Beyond Earth | CBSE Class 6 Science Notes

This note covers stars and constellations, finding directions in the night sky, sky-watching preparations, the Sun, planets and their movements, natural satellites, the Moon and its exploration, asteroids, comets, the Milky Way Galaxy and the search for life beyond Earth.

What are stars and constellations?

Light, patterns and navigation

Stars are objects in the sky that shine with their own light. Some look bright and others look dim. Groups of stars may appear to make familiar shapes, although the lines joining them are imaginary.

People have associated these patterns with animals, objects and characters in stories. Different cultures developed different names and stories for the patterns. Recognising them helped people recognise particular stars.

Navigation means finding directions for a journey. Before modern technology and the magnetic compass, sailors and travellers used star patterns to find directions at sea and on land. This skill is still used as a backup in emergencies.

In Nubra, Ladakh, eleven-year-old Yangdol and her twin brother Dorjay hear stories about stars that helped caravans find directions in ancient times. Nubra's almost cloudless weather and almost complete absence of air and light pollution make the night sky very clearly visible.

Definition: A constellation is a defined region of the sky that often includes a recognisable pattern of stars. The word is also commonly used for the group of stars forming that pattern.

Why does the definition include a region?

Earlier, star groups forming patterns were called constellations. Their boundaries varied between cultures. In the early twentieth century, the International Astronomical Union (IAU), the organisation that agreed these boundaries, officially listed 88 constellations, dividing the entire sky into 88 regions.

The distinction matters: a familiar pattern helps identification, while the modern constellation is a region of sky. The patterns are often the most noticeable features of these regions, which explains the continued common use of the older meaning.

Activity: create a star pattern

1. Look carefully at an image showing bright stars in a part of the night sky.
2. Imagine a pattern and join selected stars with drawn lines.
3. Name an animal or object resembling the pattern and write its name nearby.
4. Make more patterns, create stories about them and compare the patterns and stories with those of friends.

This activity shows how different people can imagine different shapes from stars. The names and stories help recognition; they do not turn the imaginary joining lines into physical objects in space.

How do Orion, the Dippers and the Pole Star help us recognise the sky?

Orion and nearby star patterns

Orion is a constellation often represented as a hunter. Three stars in its middle represent the hunter's belt. Some people imagine Orion, followed by his dog, battling a bull. The dog represents Canis Major, and the bull represents Taurus, two other constellations.

Sirius, in Canis Major, is the brightest star in the night sky. This description does not mean that Sirius is the star closest to Earth. Brightness in the night sky and closeness to Earth are different descriptions.

The diagram labels Canis Major, Orion, Taurus and Sirius. Red lines join stars into patterns, while green lines mark regions of sky. These lines are identification guides and are not visible in the sky.

Drawn by One Young India. See Fig. 12.3 in your NCERT textbook

In Indian astronomy, nakṣhatra can mean a certain star or a group of stars. Ārdrā is Betelgeuse in Orion. Kṛittikā is the Pleiades group in Taurus. Rohiṇī is Aldebaran, also in Taurus.

The Dippers and north

The Big Dipper and Little Dipper are distinct star patterns. The Big Dipper lies in Ursa Major, while the Little Dipper lies in Ursa Minor. In India, the Big Dipper is called Saptaṛiṣhi.

The Pole Star, also called Polaris or Dhruva tārā, is part of the Little Dipper. It appears nearly stationary in the north direction. It therefore helps locate north in the Northern hemisphere, the northern half of Earth.

Red lines outline the two Dipper patterns, and an arrow labels the Pole Star at the end of the Little Dipper's handle. The connecting lines have been drawn for identification.

Drawn by One Young India. See Fig. 12.4 in your NCERT textbook

Tribes in Central India view the four Big Dipper stars that approximately form a rectangle as a grandmother's cot, with the other three as thieves stealing it. Fishermen along the Konkan coast imagine four stars as a boat and the last three as its neck.

These stories describe imagined patterns. Keep the physical identifications separate: the Pole Star belongs to the Little Dipper, and Sirius belongs to Canis Major. The Pole Star is not very bright, whereas Sirius is the brightest star in the night sky.

How should we prepare for night sky watching?

Choose the place and conditions

Light pollution is the presence of excessive artificial light at night. Along with smoke and dust, it can make stars difficult to see in cities. On a clear cloudless night, a large number of stars may be visible.

