Planets

            Planets are the nearest and brightest celestial objects in the night sky. They are a good start for novice astronomers as they are easily visible and their movements are really interesting. As was mentioned in the earlier posts all the visible planets of the solar system (all the planets except Neptune) appear along a line known as ecliptic. Now here is a simple explanation why it is so:

The Solar system (not to scale; Pluto is no longer a planet)

         
       The solar system is nearly planar i.e. all the planets lie in a same plane. Now if you are standing on earth the planets will all be in the same line which is known as the ecliptic. To understand this look at the diagram below:

                Now if we remove the orbits, the sun and the two planets will appear in one line (as seen from the earth {blue}):

 
               Similarly the outer planets will also appear along this line:

           Thus from earth the planets and sun will always appear along the line called the ecliptic line. This line can be easily traced along the sky as it is the line along which the sun and moon moves. Once you establish the location of this line the other objects can be easily seen in relation to it. The planets appear along this line as non twinkling objects which differentiates them from nearby stars. The planets move relative to their background, you can easily plot this movement and it can be very exciting and interesting.
           Now that we have determined where the planets will appear now let us see when they will appear. The orbital lengths of all the planets are different as is the time taken by them to complete their orbits. They can be ahead of earth in their orbit or behind ( all planets revolve in the same direction) at any time. If you see the above diagrams you will notice that the planets appear either to be ahead of the sun or behind it. The planets ahead of the sun appear in the sky just before the sun i.e. in the morning whereas the planets behind the sun appear at dusk. If a planet is crossing in front of the sun or behind it relative to the earth it will not be visible until it is at least 10 degrees ahead or behind the sun. Thus the planets can either be dawn planets of dusk planets.
            Thus up-till now we have established:
           1. All the planets appear in the ecliptic line.
           2. They may appear early in the night the so called dusk planets or late in the night just before the sunrise the so called dawn planets.
            I will finish this post with a brief overview of the individual planets

            Mercury:

             It is the closest planet to the sun with the smallest orbit. It is most of the time in front of or behind the sun relative to earth. It does not get 10 degrees from the sun( the minimal angle for a planet to be visible) often and is an elusive planet.

            Venus:

              The brightest object in the sky following the sun and the moon and one of three objects capable of forming a shadow. It appears as a dawn planet for half the year and a dusk planet for the other half. It was thought to be two different planets because of this.

             Mars:

              The red planet, getting its distinctive color from iron oxide alternates with venus in being closest to us. The most visited of our neighbors it appears in the night sky as a red object. It just passed through the Leo constellation.

             Jupiter:

               The largest planet of the solar system by far, this planet is the first of the gas giants (the first four planets are called rock planets). The most bright object after Venus it is visible as a morning planet nowadays, it was one of the three planets that came together about two months ago. On its surface there is a storm having a diameter of two and half earths and it can be seen easily with a normal telescope. It is called the great red spot.

             Saturn: 

                The second gas giant, and the second largest planet, Saturn is renowned for its rings. Easily visible with a telescope they have fascinated astronomers for centuries. They are in fact belts of dust and small particles in orbit around Saturn.

             Uranus:

                The 7th planet of the solar system it is the last planet visible with the naked eye. Similar in size to and consistency to Neptune, scientists sometimes call them ice giants. It is dim planet and moves slowly through the night sky.

             Neptune:

                 The second of the ice giants and fourth of the gas giants, it is the only planet not visible to the naked eye. It is the farthest planet of the solar system. The objects beyond it are called Transneptunian objects. It is the coldest planet of the solar system. 

Easily obervable celestial objects over Pakistan nowadays (19/5/12)

         Nearly all the objects visible in the northern hemisphere can be seen from Pakistan provided they appear during the night. Nowadays the following objects are visible in the night sky in Pakistan.

Planets:

Beginners should first try to observe planets as they are easily visible and interesting. The planets always appear along the ecliptic line ( the line of the path of the sun and the moon, the red dashed line in the astroviewer software).
A differentiating feature between planets and stars is that the planets do not twinkle while most of the stars do so.
Three planets are visible nowadays:
1. Venus: visible from 7:30 pm to 8:15 pm (It will be visible till the end of May)
  Venus is the brightest object visible in the sky following the sun and moon (mag -4.35), that is why it can be seen before any other planet or star and even before sunset!! Venus is either visible at dawn or dusk. It will be observable at dusk till the end of May in our part of the world.
2. Mars: visible from sunset to 12 am.
   Also known as the Red Planet, Mars gives an orange red hue and so is easily distinguishable in the night sky.
3. Saturn: visible from sunset to 3 am.

