[LED FLASHER]

I got the 0.602 by building the circuit, measuring the frequency and the individual components and plugging the values into formula.

[LED FLASHER]

First let me apologize to Alun and others for any confusion my post of the
formula to calculate the freqency.  As it turns out the formula is incorrect.
When I did the calculation I got a negative number.  I knew that could not be
right so I ignored the - sign.
I did some checking and find that the calculation is a little more complex, but
the attachment shows a general formula that is extremly close when the Vcc is
9V.
Audioguru is correct about the reverse-biased transistor.  In the case of the 2N3904 my current data books did not list the maximum negative bias for the subject transistor, so I actually measured the avalanche and found it to be
very close to 7.5 volts.  Actually measuring the - bias of the circuit my scope
showed 5.2 volts.

[LED FLASHER]

Audioguru is correct, I was having a brain cramp.  Increasing the value of the
base resistor(39k) will decrease the flash rate.

The 2ln term actually means 2 times the natural log of the result of  the  RC calculation.
The circuit and formula is from my notes.

[LED FLASHER]

I calculate the flash rate to be 2.012 Hz.
The attached image and formula was used to calculate the flash rate.
Reducing the value of the 10uF capacitor and increasing the value of the 39k
resistor will increase the flash rate.