2.1

We experience day and night because of Earth’s rotation around its axis

Earth's side facing the Sun experiences daytime, while the opposite side experiences nighttime. The time that Earth takes to rotate around its axis such that the Sun returns to the same position in the sky defines the duration of the (solar) day, which on average is 24 hours.

2.2

We experience seasons because of the tilt of Earth’s axis of rotation as Earth moves around the Sun in a year

Earth’s axis of rotation is tilted by 23.4º relative to the line perpendicular to its orbital plane around the Sun. For this reason, during part of Earth’s orbit around the Sun, the Northern or Southern hemisphere is tilted towards the Sun while the other one is tilted away from it. The former experiences summer, as the sunlight falls more directly on its surface and the days are longer because the Sun reaches a higher altitude in the sky. On the other hand, the hemisphere tilted away from the Sun experiences winter because the sunlight falls at a highly inclined angle to Earth’s surface, causing it to spread over a larger area. The days become shorter because the Sun is at a lower altitude in the sky.

2.3

We see different phases of the Moon throughout a Moon cycle

As the Moon orbits Earth, its relative position with respect to the Sun and Earth changes. The region of the Moon’s surface which is lit by sunlight changes, producing the different phases we see from Earth — New Moon, Waxing Crescent, Full Moon and Waning Crescent taking 29.53 days from Full Moon to Full Moon. While the phases of the Moon are (more or less) the same for any observer on Earth, the orientation of the Moon will vary, depending on the observer’s hemisphere. For instance, some observers might see the crescent of the Moon open to the left while others, observing the same phase but from a different location, might see the crescent open to the right.

2.4

Eclipses occur due to special alignments of the Sun, Earth and Moon

Occasionally, when the Moon passes exactly between the Sun and Earth, the Moon blocks the light from the Sun and casts a shadow on Earth, creating a solar eclipse. Occasionally, Earth can be directly between the Sun and the Moon. In that case, Earth casts a shadow on the Moon, obscuring its surface and creating a lunar eclipse. Eclipses can be partial, when just a fraction of the object is eclipsed, or total, when the whole object is eclipsed. A lunar eclipse occurs only at Full Moon and, consequently, can only be observed at night. At any given location on Earth, you are more likely to see a lunar eclipse than a solar eclipse. Lunar eclipses also last for longer periods of time than Solar eclipses.

2.5

The tides on Earth are a result of the gravity of the Sun and Moon

The Moon and, to a smaller degree, the Sun cause tides on Earth. Slight bulges on Earth, and especially its oceans, occur both on the side closest to the Moon and closest to the Sun, and away from them. As Earth rotates, these bulges reach the shorelines, causing the water level to increase there. When the Sun, Earth and Moon are almost in a straight line (at Full Moon and at New Moon), we experience higher “Spring tides”. In contrast, when the Sun and Moon are at right angles to each other relative to Earth (at First and Third Quarter Moon) we experience lower “Neap tides”.

2.6

Light from the Sun is essential for most life forms on Earth

The Sun is the primary source of energy used by life forms on Earth. For instance, plants perform photosynthesis using sunlight, allowing their growth and, consequently, the production of molecular oxygen. That oxygen is used by animals for breathing. It is believed that the devastation of the global environment when an asteroid collided with Earth was the cause of the extinction of flightless dinosaurs and of the majority of species on Earth. The resulting explosion transported large amounts of dust into the atmosphere, blocking the Sun’s light and causing a long impact winter. Sunlight also affects our physical and mental health. When exposed to sunlight, our skin produces vitamin D, which plays an important role in our body's biochemical processes. Some studies show a relation between human depression and the lack of exposure to sunlight.

2.7

Particles from the Sun travel to Earth and cause the aurorae

During a solar eruption, charged particles (primarily electrons and protons) from the Sun traverse the 150 million kilometre journey toward Earth. They latch onto Earth's magnetic field, flow towards the magnetic poles, and interact with particles in the atmosphere. The fastest of these particles can travel from the Sun to Earth in about half an hour; the slowest take about five days. Occasionally, these particle storms disturb Earth's magnetic field, damaging satellites and power grids. Often, particles from the Sun interact with oxygen and nitrogen in Earth's atmosphere. This interaction gives rise to Aurorae — wonderful light shows that illuminate the night sky around the magnetic poles of the northern (Aurora Borealis) and southern (Aurora Australis) hemispheres.

2.8

Technology developed for astronomical research is part of our daily life