# I What does Pt mean in this formula?

1. Oct 31, 2016

### Meerio

So I'm trying to understand something about the Hulse Taylor Binary. Here they talk about the change in periode that actually changes with the period. So what does Pt mean here?
And what is actually being explained? P1year also makes no sense to me. Is that the period after one year? And what is deltaP1year?
I'm sorry but I'm quite confused about the formula.
Thx for any help

http://astronomy.stackexchange.com/...is-cumulative-periastron-time-shift-calculate

2. Oct 31, 2016

### Staff: Mentor

Pt is the period as function of time, later evaluated at t=1 year and t=10 years.

$\Delta$ P1year is the change in orbital period after 1 year relative to the original period. As you can see, the change in period over 10 years is nearly 10 times the change of period over 1 year, indicating a linear change of period over time - within the current timeframe and experimental precision.