Age of the Crab Nebula

Crab Nebula Age

This page is designed to help us determine the 'age' of the Crab Nebula. The Crab Nebula is a nearby Supernova remnant. If we can determine when the star that created it exploded, we can compare that to historical records of bright sky events, which might help us narrow-down when exactly this star blew up! This is a fun way astronomers are able to work with historians to learn about how ancient civilizations measured the stars and what real events they were measuring.

Let's start by examining an image of the Crab Nebula taken in 1956. A few 'knots' of gas have been tagged to help us map how quickly the Crab Nebula is expanding. If we can estimate how much the Crab Nebula has grown between when this photo was taken in 1956 and when the following image was taken in 1999, we can estimate how long it would have taken for the Crab Nebula to grow from a single point to the size it is today. Pick three knots and record their locations by clicking them and noting the positions listed below.

Distance from the pulsar in the horizontal direction:

Distance from the pulsar in the vertical direction:

Distance from the pulsar in the horizontal direction:

Distance from the pulsar in the vertical direction:

Once you've got the positions of the three knots, we can figure out how far each knot traveled during the time between the two pictures. Find the velocity of each knot using the formula: velocity = change in distance / change in time. Remember, the first picture was taken in 1999 and the second was taken in 1956! How fast is each knot traveling?

Okay, one last math-y step. We know how fast the knots are moving. How long would it take for each knot to travel from the pulsar to it's current position at it's current speed? Remember, we can find the time it takes for something to travel a certain distance using time = velocity / distance. Take an average of the three times you find to determine the approximate age of the Crab Nebula (i.e. the time it has taken for it to expand from that point in the center to it's current size!)

Now we can do some archeoastronomy! Compare your time to the following list of historical 'bright lights'. Could one of them be the progenitor of the Crab Nebula?

  • Chinese astronomers record bright source in year 185 CE (1814 years before 1999)
  • 'Guest Star' Sighted in Scorpius in year 393 CE (1606 years before 1999)
  • Bright star recorded by Chinese, Arabic, and Japanese astronomers (as well as a record in an Anasazi petroglyph) in year 1054 CE (945 years before 1999)
  • Bright light noted by Tycho Brahe in year 1572 CE (427 years before 1999)