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Sishu Griha Astronomy Workshop - 15 February 2025

Questions and Answers

  1. How does studying the cosmos and stars help our earth in the present time?

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  • Here are some benefits of following astronomy as a hobby:

    • One we realise how lonely we are in this vast Universe, we will start taking care of one another and treat everyone kindly. We will also start taking care of this planet because there is no other planet that can sustain life, as far as our eyes can see.

    • Once we realise that we are very small and vulnerable in this vast Universe we will give up our egos.

    • By studying the cosmos we can identify and track potential asteroids that could hit our planet. Hopefully we could deflect them or destroy them in the future with the help of space technology.

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2. Are there certain stars that we always see in the sky throughout the year if there is less light pollution and can you please send the website to see the star map for that day?

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  • Stars close to the northern and southern poles are always visible throughout the year. These are called circumpolar stars and they appear to lie within a circle that is centered at the celestial pole and tangential to the horizon. Given below are the constellations close to both the poles. You could check the stars in these constellations to get the list of stars that are always visible. 

 

Northern hemisphere: Ursa Major, Ursa Minor, Cassiopeia, Cepheus and Draco

 

Southern hemisphere: Carina, Centaurus and Crux.

 

Few websites that I use for the sky map are given below:

 

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3. In the workshop, Mr Suresh Randadath said that it is more fun to record the astronomical positon of stars and refer that log everyday. However, this turns out to be very boring. How does he say that it is more fun than to just watch the stars through a telescope ?

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  • First of all, I did not say it is fun to refer the log every day :) 

  • Great discoveries of the past was made by astronomers painstakingly logging their observations and comparing them with subsequent observations. This helps in identifying supernovae, comets, asteroids, etc.

  • It also makes astronomy more interactive and helps the astronomers to remember what they observed on a given day. Otherwise one will tend to forget after some time.

  • Since there are hundreds of objects to see through an amateur telescope, unless one make a log of what you have already seen, you will lose track of what you saw vs what you have not yet seen.

  • In summary, there is fun in observing through naked eye or telescope, but there is also fun in documenting what you saw and share it with other fellow astronomers.

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4. What is the best telescope to use to see the planets clearly from earth?

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  • Telescope buying is dependent on the budget you have.

  • Assuming you have about INR 10000 for a telescope, and you only want to see the planets, then best option is to go for a Refractor (3 or 4 inches aperture).  You could also go with a Reflector telescope of 4 or 6 inch diameter. You may check with this vendor for pricing https://www.skywatcher-india.com/

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5. What does the quality of the image of a telescope depend on?

  • It depends on what you are watching.

    • If you are watching Moon or planet, it is dependent on the focal length. A long focal length will give sharper image which is required for planets. For planets the aperture is not very important as the objects are bright.

    • If you are watching faint deep sky objects, then aperture (diameter of the lens for refracting telescope or diameter of the primary mirror for reflecting telescope) plays an important role. The wider the aperture the better.

    • The quality of the eyepiece also plays an important role in the quality of the image.

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6. What time does Saturn set usually?

  • Every rising and setting time of celestial bodies are different. But other celestial entities, including Saturn, the setting time becomes earlier every passing day of the year. It is roughly around 4 min early every day. So in short, there is no usual setting time for these entities.

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7. What is retro linear motion and how does it play a role in astronomy?

  • I presume you are asking about the retrograde motion of planets? If yes, as demonstrated in the workshop, it is about the planets as viewed from Earth, tracing a linear path initially and then suddenly pausing and taking a reverse path for sometime and then again continuing in the forward path. It is an apparent motion due to the orbit of Earth and the planets. Such an apparent motion is possible only if both  Earth and planets are orbiting the Sun. This helped to prove the Copernicus's Helio-Centric theory of our Solar system.

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8. How many stars are in the sky(how many have we discovered)?

  • Milkyway contains about 400 billion stars. There are trillions of galaxies in the universe. Milkyway is a medium sized galaxy. So you could imagine how many stars will be there in the universe. There is no definite count. It is simply countless! The night sky when viewed from a dark location, you could see about 6000 stars with naked eye and nearly 200,000 stars through a telescope.

