Earth's Motion

Earth's Rotation

• Earth's rotation is responsible for the apparent movement of the Sun across the sky and the occurrence of day and night.
• The Earth's axis is an invisible line that runs through the planet's center from the North Pole to the South Pole.
• The Earth is tilted at an angle of 23.5°, resulting in different parts of the planet receiving varying amounts of sunlight at any given time.
• This tilt is also responsible for the four seasons we experience on Earth.

Day and Night Cycle

• As the Earth rotates on its axis, one side of the Earth (or hemisphere) faces towards the Sun while the other side faces away.
• The Earth makes one rotation on its axis every 24 hours, or one day.
• As the Earth spins on its axis, the side facing the Sun moves from sunlight into darkness, appearing as a sunset from our view on Earth.
• Meanwhile, the dark half of Earth moves into the sunlight, experiencing sunrise.

Apparent Motion of the Sun

• The Sun appears to move from east to west across the sky due to the Earth's rotation from west to east.
• Shadows support this claim, as they change throughout the day.
• As the Sun appears to rise in the east in the morning, its light makes long shadows that point towards the west.
• By noon, the shadows become shorter, and as the day continues, the Sun appears to move towards the west, causing the shadows to lengthen again and point towards the east.

Historical Significance

• Before the invention of clocks, people used the Sun's apparent motion to tell time.
• The Sun's apparent motion can be used to create a sundial, allowing people to estimate time.

World War I Overview

• The war lasted from 1914 to 1918, involving the Central Powers (Germany, Austria-Hungary, Bulgaria, and the Ottoman Empire) and the Allied Powers (Great Britain, France, Russia, Italy, Romania, Japan, and the United States).
• Over 16 million people died worldwide as a result of the war.

Causes of World War I

• Germany's unification and annexation of French territories after the Franco-Prussian War of 1870 led to growing tensions in Europe.
• Germany's rise upset the European balance of powers, leading to a complex system of alliances.
• The assassination of Archduke Franz Ferdinand, heir to the Austro-Hungarian Empire, in Bosnia by a Serbian nationalist sparked the war.

Key Events and Battles

• Austria-Hungary declared war on Serbia, which was backed by Russia, leading to a chain reaction of declarations of war.
• Germany's Schlieffen Plan aimed to defeat France first and then shift forces to the east before Russia could fully mobilize.
• The Battle of the Marne halted the German advance into France and led to a war of attrition on the Western Front.
• Notable battles include Verdun and the Battle of the Somme on the Western Front, and the naval battle of Jutland between the German and British fleets.
• The war saw the first use of chemical weapons, gases, and aviation for observations, bombing, and air combat.

Global Involvement

• European colonies and British dominions, such as India, engaged in war from 1914 to 1916.
• Japan sided with Britain, seizing German colonies in China and the Pacific.
• The Ottoman Empire entered the war on the side of Austria-Hungary and Germany, opening fronts in the Middle East.

Italian and Russian Involvement

• Italy initially stayed neutral but eventually joined the Allies in 1915, attempting to annex new territories.
• Russia's army mounted several offensives on the Eastern front but was unable to break through the German lines.
• Russia's lack of advances led to economic instability and the Bolshevik Revolution of 1917, which ended Russian involvement in the war.

American Involvement and the War's End

• The United States entered the war in 1917 after Germany sank American ships and Britain intercepted a German telegram offering an alliance against the US.
• The arrival of US troops tipped the balance in favor of the Allies.
• Germany was finally forced to seek an armistice in November 1918, ending World War I.

Aftermath

• The war led to the fall of four large empires (German, Austro-Hungarian, Russian, and Ottoman) and the creation of new nations.
• Germany was forced to cut down its army and pay heavy war reparations, which was considered a humiliation by the German people.
• The Treaty of Versailles laid the groundwork for World War II.
• The League of Nations was created to promote peace, but ultimately failed to prevent the outbreak of World War II.