- Steven Francis
Tilted Earth: The Earth is blue. It's orbital path is green. The Earth's axis (going through North and South pole) is red. Your city is pink. Use the sliders down the bottom to see how the ratio of daylight hours and night hours change with tilt and latitude. Start by having the tilt = 0 degrees and latitude at 0 degrees (the equator). Slide the Day slider from 0 to 24 and see how your 'city' moves around a circle in this time. Note this circle is divided into 2 parts, yellow (day light) and purple (night). There is also a vertical grey plane going through the spherical Earth to split the Sun-lit half of the Earth from the dark-half of Earth. Note, with no TILT, your city spends 50% of the time in daylight (its 24-hour circular path is half yellow) and 50% of the time in darkness (purple). Use the Day slider from 0 to 365 to see that this is true ALL YEAR ROUND. So always 12 hours of day and 12 hours of night (ignore twilight and atmospheric effects). Next, change your latitude (only goes down for Southern Hemisphere). Note the 24-hour circular path gets smaller for lower latitudes. Yet still, with an untitled Earth, there is still 50% daylight and 50% night (over 24 hours). Now for the interesting part. Start on Day = 0 (or 1). Change the tilt to 23 or 24. Note the whole Earth tilts (axis AND city and its 24 hour circle around the Earth). At latitude = 0 (equator), this doesn't have any effect on the ratio as the centre of the 24 hour circle coincides with the pivot point from which you tilt the Earth. However, change the latitude (say roughly around 40 degrees for Melbourne) and note the circle tilts so that MOST of it is on the left side of the light/dark plane cutting through the Earth. Thus, if the Earth is on the right side of the sun (as it is on Day 1), then more of the circle is in the daylight side. So long days and short nights. Change to day 182 (6 months later) and note the Earth is now on the left side of the sun, most of the circle is on the dark side (always left, but now left is the dark side). Thus, short days and long nights. For Melbourne on Earth (tilt 23 or 24 - should be 23.5 but this slider is whole numbers only.... and latitude = 38), push play and watch how the daylight hour / nighttime hour ratio changes throughout the year. Next, lower the latitude to 67 (just inside the arctic circle) and watch over a year. Note at times it is entirely in daylight and at other times entirely in darkness. This becomes even more extreme at latitudes beyond 67 (up to 90 which is the South Pole). Finally, play with all the sliders and control your vantage point.