Interpreting recession velocity (red / blue shift)

Question

I just had to teach something that I myself have never learned, concerning recessional velocity of galaxies. Awkward!
The question was: "A line in a hydrogen spectrum has a wavelength of 486.1nm when observed in the lab, the same line is observed at 492.3nm from a distant galaxy. Determine the recession velocity of the galaxy and comment on its motion."
While the equation in the associated specification (IGCSE, Edexcel, UK) is:
change in wavelenth / reference wavelength = velocity of galaxy / speed of light
Obviously the left hand term came out less than 1, which I said suggested a red-shifting galaxy, but my tutee thought their teacher had said <1 means its blue-shifting.
Is it as simple as the fact that from the question, the line from the galaxy has a higher wavelength than the lab value, ie: redder, ie red shift?
And therefore, a suitable "comment" on the galaxy's motion would be that it is moving away from the observer?
Thanks in advance for any help.

thetada · Answer

And answers own question:
After z is measured, the distinction between redshift and blueshift is simply a matter of whether z is positive or negative. For example, Doppler effect blueshifts (z < 0) are associated with objects approaching (moving closer to) the observer with the light shifting to greater energies. Conversely, Doppler effect redshifts (z > 0) are associated with objects receding (moving away) from the observer with the light shifting to lower energies.
Frustrating. I originally thought the left hand term would be significant by its sign (positive or negative) but got flustered and started thinking it would be more or less than 1. Embarrassing.

Interpreting recession velocity (red / blue shift)

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