The social media meme I saw last week directed at teachers is that there is a time change, a full moon and a Friday the 13th all in the same week, so good luck. I am not sure about the effect of Friday the 13th, but the other two do make doing astronomy more challenging.
My complaints about the existence of daylight saving time should be getting about as predictable as the next full moon. Yes, I still think Colorado would do well to follow Arizona and Hawaii and just do away with that archaic practice.
For the last two months, I have been discussing astrophotography, and the many steps required to set up a telescope and camera to take pictures. Unfortunately, acquiring the images is only half of the work in obtaining a photo that might be interesting to look at or useful for obtaining scientific data. There are many books written on the subject of astro-photo-processing, so I can’t get far in a couple of paragraphs, but not post-processing your digital photos would be like not developing your film photos.
The most significant step in processing is dark subtraction. If you are not taking lots of photos with your lens cap on, you are not doing astrophotography right. These “dark” frames need to be the same exposure duration and have the same camera temperature as used when taking the “light” frames of your target object.
Fortunately, most astrophotography cameras can keep their internal shutter closed to make the dark exposures easier. Often, the objects that are being photographed are so dim that they are almost indistinguishable from the random thermal noise inherent in any electronic device. “Almost” being the key word here. If you open one of the “light” images with any photo-editing software package, they usually appear entirely black. However, if you use photo-editing software to subtract the dark image from the light image, you can begin to see the subtle differences in exposure. The more of the dark-subtracted images you can combine, the clearer the image will become.
Another important step in processing is to apply a flat-field image. A flat-field image, or “flat,” is one that has a uniform exposure across the entire camera sensor. There are several techniques for doing this, but I find the best way that works for me is to stretch a clean white T-shirt over the front of the telescope and take exposures of the sky at dusk.
A good flat will quantify how much dimmer the edge of the photo is compared with the center. The effect is rarely noticeable to your naked eye, but if you are trying to take a photo of something really dim, then this flat-field effect could easily be more prominent than your target object. As with dark subtraction, flat-field processing is most easily done with specialized image-processing software.
This monthThe equinox is coming up on March 20. That is when the sun will cross the equator heading north and give us a day when the sun is above the horizon for half the time. It is also the day when the sun will rise due east and set due west. In the days after the equinox (and until the fall equinox), the sun will be rising to the north of due east and setting to the north of due west. However, because Durango is at 37 degrees north latitude, the noontime sun will always be toward the south of our zenith point and never directly overhead, even in mid-summer.
March 24 should be an eventful day, at least astronomically speaking. First, that is the day of the new moon, so the night sky should be about as dark as it will ever get. It is also the day Venus reaches its easternmost elongation, or when it will appear farther from the sun than any other day during this orbit. It will be just over 45 degrees from the sun.
I should note that if you look carefully you can see Venus at mid-day. I could say simply look along the sun’s path 45 degrees to the east, but it is often anything but simple to find such a tiny dot in such a big sky.
Also on March 24, Mercury will be at its greatest western elongation. The farthest Mercury will be from the sun is only 27 degrees, and it will be in the eastern sky in the morning.
Charles Hakes teaches in the physics and engineering department at Fort Lewis College and is the director of the Fort Lewis Observatory. Reach him at email@example.com.