-Plato
Of all the activities, why astronomy? Have you ever wondered why and how you got into this rather unique hobby? Maybe its your love for the stars and the moon and our mother nature. Or perhaps your deep thirst for the sciences. But in a greater sense, our reasons might be different but we all have three things in common - 1. Our earth, 2. Our great universe and 3. Our love for astronomy.
Finding your way into this noble hobby is the first step into a great journey that will take you to a new level of satisfaction. Learning to love the night sky is the key to enjoying astronomy. Surely no set of expensive equipment can bring contentment without passion and love for the cosmos. Knowing the night sky intimately is like having a relationship - it takes time and effort. But all this will pay off in the long run as we progress in this long journey of exploring the heavens above.
A. Getting Acquainted with the Night Sky
a.1 Stars, Constellations and Asterisms
Surely each of us have taken a glance at a star-filled sky. And I can also assume that many of us have heard of "constellations". But do we really know the relevance of these things? Let us find out more about these so called constellations and the ever famous stars.
First let us discuss stars. Perhaps we all have our own definition of stars ranging from the "little fireflies stuck in that big bluish thing" to the "balls of gas burning billions of miles away" explanations. But really, what are stars? Wikipedia defines star as a "massive, luminous ball of plasma held together by gravity" which is rather very scientific but nonetheless, is the true definition of a star. So all of these little dots that we see during the night sky are stars scattered all over our very very big universe. We see them because they are very big (massive) and they are very bright sources of light (luminous) Some are near like the sun and all of the other stars are very far away. We only see stars during the night because it is dark - while during the day, the sun which is also the star nearest to the earth shines so bright that the light of other far-away stars cannot be seen anymore.
In modern day astronomy, stars are rated according to their brightness or magnitude. Brighter stars are labelled with a smaller magnitude number (-10, 1, 2, 3) while fainter stars are labelled with a bigger magnitude number (10, 11, 12, 20). This is important because constellations (to be discussed next) are composed of the brighter stars usually from magnitude 1 until 6 (maybe) and the background stars (magnitude 7 up) are too faint to be seen by the naked eye but visible in the telescopic field. There is no exact measurement of these magnitudes because atmospheric conditions change from time to time and magnitude ratings can be very subjective, depending on your eyesight, location and pollution.
Figure 1 - Magnitude Chart
So far does this definition make sense? Maybe? But the more important goal here is knowing if these stars can help us in knowing the night sky better. Individually the stars are too many - billions and trillions of them - to make any sense. However, if we group them into recognizable patterns, they may make some sense. This is where constellations come into play.
Before anything else, let us define constellations. Constellations as defined by wikipedia as "an internationally defined area of the celestial sphere". Some may object in this - area? Are constellations an area? I thought that they were patterns that we can see in the night sky by connecting the stars and forming a recognizable image just like connecting the dots of a children's activity book? Well, sadly that is not the case anymore although the latter definition (patterns formed by the stars) was true before. To give you a clearer perspective on this, lets take a look at this very familiar constellation - Orion :
Figure 2 - The Orion Constellation
As you can see in Figure 2 the black dots in the center of the picture connected by the green lines forms the familiar Orion and Orion's belt "constellation". However, in modern astronomy, the actual orion constellation is actually the whole area surrounded by the yellow broken lines. This is a constellation. But this is for scientists who does a lot of research. For the fun and enjoyment, we amateur astronomers can stick to our old and simple definition of constellations. Officially, there are 88 constellations used and recognized by modern astronomy. These constellations are based on descriptions used by the ancient Greeks. Furthermore, Ptolemy described the constellations in detail in Almagest which is one of his works.
One very useful tool for learning is the Stellarium software. The software is some kind of planetarium program that will let you see the night sky at any time of the year in the convenience of your computer. You can download the Stellarium software here and explore it for better understanding of the night sky.
Now after seeing the constellations, you might be saying that it is so hard to memorize them and all the latin names and how they look. We might not even see the whole constellation during the night because of the clouds or smoke or light pollution in our area. Is there an easier way to memorize them? Well, YES, yes there is an easier way to memorize these constellations and the way of memorizing them is called asterisms.
An asterism is not actually a method of memorizing but rather, it is a smaller part of an official constellation. To make this easier for you, here are two examples :
Figure 3 - The "big dipper" asterism
Figure 4 - The Ursa Major Constellation
As you can see from the two examples above, the big dipper is much easier to memorize and see in the night sky because most of its stars are bright enough while other stars in the Ursa Major constellation can be dim and small thus making it hard to see and memorize.
So in summary, we can see stars all over the night sky rated by their magnitude which we organize into patterns called constellations and we often memorize a small part of the big constellations called asterisms. Knowing these will help you gain more understanding of the night sky and in the later part, help you in your actual astronomical observation as well.
a.2 Star Charts
Now that we have learned the basics of the night sky - there are stars which can be organized into patterns called constellations which can also have asterisms which are a smaller part of the bigger constellation - it is now time to bring in the star charts.
But what are star charts? Basically these are charts are like maps of the night sky. Using these charts, you can see the location of the different stars of a certain constellation as well as other night sky objects not visible to the naked eye such as nebulas, galaxies and star clusters. These charts are helpful not only in locating the constellations but also very useful in locating telescope targets that cannot be seen with our eyes. Since the sky is black, we have no other clues except for the constellations. The constellations and stars are there to guide us to a particular object. Let us have a look at this photo :
Figure 5 - Ursa Major Constellation Star Map
As you can see in this sample star map, the big dipper asterism is visible as the green lines in the center while the whole area of the Ursa Major constellation is surrounded by the yellow broken lines. You can see the markings in blue such as M97, M106, M101, M51 and other markings starting with M - these are the so called "messier objects" which are objects such as nebulae, star clusters and galaxies. Using the constellation, the stars and the asterism as a guide, you can find these objects. The star map conveniently combines all these information into a series of pages classified according to constellation or a larger area showing the stars ranging from magnitude 7 stars for the simple star maps up to magnitude 13 and fainter stars for the more detailed star charts. This will all help the amateur astronomer in finding delightful objects in the night sky.
Let us put into mind that the earth is revolving around the sun and rotating on its axis. This regular revolution makes our view of the night sky change from season to season. For example, during the rainy season here in the Philippines, we cannot see the Orion constellation until around late September and the summer months, the Sagittarius constellation is very prominent in the south. To get a better understanding of this, let us see the picture below :
Figure 6 - Earth's Yearly Revolution
The photo above is an example of the Earth's annual revolution. The four arrows beside the four earths represent what direction we are looking at a particular time of the year which is a different portion of our universe. In this principle of revolution, we get a different view of the night sky every season that is changing slowly as the months pass by. As we go back to the same time of the year, we can see the same constellations - for example, if we can see the Orion Constellation high up in the sky during February, then chances are that next Feubruary, it will be up there again because of the principle of revolution.
Now there are some portions of the sky that has very little noticeable changes in terms of the constellations visible, particularly the north and south directions. Since we are rotating from east to west, the north and the south stays at the same place thus the same constellations are visible almost all year.
Hopefully after reading through this blog portion, you are now ready to familiarize yourself with the night sky. Study the constellations and asterisms well and try this simple activity : on a clear night, try to spot as many constellations or asterisms as you can and list them down together in a small notebook with the month and date. You can even draw a sketch of the constellation to let you remember it easily. By doing this simple exercise, you can familiarize yourself with the night sky little by little and reap its benefits when you start observing.
