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Colegiul Tehnic Danubiana Roman – ROMANIA –

1. SundialsHow to Build A Sundial for the school garden

1. SundialsHow to Build A Sundial for the school garden

• Basic Parts:» Hours markers» Gnomon – A device that cast a shadow on

the hour markers.

• The Gnomon must be aligned with the Earth s rotation axis for the sundial to work properly.

• Analemmatic SundialSUNDIALS come in a wide range of different types, though by far one of the most popular and 'interactive' sundials is this "SUNCLOCK", or HUMAN SUNDIAL - which uses a PERSON'S OWN SHADOW, to show the correct clock time !

Horizontal/Analemmatic Sundials

• ANALEMMATIC SUNDIAL:• Analemmatic sundials have a vertical gnomon (the pointer that

makes a shadow) that is placed in a different location depending on the date, because the sun's position in the sky differs from month to month. They are often made with the user acting as the gnomon, and the user's shadow showing the time. The design is elliptical in shape and needs to have its dimensions and lawet carefully customized for our latitude, longitude and timezone.

• In the horizontal version of the dial, gnomon position lies on the straight North-South minor axis, at a point determined by the sun's declination. The analemmatic dial may be regarded as a projection of the universal equatorial ring dial.

Analemmatic Sundial PDF Generator

2. Garden Sundial

The Sundial Face

• Begin the project by cutting a 20-inch diameter circle from 3/4-inch plywood. Give both sides two coats of primer. While it is drying, start planning a design for the sun dial face. We will choose colors, number style (Roman numerals, standard, etc.), and some kind of illustration welike. Draw some designs welike on a large piece of paper. We'll need a compass, straightedge, and protractor to place the hours correctly. Each hour must be located on a circle exactly 15 degrees from the next hour.

The Gnomon

• The gnomon is a two- or three-inch length of threaded pipe, one half-inch in diameter. It, like the flange, will rust if not painted. The diameter of the gnomon should be a little wider than the pipe's, and we'll need to improvise a conical tip for it. The total length of the pipe and the gnomon tip should not be more than three inches.

Preparing the Post•  To make the sundial work correctly, it must be properly mounted

on a carefully prepared and placed post. Use a 4 by 4 by 8 pressure-formed, outdoor-treated post. Make sure it is straight and free of large cracks. The 4 by 4 must have a carefully measured and cut angle at the top, in order to mount the sundial face correctly. To find the angle, subtract our latitude from 90 degrees. For example, if we're making our sun dial in Columbus, Ohio, 40 degrees N. latitude, we'll draw a 50 degree angle on the 4 by 4. Use a carpenter's square to draw a line at right angles to the 4 by 4, six inches from the top. That line becomes the bottom side of the angle. Now we are ready to measure the angle and cut it.

Placing the Post •  Obviously, we should choose a sunny spot for our post. Don't put

the top of the post more than five feet above the ground. If it's higher, at times we will find ourself looking into the sun and shading our eyes in order to read the time. It's best a little below eye level, but it can be any height from eye level to fairly close to the ground.

• Next dig a hole for the post. Be alert for any buried cables or lines. No matter what height we've selected, the slanted angle we cut must face north. Use a good magnetic compass or, preferably, the North Star. Your post must be perfectly vertical, and we can check this with a carpenter's bubble level.

• Set the post in cement. When firmly set, which will be a matter of several days, we'll be ready to mount the sundial face.

Attaching the Sundial Face •  Attach the sundial face with the 5/16 by 2-inch lag screw.

Tighten the screw only to the point where you can still rotate the sundial face with one hand and a little effort. Next put the flange over the center of the sundial face, with the lag-screw head showing in the center hole of the flange. Screw the gnomon pipe into the flange with your right hand as your hold the flange in place with your left hand. Position the sundial's face so that the 6 A.M. line and the 6 P.M. line are horizontal. Next, align the gnomon so that the 6 A.M. and 6 P.M. lines seem to go straight through the middle of the gnomon. The 12 noon hour line should also seem to go straight through the gnomon.

Setting the Time •  Now set the time. Holding the flange in place with your left hand,

rotate the sundial face with your right hand until the shadow of the gnomon on the sundial face reads the same as the clock time (this must be done during Daylight Saving Time). Mark the position of each of the four flange screw holes. Remove the flange. Tighten the lag screw firmly without moving the sundial face. Predrill holes for the four screws that will attach the flange. Attach the flange with the screws. Screw in the gnomon.

3. MATERIALS LIST for pocket sundial SHADOW PLOT:• 1 piece of large white paper• pencil width wooden dowel (or similar) 30.48 cm(12") to 38.1 cm (15") long• ball of clay• two 12" piece of duct tape, cut into eight 3" strips• permanent marker• timer

HORIZONTAL SUNDIAL:• small wooden disk• 3/4"-1" nail• pencil• pen• pair of scissors• index card• hammer• protractor• sheet of paper• (optional) string• wood glue

DIPTYCH SUNDIAL:• template for diptych assembly • 1 piece of heavy paper• glue• string, preferably elastic

• PREPARATIONSHADOW PLOT:• Gather materials.• If necessary, cut wooden dowel to 12" to 15" long.• Locate geographic north (see Directions section, below).

