The Time Now > Astronomy

What is astronomy?

Astronomy is a science that studies celestial objects such as the Sun, planets, moons, stars, nebulae & galaxies.

Astronomy. Space background.Space background. © iStockphoto/Sergii Tsololo

10 astronomy facts

It is often referred to as the final frontier. Astronomy is an exciting field that most people have at least some interest in. There are literally hundreds of facts that we could go through, below we narrow it down to 10 major facts in no particular order:

1. The night sky appears to be moving when you look at it. All of the stars and points of interest seem to be moving from east to west. This appearance of movement is due to the fact that the earth is rotating. The speed at which the earth is rotating is approximately 1,000 miles per hour. This is the cause of setting and rising of objects at night. You would also be able to see it during the day, as if it were six months ago, if you were able to turn the sun off like a light bulb.

A year is known as 365 days, but the earth actually takes 365.25 days to orbit the sun. This is why we had to come up with a leap year every 4 years, to account for the extra .25 that is otherwise not accounted for. Most people are aware of that, but did you know that once every 400 years we also do another leap year in addition? This is because the earth rotates around the sun a little over 365.25 times, just a fraction if you will. We compensate that by having another leap year every 400 years.

2. Certain areas of the sky are marked by constellations. The charts that you see these days will have the sky broken up into 88 constellations. A constellation of stars is a group of stars that is found to have a pattern, and is named after a mythological figure or by which form it takes. The constellations were first identified by the Greeks over 2500 years ago. They have since seemingly changed positions to where we see them today. This has caused quite the stir in the astrology world, and most people have had to acknowledge the shift in positions.

One of the most common constellations is the Big Dipper. It is one of the constellations that make up the Ursa Major. You will also be able to tell people that you know the Little Dipper is part of the Ursa Minor. The smallest constellation is known as the Crux, whereas there are several larger constellations, Ursa Major is among them. Most of the constellations that you will see were named because they look like something, although more often than not they don’t look like what they are named after .

3. There are nine planets that have been named in our solar system, although Pluto was named a “dwarf planet” in 2006, so it is no longer classified in the same group as the other planets that we have come to know. Earth, Mercury, Venus, Jupiter, Mars, Uranus, Saturn, and Neptune are the other eight planets. Pluto was first discovered to be a planet, but the astronomers all over the globe were going back and forth on whether or not it should be classified as one or not for years. Finally they came to the “dwarf planet” conclusion.

The largest planet in our solar system is Jupiter. The closest planet to the sun is Mercury. Saturn is known for the magnificent rings that accompany it. A planet is defined as a celestial body that is orbiting around a star. It also has to be big enough that it forms the shape of a sphere through gravity. If it is too big and causes thermonuclear fusion, it is not considered a planet anymore.

4. The exact number of stars is always going to be changing, therefore an exact number is essentially impossible. It is extremely hard to even guess the number of stars. You could say that there is trillions of them, and you would still be way off on the low end. A lot of the stars that you can see without a telescope, just with your eyes at night, were named as far back as ancient times. A lot of the traditions and customs that they used back then to name stars have since dramatically changed. We now have a much different process in choosing the names for our stars.

You will find that a lot of stars have Arabic names. This is because in medieval times the Islamic nations had a very developed interest in astronomy. In fact, the Big Dipper has 7 stars that are named in Arabic. Some time later, Latin became a popular choice when Europeans started to develop their strong interest in astronomy. Polaris, otherwise known as the north star, is one prime example of this.

5. It is impossible to try and name or memorize all of the stars outside of our solar system. There are tons of catalogs though at many research centers that have captured and documented hundreds of thousands of them. You will find that in most of the constellations, the star that is named with an “A” at the beginning of it is the brightest star. The next brightest would start with a “B”, and so on. One good example of this is Librae, which is the brightest star in Libra. The only downside to this methodology is that the Greek alphabet only has 24 characters. So, if a constellation has more than 24 stars, it will be impossible to name them in order of diminishing brightness.

Without the help of technology, the naked eye can see approximately 6,000 stars at night. In the northern hemisphere this number falls down to about 3,000. This is going to be the case no matter where you are at, because you are never going to be able to see the entire sky. Some sources have noted that it could be up to 7,000 stars in the entire sky and 3,500 that you can see at one time. Although there seems to be no exact number, this should give you a good estimate of how many stars you can see.

6. Catalogs have played a large role in our ability to effectively name stars and keep track of the ones that are already named. Since most astronomers are not able to efficiently use the Greek method of naming stars, they designate names and add them to these catalogs. One of the most important catalogs that you will find was created by F.W. Argelander in Germany in the mid 1800s. It was named Bonner Durchmuterung. It was at the Bond observatory and listed hundreds of thousands of stars.

In the U.S. around 1920, another very important catalog was created in order to help the astronomy field keep track of stars. It was known as the Henry Draper catalog. The listings in this catalog go by HD numbers. You can think of it as a library book number. It is not exactly the same but will help you put it in perspective. Henry Draper was a physician that died, and his widow is the one that funded the catalog and named it after him.

