Exam practice

igneous

remnants (fossils: the preserved remains of plants and animals)

limestone

sedimentary

staircase (and floors), because it is hard and takes a smooth polish.

The Earth’s outer layer (the crust) and most of its inside are made of rock, which is made of minerals. On top of the rock is a thin layer of soil, made from broken-down rock and rotted plant and animal matter. Deep inside, the Earth has hot molten rock (magma) and, at the center, a core of iron and nickel.

A rock is a hard, natural solid found on the surface of the Earth and inside it, made of one or more minerals. For example, granite is made of quartz, feldspar and mica.

(Your answer will depend on where you live.) For example: limestone for making cement and lime (as at the cement factories of Udayapur and Bhainse); sandstone and conglomerate from river banks for building houses and walls; flat stones from river beds for paving; shale and clay for making bricks and tiles.

Rocks form in three ways.

• Igneous rocks form when magma (molten rock) cools and hardens, either slowly deep underground (granite) or quickly as lava on the surface (pumice, obsidian).
• Sedimentary rocks form when sediment (pieces of weathered rock, sand, mud, shells) carried by rivers and wind settles in layers at the bottoms of rivers and seas, and the layers are pressed and cemented together over a long time (limestone, sandstone, shale).
• Metamorphic rocks form when any rock is changed by great heat and pressure deep inside the Earth, without melting (marble from limestone, slate from shale).

All three are igneous rocks, formed from cooling magma or lava.

• Granite: floors, staircases, kitchen tops, roads, monuments and historic buildings.
• Pumice: scrubbing hard skin from the feet, polishing, and making light building blocks.
• Obsidian: ornaments and jewelry; in the past, for knives and arrowheads, because it breaks with very sharp edges.

(Conglomerate, pebbles cemented together, used for building, is another.)

It is gneiss, a metamorphic rock, formed from granite (or other rocks) by great heat and pressure deep inside the Earth.

Characteristic: its minerals are sorted into light and dark bands, often bent into folds by the pressure; it is hard.

Use: building stone, curbs and paving, and polished slabs for floors and walls.

solar system

Neptune

Venus

Mars (Phobos and Deimos)

Earth

• twin planet of the Earth: Venus
• asteroid: Juno
• dwarf planet: Pluto
• red planet: Mars
• the largest planet: Jupiter

(Mercury is not needed.)

1. Neptune
2. Mercury
3. Jupiter
4. Venus
5. Mercury
6. Mercury or Venus (both have none)

The solar system is the Sun and all the heavenly bodies that go round it: planets, their satellites, dwarf planets, asteroids, comets and meteoroids.
It has eight planets. In order from the Sun: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.

1. Jupiter: the largest planet, fifth from the Sun; a gas giant with a Great Red Spot, a giant storm; spins fastest of all planets.
2. Mars: the red planet, fourth from the Sun; has two satellites, Phobos and Deimos; its day is about as long as ours.
3. Earth: third from the Sun; the only planet known to have life, with liquid water and oxygen; one satellite, the Moon.

• It is the third planet from the Sun, about 150 million km away.
• It is the only planet known to have life, because it has liquid water, air with oxygen, and a suitable temperature.
• It has one natural satellite, the Moon.
• It spins once in about 24 hours (day and night) and goes round the Sun once in about 365¼ days (a year).

Draw the Sun at one side (only part of it fits), then the eight planets in order, Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, each labeled, with their sizes in proportion as in Figure 11.20: Venus and the Earth about the same size, Mars about half, Mercury smallest; Jupiter the biggest, 11 times the Earth’s width, Saturn a bit smaller with its rings, Uranus and Neptune about 4 times the Earth. Draw the gaps between them growing larger farther out (Figure 11.19): the distances can’t really be drawn to the same scale as the sizes on one page.

Pluto, in August 2006; it is now called a dwarf planet.

• a.Its orbit crosses Neptune’s orbit, and it shares its region with many other icy bodies: it has not cleared its path round the Sun, which a planet must do.
• b.Its mass is too small (smaller than our Moon) to clear its path.

For example:

The Moon is the Earth’s only natural satellite and the heavenly body closest to us, on average 384,400 km away. It is about 3,474 km across, a little over a quarter of the Earth’s width. It has no light of its own and shines by reflecting sunlight. It has no air and no liquid water, and its gravity is about one-sixth of the Earth’s. It has mountains, craters and plains, but no life. It goes round the Earth in about 27⅓ days, and its phases repeat every 29.5 days.

A lunar month is the time from one new moon to the next, about 29.5 days (the synodic month), in which the Moon goes through all its phases.
Importance: our festivals, rituals and many cultural events are fixed by the tithis of the lunar month (for example Dashain on Ashwin shukla dashami, Buddha Jayanti on Baisakh purnima). Farmers also used the Moon’s phases to plan work.

