period?

The time taken for an object to complete one orbit.

What is the orbital radius?

The distance from the center of the object being orbited to the orbiting object.

How can stars be classified?

Stars can be classified according to their color, which relates to their surface temperature.

What does a star’s color indicate?

It indicates the star’s surface temperature—the bluer the star, the hotter it is; the redder the star, the cooler it is.

What is the temperature of a red star?

About 3000 K.

What is the temperature of a blue star?

About 30,000 K.

What happens to a star’s color as it expands and cools?

It becomes redder.

What happens to a star’s color as it contracts and heats up?

It becomes whiter.

What are the main stages in the life cycle of a solar mass star?

Nebula → Protostar → Main Sequence Star → Red Giant → Planetary Nebula → White Dwarf.

What is a nebula?

A giant interstellar cloud of gas and dust from which stars are formed.

What is a protostar?

A forming star created when gravity pulls gas and dust together, increasing temperature and density.

What is a main sequence star?

A stable star where nuclear fusion of hydrogen occurs in the core, balancing gravity and radiation pressure.

What is a red giant?

A star that has expanded and cooled after exhausting hydrogen in its core, now fusing helium.

What is a white dwarf?

The hot, dense remnant core left after a red giant sheds its outer layers and fusion stops.

What are the main stages in the life cycle of a high-mass star?

Nebula → Protostar → Main Sequence → Red Supergiant → Supernova → Neutron Star or Black Hole.

What is a red supergiant?

A very large star that expands and cools after its core hydrogen is exhausted, fusing heavier elements.

What is a supernova?

A massive explosion caused by the sudden collapse of a red supergiant’s core.

What is a neutron star?

A dense core left after a supernova explosion, composed mostly of neutrons.

What is a black hole?

The most massive stars collapse under gravity to form a black hole—an object so dense that not even light can escape.

What is luminosity?

The total amount of light energy emitted by a star per second—its power output.

What is apparent magnitude?

The observed brightness of a star as seen from Earth.

What factors affect apparent magnitude?

The star’s luminosity and its distance from Earth.

How does the apparent magnitude scale work?

The brighter the star, the lower its magnitude number.

What is absolute magnitude?

The brightness of a star if it were placed at a standard distance of 10 parsecs (32.6 light-years) from Earth.

What does the Hertzsprung–Russell (HR) diagram show?

The relationship between a star’s luminosity and its surface temperature.

What are the axes on an HR diagram?

Luminosity on the y-axis, temperature (in K) on the x-axis, which decreases from left to right.

Where are main sequence stars found on the HR diagram?

In a diagonal band from top-left (hot, bright) to bottom-right (cool, dim).

Where are white dwarfs found on the HR diagram?

Below and to the left of the main sequence—hot but dim stars.

Where are red giants found on the HR diagram?

Above and to the right of the main sequence—cool but bright stars.

Where are red supergiants found on the HR diagram?

Directly above the red giants—extremely luminous but cool stars.

What type of stars are the hottest and brightest?

Large main sequence or supergiant stars.

What type of stars are the coolest and dimmest?

Small main sequence stars (red dwarfs).