Deep Space Objects, the Celestial Sphere, and STEM Capstone

It’s a dark and clear night in Daniel Boone National Forest, and the night sky is easily the most attractive it has ever been, not a cloud or twinkling blemish in sight. Hands trembling beneath its worldly presence, I set my camera, a small Nikon d90, onto a cardboard box atop the dewy ground, its lens taking a glance at a world that was made visible by the lack of light. One click, one photo, and I release the trigger and lift the camera to peer at the screen, but it is pitch black. Looking to the sky, there are a plethora of colorful points and streaks that looking back to the camera again, there are none.

That is a recounting of my first encounter with the art of night sky photography. This delicate art is based on the simple concepts of luminosity, and the behavior of light. A long exposure camera lens will take in more light as time goes on, the more light enters the lens at different angles and points, the more contrast the resulting picture will have, and the more varying input it can have for each point on the lens. This means that you’ll have your classic HD TV advertisement, darker darks, brighter brights. As a result, stars are like beacons, and with enough time, you can even see the outlines of the galaxy.

Time really is a critical variable in this process, as without adequate lengths of time, deep space objects that you might want to highlight, such as the Andromeda Galaxy or the Eye Nebula, may not appear in frame. There, however, is another proponent of time that a nighttime photographer would have to be wary of, and that is movement. This refers to movement on the ground, such as an unstable camera stand, but more importantly the motion of the objects themselves. The moon moves quite fast across the night sky, and if great detail wants to be captured with a small camera, very long exposure times, or a larger lens would be necessary. The problem with long exposure times is that the moon will move, the problem with a larger lens is that they are expensive. For the casual photographer, there has to be a simpler solution that is both cost effective and, well, effective.

Unfortunately, there isn’t.

Modern night sky photography is taken in milliseconds, but data is sourced from lenses that are several meters across, and scientists have taken a picture of a black hole millions of billions of light years away with satellite dishes scattered across the planet, rotating ever so slightly to adjust for the rotation of the Earth, and motion around the sun. The casual photographer does not have access to these fantastic devices, and it would seem that I, with my small Nikon d90, would never be able to take a decent photo of the beautiful night sky. 

That, however, might not be the case. In STEM Capstone, a class I am taking this year at Naperville North High School, we are assigned to create projects of our choosing that satisfy goals of our choosing. I, as the introduction might imply, chose to design and create an inexpensive device that can track specific objects in the night sky.

Thus far my progress has been limited to planning, and so plan I have. The basis for the plan lies in functionality, as many things are necessary for the mechanism to work, particularly a formal definition of what I am actually doing. My plan is to create a land based device (I considered a satellite, but that seems difficult), that can take long exposure pictures over the course of several minutes or hours and can track moving objects in a calculated fashion. For objects on the celestial sphere, the hypothetical 2 dimensional spherical sheet that is a projection map of the stars around it, the program would likely assume all stars move synchronously, as despite the vast differences between their speeds, their displacement is simply too vast for such a small change in angle (10 to the negative very large number) to actually be visible on a land based camera. That leaves the set of our planets, their moons, our moon, and the International Space Station as objects to calculate angles to.

There are two options for which this can be done, the first being simply to calculate the orbit relative to the object orbited, find a common orbit, and then compare the distances. For example, Titan, one of Saturn’s moons, could be calculated by finding Earth’s vector displacement from the sun, and comparing it to the vector displacement of Saturn from the sun plus the vector displacement of Titan from Saturn. A simpler way is to state that these objects are too small to accurately take a picture of and narrow this set down to the moon and perhaps the ISS. If that consideration is taken, then finding the moon’s, or ISS’, orbit around the Earth only requires knowledge of their mass and current position at a permanently constant time (e.g. position when time is October 23rd, 2020). 

Knowing the angle to the point on the celestial sphere or to other quickly moving objects around the Earth is not enough to make this land based device to function. The machine would have to take into account its own angle of incidence upon the earth, as well as the original orientation of the camera. The second can be solved by having the device return to a neutral or origin position, and the first can be solved with a compass and a level. For all intents and purposes that this device might plausibly have, the margin of error of that technique would be well within reason.

The device itself would function with small, lightweight motors hooked upon two separate axles to control rotations in the hemisphere necessary to point towards the night sky. The specifics of the device, however, will come in a later post. Thanks for reading.