Introduction This is a detailed summary to help readers gain an understanding of some basic aspects of astronomy which are important to know, but not often taught in schools. Please contact me to give feedback or if you plan to use this as a teaching aid. Although several of the examples given here represent the view from the Southern Hemisphere, these concepts also apply equally to the Northern Hemisphere. Astronomy viewing nights I am also seeking to find people interested in astronomy, especially if they either live on or plan to travel to the Atherton Tablelands, near Cairns. I host astronomy viewing nights. We can discuss and observe the stars, clusters, planets and galaxies and point to them with a laser pointer. I can loan people monoculars or binoculars if they do not have them. I also have a powerful telescope people can look through. I will use the laser to explain many things that most people do not know about. A lot of what I will explain is not known by the experts. This is because they are my discoveries regarding the easiest way to find objects in the sky and how to find north or south using certain stars that people do not use for this purpose. I worked out a way to simply explain the important aspects of astronomy that people should know. For example, knowing about the celestial poles and the ecliptic which you can use to find objects. There is more information about the viewing nights at http://tolga.info/astronomy/astronomyviewingnights.pdf. It would be appreciated if you could print and share the page and give me the contact details of anyone interested so I can contact them when the next viewing night is planned. A transcript of what I speak about on the night is at http://tolga.info/astronomy/transcript.html Observation An incredible amount of detail can be seen with a good monocular or pair of binoculars including many nebula, open star clusters and globular clusters. Five galaxies are easily seen. Changes in brightness of variable stars are also noticeable. Binoculars have an advantage over a telescope in many ways as you can see a greater field of view and observe many more targets in a period of time. This is because it is quicker to find objects and there is no setting up required. Therefore I believe it is better for those interested in astronomy to buy either a monocular or pair of binoculars before they buy a telescope. Measuring angular separation You can accurately estimate angles two objects make to your eye by holding your hand slightly less than 60cm (2 feet) from your eye. At a distance of 573mm, 1 cm at right angles to the line of sight is 1 °. Therefore, the number of degrees can be determined from the number of centimetres between your fingers. At arm's length 1 finger thickness is approximately 1°, the knuckles approx. 8° and a hand span about 17°. You can also very quickly make a more accurate instrument to do this if you do not want to buy one off me. Get a common plastic ruler and a piece of string 1.3 meters long. Platted nylon about 2mm thick is best as you do not want it to stretch much. Drill three holes in a ruler with one in the middle and the others about 10mm from each end so they are in the centre and a slightly larger diameter than the string. Fold the string in half and tie a small loop about 40mm long near the fold so that your finger can fit through it. At the knot, tie a another piece of string about 650mm long. With your finger through the loop pull the three loose ends tight and mark the three pieces with a pen at a distance of 573mm (plus the thickness of the ruler) from the end of the loop. Thread the loose ends of the string through the holes in the ruler so the pen marks pass through. Tie knots in each of the three loose ends so inner edge of them line up with the marks. To use the instrument, hold the centre of the ruler between your thumb and index finger. Pull the strings tight so the ruler bends slightly so that it inscribes an ark that forms an approximate circle to the radius formed by the string. Hold your finger inside the small loop up to your eye and your other hand on the centre of the ruler. When you do this, the centimetre graduations will equal the degrees. For example a 20cm distance along the ruler will be 20 degrees. The below diagram illustrates how it looks. If you have to measure the angle an object is from the sun, you can stick a large enough shade level 14 welding glass or Baader AstroSolar Safety Film (supported by glass or plastic) over the zero mark of the ruler. Please contact me if you want to buy this instrument.  It is a good idea to calculate how many degrees your hand span is at arm's length. You can measure your hand span distance and the distance your hand is from your eye and use trigonometry. Another way is work out how many hand spans it takes to measure and angle of 90 degrees and divide 90 by the number. For example, if it takes 5.3 hand spans to go 90 degrees, the angle will be 90/5.3 = 17 degrees. You can use fence lines on property boundaries as a guide to do this by standing on the corner of a block of land. You can also go from a horizontal position to vertical which is 90 degrees. You need to bend over to do this so your hand is the same distance from your eye. Practice doing it both horizontally and vertically to get a consistent number of hand spans over 90 degrees. To use your hand spans to measure angles, line the tip of your thumb up with the starting point like