Illustrated Elementary Basics of our Solar System
The more we know about our solar system the more beautiful it is. So many people don’t even know that soon after the Sun sets that the planets become visible sometimes as much as one half hour before any stars can be seen and that early dawn and dusk are the best times to view the Solar System. How often I have wished that I could sit on by back lawn and picture myself in relation to the solar system and the whole Cosmos for that matter. Even though this is impossible because of the large expanses of space involved, lets give it a shot and see what we can come up with. Perhaps only one person in ten thousand know that Uranus is slightly visible in the night sky and you are now one of them.
This lesson is somewhat like a story book and you can therefore scan down and just look at the pictures as they are presented.
Terms and Axioms
Lets first start with a few definitions and axioms that will later come in handy.
The Earth and Great American Navigators
If you were standing on the North Pole of the Earth, you would be about 15 degrees or about 1000 miles from it’s slowly migrating magnet pole. Our planet's rotation causes molten iron-nickel in its outer core to circulate, creating electrical currents and a magnetic field.
The Earth spins on it’s axis and that axis is tilted 23.5 degrees from the angle we are traveling around the Sun. No one knows why the Earth is tilted but some scientist speculate that many millions or billions of years ago it was hit by a celestial object the size of mars. It’s actually a good thing that it’s tilted since if it were not, then like Uranus we could have totally dark winters that would last for 42 years.
Ships navigating the Earth before the invention of the Radio needed to navigate using a compass or celestial bodies. John Paul Jones (1747 – 1792) was Americas greatest Revolutionary war Naval commander. He was from Scotland and began sailing at the age of 13. At the age of 21 while on a voyage from Jamaica to Scotland, John Paul took command of the brig John when her captain and first mate died from fever, bringing her safely into port.
When the revolutionary war started in America, Merchant ships were quickly converted for naval battle. Jones in May 1776 took command of the sloop Providence, which mounted 21 guns. Jones soon captured 16 British vessels on a single cruise. Few people know that during the Revolutionary war that he attached the town of Whitehaven on the west coast of England. After his successful career as an American naval officer, the U.S. no longer felt that they needed a navy so he joined the service of the Russian Navy. He died at the age of 45.
In the 1700’s a book called the THE AMERICAN PRACTICAL NAVIGATOR was written by a naval captain named Bowditch and this book is still used today by the U.S. Naval Academy. The following site seems to have the book content on-line, published by the United States government, however I’m not sure if it’s complete.
Finding the Celestial Equator in your Neighborhood
In the view below, we show how you can define and mark out the Celestial Equator for your neighborhood. In this example, the Frenchman is located in Bordeaux France which has a Northern Latitude of 45 degrees. If you know the Latitude of your neighborhood, you can get the idea of how to find your Celestial Equator using it.
Planets in Retrograde
The planets as we know them go directly around the Sun, however, we watch and see them from the Earth and that's why from our point of view they sometimes go backwards or retrograde. Imagine looking at the setting Sun and with your eyes able to see Venus orbiting around the Sun, on the other far side of it. So when Venus is behind the Sun it would appear to us to be moving from our right-to-left. However if Venus was between the Sun and Earth/Us, it would be moving from left-to-right. In this manner you can see how sometimes the inferior planets like Mercury and Venus will actually fall back each night as we go out to view them at the same time. The superior planets will also go retrograde but remember it’s just from our point of view. The planets like the Sun will rise up in the East and Set in the West just like the Sun and actually move through the night sky at about the same speed as the Sun. Remember that it’s the Earth spinning on it’s axis that makes these celestial bodies move through the sky.
Since Venus and Mercury are inferior planets (between us and the Sun), they are always close to the Sun from our point of view. The superior planets like Jupiter and Saturn are always beyond the Sun. Imagine a Sun set and then imagine Jupiter beyond the Sun.
