Concept map
Use the words in the cloud to create your own concept map about the simplest kingdoms in your notebook. Write any connecting texts you need.
As a planet of the sun, the Earth revolves around the sun. Besides this, it also rotates on its own axis. Thus the Earth has two motions: the rotation and the revolution.
Rotation
The Earth rotates on its axis from west to east. The axis is an imaginary line passing through the northern and the southern poles. Earth's rotation is completed in about 24 hours — this is called the daily motion of the earth. This motion is responsible for the occurrence of day and night.
One rotation is completed when a given heavenly body crosses the observer's meridian two times in succession.
How rotation periods are calculated: The period of rotation is calculated with reference to a star and with reference to the sun. When it is calculated with reference to a star, it is called a sidereal day and when it is calculated with reference to the sun, it is called a solar day.
Solar days and sidereal days: The solar day is a time period of 24 hours, and the duration of a sidereal day is 23 hours 56 minutes. This difference of four minutes between a solar day and a sidereal day is due to the fact that the position of the Earth keeps changing with reference to the sun due to the revolution around it; while with reference to a star at infinity, it will remain unchanged. Thus, a sidereal day is the actual time taken by the planet for a rotation of exactly 360 degrees on its axis.
As a result of the apparent motion of the sun, the appearance of the night sky as seen from the Earth changes from day to day. The stars rise every day, four minutes earlier than the preceding day. Also, every night, one degree of celestial sphere is added to the eastern sky while one degree is lost from the western sky.
Earth's Revolution
Revolution
The movement of the Earth around the sun in its orbit is called revolution. This movement of the earth is also from west to east. The period of revolution is one year (365 1/4 days).
The orbit of the Earth around the sun is elliptical and not circular. Due to this, the distance between the Earth and the sun keeps changing.
When this distance is minimum, the Earth is said to be in perihelion (around January 3).
When the distance is the maximum, it is said to be in aphelion (around July 4).
The average of the maximum and minimum distances is called the mean distance and this distance of the sun from the earth is 150 million kilometers.
The apparent annual track of the sun through the fixed stars in the celestial sphere is called the ecliptic, and an imaginary plane passing through this plane and extending outward through all points is called the plane of ecliptic. This plane is imagined to be horizontal. The axis of the Earth (rotational or polar axis) makes an angle of 66 1/2 to the plane of ecliptic.
The Earth's axis points constantly to the same point (the polar star) in the celestial sphere. As a consequence the latitude on the surface of the earth at which the sun's rays fall vertically keeps changing as the earth moves it its orbit around the sun. Due to this the earth attains four critical positions with reference to the sun.
The equinoxes: On 21st March, the Earth is so positioned with reference to the sun that the sun's rays are vertical at the equator and the entire world experiences equal day and night.
The autumnal equinox: A similar situation occurs on September 23.
Summer solstice: On 21st of June the sun's rays are vertical over the Tropic of Cancer as the north pole of the Earth is inclined at its maximum towards the sun. At this time, the north pole experiences a long continuous day and the south pole a long continuous night (ergo, what we know as summer solstice). The northern hemisphere has the summer season at this time and the southern hemisphere experiences winter now. Also the days are longer than the nights in the northern hemisphere at this time.
Winter solstice: On December 22, the position of the earth with respect to the sun is such that the south pole is inclined at its maximum towards the sun and the Tropic of Cancer receives the vertical rays of the sun. This position is called the winter solstice when the sun shines continuously in the south polar region and it is a long continuous night at the north pole. This is the winter season in the northern hemisphere and the summer in the southern hemisphere. During the winter solstice, the days are longer than the nights in the southern hemisphere.
Thus, the variation in the duration of day and night and the change of seasons are due to the earth's revolution and the inclination of the axis of the earth. Also the seasons are reversed from the northern to the southern hemisphere.
The Midnight Sun
At the time of the summer solstice, there is continuous day at the north pole as the circle of illumination passes through the Arctic Circle beyond the pole. As a result, at the places situated beyond the Arctic Circle, the sun will be visible continuously even when it is night at the same longitude in the lower latitudes. This phenomenon is called the midnight sun. A comparable situation occurs in the Antarctic Circle during the winter solstice when the circle of illumination passes through this circle beyond the south pole.
In this post we are going to explore the main vocabulary about The Universe Read the text in this link Click here to test what you have learned. Task Copy the sentences in your notebook ADDITIONAL TASK Complete this fill in the gaps activity. Now, just have some fun. Let´s playVOCABULARY GAME
How Prehistoric Life is studied?
Prehistoric life can be studied through different approaches.
One important source of evidence are fossils. How you ever wonder how fossils can be formed?
Watch this video to discover it
When will the next mass extinction occur? - Borths, D'Emic, and Pritchard
About 66 million years ago, a terrible extinction event wiped out the dinosaurs. But it wasn’t the only event of this kind -- extinctions of various severity have occurred throughout the Earth’s history -- and are still happening all around us today.
Here you have a collection of interesting areas to dig deeper into stem cell research.
First hamburger made from lab-grown meat
In August last year the world's first hamburger was grown in a lab. Starting with stem cells extracted from the biopsy of a cow, a team of scientists grew 20,000 muscle fibres over the course of three months. You can find out how they then turned these fibres into a hamburger in this news article, which includes a video on the process.
Stem cell research highs and lows – interactive timeline
In 1996 the future of stem cell research looked bright, but since then its development has been fraught with troubles. This interactive timeline picks out the highs and lows.
How to clone a mammoth
Although currently unlikely, in the future it may be possible to clone a mammoth. This article looks at the role stem cells could play in this.
Resources from the Guardian Teacher Network
Understanding stem cells
This lesson introduces students to the key concepts in stem cell science. It's made up of a set of short modules, mixing group activities with teacher-led discussion.
Role play scenario
This role play is based on a public hearing of a research ethics committee, which needs to decide whether to grant a licence for a clinical trial using human embryonic stem cells to treat spinal cord injuries.
Activities to spark debate
A collection of activities to help students explore issues surrounding stem cells, including a quiz. The resource also gives information on good websites for students to look at to find out about stem cells.
Issues surrounding stem cell research
This lesson plan from the Wellcome Trust looks at implications of stem cell research and considers how it's likely to develop in the future.
The best of the web
The history of a medical sensation – timeline
This timeline from the New Scientist documents how stem cell research has developed over time. From being identified in mice in 1981 to a trial to see if it can treat age-related blindness this year.
Debating stem cells
The political and scientific arguments surrounding stem cells are considered in this article from Time magazine, which also discusses alternatives to the method.
EuroStemCell
There are a whole host of teaching resources on stem cells on the EuroStemCell website, which brings together the research of more than 90 research labs across Europe.
