Amateur stargazing (21_5_14)

I did some stargazing tonight after a long time. Throughout the summer, it has been cloudy and hazy. However, tonight was a clear sky with little haze. I took my 120mm diameter 1000mm focal length reflector telescope out to my office terrace, as it has the best view. I have a single plossal zoom eyepiece that I use for all my stargazing. It is a Seben zoom eyepiece, 7.5-22.5mm focal length.

I started out by aligning my finder scope to the optical tube. This is a very important step as it is quite difficult to find any celestial object without using a finder scope. To align the finder scope, I first locate the moon and get it in the telescope's field of view. This is much easier than locating point sources such as stars. I then adjust the alignment screws on the finderscope to bring the moon to the centre of the finderscope's field of view. Alignment complete.

Tonight, the moon was a beautiful waxing cresent (always reminds me of Cheshire the cat). The interface between the bright and the dark part of the moon, known as the terminator, exaggerates all relief features on the moon's surface by casting long shadows. To a person standing near the terminator on the moon, it would be sunrise or sunset. Craters, hills and cliffs look best near the terminator and make you feel like your telescope has very high resolution. It's always a delight to look at moon's craters with high magnification. I start off with 22.5 mm, centre the moon in the field of view and then zoom to the desired level. When you zoom using the seben eyepiece, you have to adjust the focuser to bring the image to a sharp focus.

Next I looked at Venus. Venus is the second brightest object in the night sky and is thus easy to spot. However, it is too bright to be viewed directly. It only appears as a very bright white disk/oval like shape. Venus is currently in the Gemini constellation. Tonight the Venus was in half phase and thus appeared as an oval. Even after zooming to 133x Venus was too bright and I could not spot any details. Next time I will use a filter to reduce the brightness when viewing Venus.

Next I observed Jupiter and its moons. Jupiter is currently is between Leo and Gemini. Jupiter is fun to observe and even with an average telescope, you can see 2 bands on jupiter and four of its moons (Io, Europa, Ganymede and Callisto). These four moons usually appear in-line because of their plane of orbit. Tonight all four were on the same side, with Io nearly on top of Jupiter. Sometimes, you can see the shadow cast by one of jupiter's moons on its surface! I could see 3 more very faint moons, but sometimes its hard to say whether I imagined it or if it was really there.

I then looked at Saturn, near the Scorpio constellation. Saturn is probably the best planet to look at. Its rings are very clear and about 4-5 times its diameter. It appears yellowish in colour. With my telescope I could see 2 of Saturn's moons. One directly in line with its rings and one perpendicular to them. Cassini's division is hard to see, but as conditions were favourable tonight I was able to see it. At high magnifications, it is hard to focus saturn as it appears blurry anyway. Also, my Seben eyepiece shows plenty of chromatic aberrations as I increase the zoom.

I spent quite some time looking for M4 globular cluster, near Scorpio. Usually it is easy to find, but since Scorpio's altitude was very low, I could not locate it.

Finally I looked at M5 globular cluster, in the Serpens constellation. Star clusters are fun to spot as they present a challenge. Light pollution in cities combined with the diffused glow of star clusters force you to use averted vision to observe them. The retina has lower concentration of rod cells(light sensing) at its center point(fovea) as compared to the surrounding region. Thus when you directly stare at a very dim object, you may not spot it, whereas staring somewhere near the dim object, suddenly brings it to light. However, this technique makes looking for dim objects very hard. But, M5 is a relatively easy star cluster to spot as it has a moderately bright star very close to it. So once you spot the star, you see the cluster using averted vision. Through my telescope, M5 appears as a greyish haze. It actually comprises of thousands of very faint stars concentrated in a small region. Thus, it is not very appealing visually, but it is very photogenic.

professional pic of M5 globular cluster

My viewing session was around 1.5 hours long. When I'm done I close the optical tube with my solar filter, to prevent dust settling on the mirrors.

Goto and tracking function will help me not only view but also take pictures of these celestial objects. I'm hoping to finish upgrading my goto mount in time before monsoon sets in.

Until next time,
Clear skies!

My attempts at spin casting a mirror

Telescopic mirrors are parabolic(almost concave) reflectors whose main aim is to gather as much light as possible. The light incident on the mirror is focused by the mirror's curvature at a single point on its axis. This is the focus of the mirror.
Telescopic mirrors are typically made of glass as it has a low coefficient of thermal expansion. This means that during temperature variations, the shape and exact curvature of the mirror would not be affected.

