evaluate the accuracy of their observations, to design and conduct investigations to test their conjectures, and to think critically and logically about the relationships between evidence and explanations.

Earlier in the solar system unit, Mr. Gilbert emphasized the importance and technique of gathering evidence about the world and recording it in a notebook. For example, when he challenged the students in his science classes several weeks ago to create sun clocks using sun shadows, he encouraged them to record data about the position, size, and orientation of the shadows that they studied, and to note the rate at which the shadows moved. He also asked them to include a detailed description and sketches of the way in which the shadows were observed to change. They had carefully carried out his instructions, recording their results in their science notebooks.

In earlier class sessions, Mr. Gilbert’s students learned how to construct and use several simple tools that helped them make their data and evidence gathering more accurate. One they would use in their study of the moon was a simple sextant constructed from a protractor, a plastic drinking straw, and a string with a metal washer attached to it. They had taped the string with the washer on the end to the bottom of the protractor at the 90° line. Then they taped the straw along the straight edge of the

In the illustration above, a simple sextant (as described in the text) is being used to determine the angle of inclination of the top of a flagpole. The student first sights the horizon, a 90° reading on the sextant. Then she sights the top of the flagpole, which gives a 70° reading. To determine the angle of inclination, the student must determine the difference between the sextant reading for the top of the flagpole, 70°, and the reading for the horizon, 90°. Therefore, the angle of inclination of the top of the flagpole from the student’s vantagepoint is 20°. The height of the flagpole can be determined once the distance of the student from the flagpole is measured. When observing celestial objects, the apparent angle of elevation above the horizon is found by determining the difference between 90° (the horizon) and the sextant reading when the object is sighted through the straw. For printed clarity, the protractor above contains only one scale, 180°–0°, unlike a real protractor which will also have a scale from 0°–180°. The difference between 90° and the sextant reading will always be the same on either scale.

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