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International Shadow Trackers 

This investigation funded in part through an IDEAS grant from the Space Science Telescope Institute with funding from NASA

 

More Information About Solstices and Equinoxes

Because the Earth is tipped compared to the Sun, the Northern and Southern hemispheres of the Earth alternately tip toward and away from the Sun.  This causes the Sun, Moon, and planets and stars as observed at noon or midnight (i.e. halfway between rising and setting) to look like they move North and South during the year.  Then, twice each year, they stop and reverse direction in repeating cycles.  These apparent motions of the Sun and full Moon are caused because the tipped Earth is moving (revolving) around the Sun. The length of one year is determined by the time it takes the Earth to move around the Sun once.  Astronomers have invented names to describe the position of the Sun (and also Full Moon) during this annual cycle.  Solstices are the times when the Sun (and full Moon) appears furthest North or South and Equinoxes are times when the Sun (and full Moon) appears halfway between the North and South. 

Solstice gets its name from the apparent movement of the Sun and essentially means “the Sun is standing still.”  The solstices are when the Sun appears to stop and change directions.  They usually happen on June 20 or 21 and December 21 or 22 of each year.  In the North, Summer Solstice (the beginning of summer) is in June and Winter Solstice (the beginning of winter) is in December.  In the South, Summer Solstice is in December and Winter Solstice is in June.   These are times when the Earth has both the longest and shortest days.  When people living in the Northern Hemisphere have the shortest day, and thus the beginning of winter, the people in the Southern Hemisphere have the longest day and thus the beginning of summer. 

Equinox means “equal nights.”  Every place on the Earth has equal times of night and day during an equinox. This is the time that the Sun (and full Moon) is half way through its apparent movement between furthest South and furthest North.  The Vernal Equinox is the beginning of spring in the North or fall in the South and usually happens on March 20 or 21 when the Sun appears to be moving slightly northward each day.  The Autumnal Equinox, also the beginning of spring or fall, usually happens on September 22 or 23 when the Sun appears to be moving southward.  An interesting aspect of a equinox is that the sun is rising at one of the Earth’s poles and setting at the other pole – and the poles begin a 6-month long period of day or night.

The time of the Vernal Equinox in March is especially important because this is the astronomical beginning of a new year and the basis for determining the length of a year.    

To really understand these motions, the changes we observe, and the cause of the seasons, we need to make observations over at least one year. 

 

Reference Websites

 

Learning Standards

The following are some examples of some learning standards that support this investigation:

Earth and Space Science:

Arizona Grade 5:

  • Describe the change in position and motion of the following objects in the sky over time:

  • Real motion – Moon, planets

  • Apparent motion (due to the motion of the Earth) – Sun, Moon, stars

  • Explain the apparent motion of the Sun and stars.

Arizona Grade 7:

  • Explain the phases of the Moon in terms of the relative positions of the Earth, Sun, and Moon.

  • Explain the seasons in the Northern and Southern Hemispheres in terms of the tilt of the Earth’s axis relative to the Earth’s revolution around the Sun.

Ohio Grade 5:

  • Describe the characteristics of Earth and its orbit about the sun (e.g., three-fourths of Earth's surface is covered by a layer of water [some of it frozen], the entire planet surrounded by a thin blanket of air, elliptical orbit, tilted axis and spherical planet).

Ohio Grade 8:

  • Describe how objects in the solar system are in regular and predictable motions that explain such phenomena as days, years, seasons, eclipses, tides and moon cycles.

 Scientific Inquiry and/or Scientific Ways of Knowing: 

Arizona Grade 5:

  • Formulate a relevant question through observations that can be tested by an investigation.

  • Formulate predictions in the realm of science based on observed cause and effect relationships.

  • Locate information (e.g., book, article, website) related to an investigation.

  • Conduct simple investigations (e.g., related to forces and motion, earth processes) based on student-developed questions in life, physical, and earth and space sciences.

  • Measure using appropriate tools (e.g., ruler, scale, balance) and units of measure (i.e., metric, U.S. customary).

  • Record data in an organized and appropriate format (e.g., t-chart, table, list, written log).

Arizona Grade 7:

  • Formulate questions based on observations that lead to the development of a hypothesis. 

  • Select appropriate resources for background information related to a question, for use in the design of a controlled investigation. 

  • Perform measurements using appropriate scientific tools (e.g., balances, microscopes, probes, micrometers).

  • Keep a record of observations, notes, sketches, questions, and ideas using tools such as written and/or computer logs.

Ohio Grade 5:

  • Evaluate observations and measurements made by other people and identify reasons for any discrepancies.

  • Use evidence and observations to explain and communicate the results of investigations.

  • Explain why an experiment must be repeated by different people or at different times or places and yield consistent results before the results are accepted.

  • Identify how scientists use different kinds of ongoing investigations depending on the questions they are trying to answer (e.g., observations of things or events in nature, data collection and controlled experiments).

  • Keep records of investigations and observations that are understandable weeks or months later.

Ohio Grade 8:

  • Choose the appropriate tools or instruments and use relevant safety procedures to complete scientific investigations.

  • Describe the concepts of sample size and control and explain how these affect scientific investigations.

  • Read, construct and interpret data in various forms produced by self and others in both written and oral form (e.g., tables, charts, maps, graphs, diagrams and symbols)

  • Apply appropriate math skills to interpret quantitative data (e.g., mean, median and mode).

  • Identify the difference between description (e.g., observation and summary) and explanation (e.g., inference, prediction, significance and importance).

  • Explain why it is important to examine data objectively and not let bias affect observations.