Lesson Plan

• Describe the constant speed of light in vacuum and its numerical value.
• Convert astronomical distances from kilometres or AU to metres.
• Apply the formula t = d / c to calculate light‑travel time between Solar‑System objects.
• Interpret the results in seconds, minutes or hours and compare different planet pairs.

• Projector and screen
• Whiteboard and markers
• Scientific calculators or spreadsheet software
• Worksheet with planetary distance table
• Scale diagram of the Solar System (handout)
• Student laptops or tablets (optional)

Did you know that sunlight takes over eight minutes to reach Earth? Review that you already know the speed of light and how to convert kilometres to metres. Today you will use these ideas to calculate how long light needs to travel between any two objects in the Solar System. Success will be measured by correctly computing travel times and expressing them in appropriate units.

1. Do‑now (5 min): Quick mental question – “How long does light take to travel from the Sun to Earth?” Students write answers; teacher checks prior knowledge.
2. Mini‑lecture (10 min): Review speed of light (c = 3.00 × 10⁸ m s⁻¹), unit conversion, and the formula t = d / c. Demonstrate the Sun‑Earth example on the projector.
3. Guided practice (15 min): Using the step‑by‑step method, work through the Sun‑Mars calculation together, converting km to m and then to minutes.
4. Independent practice (15 min): Students select two planet pairs from the worksheet, calculate light‑travel times, and record results in seconds, minutes, or hours.
5. Think‑pair‑share (5 min): Compare answers, discuss which distances yield the longest travel times and why.
6. Check for understanding (5 min): Quick exit quiz (e.g., clicker question) on converting seconds to minutes.

We revisited the constant speed of light and applied it to determine travel times across the Solar System. For the exit ticket, each student writes the light‑travel time from Earth to Jupiter in minutes. For homework, complete the additional practice problems, including one that requires converting the result to hours.