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Earth and Space - The Sun as a star

Grade 3IGCSE

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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The Sun is a star, which is a massive, glowing ball of gases (mostly hydrogen and helium) located at the center of our solar system.

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The Sun provides the heat and light energy necessary for life on Earth. Its surface temperature is approximately 5500∘C5500 ^\circ C.

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The Sun appears larger and brighter than other stars because it is much closer to Earth than any other star.

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The average distance between the Earth and the Sun is about 1.5×1081.5 \times 10^8 km, a distance defined as 1AU1 AU (Astronomical Unit).

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The Sun's diameter is roughly 1.39×1061.39 \times 10^6 km, which is about 109109 times the diameter of the Earth.

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The Sun is responsible for the Earth's seasons, ocean currents, weather, and climate.

📐Formulae

1AU≈1.5×108 km1 AU \approx 1.5 \times 10^8 \text{ km}

DiameterSun≈109×DiameterEarthDiameter_{Sun} \approx 109 \times Diameter_{Earth}

Tsurface≈5500∘CT_{surface} \approx 5500 ^\circ C

💡Examples

Problem 1:

If the distance from Earth to the Sun is 1.5×1081.5 \times 10^8 km and light travels at a speed of 3×1053 \times 10^5 km/s, how long does it take for sunlight to reach Earth?

Solution:

t=1.5×108 km3×105 km/s=500 secondst = \frac{1.5 \times 10^8 \text{ km}}{3 \times 10^5 \text{ km/s}} = 500 \text{ seconds}

Explanation:

By dividing the total distance by the speed of light, we find it takes 500500 seconds, which is approximately 88 minutes and 2020 seconds, for light to travel from the Sun to our planet.

Problem 2:

Why does the Sun look so much bigger than other stars in the night sky?

Solution:

The Sun is the closest star to Earth (d≈1.5×108d \approx 1.5 \times 10^8 km), while the next nearest star, Proxima Centauri, is about 4.2×10134.2 \times 10^{13} km away.

Explanation:

In astronomy, the apparent size of an object depends on its actual size and its distance from the observer. Because other stars are trillions of kilometers further away than the Sun, they appear only as tiny points of light.