☰ خطة العام · العلوم (بالإنجليزية)

Our star, tools for studying stars, and bright and dim

الأسبوع 28 · المحور الرابع «التغير والثبات»، الوحدة الرابعة «الأنماط في السماء»، المفهوم 4.3 «درجة سطوع الشمس والنجوم» (أ): نجم قريب ونجوم بعيدة · 3 دروس
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Our own star

Discovery Education Science P5: Term 2, Unit 4, pp. 160–165
GoalExplain that the Sun is a star, say what it is made of, and say why it looks so much brighter than other stars.
New words
hydrogen · the lightest gas, which makes up most of the Sunhelium · a light gas that is the second most common gas in the Sununiverse · everything that exists: all stars, planets and space
Explanation

The Sun is not a planet or a fire. It is a star, a huge ball of very hot gas that makes its own light and heat. The Sun is made mostly of hydrogen and some helium. The stars you see at night are also suns, but they are so far away that they look like tiny points of light. Light travels extremely fast, yet sunlight still takes about 8 minutes to reach Earth. Light from the next nearest star takes more than 4 years. This is why the Sun looks so big and bright to us, while other stars are tiny and faint. The Sun is not the brightest star in the universe, and it is not even one of the biggest. It looks brightest because it is much, much closer. Our life depends on the Sun’s heat and light, which warm Earth and give plants the light they need.

ObjectHow far its light travels to usHow it looks
the Sunabout 8 minuteshuge and very bright
the next nearest starmore than 4 yearsa tiny faint point
Worked examples
Where you standThe same lamp looks …
very nearvery bright
far awaysmall and dim
Think about a street lamp. From 2 m it hurts to look at it, but a lamp in the next street looks like a small dot. The lamps could be the same. Only the distance is different. Stars are like that.
Sunlight leaves the Sun at 12:00 and arrives at Earth about 8 minutes later, at 12:08. If you could see the Sun disappear at 12:08, it would actually have disappeared at 12:00. (Never look at the Sun to test it.)
ClaimRight?
brightest because biggestno
looks brightest because closestyes
Marwan says, “The Sun is the brightest star because it is the biggest.” Salma says, “It looks the brightest because it is the closest.” Salma is right. Other stars can be bigger and give out more light, but they are far away.
Class activity

Near and far (a grown-up goes with you). One evening, look at the same porch light or lit window from a few metres away and then from far down the street, at about 10 m and 50 m. Write whether it looks bigger or smaller, brighter or dimmer each time. Glance, do not stare into bright lamps. Then explain how this is like looking at stars at different distances. Never look at the Sun with anything: not binoculars, a telescope or a camera.

Practice
1
What is the Sun?
2
Name the two gases that make up most of the Sun.
3
Why does the Sun look so much brighter than other stars?
4
Sunlight leaves the Sun at 2:00 pm. At what time does it reach Earth, if the trip takes 8 minutes?
2:00