north or vertically downward. Note the point in the distance that is behind the tip of your little finger and keep your eye on it when you move your hand so that the tip of your thumb is now in line with that point. The tip of your little finger will be in line with the point that is two hand spans from the starting point. Repeat the process to get larger angles such as to find 90 degrees. You can also use your monocular or binoculars to estimate small angles. This is very useful to find objects in finder charts. Work out the field of view of your scope which is often given on the instrument. To work out the angle between two objects when looking through the scope, estimate the ratio of the angle between two objects to the maximum angle you can see through the scope. Then multiply it by the field of view of the instrument. Azimuth and altitude
It is useful to find and record the position of an object. One method is to find the azimuth and altitude. Azimuth is the horizontal direction to an object. Similar to south east or west south west but only expressed in degrees. It is the angle east of north or the angle from north in a clockwise direction looking from above. East is 90 °, south is 180 °, west is 270 °. South east would be 135 °. Altitude is the angle of elevation above the horizontal. To do this reasonably accurately and quickly you can use your hand spans like explained above. You can start measuring azimuth from any of the major compass points and add the angle on. For example, if something is in a direction slightly north of west. Find west (270°) which is at right angles to north and measure the angle north of west. If for example, it is 1.5 hand spans and if your hand spans a 17 degrees angle, then the azimuth would be 270 + 17 x 1.5 = 295° The method explained below may be simpler and more accurate to record the position of an object. However, you need to identify and know the name of a nearby distant object. It is good to learn names of the stars and planets and identify them. However, you could also use the moon or sun. If using the sun, make sure you hold your hand in front of it to shade your eyes. If the unknown object is a reasonably small angle from an object you know the name of, you can explain where it is in relation to the known object. Consider the known object to be the centre of a clock face. If the unknown object appears vertically downward from the known object you could say it is in the "6 O'Clock" position. If it is vertically above, it would be in the "12 O'Clock" position. If it appears horizontally to the left, "9 O'Clock". For example, you could describe an object as being 15 degrees in the "4 O'Clock" direction from Sirius which is the brightest star in the sky. That would mean it is slightly below a horizontal direction from and to the right of Sirius. Triangulation
Triangulation is used to calculate the distance to objects both on earth and in space. This is needed as optical illusions can easily make objects appear much closer or further away than they really are. To calculate the distance, you need to work out the angle an object appears to move (relative to north or very distant background objects) if you travel to a different location. Trigonometry enables you to calculate the distance. Two people observing even a moving object at the same time could record the position simultaneously possibly when talking on the phone. The difference between the two position readings can be used to calculate the angle between the two observations and trigonometry can be used to calculate the distance. More information about triangulation and diagrams can be seen at https://en.wikipedia.org/wiki/Triangulation_(surveying) Unusual objects
Sightings of many unusual objects are often reported such as UFO's or objects in space. Some people are even convinced that there are other rarely seen planets visible to the naked eye. To help identify unknown objects, it helps to determine their distance. To do this you can ring someone like me when you see them and then while you are on the phone, you can not only photograph them but also either measure their azimuth and altitude or describe where they are in relation to a known object like described above. If you see something unusual that appears to move slower than a meteor, please call me on (07) 4095 4354. Finding North
It is good to be familiar where north and south are so you can calculate the above. The stars provide a very accurate way to do this as described later. However, they are not always visible. A compass can be used to find north and is reasonably accurate in most places. However, you need to make a correction to find true north as the compass points to magnetic north. A more accurate way to find north at your property is to use a map that may map the boundary line of your block and you can then measure the angle to north on the map with a protractor or by using trigonometry. You can then go outside to measure the angle from your property boundary to find true north. However, the most accurate way is to set up a level table or platform and attach something with a point that will cast a shadow on the table. A bent piece of wire could even work if it is weighted down or clipped on. You then need to find the time of local noon which is the time the sun is over your longitude when the shadow is cast either exactly north or south of you. There are online tools to do this where you enter your location