— Vinita Navalkar
Open your eyes under the sky…
Do you want to see the sky in the real sense? You’ve made a good decision. There are literally thousands of objects out there to observe and it will keep you happy and busy for many years…
But haven’t we always been doing that ever since our memories can be traced back? We have even recited ‘twinkle twinkle little star’ for years together watching the sparkling diamonds in the sky.
But while doing so have you ever realised that a galaxy 2.2 million light years away can be seen with naked eyes on a clear dark night? Meteor showers where u can count at least 400 to 500 meteors in one night? Planets, Craters on moon, eclipses and the count goes on…Countless wonders await you any clear night. All you have to do is simply to look up and ask, “What’s that?” When you do, you’re taking the first step toward a lifetime of cosmic exploration and enjoyment!
The starry night is one of the most beautiful sights available. All you need to enjoy the splendour are your eyes. We often forget that there is a naked eye universe that is very rewarding. Many beginners think that since they don’t have a telescope, there is nothing for them to do. That is a huge misconception. There is a universe of things you can see with just the naked eye.
So here’s how, you can go about exploring the heavens on your own…
First thing you need to do is to get out of your brightly lit city and find a place with clear dark skies. One thing you might notice the first time you look up is that, over a period of time, you can slowly see more and more stars. This is called “dark adaptation” and it takes your eye up to an hour to become fully adapted to seeing in low light conditions. Exposure to bright lights, even for a second, can instantly destroy your dark adaptation, needing another hour to adjust again. It’s better to use red torches to give yourself a little extra light if needed. Red light, unlike white light, isn’t as harmful to dark adaptation.
To begin with, you must try to find some easily seen constellations like Orion or Big Dipper. Once you are good enough at identifying these bright constellations, you can move on to other constellations relative to these. But to do so you will require a good sky map. Using a sky map for the first time is often quite confusing. In most cases, the way you hold your sky maps matters the most. So to understand the maps properly you should have some basic knowledge about the night sky and also the conventions used while observing it.
About 6,000 stars are visible to the naked eye under the darkest conditions. All these stars appear to form a sphere surrounding the Earth, called the Celestial Sphere. But in reality there is no sphere, and the stars are actually at various distances from Earth. This comes from the misconception prevalent among the ancient Greeks who believed that all the stars are embedded in the sphere around them. In the modern era, it was Edwin Hubble, who broke the boundaries of the ‘sphere’ in the real sense and extended our Universe to Infinity!
Nevertheless the idea of the celestial sphere is conventionally very important. The positions of the stars relative to each other remain fixed from night to night and year to year. In general, stars in the same area of the sky have no physical relationship to each other, but the very human tendency to impose order upon otherwise random distributions yields patterns of brighter stars, or constellations. Many constellations of the Northern Hemisphere have been inherited from antiquity, but many Southern Hemisphere constellations were defined in the last century to fill in unlabelled regions of the sky. The sky is now officially divided into 88 constellations, which are used in modern astronomy for naming purposes.
From our fundamental knowledge we know that, over the course of the night, stars move across the sky from east to west as a consequence of Earth’s rotation on its axis. But they do so in circular paths around a celestial pole, the place where the extension of Earth’s axis would intersect the celestial sphere. It is easy to find the North celestial pole because it is coincidentally marked by the relatively bright star ‘alpha Ursa Minoris’, also known as Polaris. Simple geometry shows that the altitude angle of the pole star above the northern horizon is equivalent to the latitude of the observer on Earth.
Hold on! Now you must be wondering what this ‘alpha Ursa Minoris’ is? Well, that is how you go about naming each star in a constellation. Ursa Minor is a constellation in the northern hemisphere close to the North celestial pole. And the brightest star in that constellation is ‘alpha Ursa Minoris’ or commonly known as Polaris, or, in the Indian context, ‘Dhruva’. So there is a system to name the stars in a constellation based on their visual magnitude or brightness. It is known as Bayer’s system. It simply puts the stars in decreasing order of brightness and assigns Greek alphabets alpha, beta, gamma and so on in order. So alpha is the brightest star in the constellation followed by next bright star beta followed by gamma.
There are other systems as well to name the stars but right now I do not want to scare you with it. So let’s get back to what we were discussing in the previous paragraph.
If you can have celestial poles in the sky as a projection of your poles on the earth, then similarly you can have projection of equator and other imaginary lines of latitude and longitude in the sky as well. So we do have a celestial equator and crisscross of imaginary latitudes and longitudes out there, to guide us locate the constellations. But these celestial latitude and longitude are called differently. Celestial latitude, known as Declination (Dec), is the angular position north or south of celestial equator and Celestial longitude, measured along the celestial equator, is known as the Right Ascension (RA). Declination is measured in degrees, minutes and seconds of arc. While recognizing that the stars appear to move once around the sky in one day (24 hours), right ascension is measured not in degrees, but in hours, with 24 hours of right ascension equal to 360 degrees.
