Orion is a readily identifiable constellation in the night sky.
Visible in the UK during winter, from late autumn to early spring.
Best views are in December and January.
Appears as a large hourglass shape.
Orion's Belt is formed by three bright stars in the middle.
Prominent due to its bright stars and distinct pattern.
A bright red star marking Orion's left shoulder (or right, from Earth's perspective).
It is a red supergiant, near the end of its life.
Could explode as a supernova within the next 100,000 years.
Brightness is variable, with significant dimming observed.
Astronomers closely monitor it for signs of an imminent explosion.
Sirius is the brightest star in the night sky.
Located in the constellation Canis Major, following Orion.
Can be found by following Orion's Belt downward and slightly to the left.
Mercury
Name Origin: Messenger god
Size: 0.38 \times (Earth=1)
Position from Sun: 1st
Visibility: Low on horizon at dawn/dusk; hard to spot
Venus
Name Origin: Goddess of love
Size: 0.95 \times
Position from Sun: 2nd
Visibility: Very bright; "Morning Star" or "Evening Star"
Earth
Name Origin: Not from mythology
Size: 1 \times
Position from Sun: 3rd
Notes: We live on it!
Mars
Name Origin: God of war
Size: 0.53 \times
Position from Sun: 4th
Visibility: Reddish; best every ~2 years when close
Moons
Natural satellites that orbit planets.
Vary in size and composition.
Some have atmospheres or underground oceans (e.g., Europa, Titan).
Planets
Large celestial bodies that orbit a star.
Have cleared their orbit of debris.
Spherical due to their gravity (e.g., Earth, Jupiter).
Galaxies
Vast collections of stars, planets, gas, and dark matter bound by gravity.
Contain billions of stars.
Can be spiral, elliptical, or irregular in shape.
Distance from Earth: Earth is about 26,000 light-years from the centre.
Size: About 100,000 light-years in diameter.
Contains 200-400 billion stars.
Stars form from clouds of gas and dust.
Life cycle depends on their mass.
Nebula: A cloud of gas and dust collapses under gravity.
Protostar: The core heats up as it contracts, but fusion hasn't started yet.
Main Sequence Star: Hydrogen fusion begins, and the star remains stable for billions of years.
Red Giant: When hydrogen runs out, the core contracts while the outer layers expand and cool.
White Dwarf: The outer layers are shed, and the hot, dense core is left behind.
Black Dwarf (Theoretical): Over time, the white dwarf cools completely and no longer emits light.
Nebula: Like small stars, they form from collapsing gas and dust.
Protostar: The core heats up as gravity pulls in more mass.
Main Sequence Star: Hydrogen fusion occurs at a much faster rate due to the star's high mass.
Supernova: Once fusion stops, the core collapses and triggers a massive explosion, scattering elements into space.
Neutron Star or Black Hole:
Neutron Star: If the remaining core is 1.4-3 times the Sun's mass, it becomes a neutron star.
A dense, rapidly spinning remnant.
Black Hole: If the core is even more massive, gravity collapses it into a black hole, from which not even light can escape.
Small stars end as white dwarfs and eventually black dwarfs (if given enough time).
Large stars explode as supernovae, leaving behind either a neutron star or a black hole.