and the date as the time varies through the year. You then mark the position of the end of the cast shadow and note the time. A good time is about 9 am. You then work out how many minutes it is before local noon. Then at the same number of minutes after local noon, you mark the position of the shadow again. A line drawn between the two points will lie exactly east-west. North will be at right angles to it. An easy way to do it is to select a time that is the same number of minutes after the hour as local noon as is easy to calculate that way. For example, if local noon is at 12.18PM, then you can mark the positions of the shadow at 9.18AM and 3.18PM. This method will still be very accurate even if you are a couple of minutes late to mark the point in the afternoon. This process can be used to set up or a sun dial. It is best to get or make one to track the paths of the shadows like explained below. This will help you to find north and to learn the paths that the shadows track. There are computer programs to enable you to print out the pattern using software. You can see some examples of the shadow tracks for different latitudes at https://lyncean.education/projects/astronomy/butterfly-sundial/. It is useful to lean them if you need to find north away from home. The tracks enable you to calculate the angle your shadow makes with true north if you know the approximate time. Another way is to find the end of a shadow that is cast from a steady object where a clear point is visible. Mark the point with possibly a rock. Wait at least 5 minutes and mark the end of the shadow again. A line segment between the two markings will lie approximately east-west but you need to make a correction to find true north based on the angle to east-west that the shadow track makes. Once you have found north away from home, you can take note of the angle that your shadow makes with it as that could help guide you in a particular direction. You will need to remember the shadow moves through the day. Also, you can take note of the direction of the wind and cloud movements to help guide you. A method often taught to find north is by using a watch where you point either the hour hand or the 12 o'clock mark in the direction of the sun. However, this is not consistently accurate in most locations in most times of the year. Star motion Unlike the planets, the stars remain in fixed positions relative to the Sun. The only ones that move reasonably fast are binary stars which are so close together that they look like one star to the naked eye. Our galaxy does rotate and galaxies and stars do move relative to one another. However, these changes are not noticeable in a person's lifetime without large telescopes. Therefore, the stars are considered to remain in fixed positions and only appear to move due to the Earth's rotation and its orbit around the Sun. There is a small amount of parallax with the closest stars as explained later but this is no greater than 0.0002 degrees. This is far too small to be perceived by a small telescope. The celestial poles and equator Due to the Earth's rotation, the Sun and stars appear to rotate around the Earth’s celestial poles. Imagine if the Earth did rotate on a visible pole that extended up into the atmosphere and into deep space. The vanishing point of this pole would be the celestial pole. At the Earth’s North Pole, the North Celestial Pole is vertically above you, and the South Celestial Pole is vertically below you on the other side of the centre of the Earth. At the Earth's South Pole, the South Celestial Pole is vertically above you and the North Celestial Pole is vertically below you. On the Equator, due to the curvature of the Earth, the North Celestial Pole is on the horizon towards true North and the South Celestial Pole is towards true South, on the horizon. That is because the difference in the latitude between the Equator and the poles is 90°, and therefore it is 90° from the vertical. Because the Earth is sperical, the angle of elevation from the horizon (altitude) to the celestial poles is therefore the same as your latitude. For example, at 30° South, the South Celestial Pole is 30° above the horizon towards the South, and the North Celestial Pole is 30° degrees below the horizon towards the North. In the below two diagrams, the line showing the direction of the celestial poles does not extend too far, so the diagram will fit on the page. Imagine if this line was infinite in length. The blue line, at 30° South, parallel to the polar line, would also be infinite in length. Both lines would converge to the same vanishing point. |
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The
Celestial Equator is an imaginary line vertically above the Equator.
Imagine a large ring around the Earth in deep space which is
so far away that its position does not appear to move relative to the
stars when traveling from one place on the Earth to another. The angle
of it above the horizon will appear to move together with the stars,
but this is only due to the curvature of the Earth. In the below
diagram it is not drawn too far away, so the Earth can be seen and so
the diagram fits on the page. On the Equator, this line passes directly
above you. However, on the poles, it is on the horizon. The maximum
angle below vertical that it passes, is the same as your latitude, and
it is seen to the North in the Southern Hemisphere, and to the South in
the Northern Hemisphere.