Telescopic mirrors need to be very precise and are thus ground to precision. This is a very lengthy and time-consuming process. Making mirrors manually, by grinding it to a finish is even more so. It took me 22 hours of grinding and 4 hours of polishing to make a small 4" mirror at IUCAA. So, I wanted to make another mirror, but better this time and also in an innovative way. The ideal shape for the primary mirror of a reflector telescope is parabolic. So I thought of spin casting the mirror.

The main idea in spin casting is to heat the substance till it melts, place it on a rotating platform and spin it as it cools slowly to give it the desired curvature.
A simplified model for this is as shown

In this simplified model when steady state is achieved, no matter which material is used(glass, aluminium, etc.) the focal point will be at g/(2w^2) in metres. Viscosity would not matter as the fluid would not be moving at the steady state.
The equation of a cross-section of the mirror would be a parabola

where w is the angular velocity in radian/sec and g is acceleration due to gravity.
For my requirement(focal length~1m) the angular velocity was 28 rpm.
I used a system of pulleys to reduce the rpm of the ac motor from 722 to 28 rpm. My uncle had a fancy 3-phase ac motor speed controller that could very accurately control the rpm of the motor by changing the frequency of the ac supply(variable frequency ac motor driver). I made an optical tachometer using infrared sensors and an arduino board to measure the exact rpm and compensate for any discrepancies. So, all that takes care of the curvature. Now for the setup:

I made a small turntable out of plywood and attached a ceramic tile on it using steel plates for insulation. Using similar bent steel plates I made a holder for the crucible/mirror cell. For the crucible I used a 2 inch section of a steel pipe of diameter 120mm with steel base welded on. It was crude but that did not matter as the mirror's surface would never come in contact with the mirror cell.

Mirror cell/crucible

Optical tachometer

What I thought was that on heating the glass, it would become very fluid and on spinning it, it would acquire the exact curvature. In fact I thought the surface finish would be so good that I probably would not have to grind it at all. I knew of a liquid mirror telescope at an observatory that uses spinning mercury(liquid) as the primary mirror. This re-enforced my faith in spin casting. However things did not work out the way I had planned...


More in a later post..

Upgrading my goto telescope

Hello folks,
I am currently in the process of upgrading my goto telescope mount which I built last summer. I really enjoy building things and am rarely content with what I have made. As I was using the goto telescope, I kept thinking of ways to improve it and modify it. A few things that I learnt are:

• First and foremost the telescope should be very easy to set up and should be operable even without the motors. My first design was restricted to being controlled by a computer/smart phone(battery operated) at all times. There was no convenient way of manually using the telescope. If I wanted to tilt the telescope, I had to rotate the worm gear manually rather than directly move the optical tube by hand. This was a big bummer and it adversely affected my casual usage of the telescope. The newer mount will be very easy to use even without motor power as the motor will be disengaged when not in use. This will keep the optical tube free to rotate by hand. It will simply click into place when required and provide the drive.

Older telescope(grey) with the (black)goto telescope.
Notice the size difference..

View of the worm gear on the goto telescope

     

• Using my previous telescope, I could set it up and start viewing the moon or a planet (say jupiter) within 3-4 minutes. Whereas with the goto telescope, it would take me 15 min just to get started. 
• The goto telescope was too short and could not be used from the ground. It needed to be kept on a table-top to view anything. 
• The step angle was too large,ie when slewing the telescope slowly, the motion would become jerky rather than a nice smooth movement. I plan on fixing this by making a worm gear with a much larger gear ratio. The current gear ratio is 25:1 giving a step angle of 0.072 degrees. The new gear will give a ratio of 180:1 and a step angle of 0.01(upto 0.000625 degrees using microstepping).

So, to upgrade the telescope mount:

Step 1: Destroy earlier mount!

I will keep updating as I progress with the upgradation. 

Follow my blog to stay tuned!

NVS after 10th: Pros and Cons

To all the Nath Valley students interested in science,

After the 10th grade I faced a tough choice of whether to continue in Nath Valley in 11-12th or not. Hopefully this article will help you make that choice.

I am interested in Physics, Computer Science and Mathematics.
For my Undergrad. degree my first choice was(and still is) a good college in the US as they undoubtedly have better Basic Science courses due to much better facilities, funds and faculty. If I do not get admission to the top 10 universities in the US, in my desired field, I would prefer a very good Indian University such IISc or IIT.
Admissions in the US depend on a variety of factors. First of all you have to get very good SAT scores and SAT Subject Test scores. Further you can appear for AP exams to show that you are good at that subject and ready for adv. college level courses. Getting very good ranks in Olympiads such as the National Physics, Mathematics or Chemistry Olympiads(NSEP:-INPhO, RMO:-INMO, NSEC:-INChO, ZIO:-INIO) and representing your country in International Olympiads also definitely counts. Besides Academics, you need lots of co-curricular activities of significance such as participating in debates, MUNs cultural programmes, state/national level sports, volunteer work and so on. Also in your college application, teacher's recommendations play an important role.