Many people forget that there is also a few catalogs that were started for non-stellar objects. This can include star clusters, nebulae, galaxies, etc. You can find a 100 or so of the brightest ones in a catalog that was created by Charles Messier, a French astronomist, in the 18th century. The objects that are in this catalog are going to be referred to by their M numbers.

7. Astronomy and time have always gone hand and hand. Ever since there has been a need to keep track of time, there has been astronomy behind that. Even in ancient times they needed to be able to keep track of the seasons in order to properly plan religious events and when there would be dramatic weather changes. Today, we still rely on this information to plan our vacations, religious events, and many other things that we need to know the weather ahead of time for. We know what weather is likely to come our way depending on what season we are currently in.

Those that wanted more specific time measurements had to look to the position of the sun in the sky. Just about all of the people on earth sleep when it is dark and are active when it is light. The sun is what tells us when that is happening. One of the best inventions to keep track of this was the sundial. It was meant to help keep extreme accuracy for those that used it. For the most part, it was extremely accurate. It was the equivalent to our phones and alarm clocks now days.

To get nearly exact measurements of time, astronomers would turn to the meridian. For those of you that don’t know, the meridian is the circle on the celestial sphere that passes through both celestial poles and the zenith. You would be able to tell when noon has occurred when you are able to identify the sun crossing over the meridian above the horizon. Midnight would happen when the same thing occurred in the opposite direction, but below the horizon.

8. People eventually found out that the sun is not the most accurate way to keep time. There are a couple of reasons why. The earth’s orbit is an eclipse, not a circle. The sun is the reason why one of the points in which you would focus is blocked out. Because of this, the earth will move closer to the sun during part of the orbit, and it will move further away during the other part. The earth will then proceed to speed up during the part when it is closest to the sun, and it will slow down when it is at the part of the orbit that is furthest from the sun.

The ecliptic is the next reason, as it is inclined by 23.5 degrees. That is in relation to the celestial equator. A large portion of the suns motion around the equinoxes is in a north-south direction, rather than the majority of the time being in the east-west direction. The easterly progression from day to day during the solstices is faster than that of the equinoxes. Because of this, it is more like the earth is rotating normally, rather than in an ecliptic motion. The tropic of cancer and the tropic of capricorn are great examples of that. When the sun is over the equator, it moves slowly. When it is over the two tropics mentioned above, it starts to move faster.

They were able to solve this problem by the creation of the mean sun. The mean sun is the rate at which the sun would appear to be rotating around the earth if it were uniform. It keeps moving at a constant rate and is a much better way to keep accurate time. This way people can keep time without having to account for all of the variables that would cause time to slightly alter. It would be impossible to create a way to keep track with all of these variables.

You may hear of the term, a mean solar system day. This is the interval in which it takes the sun to cross the meridian transit of the mean sun successively. This time is also measured to be exactly 24 hours. It is meant to be the exactly equivalent to a normal solar system day. Our sense of time can be linked to this mean solar system day.

9. The mean solar system time and the apparent solar system time can be different by up to 15 minutes during the different seasons. The equation of time is what you call this difference. Astronomers have come up with graphs that will allow you to correct this equation of time. You would have to use a sun dial to accomplish this. It is going to be the apparent solar system time minus the mean solar system time. This should give you the margin of error that you can use with the sundial to come up with the appropriate time.

Time zones were invented to help make it easier on those that were dealing with commerce and transportation. It was also a great help to those that were communicating as well. All of the clocks are set to the mean solar system time. First though, you have to make sure that the meridian runs through the center of that time zone in order for it to be accurate. The earth is comprised of 24 time zones. Four of these time zones are located across the United States. These four time zones result in a 3 hour difference between the west coast and the east coast.

Sidereal time is when you base your time measurement off of the stars, and not the sun. Astronomers have been focusing on this instead of the sun for measuring time. You are able to use this sidereal time to help you aim telescopes before you go gazing into the heavens above. Just about every astronomer out there is going to have a sidereal clock to use while they are star gazing. If you are looking for a technical definition, sidereal time is the right ascension of an object on the meridian. Besides astronomers, navigators have always benefited from sidereal time. They have used it in their travels for quite some time. It might not be that useful to you and me, but that doesn’t mean that it doesn’t have a very distinct and useful purpose.

10. Gravitational pull is exerted by both the moon and the sun to the earth. This is the reason why the earth rotates the way that it does. Because of this, there is a large bulge near the equator. There is a 27 mile difference when the earth is measured by the equator, rather than pole to pole. This is why you will hear the earth referred to as a oblate spheroid, instead of a sphere. The gravitational pull does have an affect on the bulge and the earth which causes a change in the axis rotation.

If you compare the earth to a spinning top, it is a lot easier to understand. The top has to spin otherwise it is going to fall on its side. Similarly, the earth would do close to the same thing. Gravity would cause the bulge to be tugged and it would have the earth straighten out. The earth is always spinning though, so luckily there is no chance of that every happening.