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  • Writer's pictureSuresh Randadath

Khoj - Edition #3 on 19 February 2023

Updated: Feb 27, 2023

Venue: Casagrand Luxus Amphitheater


Here is a summary of the third edition of Khoj that took place on 19 February 2023. Previous editions can be found here: Edition #1: and Edition #2


What is the smallest particle?



What is outside our Solar System?

Our solar system is very small when compared to our Galaxy and the Universe. Nearest star to our solar system is 4.2 light years away. It takes light 30000 years to reach the center of our Galaxy from our Solar System. Our Galaxy is 100,000 light years in diameter. Nearest Galaxy to us is Andromeda and it is 2.5 million light years away. Universe itself is estimated to be a sphere of 92 billion light years in diameter!


Before Edwin Hubble, everyone though our Universe is nothing but our Milkyway Galaxy. But his discovery of a variable star changed all that. Read my blog Hubble Discovers the Universe for more details.


How do we know how far the stars and galaxies are?

There are six different methods used depending upon the distances, and these methods are collectively called "The Distance Ladder". For simplicity, only 3 important ones are mentioned below.

  • Radar ranging method

  • Stellar Parallax method

  • Standard Candle method



Radar Ranging

Distance calculated by bouncing a radio wave onto a nearby object like Moon and measuring the round trip time using a Radar


Stellar Parallax

Useful for measuring the distance to nearby stars. See the illustration.





Standard Candle

In this method a formula invented by the American astronomer Henrietta Leavitt is used as follows:


Distance = 10 to the power of (m-M-10)/5


m = Apparent Magnitude

M = Absolute Magnitude


An object's absolute magnitude is defined to be equal to the apparent magnitude that the object would have, if it were viewed from a distance of exactly 10 parsec.


The absolute magnitude is difficult to find out for most of the objects as they are so far away. But it can be found out for Variable Stars and Type 1a Supernovae. How that is determined is too complex to explain for the purpose of this blog.


How the size of a galaxy is determined?

This link discusses the challenges in determining the size of galaxies and the techniques used.


Basically, it is done by measuring the amount of light gathered from the galaxy on a large aperture telescope, so as to ensure whatever light that is collected is the complete light from the galaxy. Then standard calculation used for determining how much of the less luminous part of a given galaxy (outer edges) are away from the center and use those mathematical models on other galaxies to determine the size from end-to-end.


Time slows down when you travel at the speed of light


See this video that explains this:



Gravity slows time down


The clocks on the GPS satellites orbiting the Earth moves faster than the clocks on the surface of the Earth. As a result the clock on the satellite needs to be constantly synchrnoized with that on the surface of the Earth.


Likewise, someone on the surface of Jupiter (hypothetically. Jupiter does not have a solid surface) will have their clock moving much slower than that on the Earth, because of the enormous gravity of that planet. But the person on the surface of Jupiter will not see his clock slowing down. It is only slowing down compared to the clock on the surface of Earth.


See this video that explains this:


How was Neptune discovered?

Neptune was discovered due to a perturbance (disturbance) observed in the orbit of Uranus. On the night of Sept. 23-24, 1846, astronomers discovered Neptune, based on mathematical calculations of its predicted position due to observed perturbations in the orbit of the planet Uranus. The discovery was made using a telescope since Neptune is too faint to be visible to the naked eye, owing to its great distance from the Sun.



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