Rahul gives unsolicited advice

What is the best location to place a telescope? The first answer that comes to people's minds is a mountain top. Ask them why and they might not know but they just might know that most telescopes are on mountain tops, so there must be a good reason there. Well, in fact there is a reason. Telescopes work better when placed on mountain tops because there's less atmosphere for the telescope to look through, less atmosphere that can smear the images being taken leading to better science. Actually. There's a small correction. Optical and sub-mm telescopes are best placed on mountain tops. Radio telescopes on the other hand can work just as well when placed at sea level. Now. Following up to the first question, What is the best location to place a radio telescope? Because altitude doesn't matter, the main problem is radio interference. Man-made radio interference is the biggest source of noise to radio telescopes. This is the reason why the JVLA in NA is a designa...

Galaxy evolution is a tug of war between the nature of the galaxy (morphology, mass, etc) and nurturing environment of the galaxy (major or minor mergers, ram stripping, etc) and to understand it, we need to understand when nature rules over nurture or otherwise. An interesting way to resolve this question is to study isolated galaxies - isolated in the sense that there are hardly any galaxies in their vicinity. The qualitative 'hardly any' was quantified to create the Catalog of Isolated Galaxies (in 1973) and then revised by the AMIGA people for a more up-to-date study. Understanding the evolution of isolated galaxies inherently tells us more about the role that the nature of the galaxy plays in it's evolution. Today, I was reading up on some interesting papers by the AMIGA people, all three on the HI (neutral Hydrogen) profiles of select isolated galaxies. The three papers can be found here , here and here . I came across this survey recently and only today, as I wa...

For those who don't know, GMRT stands for the Gaint Meter-wave Radio Telescope. Meter because it observed radiation with wavelength of about a meter or about 300 MHz. Ohkay, with that out of the way, let's talk about the actual paper. If you have been following my blog posts, you will understand why studying faint, irregular, dwarf galaxies is important. Faint dwarf galaxies have very low mass and understanding them will help us understand galaxy formation and evolution in the low mass case. Another interesting thing I learnt from the paper, that should've been obvious to me earlier, is that the gravitational force keeping the (gas in the) galaxy together is about the same as that produced by a few supernovae. The reason they are irregular makes sense now because once these galaxies start forming their first stars, which then go on to explode, the galaxy's gas gets pushed out by the explosions. Also interesting is figure 12 from the paper, that tells us that most of ...

As I follow the endless path, looking for references in papers, I came across this - the HI rogues gallery . It is a " Collection of maps of HI in Weird Galaxies and Weird HI in otherwise Normal Galaxies " and wow is it a beautiful collection. The whole reason astronomers are interested in HI (neutral Hydrogen) in the universe is because it is the fundamental fuel that makes stars. Also, there's loads and loads of it in galaxies and in the Inter-galactic medium (theoretically).  And in galaxies, this HI extends wayy beyond the boundary defined by the stellar population of the galaxy. This fact can be used to understand the (baryonic) gravitational potential of the galaxy it is embedded in, and the dark matter halo it is embedded in. If you dig through the gallery, you will come across interesting examples showing  intergalactic debris with no optical counterparts ! This is interesting as it helps us understand the history of the galaxies, their environments and the dis...

I've been coming across a lot of work, in the optical and the radio domain to identify and understand dwarf/satellite galaxies, stellar tidal streams and neutral HI (HI is neutral Hydrogen and HII is singly ionized hydrogen i.e a proton) in the universe. This is one of many such efforts (a few of which I will write about later on) where the authors used the SKA pathfinder telescope BETA/ASKAP to observe the galaxy group IC 1459. The full paper can be found here . Let me first tell you why it's a challenge to observe neutral HI in the local universe and why these results are so interesting, IMO. All galaxies form from HI (again, neutral Hydrogen) but once the galaxy/stars start(s) forming, neutral HI close to the sources of radiation get ionized into HII. Only HI in the outer reaches of the galaxy is left unionized. And given that it's at the edge of the galaxy, it's not nearly dense enough to emit strongly. Don't get me wrong, there is still a good amount of HI i...

