Chapter 12: Beyond Earth

We first read the entries carefully and recall a few well-known facts about the night sky.

1. Satellite of Earth. The only natural body that goes round (orbits) the Earth is the Moon. Hence, item (i) must match with option (d).
2. Red planet. The planet that looks reddish because of iron-rich dusty soil on its surface is Mars; it is often nick-named the “Red Planet.” Therefore, item (ii) matches option (c).
3. Constellation. A constellation is a recognisable pattern made by a group of stars. One of the most famous such patterns is Orion, also called the Hunter. Thus, item (iii) goes with option (a).
4. Planet commonly called an evening star. The planet that shines brilliantly soon after sunset in the western sky (and before sunrise in the east) is Venus. Because of this bright appearance it is popularly called the “morning star” or “evening star.” Hence, item (iv) links to option (b).

Putting all these matches together we obtain:

Step 1 — Recall what makes up our Solar System
The Solar System consists of the Sun and all celestial bodies that are bound by the Sun’s gravity. These include:

• Eight major planets and their moons
• Dwarf planets (for example, Pluto)
• Smaller objects such as asteroids and comets
• Meteoroids, dust and gas

Step 2 — Examine each option

1. Sirius: Sirius is a bright star located in the constellation Canis Major. It is not gravitationally linked to the Sun; instead, it is about $$8.6\text{ light-years}$$ away from us. Therefore, Sirius lies far outside the Solar System.
2. Comets: These are icy bodies that orbit the Sun in highly elongated paths. Because they revolve around our Sun, they are members of the Solar System.
3. Asteroids: Rocky objects, mostly found in the asteroid belt between Mars and Jupiter, also orbit the Sun. Hence, asteroids belong to the Solar System.
4. Pluto: Although no longer classed as a major planet, Pluto is officially a dwarf planet. It, too, revolves around the Sun and so remains part of the Solar System.

Step 3 — Identify the option that is not a Solar System member
From the analysis, the only object that does not orbit the Sun is Sirius.

Conclusion
The item that is not part of our Solar System is option (i) Sirius.

Step 1 — Recall the definition of a planet
According to the International Astronomical Union (IAU), a planet is a celestial body that:

• orbits the Sun,
• has enough mass for its own gravity to make it nearly spherical in shape, and
• has cleared the neighbourhood around its orbit.

Any object that satisfies all three conditions above is counted among the eight major planets of the Solar System.

Step 2 — List the eight recognised planets of the Sun

The current list of planets, starting closest to the Sun, is:

1. Mercury
2. Venus
3. Earth
4. Mars
5. Jupiter
6. Saturn
7. Uranus
8. Neptune

Step 3 — Compare each option with the official list

Step 4 — Identify the odd one out
Pluto is the only option that does not satisfy all three IAU conditions for a planet, because it has not cleared its orbital neighbourhood. Hence, it is classified as a dwarf planet, not a major planet.

Conclusion
Therefore, the object that is not a planet of the Sun among the given options is Pluto.

Step 1 – Recall what we mean by a “bright” star
In astronomy we compare how bright stars look to us in the night-sky. The yard-stick is called apparent magnitude. A smaller or more negative magnitude means the star looks brighter.

Step 2 – List the two stars in the question

• Pole Star (also called Polaris)
• Sirius (also called the Dog Star, in the constellation Canis Major)

Step 3 – Write their apparent magnitudes
From any standard star-catalogue we find:
$$m_{\text{Sirius}} = -1.46$$
$$m_{\text{Pole\,Star}} \;(\text{Polaris}) = +1.97$$

Step 4 – Compare the numbers
The number $$-1.46$$ is smaller (more negative) than $$+1.97$$.
Because a smaller magnitude means more brightness, Sirius must be the brighter star.

Step 5 – State the result in words a Class 6 student can remember
Sirius is the brightest star we see in the night sky; the Pole Star is helpful for finding directions, but it is not as bright as Sirius.

Step 1 · Recall the accepted order of the planets
Starting from the Sun and moving outwards, astronomers list the eight major planets in the following sequence:

$$\text{Sun}\;\longrightarrow\;\text{Mercury}\;\longrightarrow\;\text{Venus}\;\longrightarrow\;\text{Earth}\;\longrightarrow\;\text{Mars}\;\longrightarrow\;\text{Jupiter}\;\longrightarrow\;\text{Saturn}\;\longrightarrow\;\text{Uranus}\;\longrightarrow\;\text{Neptune}$$

(Older books printed before 2006 may also add Pluto after Neptune, but today Pluto is classified as a dwarf planet.)

