The shell of a planetary nebula is measured by the Doppler shift of emission lines to be expanding outward at a speed of 10⁴ m/s,while its radius is measured to be 1 ly,or about 10¹⁶ m.Roughly how long has the shell been expanding? (Hint: 1 year = 3.15 × 10⁷ sec.)

Question

Quizplus · Accepted Answer

The time can be calculated using the formula time = distance/speed. Here, the distance is 10¹⁶ m and the speed is 10⁴ m/s. So, time = 10¹⁶ m / 10⁴ m/s = 10¹² s. Converting seconds to years: 10¹² s / (3.15 × 10⁷ s/year) ≈ 30,000 years.

The Shell of a Planetary Nebula Is Measured by the Doppler