Watch or step in: video and interactive film
About this app
The same explanation of the moon phases twice side by side: on the left as a linear video that can only be played and skipped, on the right as an interactive film in which you pause, drag the Moon along its orbit, change the view, ask a question at that point and answer a quiz. A counter shows interventions, questions and quiz answers on each side.
With explain mode: an AI tutor walks you through the app, points out what matters in the scene and answers your questions.
The idea
The Sun always lights one half of the Moon. How much of it we see depends on the angle between Sun, Earth and Moon: new moon when the Moon is between Earth and Sun, first quarter at a right angle, full moon when Earth is between Sun and Moon. From new moon to new moon takes 29.5 days. The Moon always shows the same side because it turns once on its axis in 27.3 days and circles Earth in the same time. Its orbit is tilted by 5.1° to Earth’s orbit, so the full moon usually passes Earth’s shadow.
What the app shows
Two cards tell the same eight sentences about the moon phases in 57 seconds. On the left the explanation runs as a linear video with a fixed camera that can be played, paused and skipped. On the right it runs as an interactive film: you pause, drag the Moon along its orbit and see the phase change immediately, switch the view between the orbit from above and the Moon seen from Earth, and ask one of three prepared questions at any point. Two insert beats then play, and the film continues where it left off. A counter on each card shows interventions, questions and quiz answers.
Try it yourself
Use “Start both” to start both cards at the same time. Pause the film on the right and drag the Moon along its orbit until it reaches full moon. Ask why there is no eclipse every month and watch the insert. At the end of the first quarter the film stops for a quiz. Finally compare the counters on both cards. Sizes and distances in the picture are not to scale, and the orbital tilt is exaggerated threefold.
Frequently asked questions
- What causes the phases of the Moon?
- The Sun always lights one half of the Moon. Depending on the angle between Sun, Earth and Moon, we see a larger or smaller part of this lit half from Earth. The lit fraction is (1 − cos e)/2, where e is the phase angle. Earth’s shadow plays no part in the phases.
- Why isn’t there a lunar eclipse at every full moon?
- The Moon’s orbit is tilted by 5.1° to Earth’s orbit. So the full moon usually passes above or below Earth’s shadow. An eclipse is only possible when full or new moon is near the line of nodes, where the two orbital planes intersect; this happens in two windows each year.
- Why do we always see the same side of the Moon?
- The Moon turns once on its axis in the same time it takes to circle Earth, 27.3 days. This tidal locking keeps the same side facing Earth. So the Moon does rotate, just in step with its orbit.
- What does the “Watch or step in” app show?
- It shows the same explanation of the moon phases twice side by side, as a linear video and as an interactive film. In the film you can pause, drag the Moon, change the view, ask questions and answer a quiz; a counter shows the interventions on each side. The app belongs to the presentation course “What is heyprof?”.
Subject: heyprof
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A VisuApp by heyprof: interactive, free in your browser, no sign-up. What is a VisuApp? · All apps