Radio and optical telescopes observe the radio and optical portions of the electromagnetic spectrum correspondingly. But radio telescopes are fundamentally different from their optical counterparts. Radio telescopes don't have  CCDs . They don't need finely polished mirrors and they are much, much bigger in size. So. Why the fundamental difference? Let's take a detour and remind ourselves of the wave-particle duality of light. The popular young's double slit experiment is explained using the wave theory of light where as photo-ionization is explained using the particle theory of light i.e using photons. A wave can be described using y = A cos( omega*t + phi ) where omega is two pi times the frequency, phi is the phase and A is the amplitude of the wave. A photon on the other hand can be described using h*nu where nu is the frequency of light. This fundamental difference is what, as you will see in a moment, lead to the differences between optical and radio tel...

I thought I'd take care of my daily blog post business earlier today so, here's the 2 page report I made for a presentation as part of a course on Laser physics & Applications - Astronomical Masers by Poruri Sai Rahul PH5814 - Laser Physics & Applications Masers are the microwave analogues of Lasers. So far, as part of the course, we’ve been looking at optical and IR lasers. Similar to optical lasers, masers can be produced by atomic/molecular species such as Ammonia, Hydrogen, Rubidium & Free electron masers and by solid state masers such as the Ruby maser & the Fe-sapphire maser. While lasers emit in the Thz regime, masers emit in the Ghz regime. Coming to the astronomical significance of masers, Astronomers equipped with spectroscopes started observing very strong spectral lines from astronomical sources. These sources were extremely bright in the radio spectrum while their optical counterparts looked like young stars. This emission was al...

As i mentioned in a previous post , student projects as part of POS was to observe a pulsar & a calibrator using the ORT and infer properties of the pulsar such as period of the pulsar, flux density and dispersion measure (and therefore distance to the pulsar). We were given a list of pulsars (refer to the post aforementioned) & corresponding calibrators and asked to choose one pair.                                             To be noted here that a calibrator for a pulsar cannot be more than +/- 5 degrees away from the pulsar as the atmospheric response is different at different angles. And we need the pulsar & the calibrator to have the same atmospheric response (DUH!). Choosing a pulsar was the first problem. I looked up properties (period, profile width and strength) of each of the pulsars from ATNF   and  NED  and chose a pulsar...

Well, there's enough content about Quasars on my blog. It's about time i talked about Pulsars - though they sound similar, they are in no way related to one another! Simply put, Pulsars are a Galactic phenomenon i.e they are found in the Milky way galaxy and Quasars are an Extra-Galactic phenomenon i.e they are found in galaxies outside out own galaxy - the Milky way galaxy!  And, pardon the technical jargon, Pulsars are rapidly spinning neutron stars which emit radiation from their polar regions. And since their spin axis is different from their magnetic axis, the radiation is perceived/observed only when the magnetic axis is aligned to our line of sight!  Basically, a Pulsar is like a light house. Light is only observed periodically and if you're not standing right in the place - you might not be able to observe it! In the case of the Pulsar, the cone of light is much smaller and the period of the pulses is very small - of the other of milli seconds.  I w...

Sorry for the late update but I've been swamped. Literally swamped with data! Never have i worked on a data set that is 30GB in size, so do accept my apology. Nonetheless, here's what happened in Week 5! So, getting to the end of my work at IIST - i'd worked on the colors of quasars and reproducing the results of a 2001 paper on the same! And the last week at IIST was just to wrap things up and finish the reports! But as you can see from my previous post here , i'd stumbled upon a peculiar (in my opinion) set of quasars! So, i was very interested in understanding them. Here   is my report on the colors of quasars. I'm now tired of making corrections to it and adding more things to it! There will always be something interesting to add or ways to make it easier to understand but i only have so much time! So, yesterday was that day - my final edits to the report! I've also shared a more detailed post on how i acquired the data and analyzed it here . This was...

