Stars and the Solar System — REET Science Notes
This page covers the 'Stars and the Solar System' topic from REET Level 2 Science, aligned with the Class 8 NCERT syllabus, with special focus on the nature of stars, constellations, and astronomical phenomena. Factual questions on the Pole Star, the Saptarishi (Big Dipper), and the reason stars twinkle come up often in the exam, so every point here is explained with clear examples.
- 0 questions in REET 2024
- Class 6–8 level
- 7 min read
How this topic is asked in REET
No direct question from the 'Stars and the Solar System' topic was recorded in the REET 2024 paper, so the question pattern here is based on the language of the Class 8 NCERT syllabus, not on any verified previous question. Note — this page focuses mainly on stars, constellations and astronomical phenomena (basic information about the planets is covered separately in our 'Solar System' EVS notes), and questions are typically likely to be based on the Pole Star, the major constellations, and why stars twinkle.
What are stars
Stars are huge, extremely hot balls of gas (mainly hydrogen and helium) that produce their own light (they are self-luminous). Nuclear fusion reactions occurring in the core of a star generate a massive amount of energy, which is what makes stars shine and stay hot. The Sun is the star closest to the Earth, and after the Sun, the nearest star is Proxima Centauri, which is about 4.2 light years from Earth.
To measure the vast distances between stars, the unit of light year is used instead of kilometres — this is a unit of distance, not time. A light year is the distance that light travels in one year (about 9.46 × 10¹² km). Because of the Earth's rotation, stars also appear to move across the sky from east to west, just like the Sun and the Moon.
The Pole Star and how to identify it
The Pole Star (Polaris) is a star that appears almost stationary (motionless) in the sky throughout the night, because it lies almost in line with the Earth's axis of rotation (close to the north celestial pole), while all other stars appear to move around it. Because of this feature, sailors and travellers have used the Pole Star since ancient times to find direction (identifying north).
To locate the Pole Star in the sky, people use the help of the Saptarishi constellation (Ursa Major / Big Dipper) — extending the line joining the two stars at the edge of the Saptarishi's 'bowl' (the pointer stars) leads to the Pole Star.
Major constellations
- Saptarishi (Ursa Major / Big Dipper)
- A group of seven prominent stars, visible in the northern sky; helps in locating the Pole Star
- Mrigashira / Kalpurush (Orion)
- A prominent constellation visible in winter; three stars appear in a row (the belt); Betelgeuse and Rigel are its major stars
- Cassiopeia
- A constellation shaped like the letter 'W', visible in the northern sky roughly opposite the Saptarishi
- Crux / Southern Cross
- A constellation visible from the southern hemisphere, which helps identify the direction of the south celestial pole
Why stars twinkle, and how they differ from planets
The twinkling of stars happens because of atmospheric refraction. Before light from a star reaches the earth, it passes through the atmosphere's constantly changing layers of density and temperature, which repeatedly bends the light's path slightly, creating the illusion of a momentary flicker in the star's brightness and position. Since stars appear to be point sources located extremely far from the Earth, this effect is clearly visible.
Planets, on the other hand, do not twinkle, because they are much closer to the Earth than stars, and so appear in the sky as an extended source — the averaging effect of the many light rays coming from them cancels out the twinkling. Meteors (shooting stars) are not actually stars at all; they are small rocky pieces from space that burn up due to friction while entering the Earth's atmosphere, appearing as a bright streak of light.
The galaxy and the colour of stars
- The Milky Way
- The vast group of stars our solar system is part of is called the Milky Way Galaxy — it includes billions of stars
- Colour and temperature of stars
- The colour of a star indicates its surface temperature — bluish-white stars are relatively the hottest, while red stars are relatively cooler; our Sun is a yellow star
The apparent motion of the Sun, Moon and stars in the sky
We see the Sun, Moon and stars appear to rise in the east and set in the west every day. In reality, this motion is not the Sun, Moon or stars actually moving — it is an apparent motion caused by the Earth's rotation on its axis from west to east. This is also why the constellations we see at night appear to gradually shift position, while the Pole Star appears almost stationary due to its special position in line with the axis of rotation.
It's important to note that different constellations are visible in the night sky in different seasons, because the Earth also revolves around the Sun, which means the part of the sky visible at night gradually changes over the course of the year — for example, the Orion constellation is clearly visible in winter, while in summer it is not visible because it stays with the Sun in the daytime sky.
How to teach this to students
Classroom activity
On a clear night, have students (as a homework activity under family supervision) locate the Saptarishi constellation and use it to identify the Pole Star — this is a simple and effective way to spark interest in astronomy.
Teaching aids
Showing a planetarium chart, a star map, or screenshots from an online planetarium app can help explain the shapes of different constellations.
Common misconception
Students often mistake a meteor (shooting star) for an actual star. Make it clear that it is really a small rocky piece from space that burns up due to atmospheric friction, not a star.
Assessment idea
Ask students why stars twinkle but planets don't — this checks their understanding of atmospheric refraction and the concept of distance.
