TOPIC 6: ELEMENTARY ASTRONOMY – PHYSICS NOTES FORM 4

Welcome to our website scholars.co.tz. In this article, are you looking for TOPIC 6: ELEMENTARY ASTRONOMY – PHYSICS NOTES FORM 4, Download Physics Notes Form Four Topic 6

WHAT IS ASTRONOMY?

The word astronomy is derived from the Greek astron, meaning “star” and nomos, meaning “laws or cultures“. The literal meaning of the word astronomy therefore is “law of the stars“.

Astronomy is the branch of science that deals with study of the origin, evolution, composition, distance and the motion of all bodies (objects) and scattered matter in the universe.

The universe is the totality of space and time together with matter and energy.

People who are involved in astronomy are known as astronomers. Astronomers study the objects that compose the physical universe, stars, planets, moons, galaxies and nebulae.

Astronomy is one of the oldest fields of science. Early astronomy involved observing the regular patterns of the motions of visible celestial objects, especially, the sun, moon, stars and planets with their naked eyes. An example of astronomy was the study of the changing position of the sun along the horizon or the changing appearances of stars in the course of the year. These were used to establish agricultural and ritual calendars.

Importance of astronomy to mankind

Astronomy has been an important tool for thousands of years. The following are some ways in which astronomy is important;

1. It was the earliest method of measuring time. A day was the duration between sunrise and sunset while a month was derived from phases of the moon. The year was derived from the changing position of sunrise.

2. It was used to develop calendars that made it possible to predict the seasons. The season was very important in agriculture as they dictated the planting time and the harvesting time.

3. It was used in both land and sea navigation based on the knowledge of the position of the sun during the day and the stars at night.

4. Today, astronomy helps us to understand where the earth and the life it supports originated from and how it evolved.

5. Astronomy presents a new frontier for exploration.

The solar system

The solar system is made up of the sun arid the celestial objects bound to it by gravity. The objects include the eight planets and their known moons and billions of small bodies that include asteroids, comets, meteoroids and interplanetary dust.

Solar system

Stars and planets

A star is a large celestial body made up of hot as known as plasma.

Plasma refers to an ionized gas in which a certain proportion of electrons are free rather than bound to an atom or molecule. Stars radiate energy derived from the thermonuclear reactions in the interior region. The sun is the largest star.

The sun is also the closest star to the earth at a mean distance of 149.60 million kilometers. This distance is known as the astronomical unit and is used to measure distances across the solar system.

Structure of a star – the sun

A galaxy is a giant collection of stars, gas and dust. Most stars in the universe are in the galaxies. Nearly all of the stars visible in the night sky are within our own galaxy, our galaxy is called the Milky way galaxy.

A planet is a major (large) object which is in orbit around a star. There are eight such objects which are in orbit around the sun. These are commonly referred to as “the planets”. They are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.

The following are the three defining characteristics of a planet:

1. It is a celestial body that orbits a star.
2. It is massive enough so that its own gravity causes it to assume a spherical shape.
3. It has cleared the neighborhood around its orbit.

NOTE: Because Pluto resides in an area of space populated by numerous other objects, it is no longer considered a planet. Pluto is now designated a dwarf planet. A dwarf planet does not meet the third characteristic, i.e. has not cleared the neighborhood around its orbit.

Differences between stars and planets

stars	Planets
Emit own light.	Do not emit their own light.
Twinkle at night.	Do not twinkle at night.
Appear to be moving from east to west.	Planets move around the sun from west to east.
Their temperatures are usually very high.	Their temperatures depend on their distances from the sun.
Countless in number.	There are eight in the solar system.
Very big in size but they appear small because they are very far away.	Very small in size as compared to stars.

TOPIC 6: ELEMENTARY ASTRONOMY – PHYSICS NOTES FORM 4

CLICK HERE TO READ IN FULL PAGE