Some Questions on Astronomy
Astronomy is a diverse topic with branches like cosmology, astrophysics etc. Some topics of these are not known to some people. So, this post will cover some of these questions...
Some Questions on Astronomy
1) Why does time stop in a black hole?
Time appears to stop to an outside onlooker when an object reaches the event horizon - the point of no return - of the black hole.
Black holes are nothing but giant tunnels in the imaginary fabric of space-time. As the flat surface gets curved as we approach a black hole, we feel a force attracting us towards it.
At the event horizon, the escape velocity required to exit the black hole is equal to the attracting force - the speed of light. Hence, one should travel faster than this limit to escape.
However, General Relativity instructs that nothing can break the speed limit and exceed the speed of light.
Hence, the light rays of the object before it enters the event horizon are captured by the onlooker, and any further information is irretrievable.
2) Why are black holes 'black'?
Black holes are not actually black. Black isn't even a colour! Black is a state of colour which occurs when there's an absence of colours. Colours appear when light hits an object and it reflects the respective colours. Black holes can pull in even light. So there's no light reflecting back to space and hence black holes appear 'black'.
3) What are 'Wormholes' and 'White holes'?
Wormholes are hypothetical regions described in the Theory of Relativity. Wormholes are like a shortcut in space between two areas in space. The entrance of a wormhole is a black hole and the exit is a white hole (another hypothetical region). We travel at light speed in a wormhole. So if a wormhole appeared before you, connected to a place 300,000 km away, you could just teleport in a second to that place!
White holes use dark energy to expel the objects that come inside, just like a mirror of a black hole that uses gravity.
4) How is the temperature of the universe 3K or -270 C?
The universe has no molecules to collide with a thermometer to measure the temperature. Hence, the thermometers don't work here. However, we could measure the cosmic rays emitted by the Big Bang.
Around 380,000 years after the Big Bang, the remaining matter condensed into atoms of hydrogen and helium. This allowed the cosmic rays to travel in a straight line. The temperature of these rays was 3000K (Kelvin). But as the universe expanded, the rays got stretched by the Doppler effect 1000 times more and now we have 3K rays left. Since the rays travelled the entire universe, the temperature is assumed to be 3K.
Fact: 1 K = -273.15 C
5) How come the universe's age was found to as 13.8 billion years?
When astronomers captured the cosmic rays or Cosmic Microwave Background Radiation, they studied their properties and found out the universe's age was 13.8 billion years old.
6) Will the moon ever collide with the Earth?
No, the moon will never get close to the Earth and in case it happens, it won't even reach the surface. Since Earth is pushing the moon 3-4 centimetres per year due to Tidal friction, the moon will never get close. But on the other hand, if the moon draws close, there is Earth's Roche limit. The Roche limit (located 18,470 km above our heads) is the point where objects that come nearer will get torn apart by the planet's gravity. The same applies to the moon. So the moon will be crushed into bits and pieces if it surpasses the Roche limit of Earth.
7) What is the reason Pluto is no longer deemed a planet since 2006?
After studying exoplanets, astronomers found out the rules for classifying a planet. According to the International Astronomical Union (IAU), a planet must-
1) orbit any star
2) get enough mass for gravity to clump it into a sphere
3) clear any objects in its orbit
Here, Pluto does follow the first two rules but orbits the sun in the Kuiper belt, which contains thousands of asteroids, comets, meteorites and more. Hence, Pluto is removed.
8) What is the difference between Astronomy, Cosmology, and Astrophysics?
Astronomy is the study of the locations and behaviour of celestial objects. Cosmology is the study of the evolution of the universe or cosmos. Astrophysics is the study of the physical properties of Astronomy.
9) How is the size of the universe 93 billion light-years long despite it being 13.8 billion years old?
The universe is not expanding uniformly, its expansion is accelerating. So it is 93 billion light-years. Check the graph in the post Universe's Doom: Three Theories.
10) What are the Geo-centric and the Helio-centric models?
Before the invention of telescopes, people could only see with the naked eye. They found out that the sun, planets till Saturn, stars and constellations, revolved around us.
They devised a model showing two spheres revolving around the Earth, one is the solar system and the other is the stars and constellations. This is known as the Geo-Centric Model where Earth is the centre of the universe.
But Polish astronomer Nicholaus Copernicus argued about this idea and made changes to it opening a shocking idea - "The Earth is no longer the center of the universe". This new model shows the sun in Earth's position and the Earth revolving around the sun. This is called the Helio-Centric Model where the sun is the centre of the universe.
11) How are Space Telescopes better than Ground Telescopes? Name some examples and their usage.