Villages and other places with less light pollution allow a larger number of stars to be seen. Tall buildings and trees may block the view. An open, dark area is therefore best for watching the night sky.

1. With adult guidance, identify a dark open area away from lights, tall buildings and trees.
2. Use a sky-mapping app to select a date and time appropriate for the objects you want to identify.
3. Choose a night without visible clouds or Moon, particularly when trying to identify the Pole Star, which is not very bright.
4. Carry a sky map or constellation pictures; a magnetic compass can help with directions and a notebook can record observations.
5. Go to the selected place with an adult at the chosen time.
6. Wait about half an hour after arriving so that your eyes adjust to the darkness.

Note: Do not go to a dark open place at night without adults accompanying you. The preparation includes choosing suitable viewing conditions as well as arranging adult company.

Visibility depends on place and time

Not all stars and constellations are visible from every place or on every night of the year. The Pole Star, for example, is not visible from the Southern hemisphere, the southern half of Earth.

Recognition requires knowing both the pattern's appearance and where to look. Sky Map and Stellarium are examples of apps used to identify sky objects. A map helps plan when and in which portion of the sky to search.

Protecting dark skies

Dark sky reserves are areas where light pollution is controlled to preserve dark skies for research. The area around the Indian Astronomical Observatory at Hanle, Ladakh, was notified as the Hanle Dark Sky Reserve in December 2022.

The observatory stands atop the highest peak of the Digpa-ratsa-Ri mountain range in Hanle, renamed Mount Saraswati. Its Himalayan Chandra Telescope is named after Nobel Prize winning scientist Subrahmanyan Chandrasekhar. It is an observatory at one of the world's highest locations.

The reserve is open throughout the year. The Indian Institute of Astrophysics has trained local people, provided with small telescopes, as Astronomy Ambassadors for visitors. This is expected to promote astro-tourism, tourism connected with observing the sky, in the region.

How can we locate the Pole Star, Orion and Sirius?

Use the Big Dipper to find the Pole Star

A recognisable pattern can guide the search for another star. The Big Dipper provides such a guide for the Pole Star. Begin with suitable viewing conditions and allow time for your eyes to adjust, instead of immediately searching for a faint point.

1. During summer, look towards the northern sky in the early part of the night, for example around 9 p.m., meaning nine o'clock at night.
2. Identify the Big Dipper and the two stars at the end of its cup.
3. Imagine a straight line through these two stars extending towards the north.
4. Follow this line for about five times the distance between the two stars. It leads to the Pole Star, which is not very bright.

The five-times guide uses the two stars at the end of the cup, not the entire Big Dipper pattern. The Pole Star's nearly stationary appearance then helps identify the north direction in the Northern hemisphere.

Use Orion's belt to find Sirius

In India, Orion is best viewed from December to April after sunset. Its central belt is particularly useful for identification because three bright stars form a short straight line. Find this small pattern before trying to recognise the hunter's full imagined outline.

1. Plan a viewing session after sunset during December to April.
2. Look for three bright stars in a short straight line around Orion's middle.
3. Identify these stars as Orion's belt and use them to recognise Orion.
4. Imagine a straight line through the three belt stars and follow it towards the east to locate Sirius nearby.

For a further observation, locate the Big Dipper and Pole Star three or four times during a clear night, at intervals of two to three hours. Draw a rough sketch each time, record the time and compare the apparent positions.

Keep the two guides distinct: the Big Dipper leads to the Pole Star, whereas Orion's belt leads to Sirius. Neither method requires visible lines in the sky. The lines are imagined using the positions of the stars.

Why is the Sun important, and why does it look different from other stars?

Our nearest star

The Sun is the star closest to Earth. It is an extremely hot spherical ball of gases that gives out a huge amount of energy. It produces heat and light and is Earth's main energy source.

The Sun is about 100 times bigger than Earth in diameter, the distance across a spherical object through its centre. Yet it looks small because it is very far away. Its distance from Earth is about 150 million kilometres.

The symbol km means kilometre, a unit of distance. An astronomical unit, written au, is approximately the distance between Earth and the Sun. It is useful for expressing distances within the Solar System, the Sun and the objects associated with it.

The nearest star after the Sun is Proxima Centauri, about 269000 au away. This means it is about 269000 times our distance from the Sun. The comparison expresses how much farther away this next nearest star is than the Sun.

Apparent size and daytime visibility

Other stars are much farther away than the Sun and therefore look like points of light. Some are much bigger than the Sun. Their small appearance does not show that their actual size is small.

