Samhain Thanksgiving Moon
A gamma burst within 3.7 billion light years of home. Close, in astronomy’s scale of distance. That is, it was not so far away that the distance the light traveled to get here puts it back in the time of the early universe, the formation phase. Hard to grasp sometimes, that astronomy measures time in the metric of distance, but 3.7 billion light years is not only a long ways away, it’s also a very long when ago.
Said another way, the light of this massive gamma burst traveled 3.7 billion years to get here. How do we know? Because light, the fastest thing in the universe, takes a year to travel a certain distance and we know what that distance is. It so happens that because we take a measure of time and out of it create a measure of distance that we can also know the when.
In case you were wondering: 186,000 miles/second * 60 seconds/minute * 60 minutes/hour * 24 hours/day * 365 days/year = 5,865,696,000,000 miles/year
OK, I thought. But how do we know how many light years away something is? I looked it up and the method for things further than 3.6 light years away is called the standard candle method. Here’s a brief paragraph to describe how it’s used, then a graphic that I found helpful.
“One example of a standard candle is a type Ia supernova. Astronomers have reason to believe that the peak light output from such a supernova is always approximately equivalent to an absolute blue sensitive magnitude of -19.6. Thus, if we observe a type Ia supernova in a distant galaxy and measure the peak light output, we can use the inverse square law to infer its distance and therefore the distance of its parent galaxy.” from this website.
this graphic is from the hyperphysics website:
