krit.club logo

Earth and Space - Stars and Galaxies

Grade 6Cambridge (IGCSE)

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

🔑Concepts

•

A star is a massive sphere of plasma held together by its own gravity, primarily composed of Hydrogen (HH) and Helium (HeHe).

•

Stars produce energy through the process of nuclear fusion, where Hydrogen nuclei fuse to form Helium, releasing energy in the form of light and heat.

•

The Sun is a medium-sized star located at the center of our solar system. Its average distance from Earth is approximately 1.5×108 km1.5 \times 10^8 \text{ km}, which is defined as 11 Astronomical Unit (AUAU).

•

A Light Year (lyly) is a unit of distance used in astronomy. It represents the distance that light travels in a vacuum in one year, approximately 9.46×1012 km9.46 \times 10^{12} \text{ km}.

•

Galaxies are giant collections of stars, planetary systems, gas, and dust. Our solar system is located in a spiral galaxy called the Milky Way, which contains over 2×10112 \times 10^{11} stars.

•

The color of a star is an indicator of its surface temperature. Blue stars are the hottest (temperature >30,000 K> 30,000 \text{ K}), while red stars are the coolest (temperature ≈3,000 K\approx 3,000 \text{ K}).

📐Formulae

Distance=Speed of Light(c)×Time(t)\text{Distance} = \text{Speed of Light} (c) \times \text{Time} (t) sentiment

1 ly≈9,460,000,000,000 km=9.46×1012 km1 \text{ ly} \approx 9,460,000,000,000 \text{ km} = 9.46 \times 10^{12} \text{ km}

1 AU≈150,000,000 km=1.5×108 km1 \text{ AU} \approx 150,000,000 \text{ km} = 1.5 \times 10^8 \text{ km}

💡Examples

Problem 1:

If a star is located 1010 light years away from Earth, how many kilometers away is it? Express your answer in scientific notation.

Solution:

9.46×1013 km9.46 \times 10^{13} \text{ km}

Explanation:

Using the formula for 1 ly=9.46×1012 km1 \text{ ly} = 9.46 \times 10^{12} \text{ km}, we multiply by 1010. (9.46×1012)×10=9.46×1013 km(9.46 \times 10^{12}) \times 10 = 9.46 \times 10^{13} \text{ km}.

Problem 2:

Light from the Sun takes approximately 500500 seconds to reach Earth. Given the speed of light is 3×105 km/s3 \times 10^5 \text{ km/s}, calculate the distance to the Sun.

Solution:

1.5×108 km1.5 \times 10^8 \text{ km}

Explanation:

Distance is calculated as speed×time\text{speed} \times \text{time}. So, 3×105 km/s×500 s=150,000,000 km=1.5×108 km3 \times 10^5 \text{ km/s} \times 500 \text{ s} = 150,000,000 \text{ km} = 1.5 \times 10^8 \text{ km}.

Problem 3:

A student observes two stars, Star A (Blue) and Star B (Red). Which star has a higher surface temperature?

Solution:

Star A (Blue)

Explanation:

In astronomy, blue light has a shorter wavelength and higher energy, corresponding to higher surface temperatures, whereas red light indicates lower surface temperatures.