It was another great dawn this morning. I have discovered that it is best to be in position to watch the sky about an hour to 45 minutes before sunrise. This will allow you to get your equipment set up and to see the complete transition through the blue hour. I like to be there in the morning at the beginning of nautical twilight, when the sun is 12° below the horizon.
What is the blue hour? Wikipedia describes it as “the period of time during twilight each morning and evening during which there is neither full daylight nor complete darkness.” I just think of it as the time when the light is incredible. So, where do you get the information to predict this time? My favorite on the web is Heavens Above. Just tell them your location, and you will get all sorts of interesting astronomical information. The information here for Los Barriles is from that site:
Daily events for 25 February
|Astronomical twilight begins:||05:29||-18.0°||92°|
|Nautical twilight begins:||05:55||-12.0°||95°|
|Civil twilight begins:||06:22||-6.0°||97°|
|Civil twilight ends:||18:42||-6.0°||263°|
|Nautical twilight ends:||19:09||-12.0°||265°|
|Astronomical twilight ends:||19:35||-18.0°||268°|
Another great source of blue hour info is at The Blue Hour Site. Check them out.
I took two photos this morning to demonstrate the difference between the sky at the blue hour and at sunrise itself. The first photo was taken 24 minutes before sunrise; the deep blue and purple of the sky is striking. The second photo taken at sunrise shows how the richness of that wonderful deep blue sky color seen during the blue hour as well as the purple are now gone. The blue hour effect does not occur every day. You will only see it if there are few or no clouds. The scientific effect causing this phenomenon is Rayleigh scattering. Click here if you want to know more.
My general rule of thumb is that I will take landscape photographs during the blue hour only when there are no clouds and when the sun is up only when there are clouds to make the monotonous sky more interesting. Some of you may point out that I could use Photoshop to add clouds to a cloudless day. Yes, I could. But we all have limits beyond which we will not go, and that is one of mine. I would love to see your morning photos. By the way, did you notice the man taking a picture of his son in the sunrise photo?