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Earth and Space - Stars and the Universe

Grade 7Cambridge (IGCSE)

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

🔑Concepts

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The Universe is a vast expanse of space that contains all matter and energy, including galaxies, stars, and planets.

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A light-year is the distance light travels in one year, which is approximately 9.46×1012 km9.46 \times 10^{12} \text{ km}. It is a unit of distance, not time.

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Stars are formed from clouds of dust and gas called nebulae. Gravity pulls the gas together to form a protostar.

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Nuclear fusion is the process that powers stars, where Hydrogen nuclei (1H^1H) fuse to form Helium (4He^4He) nuclei, releasing massive amounts of energy.

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The Sun is our closest star. Light from the Sun takes approximately 88 minutes and 2020 seconds to reach Earth.

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Galaxies are massive collections of stars, gas, and dust. Our Solar System is located in the Milky Way, which is a spiral galaxy.

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The life cycle of a star depends on its mass. Average stars like our Sun become Red Giants and then White Dwarfs, while massive stars end in a Supernova and may become Neutron Stars or Black Holes.

📐Formulae

d=v×td = v \times t

1 light-year≈9.46×1015 m1 \text{ light-year} \approx 9.46 \times 10^{15} \text{ m}

c≈3.0×108 m/sc \approx 3.0 \times 10^8 \text{ m/s}

💡Examples

Problem 1:

The star Proxima Centauri is approximately 4.24.2 light-years away from Earth. How long does it take for light from this star to reach us?

Solution:

It takes 4.24.2 years.

Explanation:

Since a light-year is defined as the distance light travels in one year, the number of light-years is equal to the number of years the light spends traveling.

Problem 2:

Calculate the distance of 11 light-year in meters using the speed of light c=3.0×108 m/sc = 3.0 \times 10^8 \text{ m/s} and the number of seconds in a year (365.25365.25 days).

Solution:

d=(3.0×108 m/s)×(365.25×24×60×60 s)≈9.46×1015 md = (3.0 \times 10^8 \text{ m/s}) \times (365.25 \times 24 \times 60 \times 60 \text{ s}) \approx 9.46 \times 10^{15} \text{ m}

Explanation:

To find the distance, we multiply the speed of light by the total number of seconds in one year (31,557,600 s31,557,600 \text{ s}).

Problem 3:

If a galaxy is moving away from us and its distance is 2.5×1062.5 \times 10^6 light-years, express this in scientific notation using kilometers.

Solution:

2.5×106×9.46×1012 km=2.365×1019 km2.5 \times 10^6 \times 9.46 \times 10^{12} \text{ km} = 2.365 \times 10^{19} \text{ km}

Explanation:

We multiply the distance in light-years by the value of one light-year in kilometers (9.46×1012 km9.46 \times 10^{12} \text{ km}) to get the total distance.