Pros of continuing in Nath Valley:

• Colleges in the US would definitely prefer CBSE board, which is used in over 15 countries, over Maharashtra State Board(duh!)
• You can get good college recommendations from teachers in Nath Valley who have known you for many years.
• Preparing for SAT is much easier in NVS(esp. the English Section) as you can get your essays corrected and clear your doubts from the English teachers, who would definitely know a lot more than State Board English teachers(eg. the SB english teacher says, "I am English Post-Graduation")
• You get opportunities to participate in co-curricular activities
• You can get leadership opportunities such as becoming a part of the Student council.

However,
College admission in India is almost solely dependant on IIT-JEE scores(for eng. colleges) and JEE preparation definitely requires some tuition such as Bansal, Gurukul etc. If you do join a tuition, then school timings clash with class timings, what is done in school seems repetitive as it has already been taught in the tuition and you do not get enough time for self-study. Thus it is better to join a college like SB or Deogiri that do not require attendance. And this arrangement is really beneficial. You have 3-4 hours of tuition per day and can put in 5-6 hours of self-study and practice, and yet have time to play an hour every day or pursue your hobbies.


Cons:

• TAKES UP TOO MUCH TIME
• Not enough time for self-study
• Not enough time for pursuing hobbies/sports
• Tuition homework + School Homework becomes a burden. 
• Repetitive and boring
• Does not really serve any purpose as far as IIT-JEE preparation and college admission is concerned
• It is about 10x more expensive than state board schools. One month's tuition fee in Nath Valley is equal to the entire year's tuition fee in SB.

Here is my schedule with Bansal and NVS:

6:45                Wake up

7:40-8:30       Bus journey to NVS

8:30-1:00       School(+bansal hw + studying for olympiads) 

1:00-1:45       Bus Journey back home

1:50-2:10       Lunch at home

2:15-2:55       Study and Bansal HW

3:00-6:00/6:30 Bansal

7:00-9:00       Study(School+Bansal+olympiads/SAT)

9:00-9:30       Dinner

9:40-~10:30   Study or Astronomy

10:30              Sleep

This is how your schedule will be(more or less) if you continue in school and join a tuition. I would have liked to have more free time. It is fairly hectic and feels very restricted. 

That said Nath Valley+Tuition wont adversely affect your performance in either of them. I have been 1st in Nath Valley throughout 11th and have maintained a class rank <=3 in Bansal.

Ex-students, classmates and juniors, please comment and add your own pros and cons to the list to make this article more comprehensive.

 

How to prepare for KVPY

I appeared for the KVPY exam in 11th and cleared the written exam as well as the interview. So, I thought I should share my experience to help others who wish to take the exam.

The KVPY is a scholarship-exam for science stream students to encourage them to take up pure-sciences. The SA stream written exam has four subjects: Maths, Physics, Chemistry and Biology. It is a 100 mark paper with equal weightage to each subject. In 2014-15 the pattern of the paper was as follows:

Part I (60 marks): one-mark MCQs 

• Maths:15 ques
• Physics:15 ques
• Chemistry:15 ques
• Biology:15 ques

Part II (40 marks): two-mark MCQs

• Maths: 5 ques
• Physics: 5 ques
• Chemistry: 5 ques
• Biology: 5 ques

At first it feels unfair that there is no choice between maths and biology, however I feel that if you are interested in science, then you should learn both of these at least till 11th.
The syllabus for maths is not very different from 10th grade, but the level of difficulty is higher. Thus Biology students will have to practice solving such questions.
The Biology section is fairly easy. Since I could not take both maths and bio in school, I was initially concerned. However, looking at the previous years' papers I noticed that the bio questions were not that difficult. Most of them are based on class 10 syllabus and the rest on life processes in cells and genetics.

Physics and Chemistry are fully 11th-12th based. You really have to prepare for just these 2 subjects.

