What would you need to measure about a planetary nebula (see the image below)to determine how long ago its parent star died?

Question

Quizplus · Accepted Answer

To determine how long ago the parent star died, one needs to measure the expansion velocity and radius of the planetary nebula. With this data, one can calculate the time taken for the nebula to expand to its current size, and therefore, estimate the age of the nebula and the time elapsed since the parent star died. The mass of the white dwarf is not directly related to the age of the planetary nebula, and measuring the temperature of the nebula would not provide useful information for dating the event.

What Would You Need to Measure About a Planetary Nebula