Capricorn: Dec.22-Jan.29 The Sundial Primer
created by Carl Sabanski
Capricorn: Dec.22-Jan.29

The Sundial Primer Index

More Sun Charts

The Sun Charts illustrated on this page were created using an on-line program at the web site of the University of Oregon Solar Radiation Monitoring Laboratory. If you would like a set of Sun Charts for your location please visit their Sun Chart Program web page at: http://solardat.uoregon.edu/SunChartProgram.html


Figure 1 illustrates sun charts for each half of the year for the Equator.  These charts are for an observer located on the Equator who is facing south.  If the chart is difficult to visualize try this. Imagine that you cut out the sun chart around the boundary and then roll it into a cylinder. The lines are inside the cylinder. Now imagine that you are inside the cylinder and at centre of the base. The north-south and east-west lines intersect at your location. The 90 solar azimuth or east is to your left and the 270 solar azimuth or west is to your right, so you will be facing south. The curved lines on the left and right sides of the chart will join directly behind you to the north. Where they join there will be a second 12 p.m. (noon) line.

Figure 1: Sun Charts - Equator

Figure 1: Sun Charts - Equator

What can you tell from the charts in Figure 1? The first thing is that the sun rises at 6 a.m. and sets at 6 p.m. every day of the year. There are 12 hours of day and 12 hours of night throughout the year at the Equator. Every day is an equinox. During the spring /summer (March to September) in the Northern Hemisphere (fall/winter in the Southern) the sun will be in the Northern Hemisphere and during the fall/winter (September to March) in the Northern Hemisphere (summer in the Southern) the sun will be in the Southern Hemisphere. At the spring and fall equinoxes the sun passes along the east-west line and will be directly above you at noon, reaching its highest elevation during the year. At the summer and winter solstices the sun will reach its lowest noon elevation of: 90 - 23.44 = 66.56.

A vertical sundial at the Equator will be have its dial plate parallel to the Equator. The height of the gnomon will be equal to the co-latitude or 90. It is perpendicular to the dial plate and parallel to the Earth's polar axis. Between the equinoxes for half the year the sun will illuminate a north facing dial and for the other half of the year it will illuminate a south facing dial between the hours of 6 a.m. and 6 p.m.. At the equinoxes neither dial will be illuminated. This is the description of an equatorial sundial.

A horizontal sundial at the Equator will have its dial plate parallel to the Earth's polar axis. The height of the gnomon will be equal to the latitude or 0. It is parallel to the dial plate and the Earth's polar axis. The sun will illuminate this dial from 6 a.m. to 6 p.m. all year round. This is a description of a polar sundial.


Figure 2 illustrates sun charts for each half of the year for the North Pole. The sun charts for the South Pole would be similar except the months would be from September to March. Perform the same visualization as described above. As you turn around in the cylinder you will see that the sun is visible all day during certain periods of the year.

Figure 2: Sun Charts - North Pole

Figure 2: Sun Charts - North Pole

What can you tell from the charts in Figure 2? During the spring/summer at the North Pole (March to September) and South Pole (September to March) the sun will never set and during the fall/winter at the North Pole (September to March) and South Pole (March to September) the sun will never rise. There will be either 24 hours of daylight or 24 hours of darkness. The sun will maintain almost a constant elevation throughout the day and it will reach a maximum elevation of 23.44 on the summer solstice. It disappears at the fall equinox and reappears at the spring equinox.

A vertical sundial at the North or South Pole will have its dial plate parallel to the Earth's polar axis. The height of the gnomon will be equal to the co-latitude or 0. It is parallel to the dial plate and the Earth's polar axis. The sun will illuminate this dial for 24 hours a day during the spring/summer months of March to September at the North Pole and September to March at the South Pole. The sun will illuminate a south facing dial from 6 a.m. to 6 p.m. at the North Pole and 6 p.m. to 6 a.m. at the South Pole. It will illuminate a north facing dial from 6 p.m. to 6 a.m. at the North Pole and 6 a.m. to 6 p.m. at the South Pole. The sundial will be in darkness for the other half of the year. This is a description of a polar sundial.

A horizontal sundial at the North or South Pole will have its dial plate parallel to the Equator. The height of the gnomon will be equal to the latitude or 90. It is perpendicular to the dial plate and parallel to the Earth's polar axis. The sun will illuminate this dial for 24 hours a day during the spring/summer months of March to September at the North Pole and September to March at the South Pole. The sundial will be in darkness for the other half of the year. This is a description of an equatorial sundial.