HORIZONTAL SUNDIAL:• Obtain materials.• Locate our latitude• Locate geographic north (see Directions section, below).• (optional) If we want to make our sundial into a necklace or key

chain, drill a hole into the wooden disk to pass the string through.• If doing this activity with a large group of weng children,, prepare

the nails in the wooden disks as well (steps 1-2 in the Directions section).

DIPTYCH SUNDIAL:• Obtain materials.• Print out the Diptych Template (see the attached Construction

Worksheet).• Locate our latitude• Locate geographic north (see the Directions section, below).

Set-Up:

DIRECTIONS

Construction & Testing:

PART I. FINDING GEOGRAPHIC NORTH TO POSITION YOUR SUNDIAL:• The sundial must be positioned with the gnomon pointing north/south and, of

course, the dial must be located where a shadow will be cast by the gnomon most of the day. Use one of the following three methods to find geographic north for our latitude.

Method 2: The Practical Method• Use a magnetic compass to determine the north/south line, but because of the

difference between magnetic north and true north, the dial reading could be off by an hour or more, depending on the local difference between magnetic and true north.

Method 3: The Lazy Method• For a first approximation, determine the the orientation at any time by using a

clock or watch, and positioning the dial so the shadow shows the correct time. However, if left in this position, an error of up to 30 minutes could result over the year because of what is known as the "equation of time." Because of the Earth's orbital motion around the sun, the solar day (approximately 24 hours) is not exactly the same length from day to day, varying by up to +/- 16 minutes a day.

PART II. BUILDING THE SUNDIAL:

A. SHADOW PLOT:

CONSTRUCTION: (refer to the attached Construction Worksheet for images) A shadow plot can also help we obtain a feel for how the sun's path changes across the sky from day to day. To best see this effect, work on the shadow plot for several weeks.• Set up our shadow plot in the morning, around 9:00am.• Find a flat location that is clear from shadows all day long.• Push a ball of clay into the ground.• Insert the wooden dowel into the ball of clay so that it stands

vertically. Use four of strips of duct tape to cover the clay to keep it from melting in the sun and help secure the dowel. The dowel must stand in this exact location for the length of the activity (from one day to several weeks), so make sure it is perfectly vertical and very secure.

• Once the dowel is in place, look for its shadow. Lay a piece of paper down on the north side of the dowel with the long edge up against the base of the dowel support. If we did not previously find geographic north (as described in the Directions section), we can now determine which direction is north since we know the sun is in the east and the dowel shadow is facing west.

Drawing the North-South line:

• Use the remaining four strips of duct tape to secure the corners of the paper. Make sure to keep the middle of the paper clear as this is where we will make our plot.

• You are now ready to start making our measurements. The shadow from the dowel should be on the piece of paper. If it is not, wait about an hour and return once the shadow is cast onto the paper. When we have the shadow on the paper, make a mark at the very end of the shadow.

• Return to the plot about once every 30 minutes and make a mark at the end of the shadow each time. It is helpful to use a timer. If we start our plot at 9:00am, we should have enough markings by 3:00pm.

USING YOUR SHADOW PLOT:• After one day of shadow measurements, we are ready to draw the

north-south line. On our completed shadow plot draw a smooth curve through all of the marks that we made, without moving the paper. The more often we took measurements, the easier it is to draw this curve accurately.

• Once we have drawn a smooth curve through the markings, find the shortest distance between the dowel base and this curve. Draw a line from the dowel base to this point. This line is called a north-south line. It is the line along which the sun casts a shadow at local noon. (Your local noon may not be exactly when the clock says noon, depending on where we are in our time zone.) This north-south line points exactly north and south. A line drawn perpendicular to this line points east and west. You need to know the exact direction of north to use our horizontal sundial.

B. HORIZONTAL SUNDIAL:

CONSTRUCTION: To align the gnomon, we must position it such that it makes an angle equal to the latitude angle where it will be used with the horizontal face of the sundial (refer to the attached Construction Worksheet for images). The easiest way to get the nail into the wooden disk at this angle is to do the following:• Hammer the nail straight into the center of the wooden disk,

making sure not to hammer the nail through the back of the disk.

• Hammer the nail from side so that it begins to bend over. Continue to bend the nail over until it is at the same angle as our latitude. If the nail becomes loose, use a little wood glue at the base to secure it.

• To begin construction of the hour line template, use a pencil to draw a horizontal line on the piece of white paper.

• Align the protractor on the horizontal line and make a pencil tick at the 90-degree mark.

• Draw a vertical line from the tick mark down to the horizontal line. You have just created the noon and six o'clock lines!

• Use a protractor and make a pencil tick at the following angles FROM THE VERTICAL NOON LINE (on both the left and right hand sides of the vertical line): 10.7, 22.2, 35.3, 50.8, 69.2, and 90. These coincide with 1, 2, 3, 4, 5, and 6 hours from noon, respectively.

• Use the straight edge of the protractor and connect each tick mark to the intersection of the horizontal and vertical lines.

Hour Line Markings for 45 Latitude:

Equatorial Sundial

Horizontal/Analemmatic Sundial

Globe Sundial

CD Sundial

Digital Equatorial Sundial

Universal Ring Sundial

SUNDIAL - idea to realisationour shadow tells time

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