The images captured by Ground Telescopes are found to be slightly distorted in intensity caused by the wind. Space Telescopes are better since there is no wind in space. Examples are - Gaia, which is used to monitor stars in the galaxy, Kepler, used to find exoplanets, Hubble Space Telescope, a telescope used for space exploration and finally, The James Webb Space Telescope, a successor to Hubble.
12) What are Dark Matter and Dark Energy? Who discovered them?
Astronomer Edwin Powell Hubble stated the idea of Dark matter and Dark energy. According to Hubble, the mysterious energy accelerating the universe's expansion is Dark energy. The huge, invisible clump of gravity is Dark matter. These are not made of regular atoms; we can't interact with them in any way.
13) What is the 4th Dimension or Space-Time?
This is a confusing topic and has its roots in Einstein's Theory of Relativity.
The Theory of Relativity states that any motion happening in this universe is relative to time. This means the walking of people, the motion of electrons in the atom and even you, reading this post is happening due to Time ticking. We all live in the universe or space. In the theory, Space and Time are combined into a new dimension also known as the 4th dimension or Space-Time.
14) What are the binary systems of Stars and planets? Is there any binary system of objects in our solar system?
When stars get close, they apply gravitational force on each other and orbit each other! The same applies to planets and other objects like asteroids and dwarf planets. These orbiting objects are known as Binary Systems. The objects eventually draw close and merge with each other. Examples of Star systems are -
1) Alpha Centauri A & B
2) Antares A & B
3) Polaris A, Polaris Ab & Polaris B
Despite its name, binary systems may contain more than 2 objects! Here in the third example, Polaris is a star also known as the Pole Star. The Pole star has two little companions, Polaris Ab and Polaris B!
Yes, the solar system contains binary systems of objects, which are definitely not stars and planets. Examples are -
1) Binary System of an Asteroid Didymos and its smaller companion Didymos B or Dimorphos.
2) Binary System of a dwarf planet Pluto and its moon Charon!
Many people are unaware that Pluto is a binary system. So, Pluto is in fact, revolving around its largest moon Charon, which is half its size.
15) Is Jupiter a failed brown dwarf?
The largest gas giant in our solar system has a hidden fact. Jupiter is a failed star.
Failed stars are big objects with the same elements required to make a star but don't have surplus mass to trigger the pressure for nuclear fusion.
To become a star with the same mass as our sun, Jupiter needs to have 2000 times its current mass. However, to become one of the most petite stars, Jupiter just needs 80 times its current mass.
16) What are Galilean Moons and what are their facts?
The four largest moons of Jupiter are discovered by scientist Galileo Galilei, hence their name. These moons are Ganymede, Europa, Callisto and Io.
With the reputation of being the only moon in the solar system that is bigger than Mercury, Ganymede (The largest Galilean moon) is also the only moon to have a magnetic field. The Hubble Space Telescope has found evidence of water existing beneath its surface, so Ganymede is also a likely target for human settlement outside Earth!
Europa (3rd biggest of the Galilean Moons) is the only moon to have the smoothest sold surface. The biggest bumps or mountains on Europa measure at least a few meters. Also, it is covered with ice; another likely target for humans.
Callisto (2nd biggest Galilean moon) claims the reputation of being the most heavily crated and the oldest moon in the solar system.
Io (The smallest Galilean moon), is the most volcanically active object in the solar system.
17) What is the mini solar system and why is it called so?
Jupiter and its 79 moons are like a system of moons orbiting the planet in the solar system. Hence it is called a mini solar system.
18) What is the most enormous explosion in the universe?
The explosions on Earth caused by Nuclear bombs and other weapons are negligible to the explosions created naturally. Explosions of this sort from the lowest energy exerted to the highest are -
The sun's nova in its creation, the supernovae of giant stars, the formation of black holes, and the merger of stars, the merger of black holes and supermassive black holes. We can say that the most enormous explosion in the universe would be The merger of two neutron stars or there is a chance that the merger of two colossal black holes might take the place.
19) What is M in M1, M31 etc and NGC, WASP and SETI?
M stands for Messier in M31. This is a list of space bodies discovered by astronomer Charles Messier. It is a catalogue name for the bodies which he found.
Just like 'Messier', NGC is a catalogue name for objects. It stands for New General Catalogue.
WASP is the name of an organisation that discovers planets. It is Wide Angle Search for Planets.
SETI is Searching for Extraterrestrial Intelligence. It is another organisation that looks for signs of alien life on other planets.
20) Is Venus the brightest object in our solar system or not?