 It is important to know that the Sun and stars rotate around the celestial poles, so their path across the sky can be visualised. This enables you to locate and identify stars, determine where North and South are, and can enable you to know what time it is. Because a given star rotates around the celestial pole, the angular separation between the star and the celestial pole remains constant from a fixed location on Earth. When you look South in the Southern Hemisphere, a star very close to the South Celestial Pole will trace a small circle around the South Celestial Pole. The Sun, and the stars which are closer to the Celestial Equator, form a larger circle and therefore rise and set in most places in the world. The three images below show three positions of the Southern Cross as it rotates around the South Celestial Pole (over about 6 hours or quarter day/rotation). The South Celestial Pole is represented by the large blue dot. Each star remains the same angular separation from the South Celestial Pole. |
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You can
predict the path that a celestial object takes by holding one
end of a piece of cotton in one hand and stretching the arm with that
hand out in front of your eyes so your fingers holding the cotton are
in front of the celestial pole. With your other arm stretched out,
slide the fingers of your other hand along the cotton until they are in
front of the celestial object you want to predict the path of. Keep the
cotton tight between both your hands. While holding the end of the
cotton in front of the celestial pole, rotate the other hand, (that is in front
of the celestial object), in a circle by using the length of cotton as
the radius. Try to keep your hands at a constant distance from your
eyes.
 A stick or some rope could also be used. To save having to find cotton or a stick, I normally hold my elbow up in front of the celestial pole and line part my hand or arm up with the celestial object and rotate my arm by keeping my elbow lined up with the celestial pole. If a celestial object is close to the celestial pole, you could use a hand span as the radius by keeping one finger over the celestial pole, and another one over the celestial object, and then rotate your hand. If you notice a celestial object in an unfamiliar position and you do not know what it is, you can use the technique to trace the path it will take. This may cause you to remember what it is, because you may have noticed the celestial object in these different positions many times before. The above technique can also be used to trace the path of the Sun, which is very useful as it can enable you to predict what places the Sun will shine, or where shadows will be during different times of the day. It is often important to know this because some things require shade during the day, while other things require sun. The tip of your shadow will also track around the celestial poles. During the daytime these technique can help you to determine the time, and to determine where North is. Due to the Earth's rotation, the Sun appears to scribe an arc across the sky and rotate around the celestial poles every 24 hours. Therefore every hour it moves 15° around the celestial poles or passes through one degree every 4 minutes. This can help you determine North without having to use a watch. The Earth's orbit and the Ecliptic
Because the Earth orbits around the Sun every year or 365 days, the Sun appears to move almost one degree per day from West to East relative to the background stars. This is calculated by diving 360 degrees by 365 days, which gives 0.9863° per day. In order for the Sun not to rise at a later time each day, a 24 hour day is made the length of time for the Earth to rotate 360.9863° on its axis. Stars therefore rotate an average of 15.04° (360.9863/24) per hour around the celestial poles, which is only slightly more than the Sun. This explains why the stars appear to move from the East to the West relative to the Sun at almost 1 degree per day and why the stars appear to rise about 4 minutes earlier every day. It should be noted that 0.9863° per day is the average figure over the year, so it varies slightly throughout the year due to the Earth's elliptical orbit around the Sun. The time of local noon, (which is the time the sun is above your degree of longitude) therefore changes slightly throughout the year. The Sun rises the same number of minutes before local noon as it sets after local noon. The Sidereal day is the time it takes the Earth to rotate 360° relative to the stars. Its length is 23 hours 56 minutes and 4 seconds. The path that the Sun appears to move through the stars due to the Earth’s orbit around the Sun is called the Ecliptic. You could imagine it as a line as far away as the Sun going around the Earth. It is angled to the Celestial Equator, due to the tilt of the Earth axis at 23.4°. This explains why the position of the Sun moves through the year between the Tropic Of Capricorn and the Tropic Of Cancer, and why there are seasons.  The orbit of the planets A superior planet is one that is further from the Sun than the Earth. It is in opposition when it is on the opposite side of the Earth relative to the sun and the three bodies (sun-earth-planet) are therefore in line as shown in the below diagram. It is about at its closest point to the Earth when in opposition. Inferior Planets (Mercury and Venus) are those closer to the Sun than the Earth. They are said to be conjunction when they are between the Sun and the Earth.  