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Upper Elementary Science - II
3.21 More about the Sun

Composition: The Sun is made up of about 2 x 1030 kilograms of gas. It is composed of about 75% hydrogen and 25% helium. About 0.1% is metals (made from hydrogen via nuclear fusion). This ratio is changing over time (very slowly), as the nuclear reactions continue, converting smaller atoms into more massive ones. Since the Sun formed 4.5 billion years ago, it has used up about half of its initial hydrogen supply.

Our Sun is a second or third generation star. Second generation stars do not just burn hydrogen, they also burn heavier elements, like helium and metals (elements heavier than hydrogen and helium). The element helium was named after the Sun (called "Helios" in Greek) because it was first discovered on the Sun. Helium is plentiful on the Sun but rare on Earth. The element helium was discovered by Jules Janssen during the total solar eclipse of 1868 when he detected a new line in the solar absorption spectrum; Norman Lockyer suggested the name helium.

The composition of the Sun is studied using spectroscopy in which the visible light (the spectrum) of the Sun is studied.

How is energy produced in the Sun? The energy in the Sun is produced by the nuclear fusion and nuclear fission reaction during which hydrogen nuclei is converted to helium nuclei.

Age of the Sun: The Sun formed 4.5 billion years ago, as the solar system coalesced from a cloud of gas and dust.

Directions: Answer the following questions.
Q 1: Sun is a ___ generation star.

Q 2: In the sun hydrogen atoms fuse to form
higher hydrogen

Q 3: Energy in the sun is a result of the
nuclear fission
nuclear fusion

Q 4: Our planetary system is

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Question 6: This question is available to subscribers only!

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