Venus is called the morning and evening star because it appears bright in the sky. No wonder why Venus is the brightest planet in the solar system. This is the case for planets.
However, Venus is not the brightest object in the solar system, just only the brightest planet. It turns out that, Saturn's moon Enceladus, which also has an icy surface like Europa reflects about 100% of the sunlight that falls on it. This is more light than the reflection of light from Venus!
21) Will Saturn's rings last eternally or not? Will there be any planet that is bound to have rings like Saturn?
The rings of Saturn are predicted to be destroyed in a few billion years! Even now Saturn is slowly eating its closest ring, The D ring. So they would eventually be destroyed.
Yes, Mars is bound to have rings like Saturn before the entire destruction of Saturn's rings.
At that time, Mars' moon Phobos will reach its Roche limit, where it will get torn apart and form rings.
22) How many moons does each planet have?
As we know, Mercury and Venus are deprived of any moon. Earth has one moon known as Lunar. Mars has two moons called Phobos and Deimos. Jupiter has 79 moons and Saturn has 69 moons. Uranus and Neptune have 27 and 14 moons respectively.
23) How are telescopes time machines?
Telescopes are indeed time machines as the light they are receiving is emitted in the past. If a star is 2500 light-years away, we would only receive any intensity changes after 2500 years. Similarly, any changes in the sun would only be visible after 8.2 minutes. Even though light is the fastest thing in the universe, it needs time to go from one place to the other.
24) What are the different types of galaxies?
The galaxies have types according to their shape. These are-
- Spiral Galaxies
- Barred-Spiral Galaxies
- Elliptical Galaxies
- Irregular Galaxies
Barred spirals have a bar-shaped gas region near their centres. But the rest has the shape of a loop. Examples - The Milky Way galaxy
Elliptical galaxies take the form of squashed balls with unusually bright centres. Examples - IC 1101
Irregular galaxies do not take any specific form. Examples - The Antennae Galaxies
25) What do you mean the universe is 'expanding'?
The universe is not expanding into new space, but it means that new space is being generated. This creation rate is at 73 km/s / megaparsec.
26) Why is Mars looked at as a place for the settling of humans in the next generations? Are there any complications?
Mars is a target for future human settlement as it has ice on its surface and is created with smooth terrain like on Earth. But Mars lacks oxygen and has 95% Carbon Dioxide in its atmosphere. Also, the temperature is very low.
Apart from complications under the control of humans, Mars has no magnetic field! The magnetic field protects us from the sun's harmful radiation.
Well, Mars is suspected of hosting aliens on it. If this is true, then Mars might not be an excellent place for settling as the Aliens might wage wars on us. However, this statement is just an idea, not reality.
27) What is a tesseract and can we draw it on paper?
Tesseract is a 4D cube. Let's understand the shapes of dimensions first.
A dot is 0D (no length)
A line is 1D (only length)
A plane is 2D (length & breadth)
A cube is 3D (length & breadth & height)
As seen in Q13, The changes of an object in space are relative to time. So a 4D cube would result in a cube that looks like it's in two positions at the same time and looks wavy.
Yes, it can be drawn on 2D paper. Just connect two cubes with lines just like you connect two squares while making a cube. It would look wavy and bizarre, but you know everything looks weird when they are drawn on an object that is located in the previous dimension.
28) Why is the sun shining despite the temperature of the universe?
Contrary to popular belief, the sun is not a ball made of fire, but a ball of glowing gas. So the sun is still shining despite the freezing temperatures it is surrounded with.
29) What are Dyson Swarm and Dyson Sphere?
Dyson Sphere and Dyson Swarm are ideas created by mathematician, Freeman Dyson. The Dyson Sphere is a sphere-shaped megastructure that is built around the sun. This huge and hollow ball is used to store the energy exerted by the sun and convert it for our use. The pros of this megastructure are that it captures all of the energy. The cons of this mechanism are that it requires a substance that is resistant to solar radiation and is very strong. This substance is also required in large quantities. But the substance we are talking about is much stronger than anything found on Earth. The cost of the construction would be gargantuan. Also, it would be struck regularly by comets and meteorites that may push it closer to the star.
Dyson Swarm, on the other hand, is a swarm of small satellites that surround the sun or other planets. This mechanism captures most of the energy given out. Both megastructures are hypothetical and there's a chance of them being built in the far future.
30) Will the Sun become a black hole?
It is a straightforward answer that the Sun will never become a black hole. Why? Because to become a black hole, the Sun needs to be 20 times more massive!
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Aditya VN Kadiyala
Very useful information, nice presentation!!!
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