Step 2 · Compare this list with Fig. 12.12
Look at the positions of the planets in the artist’s picture.
• If the picture already follows the sequence written above, the order is correct.
• If any planet appears in the wrong place — for example, if Earth is shown after Mars or Jupiter is drawn before Mars — the order is not correct.

Step 3 · Write the correct names in the boxes
Starting from the box closest to the Sun, fill the boxes one by one with these names:

1. Mercury
2. Venus
3. Earth
4. Mars
5. Jupiter
6. Saturn
7. Uranus
8. Neptune

Now the artist’s diagram shows the Solar System in the universally accepted order.

Step 1 : Recall the shapes of the two dippers
The Big Dipper (also called the Great Bear or Ursa Major) is made up of seven bright stars.

• Four stars form a large quadrilateral – this is the bowl of a ladle.
• Three more stars form a bent line attached to one corner of the bowl – this is the handle.

• It too has a four-star bowl and a three-star handle.
• The star at the end of its handle is the famous Pole Star (Polaris).

1. Draw straight lines to connect the four bowl-stars so that they make a four-sided figure.
2. From the top-right corner of this bowl draw a line to the next star (first in the handle), then to the second, and finally to the third (end of handle). Now the ladle shape is clear.
3. Write the label “Big Dipper (Ursa Major)” close to it.

1. The Pole Star is the end star of the Little Dipper’s handle.
2. Find two fainter stars in a slight curve away from Polaris – join them to form the rest of the handle.
3. From the last of these, locate four more faint stars making a smaller bowl as in Fig. 12.4. Join them to display the bowl.
4. Add the label “Little Dipper (Ursa Minor)”.

Step 1 – Observe the given star-field
Fig. 12.14 shows a group of bright stars. Four of them form a big slanting rectangle, three fainter ones lie almost in one straight line at its centre and one still brighter star appears a little below this group.

Step 2 – Mark the four corner stars of Orion

• Top-left bright star  →  Betelgeuse
• Top-right bright star  →  Bellatrix
• Bottom-right bright star  →  Rigel
• Bottom-left bright star  →  Saiph

Step 3 – Join these four stars
Join Betelgeuse to Bellatrix, Bellatrix to Rigel, Rigel to Saiph and Saiph back to Betelgeuse so that a large tilted rectangle (actually a quadrilateral) is obtained. This outlines the body of the constellation Orion.

Step 4 – Identify and connect the three stars of Orion’s Belt
The three nearly collinear medium-bright stars situated midway between the long sides of the rectangle are the Belt stars (Alnitak – Alnilam – Mintaka). Draw a single straight line joining these three to show the Belt.

Step 5 – Draw the shoulders and legs

• Draw a short line from Betelgeuse (left shoulder) to the central Belt star, and another from Bellatrix (right shoulder) to the same central Belt star. These complete Orion’s shoulders.
• Similarly, draw short lines from Rigel (right leg) and Saiph (left leg) up to the central Belt star to indicate Orion’s legs.

Step 6 – Locate and label Sirius
Extend an imaginary line through the Belt stars downward (south-east direction in the sky). The very bright star you meet first is Sirius (the brightest star in the night sky and the main star of the constellation Canis Major). Write the name “Sirius” beside this star.

Resulting sketch
Your finished diagram now shows Orion with its characteristic hour-glass shape and Belt, and the star Sirius correctly identified just below the Belt-line extension.

Step 1 — Stars always shine: All the stars, like our Sun, produce their own light all the time. So their light is always reaching the Earth.

Step 2 — Why are they visible at night? At night the side of Earth on which we stand is turned away from the Sun. The sky is therefore dark, so even the faint light coming from the very distant stars can enter our eyes without much brighter light competing with it. Hence we can see the stars clearly.

Step 3 — Dawn and dusk: • Dawn (early morning) begins as soon as the Sun is just below the horizon. Its light starts to spread through the atmosphere.
• Dusk (early evening) is the opposite situation, when the Sun has just set and its light is slowly disappearing from the sky.