In ancient times people didn’t have TV or the internet and they had less light pollution so they spent more time viewing the night sky. One of the first things that they noticed was that 99.9999 percent of the celestial bodies looked the same night after night. They realized that there was only a few bodies that changed. The only things moving were the Sun, Moon, Mercury, Venus, Mars, Jupiter, and Saturn. Some people have said that when the Bible speaks about the stars that it really is speaking about these celestial bodies which the ancients called the ‘Wanderers’. I recently read that the planet Uranus is faintly visible and may have been seen by the ancients as well. Careful pronunciation of Uranus may be necessary to avoid embarrassment; say "YOOR a nus" , not "your anus" or "urine us". In the Spanish language, the days of the week are named after the planets. We’ve all heard of Marti Gras which means ‘Fat Tuesday’ where Tuesday is ‘Marti’. Here are the days of the week in Spanish:
Sun (this is a star rather than a planet)
Now as illustration 2 below shows, the middle celestial body is close to the horizon and is either raising or setting. The highest celestial body could be raising, setting, or at it’s apex. The lowest celestial body is under the Frenchman and is not visible to him. The important thing to understand is that they are all in the same plane which we call the ecliptic. The ecliptic is the plane of the Solar System or as explained above the floor of the gymnasium where you could lay out the model of the solar system. If you are new to this study you will now for the first time realize that when you walk around on the Earth that you’re probably not aligned very perpendicular to the plane of our Solar System. Now are you getting dizzy?
In the illustration 3 below you can see another view that shows the plane of the Solar System. Isn’t it beautiful?
In reality the planets don’t perfectly align with the plane of the solar system. Mercury and Pluto are out of whack the most. They don’t have perfect circular orbits either and therefore will go faster when they’re in certain parts of their orbit. When their orbits are out of whack like we see with Mercury, a celestial almanac will give us their declination in degrees North or South from the Celestial Equator.
During Winter in the Northern latitudes, the Sun, Moon and other planets will follow an arc that is farther to the South and therefore they have a more southern declination. The opposite is true during the Summer.
How to Specify a Location in the Sky
Now if you’re outside looking at the night sky and I’m also outside looking at the night sky but we are in different cities talking to each other on our cell phone, how can I direct you to a particular location in the night sky? First lets say that we’re both in a Northern latitude. I can do this by giving you two coordinates just as we would give a latitude and longitude on Earth. The first one is the declination which we have already explained. Remember that I will give you this number as 0 to 90 and I can specify it a positive which also means North and I can specify it as negative which also means South. If I said it was 10 degrees North it would mean that it was 10 degrees toward the North Star. I could also say that it was +10. The declination is like the Earths latitude where 0 degrees latitude is the equator.
Now I need to specify where across the sky I want you to look in terms of East and West. Again we can use a hola-hoop but this time we won’t cut it in half. We will mark it with 24 marks, start at one point with the number 0, then moving around it clock wise, write the number 15, then 30, then 45, then 60 etc. until we have marked to 360 which is also the 0 where we started. Note that half way around must be 180 degrees, and one quarter around is 90 and 270 degrees etc. If you really wanted to do this you could use a students protractor to lay it out.
Now see illustration 4 below to see the vertical line drawn through the constellations Cassiopeia and the big dipper. Now face North, align the full hula-hoop on the Celestial Equator and align the 0 mark on the hula-hoop to the vertical line that passes the Cassiopeia constellation and line the 180 mark to the bottom of the vertical line . In this manner I can specify a particular point in the sky which is similar to giving any longitude point on the Earth. The blue line in the illustration below which is aligned to your zero mark can be called the Celestial Meridian which is similar to the Greenwich Meridian line which is 0 longitude on Earth. Note that this method is called ‘right ascension’ and is used by astronomers and celestial navigators but not star gazers. Star gazers use a system called azimuth. The azimuth is the degree of a 360 degree circle where the 0 point is found using the North on a compass. The star gazers will also use the word ‘elevation’ in place of declination because they are measuring up from the horizon.
Now you can see that it’s almost like there is a greater ball around the Earth that has latitude on longitude lines on it just like the Earths and that the latitude lines have a zero point as does the longitude lines. Remember that this imaginary ball can be thought of as either 100 feet above us or a million miles because it doesn’t matter as long as we know that it’s there for our use. If you think of it like a big balloon it might help to think of the North Star as the balloon valve. As the Earth spins once each day, half in the night, we don’t feel the Earth turn but we can see the vertical line as shown in illustration 4 above move around like the hour hands of a 24 hour clock. Also note that the Earths longitude goes to East 180 and West 180 but in Celestial Navigation it goes from 0 to 360 and is called ‘Right Ascension’.