The Sun appears much bigger because it is much closer to us than other stars. During daytime, its extreme brightness prevents us from viewing other stars from Earth. Their absence from our view does not mean they stop existing during the day.

How sunlight supports life

The Sun's heat keeps Earth at a temperature that makes life possible. Sunlight is essential for plants to grow. Plants provide food and oxygen to animals, including humans.

The Sun is responsible for climate, seasons, weather, the water cycle and winds, all important for sustaining life. Its importance as the source of light and heat led most ancient civilisations to give it the status of a deity. In India, it is worshipped as Sūrya.

Note: The Sun is the largest and heaviest object in the Solar System and produces almost all its energy. Other Solar System objects shine because their surfaces reflect sunlight.

What makes up the Solar System, and how do planets move?

Members and movements

The Solar System consists of the Sun, eight planets, their moons and many smaller objects, including asteroids and comets. Asteroids are small rocky objects, while comets contain dust, gases, rocks and ice. Most Solar System objects move around the Sun.

Revolution is the movement of an object around the Sun. A planet is a large, nearly spherical object that revolves around the Sun. Earth is a planet and completes one revolution in nearly one year.

Rotation is the turning of an object about its axis, an imaginary line about which it turns. Earth rotates while revolving around the Sun. One full rotation takes about 24 hours, called a day. Other planets also rotate about their axes while revolving.

The order of the planets

In order of increasing distance from the Sun, the eight planets are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. Earth is third in this sequence, between Venus and Mars. The order describes distance from the Sun, not order of size.

The artist's representation labels the Sun and all eight planets in sequence, with the asteroid belt between Mars and Jupiter. Curved paths surround the Sun. Object sizes and distances are not to scale.

Drawn by One Young India. See Fig. 12.7 in your NCERT textbook

Not to scale means the drawing does not preserve actual relative sizes and distances. Use this representation to learn the arrangement, rather than measuring it to calculate the real gaps between planets.

Names used across India include Budha for Mercury, Śhukra for Venus, Pṛithvī for Earth, Mangala for Mars, Bṛihaspati or Guru for Jupiter, and Śhani for Saturn. These are names for the same objects, rather than additional planets.

Where does Pluto belong?

Pluto revolves around the Sun beyond Neptune and is smaller than Earth's Moon. It was called a planet when discovered. After other similar small objects were discovered, the IAU redefined the requirements for a planet in 2006.

Pluto and these smaller objects are now called dwarf planets, a category distinct from the eight planets. Thus, being outside the list of eight planets does not put Pluto outside the Solar System.

How do the planets differ, and how can we observe them?

Inner and outer planets

The four inner planets, Mercury, Venus, Earth and Mars, are nearest to the Sun. They are smaller in size and have solid surfaces with rocks. The four outermost planets are Jupiter, Saturn, Uranus and Neptune.

The outer planets are much larger than Earth and mostly made of gas and ice. These giant planets have large, flat, ring-like structures made of dust particles and rocky material. Their composition is “mostly” gas and ice, not entirely so.

Colours, names and temperature

Mars is called the Red Planet because its reddish soil makes it appear red. Earth is the Blue Planet because water covers a large portion of its surface, making it appear blue from space.

Planets get most of their energy from the Sun. In general, planets farther from it are colder. However, an atmosphere, the gases surrounding a planet, can trap heat and significantly change its temperature. Venus is hotter than Mercury despite being farther from the Sun.

Venus is usually seen shining brightly at dawn and dusk. It is commonly called the Morning Star or Evening Star, although it is a planet. After the Sun and Moon, it is the brightest object in the sky.

Finding planets and using instruments

Venus is the easiest planet to identify. With an app's help, look near the east before sunrise at dawn, or near the west after sunset at dusk. These are different viewing opportunities, not instructions to search both directions at once.

Mercury, Mars, Jupiter and Saturn can also be seen with the naked eye, meaning directly without a viewing instrument. Their great distances make them appear as shining dots. Unlike planets, stars appear to twinkle a lot.

Binoculars and a telescope are instruments that make sky objects appear brighter and larger. A telescope also reveals many dim objects invisible to the naked eye. Higher education institutions, amateur astronomy clubs, museums and planetariums organise opportunities for sky watching.

What are natural satellites, and what have we learnt about the Moon?

Moons and their movements

Objects moving around planets are commonly called satellites and are smaller than those planets. Moons are their natural satellites. Earth has one Moon, Mars has two moons, and Jupiter, Saturn, Uranus and Neptune have a large number of moons.

