The solar system
How many planets are there in the solar system, and what changed?
Eight. Pluto was reclassified as a dwarf planet by the International Astronomical Union in 2006 because it does not meet the criterion of having cleared its orbital neighbourhood.
Which planet is the largest, which the smallest, and which the hottest?
Jupiter is the largest and Mercury the smallest. Venus is the hottest - not Mercury - because its dense carbon dioxide atmosphere traps heat through a runaway greenhouse effect. That 'why' is the point of the question.
Why is Mars called the Red Planet?
Because of iron oxide - essentially rust - in its surface material, which gives it a reddish appearance. Mars also hosts Olympus Mons, the tallest known volcano in the solar system.
Which is the largest moon in the solar system, and which moon has a substantial atmosphere?
Ganymede, a moon of Jupiter, is the largest - bigger than the planet Mercury. Titan, a moon of Saturn, has a thick nitrogen-rich atmosphere. The four largest moons of Jupiter - Io, Europa, Ganymede and Callisto - are called the Galilean moons.
Where is the asteroid belt, and where is the Kuiper Belt?
The asteroid belt lies between the orbits of Mars and Jupiter; the Kuiper Belt lies beyond Neptune and contains Pluto and many other icy bodies.
What is the difference between a solar and a lunar eclipse?
In a solar eclipse the Moon passes between the Sun and Earth, blocking sunlight. In a lunar eclipse the Earth passes between the Sun and Moon, casting its shadow on the Moon. Solar eclipses occur at new moon and lunar eclipses at full moon.
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The Sun, stars and galaxies
What kind of star is the Sun, and how long does its light take to reach Earth?
A main-sequence star often described as a yellow dwarf, composed mostly of hydrogen and helium and roughly 4.6 billion years old. Its light takes about eight minutes and twenty seconds to reach us.
What is a light year?
A unit of distance, not time - the distance light travels in one year, about 9.46 trillion kilometres. Questions frequently test whether candidates know it measures distance.
Which is the nearest star to the Sun, and our nearest large galaxy?
Proxima Centauri, about 4.24 light years away, is the nearest star. Andromeda is the nearest large galaxy to our own Milky Way.
What is a black hole, and what is its event horizon?
A region where gravity is so strong that the escape velocity exceeds the speed of light, so nothing can escape. The event horizon is the boundary beyond which escape becomes impossible. The first image of a black hole's surroundings was released in 2019 by the Event Horizon Telescope collaboration.
Roughly how old is the universe, and what theory describes its origin?
About 13.8 billion years, according to the Big Bang model, which describes the universe expanding from an extremely hot, dense early state. Evidence includes the cosmic microwave background radiation and the observed expansion of galaxies.
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Human spaceflight firsts
| First | Person | Year |
|---|---|---|
| First human in space | Yuri Gagarin, aboard Vostok 1 | 1961 |
| First woman in space | Valentina Tereshkova | 1963 |
| First humans on the Moon | Neil Armstrong and Buzz Aldrin, Apollo 11 | 1969 |
| First Indian in space | Rakesh Sharma, aboard Soyuz T-11 | 1984 |
Why do astronauts appear to float on the International Space Station?
Not because gravity is absent, but because the station and everything in it are in continuous free fall around the Earth. This state is properly called microgravity, and the misconception that there is 'no gravity' in orbit is exactly what the question tests.
At roughly what altitude does the International Space Station orbit, and how long is one orbit?
About 400 kilometres above the Earth, completing an orbit in roughly 90 minutes - so its crew sees around sixteen sunrises a day.
Which spacecraft launched in 1977 is now in interstellar space?
Voyager 1, which crossed into interstellar space after passing the outer planets. It carries the Golden Record, a collection of sounds and images from Earth.
Which two major space telescopes are most often asked about?
The Hubble Space Telescope, launched in 1990 and operating mainly in visible and ultraviolet light, and the James Webb Space Telescope, launched in December 2021 and observing primarily in the infrared from a position far beyond the Moon.
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India's space programme
ISRO questions have grown from a niche topic to a regular feature in Indian competitive exams and quizzes. These are the missions that matter.
Who is regarded as the father of the Indian space programme, and when was ISRO formed?
Vikram Sarabhai, and ISRO was established in 1969. India's first satellite, Aryabhata, was launched in 1975.
What was Chandrayaan-1's most significant finding?
It provided evidence of water molecules on the Moon's surface, which reshaped scientific thinking about lunar resources. It was launched in 2008.
What made Chandrayaan-3 significant?
It achieved a soft landing on the Moon in 2023, making India the fourth country to land softly on the lunar surface and the first to do so in the region near the lunar south pole - an area of particular interest because of suspected water ice.
What was notable about India's Mars Orbiter Mission?
Mangalyaan, launched in 2013 and entering Mars orbit in 2014, made India the first country to reach Mars orbit on its first attempt, and it was achieved at a remarkably low cost compared with other Mars missions.
What is Aditya-L1 studying?
The Sun. Launched in 2023, it is India's first dedicated solar observatory, positioned near the first Sun-Earth Lagrange point so it can observe the Sun continuously without eclipses.
Name ISRO's main launch vehicles.
The PSLV (Polar Satellite Launch Vehicle), the GSLV (Geosynchronous Satellite Launch Vehicle) and the LVM3, ISRO's heaviest launcher, previously known as GSLV Mk III. PSLV is the workhorse with a long record of successful launches.
Which women of Indian origin are most often asked about in space quizzes?
Kalpana Chawla, the first woman of Indian origin to go to space, who died in the Columbia disaster of 2003, and Sunita Williams, known for her long-duration missions and spacewalking records.
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How to revise space topics
- ✓Learn the 'why' behind each superlative. Venus being hotter than Mercury, Ganymede being larger than Mercury, and light years measuring distance are all questions about understanding rather than recall.
- ✓Group the firsts as one memory item: Gagarin 1961, Tereshkova 1963, Apollo 11 in 1969, Rakesh Sharma 1984.
- ✓For Indian missions, learn the mission, the year and the one thing that made it notable. That triple answers almost every ISRO question.
- ✓Watch for misconceptions the questions are built on - 'no gravity in space', Pluto being a planet, the Sun being the largest star.
- ✓Space is a live field, so check current mission status before relying on older material.