The River-Mouth Observation Notebook
Where a river enters a large lake in the northern United States, a raised overlook gives visitors an open view of the sky. A science club uses the overlook to collect observations. The club wants to help visitors choose when to return for another observation. Its notebook includes three kinds of records: shadow measurements, sunrise and sunset times, and sightings of a star pattern called Orion. Each record describes observations at this one location, not conditions everywhere on Earth.
On a clear fall day, the club placed a 20-centimeter post upright on level ground. Members measured from the base of the post to the tip of its shadow. They left the post in the same spot and measured with the same ruler each hour. Their measurements were: 9 a.m., 40 centimeters; 10 a.m., 30 centimeters; 11 a.m., 26 centimeters; noon, 24 centimeters; 1 p.m., 26 centimeters; 2 p.m., 30 centimeters; and 3 p.m., 40 centimeters. They recorded only these seven times. They watched the shadow rather than looking directly at the Sun.
For three nearby fall days, the club also recorded sunrise and sunset times from a local observation station. Those times were rounded to the nearest hour. Earth turns on its axis about once every 24 hours. Sunlight reaches the side facing the Sun, while the side facing away has night. A graph can help the club compare the timing of these events from one day to the next.
The star records came from a full year. Members checked for Orion at 9 p.m. on six clear nights in each season. They used the same overlook, with no trees or buildings blocking the view. They recorded whether Orion’s main pattern was visible. Earth also travels around the Sun during the year. These star records concern only Orion at the chosen observing time; the club did not count every star pattern in the sky.