More generally, an object moving around a much larger object can also be called a satellite. In this broader sense, Earth can be considered a satellite of the Sun. The usual planet-and-moon description is therefore not the term's only use.

The Moon is Earth's natural satellite and our nearest neighbour in space. It takes about 27 days to complete one revolution around Earth. It is about 3,84,000 km away, and its diameter is about a quarter of Earth's diameter.

The lunar surface

There is hardly any atmosphere on the Moon. Its surface has craters, circular bowl-like structures. Most formed when asteroids or rocks from space struck the surface. These features remain for a very long time in the absence of atmosphere, water or life that would alter them.

Photograph: Images of the Moon (NCERT Class 6 Figure 12.9). Image (a), taken by Cartosat, shows the Moon with light and dark areas. Image (b), taken by cameras aboard Chandrayaan-3, is a close-up showing numerous circular craters. These are spacecraft images, not drawings.

India's Chandrayaan missions

Chandrayaan is the name used for India's Moon missions. Spacecraft allow humans to explore the Moon despite its distance. The three launched missions and the planned fourth mission serve the effort to understand it better.

Vikram was the lander, the part designed to land, carrying the Pragyan rover, a vehicle for exploring the surface. A soft landing is a controlled landing without a destructive impact.

The mission made India the first country to achieve a landing near the Moon's little explored south pole. Chandrayaan-4 is being planned to bring back soil and rock samples. Keep the distinction between a completed landing and a planned mission.

How are asteroids and comets different?

Rocky objects and the asteroid belt

Asteroids are small rocky objects in the Solar System with irregular shapes, unlike the nearly spherical Sun and planets. Their sizes range from 10 metres to about 500 km. The symbol m stands for metre, a unit of length.

Many asteroids revolve around the Sun along paths between those of Mars and Jupiter. This region is the asteroid belt. The word “many” matters: the description does not place every asteroid there. Occasionally, some asteroids pass very close to Earth.

Comets and their tails

Comets are visitors from the outer regions of the Solar System, made of dust, gases, rocks and ice. As a comet approaches close to the Sun, frozen material starts evaporating, changing into gas. This escaping material forms its tail.

As comets move away from the Sun, they appear dim and cannot then be seen with the naked eye. Many revolve around the Sun and approach it periodically, meaning repeatedly at intervals. Their visibility and appearance therefore relate to their approach to the Sun.

However, a few comets escape from the Solar System. A few others break up or fall into the Sun or other planets as they approach. Do not turn “many return periodically” into a claim that every comet returns.

The picture shows a bright rounded region with a long pale tail extending to the right against a star-filled background. It illustrates a comet's tail without labelling distances or separate internal parts.

See Fig. 12.10 in your NCERT textbook

Halley's Comet and cultural names

Halley's Comet appears every 76 years, and its last appearance was in 1986. In Sanskrit and a few other Indian languages, a comet is called Dhūmaketu. Tribal names include Pucchya-Taro, meaning a star with a tail, and Zendya-Taro, meaning a star like a flag.

In many cultures, comets were feared and were earlier believed to bring bad luck. Scientific understanding identifies them as icy-rocky visitors making a trip close to the Sun. Their cultural names and earlier fears should be distinguished from their material composition and movement.

What lies beyond the Solar System?

Our home galaxy

A galaxy contains millions to billions of stars. The Solar System belongs to the Milky Way Galaxy, also called Ākāśha Gangā. Our Sun is therefore one star within a much larger collection of stars.

From a dark location away from city lights on a moonless night, the Milky Way can be seen as an extended faint band of light. This band stretches across the sky from near north to south. Appropriate darkness helps make this faint feature visible.

Photograph: The Milky Way from Ladakh (NCERT Class 6 Figure 12.11). The photograph shows a broad, uneven band of light crossing a star-filled sky. It records the Milky Way as seen from a very dark location in Ladakh, India.

The Universe includes the Milky Way and the many other galaxies beyond it. Scientists study stars and galaxies to understand the Universe. The Solar System, a galaxy and the Universe refer to different levels of this wider picture.

The search for life elsewhere

Exoplanets are planets discovered revolving around other stars in our galaxy. The search for life elsewhere has been directed mostly towards them. This distinguishes them from the eight planets revolving around our own Sun.

We do not know yet whether life exists elsewhere in the Universe. Scientists have not found evidence of such life, and the search continues. Lack of evidence so far is not proof that life cannot exist elsewhere.