How to imagine the Celestial Sphere
If we want, we can imagine that all objects in the sky are lying on the celestial sphere, something like a very large balloon with poles one on the north and the other on the south ends of this balloon. This sphere can be a very practical tool for finding or pointing to objects in the sky or areas of the sky much like we do with the Earths latitude and longitude.
To gain a better understanding of this Celestial Sphere lets examine how the Earth is divided up into latitude and longitude lines. Remember that latitude runs across the Earth like rungs of a ladder while longitude runs up and down. The Earth rotates on it’s axis once every 24 hours so they can divide the 360 degrees of longitude into 24 equal parts of 15 degrees and each part could be called an angle hour, or the amount that the Earth rotates in 1 hour. If you look at a map of the United States you can see that most of the United States is contained in three of these hour angles or between 75 degrees west longitude and 120 degrees west longitude. As the Earth rotates and we observe the night sky, we can see how the stars move over-head 15 degrees each hour, or 180 degrees in 12 hours. It’s important to remember that the Earth is always rotating and therefore the sky above seems to move over our heads and any given star except the north star will rotate 180 degrees (half a circle) around the north star in 12 hours. A star trail is a picture taken of the stars around the north star with a long exposure time that allows you to see how the stars rotate around the north star. You can see one of these pictures by entering ‘star trail’ into any web search engine.
It’s interesting to note that a nautical mile, used for ocean navigation, is different from a standard mile because for one thing it’s approximately 1.15 of a statute mile which is 5280 feet. The nautical mile is 1/60 of a degree of the equator. It can also be thought of as 1 minute of arc in latitude, whatever that means. The Earth rotates 1 degree of longitude every 4 minutes.
Now to the good part and back to the Celestial Sphere. If you live in the Northern Hemisphere, and can see the north star, look at it and then using the picture below place the center point of the web of the picture over the north star. If you live in the Southern Hemisphere use this site http://www.dibonsmith.com/downunder.htm to find the pivot point where all of the star orbit the southern hemisphere and use the picture below to place the center point of the web of the picture over this southern position.
The picture below is one taken by me of my mothers flower pot holder that is formed like a bowel and with it’s web like appearance has a center point and that it has 12 spokes coming out. In your imagination, align the center point up with the north star or south pole star and further imagine each sector or pie part widens as it extends out over your head and then contracts as it approaches the opposite pole of your imagined Celestial Sphere. The question now is at which point in the sky is each sector the widest? If you live at a northern latitude of 45 degrees in Bordeaux France, imagine that the widest part of each sector is 45 degrees south of your zenith (straight over-head). You can further see ‘Celestial Equator’ in illustration 1 above to understand where the widest part of each sector could be found.
If we were in France, we wouldn’t be able to see the southern pole because it would be below the horizon. Each sector can be called a double hour angle of 30 degrees. Once you are outside at night and can imagine this, you can use illustration 4 above to align the 0 index point which would be similar to the Earths Greenwich longitude 0, however, remember that on the Earth we use 0 to 179 west longitude and 0 to 179 east longitude but in the Celestial Sphere we just use the full 360 degrees from 0 to 359.
With this view you can imagine one half of the Celestial Sphere.
What happens two times a year?
Two things happen two times per year. First is the Spring and Fall Equinox and Second is the Winter and Summer Solstice. Solstice means that the Sun stands still. Equinox means that something is equal.
On the equinox days there are equal amounts of daylight and darkness. Also the Celestial Equator aligns with the Ecliptic. These occur sometime around March 21st and September 21st plus or minus a few days.
On the Summer Solstice the days start to get shorter in the Northern Hemisphere. On the Winter Solstice the days start to get longer in the Southern Hemisphere. These occur sometime around June 21st and December 21st plus or minus a few days.
Calendars and the Rotation of the Earth (complicated stuff)
Did you ever wonder why the month of December is the 12th month but usually the word deci means 10. Or how about Octal meaning 8 but October is the 10th month. Do you get the feeling that something is out of whack? Well then you’re right. Originally October was the 8th month but Emperors, Kings, Popes and Astronomers have had to keep adjusting our calendars in order to keep things in sync. What is it that they are trying to synchronize? Believe me it’s way to complicated for me to understand but I can supply the questions easier than the answers.