Adhik maas (mal maas, purushottam maas) is an extra lunar month, a lunar month with a repeated name.
A lunar month takes the name of the solar month in which it begins at a new moon. A lunar month is about 29.5 days, and most solar months are a little longer. So sometimes two new moons fall within one solar month; then two lunar months begin in it, and both get the same name. The repeated one is the adhik maas. Because 12 lunar months are about 11 days shorter than the solar year, an adhik maas is needed about every three years to keep festivals in their seasons.

Kshay maas is a lunar month that is skipped: its name is missing from that year’s lunar calendar.
A lunar month is named after the solar month in which it begins at a new moon. In winter, around Poush, the Earth is nearest the Sun and moves fastest, so the solar months are shortest, about 29.4 days, a little shorter than a lunar month. Very rarely, such a solar month passes with no new moon in it, so no lunar month gets its name. It happens only between Kartik and Magh, and very rarely; a year with a kshay maas has two adhik maas as well.

The changes in the shape of the bright part of the Moon, as seen from the Earth during a lunar month, are called the phases of the Moon. They happen because the Sun always lights half the Moon, and as the Moon goes round the Earth we see different amounts of that lit half.

Draw the Earth in the middle, the Sun’s rays coming from one side, and the Moon at eight points round the Earth, each with its half facing the Sun lit. Beside each, draw how it looks from the Earth and label it: new moon, waxing crescent, first quarter, waxing gibbous, full moon, waning gibbous, last quarter, waning crescent, as in Figure 11.36.

The first (completely dark) is the new moon; the second (a full bright disc) is the full moon. The differences are those in question g: at the new moon the Moon is between the Sun and the Earth and its lit side faces away from us; at the full moon the Earth is between the Sun and the Moon and we see all of its lit side; the new moon ends the dark half and the full moon ends the bright half.

solar eclipse

lunar eclipse

solar eclipse

straight line

total eclipse (seen from the umbra; the penumbra gives a partial eclipse)

A lunar eclipse happens when the Earth is between the Sun and the Moon, in a straight line, so that the Earth’s shadow falls on the Moon. The Moon is on the far side of the Earth from the Sun only at the full moon. So a lunar eclipse can happen only on a full moon (and only on those full moons when the Moon is exactly in line).

A solar eclipse happens when the Moon is between the Sun and the Earth, in a straight line, so that the Moon’s shadow falls on the Earth. The Moon is between the Sun and the Earth only at the new moon. So a solar eclipse can happen only on a new moon day (and only on those new moons when it is exactly in line).

A shadow is a dark region behind an opaque object, where the object stops light from reaching.
Light travels in straight lines. When an opaque object is in the path of the light, the light can’t pass through it or bend round it, so the region behind the object gets no light (the umbra) or only part of the light (the penumbra). That dark region is the shadow.

A lunar eclipse. The Sun, the Earth and the Moon are in a straight line with the Earth in the middle, so the Earth blocks the sunlight and its shadow falls on the full Moon. The Moon, which shines only by reflected sunlight, goes dim. If the whole Moon is in the Earth’s umbra, it is a total lunar eclipse; if part of it is, a partial lunar eclipse. It happens only on a full moon, and can be seen from the whole night side of the Earth.
Diagram: as in Figure 11.43: the Sun, the Earth, the Earth’s umbra and penumbra behind it, and the Moon in the umbra, all labeled.

A solar eclipse. The Moon comes between the Sun and the Earth on a new moon day and casts its shadow on the Earth. From the Moon’s umbra the Sun is hidden completely (total eclipse); from its penumbra, partly (partial eclipse).
Diagram: as in Figure 11.45: the Sun, the Moon, the Moon’s umbra reaching a small patch of the Earth and its penumbra a larger area, all labeled.

• a.Light travels in straight lines.
• b.The Earth revolves round the Sun, and the Moon round the Earth.
• c.So the Sun, the Earth and the Moon sometimes come into a straight line.
• d.The Earth and the Moon are opaque, so they cast shadows.
• e.Only the Sun is luminous; the Earth and the Moon shine by reflected light.

• i.It is a solar eclipse: the Moon is between the Sun and the Earth, and its shadow falls on the Earth, so from the shadow the Sun is hidden partly or completely.
• ii.On aunsi, the new moon day.
• iii.A total solar eclipse.

In a lunar eclipse the Earth’s shadow falls on the Moon. The Earth is about 4 times as wide as the Moon, and its umbra, where the Moon crosses it, is still about two and a half times as wide as the Moon. So the Moon takes a long time to cross it: totality can last up to about 1 hour 45 minutes.
In a solar eclipse the shadow is the Moon’s, which is small: its umbra only just reaches the Earth, as a patch at most about 270 km across, and it races across the ground at over 1,700 km/h as the Moon moves. So any one place is in the umbra for only a few minutes, at most about 7½.