Step 4 — Scattering of sunlight in the atmosphere: Molecules of air and tiny dust or water droplets act like millions of minute mirrors. They scatter the Sun’s light in all directions. As a result the whole sky becomes bright, even if the Sun itself is not yet above the horizon.

Step 5 — Brightness comparison: The Sun is enormously brighter than any single star. A simple way to state this is
\[ I_{\text{sun (day sky)}} \approx 10^{10}\, I_{\text{average star}} \]

where $$I$$ stands for light intensity. Because $$I_{\text{sun}}$$ is nearly ten billion times larger, the scattered sunlight floods the eye and the much weaker starlight is lost in the glare.

Step 6 — How the eye reacts: The human eye adjusts its pupil and retina to the brightest light that is present. In bright daylight the eye “closes down” so that the starlight, which is ten orders of magnitude weaker, no longer produces a signal big enough to be noticed.

Step 7 — Result: • At dawn the increasing brightness of the scattered sunlight overpowers the faint starlight, so the stars seem to fade and finally disappear.
• At dusk the brightness of the sky decreases after the Sun sets. When the scattered sunlight becomes weak enough, the same faint starlight once again becomes detectable, and the stars appear to “switch on.”

Step 8 — Why astronauts see stars even in daytime: Outside Earth’s atmosphere there is practically no air to scatter sunlight, so the sky looks black even on the day-side of a spacecraft. Under those conditions the stars remain visible all the time.

Therefore, we do not actually lose the stars during the day; their light is simply masked by the overwhelming brightness of the Sun’s scattered light in our atmosphere.

Step 1 – Preparation of the observation chart

Step 2 – Actual sky-watching

1. Choose a clear, cloud-free night and an open place away from bright street-lights.
2. First fix the Pole Star. Look for the imaginary line joining the two edge stars (Merak and Dubhe) of the Big Dipper’s ‘bowl’. Extend this line about five times— the moderately bright, solitary star you reach is the Pole Star.
3. Note the exact clock time. Sketch the Big Dipper and the Pole Star on a sheet. Label the time.
4. Return after roughly 2 h and repeat. Do this at least three more times.

Step 3 – What is seen?

• The Pole Star stays almost exactly where it was, every time.
• The seven stars of the Big Dipper have turned slowly anticlockwise (looking at the north) around the Pole Star.

Step 4 – Sample sketches

Draw four small circular diagrams, one for each time. Mark the Pole Star at the centre of every circle. Around it mark the Big Dipper as follows (rough example):

• 8 pm – Bowl at left, handle upward.
• 10 pm – Bowl slightly up-left, handle slanting up-right.
• 12 midnight – Bowl on top, handle right.
• 2 am – Bowl right, handle down.

Add arrows showing the sense of rotation—counter-clockwise.

Step 5 – Explanation

The apparent motion is due to the rotation of the Earth from west to east. Because the Pole Star lies almost on the Earth’s axis of rotation, it seems stationary, whereas every other star appears to move in a circle around it once every 24 h. Hence the Big Dipper looks as though it is slowly revolving around the Pole Star.

Conclusion

Yes, the Big Dipper definitely appears to move. Successive sketches prove that it shifts its position counter-clockwise round the Pole Star while the Pole Star itself keeps nearly the same place in the sky.

Step 1 – Observe the night sky
Go out after sunset, look up, and notice the Moon, bright and dim stars, maybe a planet, shooting stars, and the dark, velvety background.

Step 2 – Collect words and feelings

• Words: twinkle, shimmer, silver, quiet, mystery, sparkle, blanket, lanterns, melody, infinity
• Feelings: calm, wonder, tiny-but-safe, curious, dreamy

Step 3 – Choose form: poem
You can write in short lines so the poem feels light, like the stars themselves.

Step 4 – Draft
Arrange the words and feelings into lines, letting sound and rhythm guide you.

Draft lines
Twinkling quilt / silver hush / distant campfire /...

Step 5 – Revise
Read aloud, remove extra words, keep imagery clear.

Finished Poem

Twinkling quilt above my head,
Stitch of stars on velvet bed.
Moon, a lantern, glides so slow,
Pouring milk-white, gentle glow.
Planets march in silent file,
Shooting sparks that last a while.
Night-wind hums a lullaby,
Cradling dreams that learn to fly.
Though the cosmos feels so wide,
I feel snug with sky as guide.

Step 6 – Share
Read it to family or paste it in your science notebook next to drawings of constellations.