Keep the uncertainty in the conclusion. Neither “life has certainly been found elsewhere” nor “life exists only on Earth” follows from the evidence described here. The appropriate statement is that the question remains open and is being investigated.

Glossary

• Star — An object that shines with its own light, such as the Sun.
• Constellation — A defined region of sky that often includes a recognisable pattern of stars.
• Light pollution — The presence of excessive artificial light at night, making observation of the night sky difficult.
• Pole Star — Polaris, a star in the Little Dipper that appears nearly stationary in the north direction.
• Astronomical unit — A distance approximately equal to that between Earth and the Sun, written as au.
• Planet — A large, nearly spherical object that revolves around the Sun.
• Revolution — The movement of an object around the Sun; the term also describes the Moon's movement around Earth.
• Rotation — Turning about an axis, as Earth does in about 24 hours.
• Natural satellite — A moon moving around a planet, such as Earth's Moon.
• Crater — A circular bowl-like surface feature; most lunar craters formed through impacts of asteroids or rocks.
• Asteroid — A small rocky object of irregular shape found in the Solar System.
• Comet — An object containing dust, gases, rocks and ice that develops a tail near the Sun.
• Galaxy — A collection containing millions to billions of stars, such as our Milky Way Galaxy.
• Exoplanet — A planet discovered revolving around another star in our galaxy.

Common errors and misconceptions

• Misconception: A constellation is only a few stars joined by real lines. Correct: It is a defined region of sky, often containing a recognisable pattern; joining lines are imaginary.
• Misconception: The Pole Star is the brightest star in the night sky. Correct: Sirius is the brightest; the Pole Star is not very bright and appears nearly stationary towards north.
• Misconception: Venus is a star because it is called the Evening Star. Correct: Venus is a planet, usually seen shining brightly at dawn or dusk.
• Misconception: Every planet farther from the Sun must be colder. Correct: This is the general trend, but atmospheres can trap heat; Venus is hotter than Mercury.
• Misconception: Earth's rotation and revolution both take one year. Correct: Rotation takes about 24 hours; revolution around the Sun takes nearly one year.
• Misconception: Pluto is no longer part of the Solar System. Correct: It still revolves around the Sun but is classified as a dwarf planet.
• Misconception: Every comet returns repeatedly near the Sun. Correct: Many return periodically, but a few escape, while others break up or fall into the Sun or planets.
• Misconception: Scientists have proved that life cannot exist elsewhere. Correct: No evidence has been found so far, but the search continues and the question remains open.

Exam-style questions with model answers

Q1. State the modern meaning of constellation and explain why drawings use lines between its stars. [2 marks]

1. A constellation is a defined region of sky that often includes a recognisable pattern of stars.
2. Drawn lines help identify the pattern; they are imaginary and are not visible as lines in the sky.

Q2. Describe how to locate the Pole Star using the Big Dipper, including when to look, which stars to use and how far to extend the imaginary line. [3 marks]

1. Look towards the northern sky during summer in the early part of the night, for example around 9 p.m., and identify the Big Dipper.
2. Find the two stars at the end of its cup and imagine a straight line passing through them towards the north.
3. Extend this line to about five times their separation to locate the Pole Star, which is not very bright.

Q3. Give four preparations for a night sky session intended to identify the Pole Star. Include location, viewing conditions, adult company and adjustment to darkness. [4 marks]

1. Identify an open dark area away from artificial lights, tall buildings and trees so that the sky is less obstructed.
2. Use a sky-mapping app to choose the date and time, and select a night without visible clouds or Moon.
3. Go to the selected place with an adult; do not visit a dark open area at night without adult company.
4. After arriving, wait about half an hour for your eyes to adjust to the darkness and see the sky better.

Q4. List all eight planets in increasing distance from the Sun. Describe the inner and outer groups, state the general temperature trend, and explain why Venus is hotter than Mercury despite being farther away. [5 marks]

1. The complete order is Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune, starting with the planet nearest the Sun.
2. The inner four, Mercury, Venus, Earth and Mars, are smaller planets with solid surfaces that have rocks on them.
3. The outer four, Jupiter, Saturn, Uranus and Neptune, are much larger than Earth and mostly made of gas and ice.
4. Planets receive most of their energy from the Sun, so those farther away are colder in general, rather than without exception.
5. An atmosphere can trap heat and significantly change a planet's temperature. This explains why Venus is hotter than Mercury despite its greater distance.

