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  2. Types of solar eclipses.
  3. The Sun as a light source.
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For example, if it is Summer, ask the children if they think it is summer all around the world? If they say no, ask them why.

Audioslave - Shadow on the Sun [HQ]

If the students do not know, then refer to the post activity experiment section. Repeat step 3 over different periods of the day e. Also ask the children to note how the sun is moving across the sky each time the experiment is carried out. Ask the children to write out and draw their findings at the end of the day and discuss their observations in groups. Have the students compare the measurements from the day and make a conclusion from their findings. Repeat the exercise in the next season over the period of one year.

Did the shadows at noon get bigger? This will be the case if the season got colder e.


Did the shadows at noon get smaller? This will be the case if the season got warmer e. This should enable the students to visualise why each hemisphere has opposite seasons. It should also help students visualise what causes the seasons and its changes.

Lastly, the experiment will enable the students to understand day and night and will link to the main activity. The students should make the relation between shadow length and the time of day and year. Our experience shows that the shadow always moves clockwise around the object casting it.

Daytime Shadows | National Schools' Observatory

Its length continuously diminishes between sunrise and noon and, afterwards, prolongs again correspondingly. Measuring the shadow length is necessary to learn the principle behind time and seasons. To understand how shadows vary in length at different times of the day and how they change over the seasons. To gain hands on experience with scientific practices through observation, recording and concluding based on data in order to understand the process of scientific inquiry.

Understand how seasonal changes affect life on Earth.

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Learn how to tell the time without a clock. What are the practical applications of this experiment? Example: Timekeeping with Sundials. Weather conditions that allow shadows to be cast with the Sun, i. Before the Activity: Ask the students what would happen if this activity were carried out on a cloudy or rainy day. Main Activity: Step 1: Begin the activity in the morning and ask the children to look at various objects that cast a shadow.

Step 2: Observe the solar shadow with the children and ask them to note the direction of the shadow. The maximum duration for an annular eclipse is 12 minutes 30 seconds. However, an annular solar eclipse is similar to a total eclipse in that the moon appears to pass centrally across the sun. The difference is, the moon is too small to cover the disk of the sun completely. Because the moon circles Earth in an elliptical orbit, its distance from Earth can vary from , miles to , miles.

So if the moon is at some greater distance, the tip of the umbra does not reach Earth. A good analogy is putting a penny atop a nickel, the penny being the moon, the nickel being the sun. In most cases, an A-T eclipse starts as an annular eclipse because the tip of the umbra falls just short of making contact with Earth; then it becomes total, because the roundness of the planet reaches up and intercepts the shadow tip near the middle of the path, then finally it returns to annular toward the end of the path.

Of all solar eclipses, about 28 percent are total; 35 percent are partial; 32 percent annular; and just 5 percent are hybrids. Eclipses do not happen at every new moon, of course. But as a rule, at least twice each year and sometimes as many as five times in a year , a new moon will align itself in just such a way to eclipse the sun. That alignment point is called a node. Depending on how closely the new moon approaches a node will determine whether a particular eclipse is central or partial.

This interval is known as the Saros cycle and was known as far back as the days of the early Chaldean astronomers some 28 centuries ago. After this interval, the relative positions of the sun and moon relative to a node are nearly the same as before. That third of a day in the interval causes the path of each eclipse of a series to be displaced in longitude a third of the way around Earth to the west with respect to its predecessor. For example, on March 29, , a total eclipse swept across parts of western and northern Africa and then across southern Asia.

One Saros later, on April 8, , this eclipse will recur, except instead of Africa and Asia, it will track across northern Mexico, the central and eastern United States and the Maritime provinces of Canada. As a solar eclipse approaches, the mainstream media often will provide a variety of warnings and advisories against looking at the sun with bare eyes, as blindness could ensue. This has given most people the idea that eclipses are dangerous.

The sun constantly emits invisible infrared rays that can damage your eyes. Ordinarily, we have no reason to gaze at the sun. Binoculars or a small telescope mounted on a tripod can also be used to project a magnified image of the sun onto a white card. The farther away the card, the larger you can focus the image. Look for sunspots. Notice that the sun appears somewhat darker around its limb or edge. This method of solar viewing is safe so long as you remember not to look through the binoculars or telescope when they are pointed toward the sun; put another way, never look directly at the sun when any part of its blindingly bright surface is visible.

Open a sun-facing window and place the covered mirror on the sunlit sill so it reflects a disk of light onto the far wall inside. The farther away from the wall is the better; the image will be only 1 inch across for every 9 feet or 3 centimeters for every 3 meters from the mirror. Modeling clay works well to hold the mirror in place. Experiment with different-sized holes in the paper. Again, a large hole makes the image bright, but fuzzy, and a small one makes it dim but sharp. Darken the room as much as possible. What do you see? Is it worth a photograph? You will see scores of partially eclipsed suns projected through pinhole gaps between the leaves.

This is caused by diffraction, a property of light. According to Vince Huegele, an optical physicist at the NASA Marshall Space Flight Center, the light rays do not shoot straight by the rim of the gaps, or a pinhole, but bend around the edge. This wave effect creates a pattern of rings that resembles a bull's eye. Acceptable filters for unaided visual solar observations include aluminized Mylar. Some astronomy dealers carry Mylar filter material specially designed for solar observing.

The most common way to draw declination arcs on a sundial is for each Zodiac change. This leads to 7 arcs, 5 of them being crossed twice by the Sun when its declination is increasing and when it is decreasing , plus two for solstices extreme declinations. From left to right, a sundial with arcs of solstices plus the equinoctial line , a sundial with the 7 declination arcs, and a sundial with an arc for the first day of each month.

Ancients often used markers based on sunrise or sunset. For example, Italian hours count 24 hours from the last sunset to the next one; Babylonian hours count 24 hours between two sunrises. These hours are sometimes visible on old sundials. Unequal hours were also used.

The Shadow Knows: How to measure time with a sundial

They count 12 hours between sunrise and sunset, or during the night between sunset and the following sunrise. Their duration vary from 40 to 80 minutes depending on the moment of the year, that is why they are called unequal hours. Toggle navigation Home. Download Shadows Sundials Understanding sundials Choose a place for your sundial Build your own sundial Classic sundial with a polar style Analemmatic sundial Cylindrical sundial Bifilar sundial Bibliography on sundials Sundial makers Glossary of technical terms Useful links on sundials Astrolabes Photos FR.

Understanding sundials A sundial is a device that tells time using the position of the Sun, or more precisely using its hour angle, or sometimes its altitude. Sundials are usually installed on a wall facing south, or horizontal on a column, or sometimes oriented and inclined by any angle, and even drawn on curved surfaces. Understanding sundials.