Bright Stars:

After you have seen some of the planets and are able to navigate through the night sky, you should see some of these easily observable stars (the following stars are visible nowadays) :

1. Arcturus

2. Vega

3. Antares

4. Altair

5. Spica

6. Regulus

Constellations:

After viewing some of the planets and some bright stars, next up are constellations. Viewing constellations can be a bit tricky. The astroviewer software will be a great help in this. Following is a list of some of the constellations visible at this time of the year in Pakistan.  

1.Big Dipper Asterism 

  This asterism is in the Big Bear (Ursa Major) constellation and is one of the most important in the night sky. It can be used to find other stars like Polaris etc. We will discuss this in a future post.

2. Maiden (Virgo)

3. Herdsman (Bootes)

4. Great Bear (Ursa Major)

5. Lyre (Lyra)

6. Lion (Leo)

7. Strongman (Hercules)

       

Finding Your Way In The Sky

Now that we know what to expect to see when we look at the sky, the next thing to learn is where to look and when to look.
There are a lot of software available online which plot the night sky for you, one is AstroViewer, available for free (Only the online version is free, the downloadable version is not. But once you have opened the software, it doesn't require an internet connection any more).
A mini version of this software can be accessed from the left panel of this page. The full software can be started from this link  AstroViewer night sky map . (It may need java update).

When you open the software, it would be somewhat like this:

Setting Your Own Location:
First you will have to customize the program. In the left hand panel of the software click on Location/City Tab. A box will appear like this:

For Pakistan, only coordinates of Karachi are present in the software, for any other place click on enter coordinates and enter the coordinates and name of the city:









In relation to our blog, we have given the coordinates of Rabwah and Lahore in the left panel, for other places you will have to google the coordinates.
Once you enter the coordinates, the program shows the sky directly above you at that particular time. Confirm the time which is being shown in the left side of the program. If there is any difference from your local time, you will have to keep that in mind (for example when planning on seeing some object). I couldn't find any option to adjust the time to your local time.

Other Options:
Now that your location has been set, you can move the time backwards or forwards from the left bar below the location (or enter the date from calendar) and the software will immediately show the sky as it was or will be at the specified time and date. This comes in handy if you want to see what objects will be visible in the coming hours, days, months, or years. And when you click on the "now" tab, the sky swings back to that particular time.

How To Understand The Map:
Coming to the sky map now, it may look complicated with all kinds of dots and lines but in reality it is pretty simple.
The red circle is the whole of the sky above you. The center of the sphere is the zenith, the point exactly above your head. And so the area from the center of the sphere to the edge in any direction is the sky from directly above your head to the horizon in that particular direction.
The red dashed line crossing the circle is called "ecliptic". It is actually the path of the sun. Its importance is that moon and all the planets will always be at or near this line. This is so because all the planets in our solar system are revolving around the sun in the same plane.

How To Find Any Object From This Software In The Real Sky?
We will take the example of Venus for this. The yellow object on the left of the sun is Venus, (The program tells you all the details of any object when you right click on it. You can also search any object by name).

First of all activate the altitude scale from the left panel by clicking on it, a line will appear in the circle:

Now move the desired object (in this case Venus) on that line from the bottom scrolling button:

Now zoom the sky by moving the left scroll upwards. Then bring the object in view by moving the right scroll upwards:

Now you have to note two things from the program
1. Direction
2.Altitude

The direction of Venus in this case is slightly towards the northwest of west, and its altitude is between 45^o and 50^o.         .
What this means is that you will have to face in this direction at this altitude to view the object.

How to Know The Direction?
The easiest and best way is to have a compass with you, (costs near Rs 100). But even if you don't have one you can estimate the directions fairly accurately both during daytime and night time.
If you know the direction in which sun sets everyday, that is West. The direction of horizon from where the sun rises is East. If East is on your right hand and West on your left, then your face is towards North and your back towards South.
During the night time, directions are pretty easy if you can find the North Star which is quite easy and will be discussed in a future post.
What remains is "Boxing the Compass". This is the further division between North, South, East and West e.g in between North and West is Northwest, and in between Northwest and North is 'North Northwest'. Following diagram explains this..

How to Know The Altitude?
At any time, the sky directly above your head, the zenith, is 90^o.
The horizon (where earth and sky seem to be meeting) is 0^o.
Midway between the two is 45^o and so on. 