Q5. Explain why the Sun looks larger than other stars, why other stars are not visible during daytime, and how sunlight supports animals through plants. [3 marks]

1. The Sun is much closer to Earth than other stars, so it appears much bigger, even though some distant stars are actually larger.
2. During the day, the Sun's extreme brightness prevents us from viewing other stars from Earth; they do not disappear from space.
3. Sunlight is essential for plant growth. Plants provide food and oxygen to animals, including humans, linking sunlight with the support of animal life.

Q6. Give the launch year of Chandrayaan-1, the launch year of Chandrayaan-2, and the launch month and year of Chandrayaan-3. Then describe Chandrayaan-3's landing, including its date and vehicles, and explain its significance and commemoration. [5 marks]

1. Chandrayaan-1 was launched in 2008. It was India's first mission to the Moon, undertaken to improve understanding of Earth's natural satellite.
2. Chandrayaan-2, India's second mission to study the Moon, was launched in 2019 as part of the continuing effort to understand it.
3. Chandrayaan-3 was launched in July 2023. It was the third of the three launched Indian Moon missions described here.
4. On 23 August 2023, the Vikram lander, carrying the Pragyan rover, successfully soft-landed on the Moon near its little explored south pole.
5. This made India the first country to achieve a landing near that region. The Government of India declared 23 August National Space Day.

Q7. Compare asteroids and comets by material and movement, and explain how a comet's tail forms near the Sun. [3 marks]

1. Asteroids are rocky and irregular in shape, whereas comets contain dust, gases, rocks and ice, giving the two types different material compositions.
2. Many asteroids move in the belt between Mars and Jupiter. Many comets approach the Sun periodically, although some escape or break up.
3. When a comet approaches close to the Sun, its frozen material begins evaporating. This escaping material forms the comet's long tail.

Q8. What are exoplanets, and what is known about the existence of life elsewhere in the Universe? [2 marks]

1. Exoplanets are planets discovered revolving around other stars in our galaxy, and the search for life has focused mostly on them.
2. Scientists have not found evidence of life elsewhere so far. We do not know yet whether it exists, and the search continues.

Key takeaways

• Stars produce their own light, while other Solar System objects shine because they reflect sunlight from their surfaces.
• Constellations are defined sky regions; familiar star patterns and imaginary joining lines help people recognise them.
• The Pole Star appears nearly stationary towards north, helping locate that direction in the Northern hemisphere.
• Dark open surroundings, suitable weather, adult company and time for eyes to adjust improve a night sky session.
• The eight planets revolving around the Sun are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune, in that order.
• Earth rotates in about 24 hours and revolves around the Sun in nearly one year.
• The Moon is Earth's natural satellite, takes about 27 days to revolve around Earth and has many circular craters.
• Many asteroids move between Mars and Jupiter; comets develop tails as their frozen material evaporates near the Sun.
• Our Solar System belongs to the Milky Way Galaxy, and evidence of life elsewhere has not yet been found.

Test yourself

What is the difference between Sirius and the Pole Star as sky-watching guides?

Sirius is the brightest star in the night sky. The Pole Star is not very bright but helps identify north through its nearly stationary appearance.

When is Orion best viewed in India, and how can its belt help locate Sirius?

Look after sunset from December to April. Extend an imaginary straight line through Orion's three belt stars towards the east to find Sirius.

Why should the distances in an artist's Solar System picture not be measured as actual relative distances?

The picture fits objects onto a page and is not to scale. Its relative sizes and distances do not match the actual ones.

Why is Venus called the Morning Star or Evening Star even though it is a planet?

Venus is usually seen shining brightly at dawn and dusk. These familiar names describe its appearance, not its classification as a star.

Which is outside the Solar System: Sirius, asteroids, comets or Pluto?

Sirius is outside the Solar System. Asteroids, comets and the dwarf planet Pluto are members of it.

A planet's name has four letters: the first is in MAN but not CAN; the second is in ACE and FAN; the third is in RAT but not CAT; the fourth is in SUN but not FUN. What is it?

The letters are M, A, R and S, giving MARS. Mars is the planet called the Red Planet because its soil is reddish.

How often does Halley's Comet appear, and when was its last appearance?

Halley's Comet appears every 76 years, and its last appearance was in 1986.

How does the Milky Way look from a dark place on a moonless night?

It appears as an extended faint band of light across the sky from near north to south.