Observations in Astronomy
by Ron Kurtus (revised 31 January 2011)
Throughout the ages, people have observed the movement of the Sun during the day and the behavior of the Moon and stars at night. They have wondered what caused such activity.
In more recent times, scientists and astronomers have been able to study these objects in space to explain their movement. By making observations in astronomy, you can experience and learn about this science.
Questions you may have include:
- What type of observations did ancient people make about the sky?
- What inventions helped our modern observations?
- What sort of observations can you make?
This lesson will answer those questions.
Observations made by ancient people
Ancient people studied the movement of bodies in the sky. The Sun was very important to them, because it was the source of warmth, growth and even ability to tell time. In fact, the ancient Egyptians even worshipped the Sun through their god Ra—the sun god.
People observed how the Sun came up in the east in the morning, traveled across the sky each day, and went down in the west. At first, they couldn't figure out how the Sun got from the west back to the east in the morning. Even after it was determined that the Earth was round, people still thought the Sun somehow traveled around the Earth.
The movement of the sun each day established the day as a unit of time. Later, the invention of the sundial allowed people to break the day into smaller units called hours.
Ancient people also noted how the position of the sun changed with the seasons. The sun is lower in the sky in the winter and higher and more direct in the summer. The year was also established as a unit of time, as a cycle of the seasons. From the study of the changing positions of the sun during the different seasons, calendars were invented to keep track of the parts of a year more accurately.
(See Our Solar System for more information about the Sun and the planets).
People also observed how the Moon travels across the sky. They noticed that it went through a cycle of different shapes. The cycle of the Moon was measured to be about 28 days.
The ancient people never really thought about what the Earth was and how it related to the moon until years later, when theories stated that the Earth was round, that the Earth traveled around the Sun, and that the Moon traveled around the Earth.
People watched the stars and observed how they appeared in configurations or constellations. Two notable constellations are Orion and the Big Dipper. Most of the stars were seen to rotate around the North Star. The North Star can be found by following the front edge of the Big Dipper.
(See Characteristics of the Universe for more information).
Some "stars" did not seem to rotate around the North Star. They had their own paths and were called planets. The ancient people noticed that the stars that rotated around the North Star seemed to twinkle, while the planets didn't. That was an easy way to identify which was which.
Ancient Greeks and Romans gave names to the various planets. However, we primarily use the Latin version of the names. The brightest "star" seen in the night sky is the planet Venus, named after the Roman goddess of love. The red planet is Mars, named after the Roman god of war.
One thing that startled people watching the sky at night were shooting or falling stars. They were thought to be stars that fell off the "roof" in the sky.
The view the ancient people had about the objects in the sky were taken strictly from their observations and studying what they saw with their naked eyes. Later, when telescopes were used, their concepts of the sun, moon, planets, and stars changed.
Inventions help modern observations
The invention of the telescope created a tremendous transformation in the study of the heavens. Around 1600, Galileo used one of the first telescopes to witness the rings around the planet Saturn and the moons around Jupiter.
Now astronomers can get a closer look at the moon, the planets and distant stars. It allows them to measure motion of these bodies more accurately, such that they can predict where the objects will be in the future.
Huge telescopes allow astronomers to look even deeper into space. Other telescopes were invented that measure radio waves and x-rays sent from distant galaxies.
Another very important invention in the study of objects in space was the spectrometer. This device examines the different colors that make up the light from a distant star. Each element gives off its own color distribution when it gives off light, such as during burning or intense heat.
The distribution of colors measured by the spectrometer allows scientists to determine the chemical composition of the distant stars. If the colors seem to be shifted, it is possible to determine the velocity of the star. This method is very similar to the Doppler Radar used in weather forecasting to tell the motion of a storm.
Since the color distribution measured by the spectrometer seems shifted toward the color red (called the "red shift"), it is an indication that most stars and galaxies are moving outward, away from the Earth, as if there had been an explosion. This resulted in the "Big Bang" theory of the Universe.
Make observations yourself
Look in the sky and make some observations yourself. Just about everyone has noticed the moon, but you would be surprised at the number of people who just haven't paid any attention to the stars in the night sky. Some say that they live in the city, so it is difficult to see the stars, but others are just not curious enough to care about the world around them. Be curious and observant.
I observed with telescope
A friend of mine is interested in astronomy and has his own telescope. He let me look through it at Saturn, and I was able to see the rings around the planet. It was truly amazing and freaked me out to see this little dot of light enlarged and to see the rings. It is one thing to see a photograph of it, but it is something else to see the real thing.
Look in the sky
If you get a chance, use a telescope or binoculars to look at the Moon, stars, and planets yourself. See if you can identify Mars, Venus, the phases of the Moon, and the Big Dipper. Find the North Star. Notice the movement of the stars at different times at night. Keep your eyes open for meteors and for the Milky Way.
Do you notice how things change at different times at night, on different nights, and different times of the year? Try to figure out why these things happen.
The study of astronomy involves the observation of the various objects in space. It is mostly done at night because the light from the sun overpowers the light from the dimmer planets and stars.
Ancients could only observe with their eyes, while we now have many instruments to aid us in our studies, such as the telescope and spectrometer.
Be curious about things; Be observant and you will excel
Resources and references
Space Weather - News about Earth-Sun environment
Questions and comments
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Observations in Astronomy