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9. I have read that there was a recently discovered a supermassive black hole with 4 billion solar masses which existed 2.6 billion years after the universe was created but how did that happen. The feeding limit of a black hole can not allow that?

  • Great question! I presume you are talking about a supermassive black hole that was formed 800 million years after the big bang? If yes, it is a mystery that is not solved yet. It is a dormant blackhole (it is not sucking in matter anymore). But scientists do not know yet know how such a massive blackhole can form in such a short time. It questions the feeding limit (Eddington Limit) as well. This is the beauty of astronomy and astrophysics. We are always discovering new things that makes the existing theories invalid at times.

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10. What is astronomy?

  • A science that constantly rediscovers and corrects itself, based on observation of celestial objects.

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11. Why was the moon in orange colour during Moonrise?

  • Moon gets an orange hue when it is low in the horizon, just like how Sun becomes yellow/orange towards sunrise and sunset. It is because of the scattering of light. The colours with shorter wavelengths (blue end of the spectrum) gets scattered away before the light from the Moon reaches us. This is because when the Moon is low in the horizon the distance travelled by the light ray is longer. Also since it passes closer to the ground more blue light tends to get scattered away due to the dust. So only the colours with longer wavelength (red end of the spectrum) reaches the observer.

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12. What were the two stars that rotate each other and why couldn't we see the other stars that were high up in the sky when it was visible in naked eye?

  • Two stars that rotate each other are called Binary Stars

  • I did not understand the second question. If you are asking why we could not see the other star in the binary system, then I think you are referring to the companion star of Sirius (Sirius B). If yes, then it is because the companion is a white dwarf that is very small and has a low magnitude compared to the brilliant Sirius A. Through better telescopes and better sky condition Sirius B can be seen when Sirius B is farthest from Sirius A (like in 2025)

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13. Do erect telescopes have errors such as parallax error, or zero errors?

  • I did not understand the term "erect telescope". Telescopes are always erect and pointed to the sky. Parallax error can happen if the eye is not positioned perpendicular to the eye piece when viewed through a telescope. For Reflector telescopes, collimation is important to ensure the Primary Mirror and the Secondary Mirror are aligned. If they are not aligned the image will lose sharpness.

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14. How long do you think it is from the time people are going to start living on mars?

  • Elon Musk estimates this to be 20 years from now. But that will be for people to live in enclosed spaces since Mars does not have an atmosphere. Creating a Martian atmosphere will require terraforming the planet, and creation of an artificial magnetic field (without magnetic field, the atmosphere will not last long). That will take 100 years or more.

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15. How are stars born and how do they die? You had briefly touched upon nebulae in the last session, but I am interested to know a little more about it.

 

16. Are aliens real? If yes what is the evidence backing it?

  • My personal belief is that they are real, because though life is very rare in the Universe, there are trillions of galaxies with billions of stars in each of those and many planets orbiting those stars. It is highly unlikely that there is no life in at least some of these planets. But there are no evidences so far. We have not heard from any aliens so far because the Universe is a big place.

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17. Is mars actually a good place to live in? can we actually live on mars?

  • Among all other planets that we know so far, Mars is the most ideal planet to live (comparatively). But it is still a hostile world for humans due to the following reasons:

    • It is very cold

    • It has nearly no atmosphere

    • It does not have a magnetic field to protect it from harmful radiation from the Sun and space.

  • But we can still live on Mars inside a protective enclosure that is shielded from harmful radiation, where we can grow our own food.

  • Terraforming, to create atmosphere and artificial magnetic field, will not be easy and will take 100 years or more for us to have those technology.

  • But despite these challenges, we must try to become a multiplanetary species so that if life perishes on Earth (due to natural or manmade calamities), human species can still survive.

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18. Why do black holes spew out matter in quasars

  • It is not the black hole itself that spew out matter (because nothing comes out of black holes). It is the matter that is in the neighborhood of a blackhole that gets ejected into space due to the tremendous magnetic field that surrounds a blackhole. Depending upon the direction of this magnetic field with respect to the matter in the neighbourhood, the matter can get ejected into space and it appears as Quasars when viewed head on.

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