Are All The Objects Shown in The Software Visible?
Although most will be visible on a clear night sky, it isn't that simple. The requirements for any object to be viewable are:

1) It should be night time. If an object is passing through your sky during the day, you cant view it because of the sunlight.
2) For planets, Elongation should be more than 15^o. For the distant planets i.e Uranus and Neptune it should be more than 20^o. (Elongation is the angle which a planet makes from the sun as viewed from the earth)
3) Altitude of any object, be it a star or a planet should be more than 10^o, otherwise it is almost impossible to see.
4) Last and perhaps the most important are the Atmospheric conditions and Light Pollution. If atmospheric conditions are bad such as clouds or increased humidity then visibility will be low. Similarly light pollution in cities is a big problem, the city lights bounce back from the atmosphere and produce an orange hue in the sky severely hampering the visibility.
So don't expect to see a lot of things in a city for example Lahore, but in towns and countryside visibility should be pretty good, e.g in Rabwah.
5) Apparent magnitude(mag):
It is the relative brightness of the object as perceived by  an observer on earth in perfect viewing conditions. The scale goes from negative to positive i.e. brighter the object lower is its apparent magnitude. For example Venus the brightest object (excluding the moon and the sun) has an apparent magnitude (mag) of -4.48 as compared to Mars which has a mag. of 0.23. An eye with normal vision is able to perceive objects of upto +6 in magnitude. The brightest star in the sky (of course after the sun) is Sirius (8.6 light years) with a mag of -1.4 whereas the Andromeda galaxy (2.2 million Light years) has a mag of 4.5

There are many other useful options in this software which will become apparent with further use.

Beginner's Guide

                   Most of the people think that the sky can only be observed through telescopes and the like, but it is a wrong notion. Although most of the deep sky objects and planetary surfaces are seen best through telescopes, a great deal of objects can be viewed with naked eye. So stargazing can be broadly divided into 3 categories;

        A. Naked eye observation.

        B. Observation through binoculars.

        C. Observation through proper telescopes.

         We will get to the assisted stargazing in due time but in the beginning more emphasis will be placed on Naked eye Observation as it is free, easy and exciting. Here are some simple pointers that will get you started.

     

 A good place to start is by knowing the different celestial objects that are visible to the naked eye. You would be amazed at how much and how far you can see into the space with your eyes without using any equipment. Some of the objects that are thus visible are mentioned below:

Jupiter Surface

1. All the planets of our solar system except Neptune.

A Starry Night

2. A total of about 6000 stars. (Although at one time about half of them are visible)                                                       

A Constellation-Bootes

3. Almost 74 constellations.

 But, what are these constellations anyway? Constellations are basically groups of stars that appear as different shapes and have been recognized as such by people throughout centuries. For example if someone saw 4 stars in shape of a square everyday, he named them "square". This then became a constellation. So basically there can be hundreds and thousands of different constellations!! But 88 have been recognized as standard constellations by IAU. (Actually 14 of them are south polar constellations, so being in the northern hemisphere we can see the rest 74 in different times of the year.) We will discuss these constellations further in future posts.

A Meteor

4. Meteor Showers. These are the beautiful

shooting stars and are BEST viewed through

naked eye!

  

Orion Nebula

5. Some Nebulas eg Lagoon Nebula and Orion Nebula.

Nebulas are basically dust clouds (well not our average Pakistani dust clouds), these are stellar dust clouds formed when some stars die. They are extraordinarily beautiful when you see them through the Hubble Telescope. But to the naked eye they appear no different than any other star.

International Space Station

6. Some objects that you would not have excepted to see because they are man made!! Like the International Space Station!! Yes you can see it. On second thought it should not be really that difficult because it is pretty close to us, only 350 miles above our heads compared for example to Arcturus (one of the most easily seen stars, as we will see in later posts) which is 37 lightyears (ly) away, 

(1 Lightyear = 5878630000000 miles!!!)

The Andromeda Galaxy

7. Some really really far objects (called Deep Sky Objects, DSOs) like the Milky Way, Andromeda Galaxy, Triangulum Galaxy, Pleiades (Seven Sisters) etc. These are somewhat difficult to view and require good viewing conditions.

In the next posts we will discuss the basic principles for stargazing........

                                                                                                                                                                                                                                                  

Rabwah Amateur Astronomy Club (RAAC), Pakistan

Hubble Ultra Deep Field

Welcome to the official blog of  RAAC, an amateur organization of astronomers. One of the first of its kind in  Pakistan, it has been made in the hope to provide a platform for amateur astronomers to share their experiences and help each other in discovering the wonders of our amazing neighborhood called space.
        From the start of time, mankind has looked to the heavens with awe, curiosity and sometimes fear. What looked like diamonds studded in the heavens, the concept of stars has changed from little twinkling lights to balls of fire so massive to shame our sun, from earth being the center of the universe to just a small planet revolving around a small star in a small galaxy in a HUGE universe. The more we peel back the skin of the sky the more enticing,beautiful and deep it becomes!!!
         We ourselves are beginners in this great and majestic field and hope to help others setting foot in the arena by mutually sharing our knowledge and findings. We hope to plan and conduct activities aimed at novice stargazers! Your help and encouragement will go a long way to make this possible. At the moment you can join the club only by subscribing to this blog (click on google join this site in the right bar), we hope that in near future we will start formal registration for the members of the club.
Thanking you all,
RAAC Team