Well now the question of where to start these measurements from arises? We need a reference point somewhere in the sky similar to the Greenwich meridian we have on Earth. For that we define another imaginary circle in the sky known as ecliptic. Now this circle is nothing but the apparent path traced by the sun throughout the year. And due to the tilting of earth’s axis, this ecliptic circle intersects the celestial equator at two points namely Vernal Equinox and Autumnal Equinox. Out of these two points the Vernal equinox point is considered as the reference point to begin the RA measurements. From vernal equinox, each 15 degree is one hour of RA. Each zodiac constellation is approximately of 30 degrees extension i.e. of two hours of RA. Therefore, 12 zodiac constellations make total of 24 hours of RA equivalent to 360 degrees of circle. Zodiac constellations are nothing special; it’s just that the sun passes through them.
With this basic information about the conventions in sky, you can start using your maps. You will find the network of RA-Dec lines going through the constellations. But wait! You cannot use the map of Mumbai if you have to roam about in Delhi. So make sure you have the right map for right season and time. If you have a single page map of the whole sky or at least half the sky, it will be easier to begin with.
Now try to find at least one of the patterns from the map, or vice versa. If you are observing a winter sky from Northern hemisphere then you will distinctly notice the Orion constellation. Mark that onto your map and try to align your map overhead with the actual constellation in the sky. Once you do so, try to imagine the shape of the hunter with a sword and a shield kneeling. This can be done easily by playing the dot game which all of us have played sometime back in school. And let me tell you all of us are pretty good at it!! All you have to do is replace the dots on the paper by stars in the sky and join lines. Your job is done! You have just identified the most prominent of all constellations- Orion the Hunter!
Now what comes next? Of course the other constellations surrounding the Orion! Try to identify in the similar way by holding the map overhead aligned with Orion. You may not be able to find the exact patterns very easily this time. You may even mix up the stars from one constellation into other. Don’t get frustrated! Remember all it takes to be a good sky observer is imagination, patience, persistence and lots and lots of practice!
Now if suppose there is no Orion in the sky, then what will you do? Do not worry; there will be another prominent constellation of Big Dipper to guide you this time. But now where should you look for this Big Dipper? Look towards your north and you will see a big trapezium with a tail made up of three bright stars. It is known as Ursa Major constellation or more commonly as ‘Saptarshi’ in India. Ancient Indians managed to associate seven sages with the seven bright stars in the constellation. But the people residing in latitudes farther north to India imagined a Polar bear going round the Pole star. This constellation is very important constellation because it can be used as directive to find the Pole star which is relatively less bright. So how do you do that? Simply draw a line through the first and the second star of the trapezium and extend it northward. Some distance apart you will find the pole star!
Yet again what will you do if this constellation sets and you want to find the pole star? (The pole star never sets for Northern hemisphere and some stars, known as circumpolar stars, go around the pole star without setting either. The number of circumpolar stars seen is dependent on the latitude of the place of observation.) There is another constellation in the sky which kind of plays hide and seek with the Big Dipper, known as Cassiopeia. This is almost 180 degrees away from the Big Dipper so one sets and the other rises making things easier for us. You will be able to find this constellation with ease from its distorted ‘M/W’ shape. It has relatively less bright stars as compared to the Orion of Ursa Major stars. Now simply draw a perpendicular bisector for the line joining the third-fourth star and you reach the Pole star!
Doesn’t sky observation seem to be very simple? Simply playing the dot game? Oh yes, it is!! Until you decide to stay awake for the whole night out on an open field, away from your city in bone crackling cold weather!! So before you plan to go for observations, make sure you carry all the important and necessary things with you like warm clothes, enough water and food to last for the whole night, repellents creams and other general medicines. Remember, to actually do a good sky observation you have to be at an isolated place, where you might find lots of insects and other reptiles and lack of any medical help. So be prepared with your own resources.
Once you are thorough with identifying the basic shapes and patterns, the next step you need to take is try and relate them to each other. That is the best way to remember the sky! You can develop your own way of relating different constellations or you can follow the traditional way of linking them by mythological stories. Well, let me tell you it actually works! For example, there is a story of linking up constellations of Andromeda, Cassiopeia, Perseus, Cetus and Cephus. All these constellations are grouped together in the northern part of the sky and can be easily linked and remembered. You can also imagine a pattern other than the traditionally defined pattern for any particular constellation. That will make things easier for you to remember. For example, constellation of Virgo is imagined to be a girl, but to remember it easily you can fit a broken chair in it. Nevertheless you can actually fit a standing girl, once you become an expert in your dot game. There are many other constellations like Sagittarius in which the bright stars help you fit a tea-pot better rather than a warrior on a horse with bow and arrow. Fitting a teapot in Sagittarius actually helps to link it with one of the arms of Milky Way which starts near the ‘spout’ of the teapot. The arm actually looks like a steam coming out from the teapot.
