sun, earth and moon
How do sun, moon and earth turn around each other? How comes there' seasons, day and night, or the tides. Discover the link to all of it in this GeoGebrabook. Besides applets I created myself some are translations and/or adaptations of existing material I used with most gratitude. Th work of people like Fabrice Vanolli, François Morin, Steven Francis and Marc Dewi Freitag helped me on my way.
Table of Contents
- earth's orbit
- apparently a circle
- the ellips
- apparent movement of the sun
- axial tilt
- axial tilt
- the seasons
- latitude and the seasons
- altitude of the sun
- midday sun in the northern hemisphere on ...
- day and night
- angle of incidence of the sun on the equinox
- the sun during the year
- sunrise and sunset
- sun, earth and moon
- the orbit of the moon
- eart's orbit and moon's orbit
- moon fases
- moon fases in the picture
- sun and moon in the sky
- tides
- Venice
apparently a circle
Next applet shows the earth's orbit around the sun. Apparently it's a circle with the sun in the centre. But when dragging the earth on its orbit you'll see there's more...[br]Select the checkbox to show more details on the earth's orbit.
The earth's orbit is not a circle but an ellips with two foci. When the distance between these two increases, the ellips has got a greater eccentricity and its form gets flatter. When the two foci coincide, the eccentricity is 0 and the form becomes a circle.[br]The sun is placed in one of the two foci. This is the reason that the distance between earth and sun is not constant. The point on the orbit with the shortest distance is called the [i][b]perhelion[/b][/i], the point with the greatest distance is called [i][b]aphelion[/b][/i]. You can hardly distinguish the earth's orbit from a circle since the eccentricity is very small. Move the sun to the right and see how the earth's orbit changes with it.
properties of an ellips
You can read more about the properties of an ellips in next worksheet.
axial tilt
The axis of the earth is not perpendicular to the plane through the elliptical earth's orbit. It's tilted by an angle of 23,5°. The consequence is that through the year a different part of the earth is tilted towards the sun, which explains the seasons. [br]If the north pole it tilted towards the sun, it's summer on the northern hemisphere and winter on the southern.[br]Drg the centre of the earth along its orbit around the sun and see how the axial tilt correspond with the succession of the seasons.
axial tilt
During a period of some 40 thousand years, the axial tilt varies between 22,1° and 24,5°. A greater angle means a greater contrast between the seasons on earth, warmer summers and colder winters. A smaller angle means colder summers and milder winters.[br]The axis of the earth describes a full circle within each 26 thousand years. Nowadays it's summer on the northers hemisphere when the earth is in the aphelion, so on its farthest point to the sun. For a summer in the perihelion we have to wait for another 13 thousand years. This effect is called precession.
midday sun in the northern hemisphere on ...
The sun in Brussel or elsewhere
How high in the sky is the sun in Brussel on ...[br]Move the slider with the day or click in the bottom left corner on the arrow to start the animation and follow the axial tilt during the year.[br]Click on the checkbox [i]graph[/i] to show the inclination of the sun throughout the year. Change the latitude and see how the graph changes. See what happens above the north pole circle and in the tropical zone.
the orbit of the moon
ellips
Just as the earth's orbit around the sun, the moon to follows an elliptical orbit around the earth. The earth is placed in one of the two foci. So the distance between earth and moon is not constant. Drag the moon on its orbit and see how distance changes.[br]The point with the greatest distance to the earth is the [b]apogeon[/b] (distance about 405 490 km). The nearest point is the [b]perigeon[/b] (about 363 350 km).