The planets orbit around the Sun and therefore move relative to the stars. The planets orbit in almost the same plane as the Earth does around the Sun. Therefore, they pass very close to the Ecliptic path. Planets closer to the Sun move faster. Most of the planets and asteroids in the Solar System are further from the Sun than the Earth is. When these planets get close to being behind the Sun as seen from the Earth, they will move from West to East relative to the stars. Due to the Earth's orbit, they then go into retrograde when they are near opposition. They then move westwards. However, over a course of a year, these planets and asteroids move from West to East overall. In retrograde, these planets appear to move in the opposite direction to what they are orbiting because the Earth (which is orbiting faster around the sun) is overtaking them. You can see an example of retrograde motion if you are passing a car on a highway. The car that you are passing appears to travel backwards even though it is moving forward. The motion of the planets, asteroids and comets around the sun obey Kepler's Laws which are well worth learning. The mathamatics is perfect like clockwork and is evidence of creation. The Moon's orbit The moon orbits earth once every Sidereal month which is 27.3 days. This is also the time it takes the moon to return to the same star. The Moon also moves across the sky in a path very close to the Ecliptic path. Twice every Sidereal month it passes right over the Ecliptic path and a solar eclipse will occur at that time if the Sun is behind it when the Moon is new. A lunar eclipse will occur as the Moon crosses the Ecliptic, if the Moon is full. The two points where the Moon cross the Ecliptic are called the Nodes. The Sun passes through them twice a year as the Earth orbits around the Sun. The times of the year when this happens are called the eclipse seasons, which extend approximately 17 days before and after each node crossing. If the Moon is new or full during these times, a solar or lunar eclipse will occur somewhere on Earth. There is slightly less than 6 months between each eclipse season. Therefore, they occur slightly earlier each year. Because the earth orbits the sun, the time between the same moon phase is longer and is called the Synodic month which is 29.53 days. The Celestial Sphere The positions of celestial objects along with the celestial poles, Equator and Ecliptic are also projected on to the Celestial Sphere which is an imaginary sphere that could be visualized as being transparent and lying out in deep space. This sphere would be like a transparent globe of the world with the Celestial Equator and celestial poles marked on it in the positions described above. The Celestial Sphere would also contain imaginary lines to mark the celestial coordinates, and these would be very similar to the lines of latitude and longitude on a globe of the world. Imagine if you had a very large transparent globe of the world with your head in the centre of it. The surface of the globe would be like the Celestial Sphere. The directions (North, South, East and West) would appear the same to you as on the Celestial Sphere. The poles of the globe would appear orientated like the celestial poles, and the globe's equator would appear orientated like the Celestial Equator. The coordinates of latitude and longitude would be orientated like the celestial coordinates. Celestial directions The diagram below shows that when you look South, the celestial western side is to your right for an object above the South Celestial Pole, but to the left for objects below it (between the South Celestial Pole and the horizon). For objects to the right of the South Celestial Pole, the western side is downward, and for objects on the left of the South Celestial Pole, the western side is upwards. If an arrow is pointed towards the South Celestial Pole, the arrow would be considered to point celestial South. Arrows pointing in the opposite direction or away from the South Celestial Pole would be considered to be pointing celestial North, as shown below. Just like on a terrestrial globe of the world, the northward pointing arrows on the opposite sides of the pole appear to point in the opposite directions when the globe is viewed from a distance. However both point North.  Below is another diagram showing an example of how two stars appear to rotate around the South Celestial Pole that is represented by the blue dot in the centre of the diagram. Four positions are shown which would each be 6 hours apart. The brown line drawn through the two stars shows that they point just to the West of the South Celestial Pole. Therefore, the star closer to the Celestial South Pole would be considered to be almost celestial South of the outer star. It is only slightly West of celestial South. The outer star would always remain almost celestial North of the inner star that is closer to the pole. A star would be considered to be exactly celestial South of another star if a line drawn through the two stars points exactly to the Celestial South Pole. Celestial directions therefore can differ to terrestrial directions. For example, when the stars are in position 3 below, the outer star is terrestrial South of the inner one, but it still remains Celestial North of the inner one.  When you look North, the celestial western side is to your left for an object above the North Celestial Pole but to the right for objects below it. For objects to the right of the North Celestial Pole, the celestial western side is upward and for objects on the left of the North Celestial Pole, the celestial western side is downwards. Celestial
