Galileo Sunspots Model
This device-friendly model illustrates the "motion" of sunspots across the face of the Sun as seen from a telescope on Earth. Many features of this motion were first noted by Galileo in the early 1600s. Students can use this simulation to recreate Galileo's observations, as well as determine the (synodic) period of the Sun's rotation and the obliquity of the Sun's equator. It will help students visualize that sunspots really don't move along the Sun's surface as a car moves along a highway. What observers perceive as sunspot "motion" is a combination of the Sun's rotation (spin) and the plane of the Earth's orbit around the Sun.
Naked Eye Sidereal and Solar Day JS Model
This model illustrates the difference between the sidereal and solar day. The sidereal day measures the rotation of Earth relative to the stars rather than the sun. It is the time it takes for a particular star to rotate around the Earth (from the Earth's perspective) and end up in the same part of the sky as it started. A sidereal day is 23 hours, 56 minutes, and 4.1 seconds. BUT WAIT! In the time it takes Earth to spin on its axis, it also covers 2.5 million kilometers by moving along its orbit around the sun. Because of this double-movement, the sun will not appear in the same part of the sky at the end of one Earth rotation. It will take another four minutes for Earth to end up facing the sun again. This gives us our 24-hour "day", defined by astronomers as a "solar day".
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PhET Simulation: Pendulum Lab
This popular PhET sim, now available in HTML5, can help students gain understanding of what periodic motion means and how "period" is defined in physics. You can measure the period with tools provided in the simulation. Click "Period Trace" to see what constitutes one complete period. For deeper exploration, change the gravitational constant to Moon, Jupiter, or a value of your choice.
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