A trick to remember this
Remember the trick for finding the Pole Star — 'the two pointer stars at the edge of the Saptarishi's bowl point in a straight line towards the Pole Star.' And remember this: 'stars twinkle (far away, point sources); planets don't twinkle (close, extended sources).'
Practice questions
Question 1
Why are stars self-luminous?
- Aक्रोड में नाभिकीय संलयन से ऊर्जा उत्पन्न होने से
- Bसूर्य के प्रकाश को परावर्तित करने से
- Cवायुमंडलीय अपवर्तन से
- Dचंद्रमा के प्रकाश से
Explanation
Nuclear fusion reactions occurring in the core of a star generate a massive amount of energy, which is why it produces its own light and heat.
Question 2
Light-year is a unit of what?
- Aसमय
- Bद्रव्यमान
- Cऊर्जा
- Dदूरी
Explanation
A light year is a unit of distance — it is the distance light travels in one year; despite having 'year' in its name, it is not a unit of time.
Question 3
Which constellation is used to locate the Pole Star?
- Aकैसिओपिया
- Bओरायन
- Cवृश्चिक
- Dसप्तर्षि (Ursa Major)
Explanation
Extending the line joining the two pointer stars of the Saptarishi constellation's bowl leads to the Pole Star.
Question 4
The main reason stars twinkle while planets do not is
- Aग्रहों में प्रकाश नहीं होता
- Bतारे बिंदु-स्रोत हैं, ग्रह विस्तृत स्रोत हैं
- Cग्रह तारों से बड़े होते हैं
- Dतारों का कोई वायुमंडल नहीं होता
Explanation
Because they are extremely far away, stars appear as point sources, so the effect of atmospheric refraction is clearly visible; nearby planets appear as extended sources, so this effect cancels out.
Question 5
After the Sun, the star closest to Earth is
- Aसीरियस
- Bबेटलज्यूस
- Cध्रुव तारा
- Dप्रॉक्सिमा सेंटॉरी
Explanation
Earth's nearest star after the Sun is Proxima Centauri, located about 4.2 light years away.
Question 6
What is a meteor (shooting star) actually?
- Aमरता हुआ तारा
- Bएक ग्रह
- Cवायुमंडल में जलता चट्टानी टुकड़ा
- Dएक उपग्रह
Explanation
A meteor is not actually a star — it is a small rocky piece from space that burns up due to friction while entering Earth's atmosphere, appearing as a bright streak of light.
Question 7
The 'W'-shaped constellation, which appears roughly opposite to Ursa Major, is called
- Aकैसिओपिया
- Bओरायन
- Cक्रक्स
- Dवृश्चिक
Explanation
The Cassiopeia constellation is shaped like the letter 'W' and is visible in the northern sky roughly opposite the Saptarishi.
Question 8
The vast group of stars that our solar system is a part of is called
- Aनक्षत्र
- Bउल्कापिंड
- Cआकाशगंगा (Milky Way)
- Dधूमकेतु
Explanation
Our solar system is part of the vast group of stars called the Milky Way Galaxy, which includes billions of stars.
Question 9
When conducting a night-sky constellation identification activity, the most suitable method for the teacher is
- Aस्टार-मैप या तारामंडल चार्ट की सहायता से वास्तविक आकाश में नक्षत्र पहचनवाना
- Bकेवल किताब से चित्र दिखाना
- Cकेवल नाम रटवाना
- Dटॉपिक को छोड़ देना
Explanation
Identifying constellations in the real sky with the help of a star map develops both interest in astronomy and practical understanding among students.
Question 10
If a student thinks a meteor (shooting star) is an actual star, the teacher should clarify that
- Aयह सही है
- Bयह वायुमंडल में जलता चट्टानी टुकड़ा है, वास्तविक तारा नहीं
- Cयह सूर्य का टुकड़ा है
- Dयह चंद्रमा से टूटकर आता है
Explanation
A meteor is a small rocky piece from space that lights up while burning due to friction in the Earth's atmosphere — it is not the breaking of an actual star.
Frequently asked questions
Why do stars produce their own light?+
Nuclear fusion reactions occurring in the core of a star generate a massive amount of energy, which is what makes them self-luminous.
How do you identify the Pole Star in the sky?+
Extending the line joining the two pointer stars at the edge of the Saptarishi constellation's bowl leads to the Pole Star.
Why do stars twinkle but not planets?+
Stars appear as point sources because they are very far away, so atmospheric refraction makes their brightness twinkle, while nearby planets appear as extended sources, which cancels out this effect.
What is a light year a unit of?+
A light year is a unit of distance (not time) — it is the distance that light travels in one year, about 9.46 × 10¹² km.
Which is Earth's nearest star after the Sun?+
Earth's nearest star after the Sun is Proxima Centauri, located about 4.2 light years away.
Read next
Official Sources
Change Log
- 17 September 2026 — English page published — mirrors the fact-checked Hindi page, independently bilingual-accuracy checked