coordinates The position of a celestial object can be determined by the Declination (angle North or South of the Celestial Equator) and the Right Ascension. These are known as the celestial coordinates and are similar to Latitude and Longitude on a map of the Earth, but Right Ascension is expressed in hours, minutes and seconds, rather than in degrees East or West as is the case with terrestrial longitude. Right Ascension is measured eastward from an arbitrary zero point in the sky where the Sun crosses the Celestial Equator during its northward motion at the vernal equinox. To find the Right Ascension, project a line between the closest celestial pole to a celestial object and the object. Then project another line from the same celestial pole to the point in the sky where the Celestial Equator and Ecliptic intersect, where the Vernal Equinox in March occurs. The angle between the two lines is the Right Ascension, where 15 degrees is one hour. Navigation by the stars Polaris, or the North Star is used by many people to determine North, because this star is very close to the North Celestial Pole and therefore appears to remain stationary. However, the problem is this star is only visible in the Northern Hemisphere and is often obscured by cloud. Therefore, it is important to know others stars to determine North as described below. A line projected through any bright star and a fixed point (among the stars) in the sky will always point to the North or South Celestial Pole. These fixed points can be determined from star charts and are worth remembering to enable you determine the position of the celestial poles. The points can be determined by measuring the angle from a nearby bright star or bisecting a line (at a certain ratio) between a bright star and a nearby fainter star. Alternatively, the angle to a line between two bright stars and a line from one of these stars to the celestial pole will always be a constant angle. A good way to find the North or South Celestial Pole is to find pairs of bright stars that lie approximately North/South, as in the examples below. The angle between the two bright stars and the meridian line (lying North/South) is then noted to enable finding the poles. Star charts can determine this from the difference in the right ascension. Just as in the stars shown in the above diagram, the top and bottom stars on the Southern Cross point only slightly West of the South Celestial Pole. This is also the case for the two brightest stars Sirius and Canopus. Closer groups of stars can also be used. For example, the arrow shape of the Saucepan in Orion points only slightly West of the North Celestial Pole. The two outer or southern stars of the bowl of the Big Dipper (Ursa Major) point slightly East of the North Celestial Pole. A line drawn from Procyon, through the mid-point between Pollux and Caster in Gemini, points almost exactly to the North Celestial Pole. Other stars that also point almost exactly to the North Celestial Pole are the two western stars of the Great Square of Pegasus, along with Rigel in Orion and Capella in Auriga. Mirzam, just to the west of Sirius and Canopus can also be used to find the South Celestial Pole. More examples are given in the astronomy night speach transcript. To find the celestial north or south poles, project a line through the above pointer stars down to the altitude that the south or north celestial poles must be for your latitude. Remember that the altitude of them is equal to your latitude and in the southern hemisphere, the celestial south pole is above the horizon and in the northern hemisphere the celestial north pole is above the horizon. The two poles are 180 degrees apart, so one of them is always below the horizon unless you are on the equator. The celestial north pole is always to the north and the celestial south pole always to the south. Learning this can be very useful to enable navigation. Learning and identifying stars It is a good idea to learn the names of the brightest stars first and remember where they are as that can help you locate other objects. It is also very important to learn the path they appear to move across the sky as described above, as that can help you locate them. The directions referred to below are only approximate and also referring to the celestial directions. A good method is to group a pair of bright stars from different constellations together. This will also help you to navigate by the stars, as explained above. For example, Canopus in Carina is South of Sirius in Canis Major; Rigel in Orion is south of Capella in Auriga; Procyon in Canis Minor is South of Pollux in Gemini; Altair in Aquila is South East of Vega in Lyra; and Spica in Virgo is South West of Arcturus in Bootes. The Southern Cross in the constellation of Crux is West of the stars forming a triangle in Triangulum Australe, which is West of the star Peacock in Parvo, which is West of Alpha and Beta Grus in Gruis, which is West of Achernar in Eridanus, which is West of Canopus in Carina, which is West of the False Cross in Carina & Vela, which is West of The Southern Cross. Fomalhaut in Piscis Austrinus is North of Alpha and Beta Grus in Gruis. Some bright stars have a nearby, dimmer star or a group of dimmer stars that have an angular separation of between about 1 and 7 degrees away from the brighter star. These are an indicator of what the brighter star is and this is a big help in identifying them when cloud or trees obscure other surrounding stars. For example, there is a fainter star (Tarazed) about 2 degrees North West of Altair, and another one (Mirzam) about 6 degrees West of Sirius. Two fainter stars form an almost equilateral triangle with the star (Sheat) on the Northwest corner of the Great Square of Pegasis. Parallax The distance to closer stars can be calculated by using parallax, which is calculated from the angle that the star appears to move against very distant stars and galaxies due to the orbit of the Earth around the Sun. This is shown in the below diagram. The distant stars and galaxies would have to be so far away that they would not have any parallax angle themselves.  Precession Of The Equinoxes