In the summer after the 10th board exams, my friends and I started studying 11th std. physics from HC Verma's Concepts Of Physics. We were studying for KVPY as well as NSEP and so focussed most of our time on physics.
We would read and try to understand as much as we can from HCV and clear each others doubts or look up our doubts online. We made it a point to understand all the derivations and then try to derive the formulae ourselves. After reading up on a particular chapter, we solved the Exercises given at the end of the chapter and then solved further questions on the same topic from I.E. Irodov's Problems in General Physics. Solution books are available for both of these books and are immensely useful. (While solving Gravitation, we learned many substitution techniques required in calculus, using the solution book for Irodov!)
In this manner, we finished most of 11th st. physics in 2 months or so and then started 12th std. physics. For class 12 physics I referred to Sears and Zemansky's University Physics for better explanations along with HCV.
Having study partners really helped me as it kept me going at that pace. Sometimes my friends were ahead of me in the syllabus and thus I had to study even if I felt lazy or tired. Sometimes I gave them the incentive to study. Also, studying in a group and solving questions together is really fun. We would solve physics questions, maths olympiad papers and occasionally even watched movies.

The chemistry section is pretty hard. I am not very interested in chemistry and find it hard to study on my own. So I pretty much neglected it...(and paid for it. I lost only 3 marks in physics and around 12 in chemistry). The Chemistry section has a lot of questions from General Organic Chemistry. However, you also have to study other chapters like gaseous state, thermodynamics and equilibrium.


The written exam is what really counts. The weightage for written is 75% and 25% for interview. Usually the cutoff is low for the written exam(40s out of 100) but that is where you can really score. So one should prepare well for the written exam.


There are a lot of conflicting posts about the interview for KVPY. Many claim that it is very strict and the teachers are mean and out to there to get you and so on. Well, it isn't.
The interview was very friendly and casual. The interviewers were very amicable and supportive. There are 2 interviewers per subject, so 8-9 interviewers. The interview lasted about 40 minutes.  They asked me about 10-12 questions subject-wise. First they read my self-appraisal form and asked me about my science-exhibition project(Automated Telescope). Then one of the physics teachers asked me solve a question on the whiteboard showing all the steps. It was a simple question and I think he just wanted to see how I tackled the question rather than my ability. The question was find the total distance travelled when a ball is dropped from a height 'h' with coeff. of restitution 'c'. The other physics teacher asked me what I knew about Quantum Mechanics and why I liked it(self-appraisal form). When I made a mistake in something, the teachers did not say I was wrong but instead guided me to the right answer. The bio teacher asked me vague questions and the maths teacher only asked me one question(what are limits?) The chemistry teacher asked me a few questions which I was unable to answer to his satisfaction.

I felt that I could have done much better than I did in the interview. I was anxious about the outcome and kept thinking that the interview didn't go so well.
However, about 6 weeks later(mid March) when the results were declared online, I found out that I had cleared the exam with an AIR of 92.
Of the four of my friends, with whom I studied, 3 were selected.

I feel that the interview does not really affect the results by a lot. One of my friends said in the interview that he wasn't even sure if he wanted to do pure sciences! and he was still selected.

I hope this was helpful and informative.
All the best for KVPY aspirants!

The making of a goto telescope

Hi everybody

I recently met Mr. Tushar Purohit from IUCAA Pune on his visit to
Aurangabad and got an opportunity to show him the automated telescope
I made. Impressed, he said that he would publish an article about how I
made the telescope, in an international astronomical magazine that IUCAA has
started.
So, here is that article:

“Making of a goto telescope”

I am Anant Kale, student of class 11, Nath Valley School, Aurangabad.  I am interested in astronomy, physics, mathematics and I wish to pursue higher studies in physics.

I got interested in Astronomy after joining the astronomy-club in our school which involves students in activities such as star-gazing, watching special celestial events and making telescopes. I would specially like to thank my physics teacher Mr. Suryavanshi because of whom I was able to attend a telescope making workshop in IUCAA Pune.

Last summer, I set out to make a low cost, fully automated, ‘goto telescope’ using a 100mm diameter primary mirror with a focal length of 650mm. It has full ‘goto’ capabilities and can be operated using any smart phone, laptop or tablet pc.

The user can enter coordinates in altitude-azimuth form or equatorial form using a smart phone or laptop and the telescope will slew to the desired coordinates. The total cost of this telescope was approximately Rs 7,500 and took 2-3 months to make.

The primary mirror was made at a mirror making workshop in IUCAA, Pune, under the guidance of Mr. Tushar Purohit. After manual grinding and polishing the glass for about 20 hours, the integrity of curvature of the mirror was tested using ronchi test and the mirror was coated with aluminum.