Very well, a post after 3 months, well 4 months if you don't count the one in feb. And what a semester has it been. The trip to nainital, weekly arxiv papers on astrophysics, the end semester exams, running around looking for a summer project and now that the summer project is confirmed - running around deciding on a project for the next semester. I guess (my) life will always be fast paced (read as awesome). The reason why i've finally come around to writing again is not because i haven't had free time - nope, that argument is always moot unless you're an astronaut on the apollo 13. It's because my mind is finally calm again, now that my end semester exams are over. And in general, now that my semester is over. Alas, the summer of 2013 is upon us. I have always looked forward to the summer, my expectations for a summer haven't always been met (the last one was okay ) and my plans hardly ever worked. Well, probably because most of my plans started with me i...

If you are a complete noob, Radio Astronomy deals with the study of emissions in the radio wave part of the electromagnetic spectrum i.e ~10 MHz to 10 GHz. The emissions might be from the sun, inter-planetary i.e from other planets in the solar system, extra-solar, galactic or extra-galactic in nature. It also deals with the mechanism behind the emission of energy in this spectrum. Various process contribute to emissions from astronomical sources, synchrotron emission causing some of the stronger emissions.  I've already written a lot about what i've done in radio astronomy, the radio jove project that i've worked on, doubts i had regarding the project, the observable range in radio astronomy   and   building a radio telescope . I also implemented a different method of data acquisition (different from the method used in radio jove) about which i've written here .  So, i've already given a lot of opinions regarding radio astronomy. Now, i thought it'd be ...

A really important hurdle to clear in the process of radio astronomy is to decide on a frequency band to listen to and this is not a trivial process. because there is quite a bit of terrestrial communication(comm) signal and extra-terrestrial satellite comm. signals, we can't just build a antenna at any frequency and expect to be able to see extra-galactic radio signals.  This was one of the things i was having a hard time figuring out because there apparently are quite a few bands where we have less comm. noise but no explicit information on the spectrum allocation and the bands alloted specifically for radio astronomy.  I browsed through pages finding partial answers like this  one, which is relevant to australia and gives a brief outline of the bands where one can try observe using a radio telescope without having to worry about comm noise.  but that still wasnt satisfactory because i wanted to look at the indian scenario.  and then i struck gold. The...

Well, as I written before here and here , I am currently working on radio astronomy. I had been putting off working on it for almost 2 years until last summer when things finally picked up some pace. Well, atleast in one sense. The first thing any amateur astronomer interested in pursuing radio astronomy and building a radio telescope should know about is The Radio Jove project. It is an amateur radio astronomy project backed by NASA based on a dipole antenna capable enough to observe radio emissions from jupiter and the sun. As for why this particular frequency was chosen instead of others, i have no answer. The sun is a black body and emits a continuum radio spectrum and jupiter has an emission peak at 20.1MHz. You can read up more about the emissions processes on wiki or google for the, that is not the topic for this blog post.  Now, looking at the material from the project  site , I estimate that the original team stopped updating the manuals after version 1.2,...

A telescope. What do you think it is?! The common perception is that a telescope is a device which is used to look at the stars! Telescopes have mirrors oriented in a a particular fashion which helps us look at stars! Well, this is just part of the story and the tip of an ice berg. A telescope can be described as any device which has the following parts A reflecting surface, to reflect the incoming electromagnetic radiation A receiver which can decipher this electromagnetic signal into a digital signal which we can understand and analyze! So, in the common perception, the reflecting surface is a mirror, one which has been ground to a micrometer finish and one which has been coated to be a (perfect) reflecting surface. And this setup is for observations in the visible part of the electromagnetic (EM) spectrum.  Note :   In the context of this blog post, light will refer to EM radiation of any frequency and not just the visible frequencies ...

So, continuing from the previous part - Building a Radio Telescope, this post will cover the data collection and analysis part of my project. BTW, this post will be very intensive in terms of technical language used. So, be warned. But i suggest you read through it anyway ... There are surely a lot of different ways to go about saving data from a radio antenna and use analyse the data on a computer but well, i couldnt find them. And the method of data collection mentioned  here ,  where they use a modulator and down convert the original signal to the range of Hz and feed this signal into the audio jack of a computer. And using the relevant   Sky Pipe   soft ware, you can analyse this signal for radio bursts from the sun and signals from jupiter. You can save this data from the program onto .png files or .txt files, archives of saved data which are available  here But, i don't think that this is an efficient way to save and analyse this data. So, i suggest...