The elevation (number of degrees above the horizon) and azimuth (direction) of the stars are almost exactly the same on the same date and time each year. There is only slight variation, which is corrected by the leap year. The overall angles only change very slowly, so it may be only barely noticeable in a lifetime. This is because the Earth has a slow wobble where the position of celestial poles change, as shown in the below diagram. One complete rotation of the celestial poles takes approximately 26,000 years. This causes the dates of the seasons to slowly change. In approximately 13,000 years the time of the year that summer is now experienced will then be winter. This is called the Precession Of The Equinoxes. The Sun is also not in front of the same constellations in the relating months as it was when the signs of the Zodiac were listed thousands of years ago. Hence Astrology is not credible.  Reading star charts Circular star charts have an advantage over flat ones as they are easy to orientate and have the celestial poles in the centre. You simply hold the chart up between your head and the sky, and line up the celestial pole on the map with the celestial pole in the sky. This orientates the stars roughly how you see them after you take into account the curve of the Celestial Equator on the map. An example of a good one is at https://collections.lib.uwm.edu/digital/collection/agdm/id/34095 . Flat charts are often used to map stars close to the Celestial Equator. However, they are also used for stars close to the poles, like the Big Dipper (Ursa Major). They have an advantage over circular ones because there is less distortion for stars close to the Celestial Equator. However, they can be difficult to orientate and visualize, especially in the Southern Hemisphere for stars in the North. You need to imagine yourself lying down with your head facing North, holding the star chart upwards to orientate it. I normally find it easier to just convert the directions where the eastern side is on the left hand side, which is the opposite side to a geographic map. For example, the bottom right hand side is South East on a geographic map, but converts to South West on a flat astronomy chart. Circular star charts I use enable you to work out the position of stars in the sky as they have the months listed around the outside. This enables you to work out the date of a particular star which is when it is vertically above your local standard time meridian at midnight. Depending where you live it would still be fairly close to above you local longitude at midnight. A method you can use to get a rough idea where stars are at a certain time is described below. Of a night, imagine where the sun would be 12 hours from now. The stars corresponding to the current date on the chart would be close to the right ascension that the sun is imagined to be on. Stars with a right ascension 30 degrees to the east of them would appear one month later on the chart and ones 60 degrees to the west of the current ones would be two months earlier on the chart. This is because the stars appear to move about 1 degree per day relative to the sun. Cepheid Variables
A number of stars that can be observed through binoculars vary in brightness. They include Cepheid Variables which are important as they enable calculating distances to galaxies. Cepheid Variables have a bright and dim cycle, which duration is proportional to their absolute magnitude, which is how bright they would appear when viewed from a standard distance of 10 parsecs or 32.6 light years. The apparent brightness (apparent magnitude) seen from Earth can therefore be used to calculate their distance. The distances to closer Cepheid Variables were calculated using parallax and this enabled working out the above ratio. It is assumed that more distant Cepheid Variables have the same relationship between the bright and dim cycle as the nearby ones. Star colours and temperature
Some stars also have unusual colours. For example, Betelgeuse, Aldebaran and Antares have an orange-red colour but are referred to as red stars. Arcturus is an orange star. By comparison, Alpha Centauri appears pale yellow and Beta Centauri has a bluish white tint. The colour of a star is an indication of its surface temperature. The red stars are estimated at 3000 to 4000 degrees Celsius, a yellowish colour is estimated at 5000 to 6000 degrees and a bluish white star has an estimated surface temperature of 10000 to 15000 degrees. Conclusion
There are a number of useful websites such as http://www.heavens-above.com/ which inform you of many interesting objects in the night sky in your local area, including times of International Space Station passes, satellites, comets and asteroids. There is a live sky chart for your area that also shows the planets and positions of the Moon and Sun. Stellarium is useful free software that enables you to see the stars in their correct positions in real time on your computer. Some other useful links are on my astronomy links page. I would appreciate any feedback regarding this page. I would also like the contacts of anyone that is interested in this especially if they are travelling to the Atherton Tableland or Cairns where we plan to have astronomy viewing nights. I could host a special viewing night for someone that is interested. |
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