Earth and Space: Earth in space

Our solar system was born from a giant, spinning cloud of gas and dust called a nebula, about 4.6 billion years ago. The force of gravity caused this cloud to collapse in on itself. Most of the material gathered at the centre, becoming incredibly hot and dense, forming our Sun. The remaining gas and dust flattened into a spinning disc around the young Sun, known as a protoplanetary disc. Within this disc, tiny dust particles began to stick together. Through a process called accretion, these clumps grew larger and larger, attracting more material with their increasing gravity. Over millions of years, these clumps grew into planetesimals, then protoplanets, and finally into the planets, moons, and asteroids we see today. The inner, hotter part of the disc formed the rocky planets (Mercury, Venus, Earth, Mars), while the outer, cooler regions allowed gas and ice to form the gas giants (Jupiter, Saturn) and ice giants (Uranus, Neptune).

Gravity is the fundamental force of attraction between any two objects that have mass. The more massive the objects and the closer they are, the stronger the gravitational force between them. This force is what keeps the entire solar system together. A planet or satellite moves in an orbit when there is a balance between its forward motion (its velocity) and the gravitational pull from a larger body. Imagine throwing a ball horizontally; it travels forwards but is also pulled downwards by Earth's gravity, so it follows a curved path. If you could throw it fast enough, the curve of its path would match the curve of the Earth, and it would continuously 'fall' around the Earth without ever hitting the ground. This is an orbit. The gravitational force from the Sun provides the 'pull' (the centripetal force) that constantly changes the direction of the planets' motion, keeping them in their elliptical orbits.

Tides are the regular rise and fall of the Earth's oceans. They are caused primarily by the gravitational pull of the Moon, with a smaller contribution from the Sun. The Moon's gravity pulls on the entire Earth, but it pulls hardest on the side of the Earth closest to it. This pulls the water on that side into a bulge, creating a high tide. A second high tide bulge also forms on the opposite side of the Earth. This is because the Moon pulls the solid Earth away from the water on the far side. The areas between these two bulges experience low tides. As the Earth rotates on its axis once every 24 hours, any given point on the coast passes through both high tide bulges, resulting in two high tides and two low tides approximately each day.

There are two special types of tides:

• Spring Tides: When the Sun, Moon, and Earth are aligned (during a New Moon or Full Moon), their gravitational pulls combine. This creates extra-high high tides and extra-low low tides.
• Neap Tides: When the Sun and Moon are at right angles to each other relative to the Earth (during the first and third quarter moons), their gravitational pulls partially cancel each other out. This results in less extreme tides, with lower high tides and higher low tides.

An eclipse happens when one celestial body blocks the light from another. From Earth, we can see two types: solar and lunar eclipses. Their occurrence depends on the specific alignment of the Sun, Earth, and Moon.

Solar Eclipse: This occurs when the Moon passes directly between the Sun and Earth, casting a shadow onto the Earth's surface. For observers within this shadow, the Sun's light is blocked. This can only happen during the New Moon phase. Because the Moon is much smaller than the Earth, its shadow only covers a small area, so a total solar eclipse is a rare event for any given location.

Lunar Eclipse: This occurs when the Earth passes directly between the Sun and Moon, casting its shadow onto the Moon. This darkens the Moon, which can often appear red as some sunlight is filtered and refracted through Earth's atmosphere. A lunar eclipse can only happen during the Full Moon phase. Since the Earth's shadow is much larger than the Moon, a total lunar eclipse is visible from anywhere on the night side of Earth.

Eclipses do not happen every month because the Moon's orbit around the Earth is tilted by about 5 degrees relative to the Earth's orbit around the Sun. This means that most of the time, the Moon's shadow passes above or below the Earth (for a solar eclipse) or the Moon passes above or below the Earth's shadow (for a lunar eclipse).