The brightness of images formed in a telescope is proportional to the square of the aperture. Thus it is exponentially more difficult to locate faint objects on small telescopes. Goto capabilities are thus very valuable for amateur astronomers using small aperture-telescopes. They enhance the viewing experience by eliminating the time and effort often spent in locating objects of interest, in the polluted urban skies.

Making the telescope was an enjoyable and informative experience. It helped me learn many things about telescope-making, optics and electronics.

The optical tube is a standard size PVC plumbing pipe attached to the mount using a metal clamp. The clamp is a 2mm thick steel plate bent into a circular shape with two nuts on diametrically opposite ends to bolt the supports. The telescope mount is of Dobsonian design which is simple to make and easy to motorize. The mount is small and compact with a height of 18 inches. It can be used as an alt-az mount as well as an equatorial mount. When it is placed on a surface parallel to the ground it behaves as an Alt-Az mount; when placed on an inclined surface with angle of inclination equal to altitude coordinate of the pole star, it can be used as an equatorial mount.

To motorize the telescope, high precision stepper motors were used for both axes (14PM-M201 MINEBEA CO. stepper motor, 200 steps per revolution) giving an accuracy of 0.075°. All the electronics are controlled using a microcontroller Arduino Due. The Arduino series microcontrollers are versatile and easy to use. They can be programmed using C++ language. They can receive inputs from sensors, serial monitors or computers and give desired outputs. The Arduino Board was programmed to receive the coordinates of the celestial object as input from a laptop or even smart phone.

The microcontroller calculates the number of ‘steps’ that the stepper motor has to rotate depending on the step angle and gear ratio and sends the corresponding output to a motor driver. In this case there are 200*25/360=13.89 steps per degree. The motor driver comprises of a dual H-Bridge integrated circuit(L298). It provides the necessary power gain to the output from the Arduino. As the motor rotates the telescope slews to the correct coordinates.

For the altitude/declination drive, a stepper motor with a worm gear pair of gear ratio 1:25 was used. The slew speed was set to 2 degrees per second. However there were several difficulties while making the azimuth/RA drive as it required a significantly more powerful motor while maintaining precision. The first attempt using the same stepper motor with a worm gear was not satisfactory as it could not provide enough torque. In the modified design, the drive will be provided to the circumference of the telescope instead of the axis thereby reducing the torque-demand.

   

For convenience and ease of use, a hand-held controller was added to operate the telescope manually. This is very useful when the coordinates are not known and to make finer corrections to compensate for drift.

This whole telescope making experience has been very instructive and enjoyable and has further increased my interest in astronomy. I hope to set out on bigger and better projects in the future.

  

 

PICTURES TAKEN FROM MY TELESCOPE

 

Project Telescope

Overview

In the summer break after my 10th boards, I took up the ambitious project of making a fully automated, goto-tracking telescope from scratch. In my first telescope I had used ready-made optics and an old telescope mount that I got from my school. After using it for a few months, I realised that it was very hard to locate distant and faint celestial objects from within city limits. Also it was difficult to keep the telescope aimed at a particular object when using high magnification. This was because of the Earth's rotation. At high magnification, the Earth's seemingly slow rotation(1/1440 rpm!) makes stars and planets zoom right across the field of view in a matter of a few seconds. So, I decided to make a tracking, goto telescope.

There were several stages to this project.

Firstly, making the optics. I wanted to learn how to make a telescopic mirror and so decided to use the mirror that I would make. To do so, I went to a 6-day training camp to IUCAA, Pune, India. There I was instructed by Mr. Tushar Purohit. He taught me how to grind a mirror blank to get a perfectly smooth spherical shape and showed me how to polish a mirror to prepare it for aluminizing. 

Secondly, the telescope mount. I wanted to make a sturdy mount that was easy to operate and so went for a dobsonian design. This is a form of an altitude-azimuth mount made popular by John Dobson (hence the name dobsonian). I made several modifications to the original design to incorporate the gears and motors required for automated movement.

Third step was the automation. Here ‘Automation’ means that I should be able use the telescope hands-free, with very high precision. I can enter coordinates of a celestial body and the telescope will automatically point to it. The idea was to have a system that is easy to setup and use and also one that would not prevent manual operation. So I used two stepper motors for the two axes which are controlled using an Arduino microprocessor. The Arduino microprocessor is a versatile programmable board with several applications. It can communicate with mobile devices(smart phones, tablets, laptops etc.) as a serial monitor. So I have used a smart phone to receive the coordinates. Once it is correctly positioned, the telescope tracks the movement of the stars, so that they remain in the field of view.

As this is an elaborate project, I will explain each part in detail in separate posts.

Stay tuned for the latest posts.