To arrive at a stage where you can identify at least 70% of the sky is not a one night’s job! You have to spend many months together skipping the weeks around full moon day.
The next step you can take is to begin with telescopic observations. Once you are familiar with the patterns as seen by the naked eye you can first try to find some of the bright stars through a telescope or a pair of binoculars.
Initially, it will be very difficult to figure out the direction in which your telescope is pointing and the actual direction you want it to point to, but with practice you will master this skill as well. Another issue you might face in the initial days of telescopic observations is that, the stars which appear dim to naked eyes appear very bright in the telescope/binoculars. This can confuse you to some extent in identifying the stars you see in the field of view of the telescope.
Remember you will not be able to see complete constellation at a time, from any of the amateur telescopes that we use. What you will see is a part of the constellation or in some cases only a single star with the maximum wide angle eyepiece that you use. So you have to learn the skill of hopping from one star to another in the same constellation while watching from the telescope.
It is necessary to know a few things about your telescope as well. To explain different telescopes and their properties, will require a separate article and hence it is out of the scope here. So I will just discuss those points which you will need to start off with. Generally to begin with, you can use a 3 to 6 inch diameter telescopes. This diameter is actually the diameter of the primary mirror/ lens of your telescope. Do not go for higher diameter telescopes initially till you are comfortable with basic handling of it. After you choose a proper telescope, the next important step is to use the right eyepiece for right objects to be seen. The magnification power of the telescope depends on the ratio of the primary objective focal length to eyepiece focal length. Eyepiece of 25 mm or 32 mm focal length is ideal for most of the objects you would like to see. But you can increase the magnification to observe the planets in greater details. Here you use a 9 mm or a 12 mm eyepiece. Remember that the eyepiece size has to decrease to have greater magnification. So if you have the primary focal length to be around 1000 mm, then using an eyepiece of 25 mm will give you a magnification of 40x. It goes without saying that higher magnification reduces the field of view of the telescope. Another important part of the telescope is the finder scope. This is nothing but a small refracting telescope attached to one side of the telescope tube. It is easy to find objects using this finder scope because you can directly aim it at the objects. In most of the cases the eyepiece of the telescope is perpendicular to the length of the telescope which makes it difficult to trace anything in sky.
Okay, you’re pretty sure you’ve finally got your telescope aimed at the object of your desire. The crosshairs of your finder scope are on its exact location, according to the star charts you’re using. Now what can you hope to see?
Probably a lot less than you were expecting but more than the disappointing first impression leads you to believe.
If your target is a bright star, it will be obvious and beautiful but contain no detail. Seen in a telescope, a star is a tiny blaze of brilliant light that looks pretty much as it does to the naked eye, only brighter. Much more interesting, but generally more difficult, are deep-sky objects: nebulae, star clusters, and galaxies. Hundreds of these ghostly glows and subtle smudges are within reach of a modest telescope.
Let’s say you’ve targeted Messier 87 (M87), an enormous elliptical galaxy in the springtime evening sky 55 million light-years away. At the eyepiece you’ll see a small, shapeless, very dim gray smudge floating among a few pinpoint stars. While finding it should bring a thrill of accomplishment, many novices are let down by the sight. (Not to me though!!) “Is that all there is to galaxies?” Will be your first reaction. “It’s nothing like the pictures in the books!”
You’ve just come up against the fact that the human eye cannot perform anywhere near as well as a camera does at very low light levels. Your eye’s view of a galaxy will never match the spectacular photos in books and magazines. But here lies the real challenge. Many deep-sky objects do show a surprising wealth of detail when studied long and well even with your naked eyes.
Observers for last 400 years have been observing this Universe unfold new mysteries. Many good observers from the past have created their own lists of such objects like Messier lists by Charles Messier (M87 is one such object), New general catalogue by William Herschel which are now accepted worldwide with few corrections to them.
People who do the kind of observing I am talking about are not really doing science. But the fact remains that many discoveries have been made by amateur astronomers in the past and are being made today as well. The latest example was added just last month, when an amateur from Australia noticed an abnormality near Jupiter that experts lauded as one of the most significant finds ever by an amateur. Possibly a comet or meteoroid slammed into the planet, was swallowed up in its atmosphere of ammonia and methane, and left a visible scar.
Many deep-sky observers would recognize something of scientific interest if they saw it, and would be able to contact scientists who might want to study it further, but that’s not why most of us go sky-watching. If galaxies were birds, then what we do would be called bird watching, not ornithology. “Cosmic bird watching” might be a good catch-phrase for what deep-sky observing is all about!!