The purpose of the mount is to locate and track celestial objects as they move across the sky. For astrophotography, it is particularly important that the telescope be equatorially mounted. This means the main axis of the mount (the one the telescope is pointing along in the image) must be pointed directly north (or south if in the southern hemisphere). Because all the stars appear to rotate around the north celestial pole over the course of the night, if the telescope is aligned with that pole it only has to rotate on a single axis as the stars move through out the night. Equatorial tracking means that a tracked image with a long exposure time will have pinpoint stars rather than stars that appear to rotate around the center of the image because the stars and the mount are rotating on the same axis. When working together with a camera and software, the mount is also able to do advanced actions such as guiding and plate solving. The following is a list of functions the mount preforms in order to make sure the camera can get proper images.

• Polar Alignment : the process of aligning the axis of the mount to point north so that there is no star rotation on the edge of long exposure images.

• Slew to Target : given a target by the computer, the mount moves to where the object should be located in the sky according to date, time, and location

• Plate Solving : often, the initial slew to target isn't very accurate. To get to the right location, the camera takes an image, compares the stars in the image to a database, figures out the coordinates of the current star field, and tells the mount to slew to where the original target should be based on that data.

• Tracking : the mount tracks the stars as they move across the sky

• Guiding : images are taken approximately every second through the small guide scope / mini camera on top of the main telescope, and based on how the stars in the image move, tiny corrections are continuously sent to the mount. This allows for the type of high precision and stability required for photography where the aperture is open for often minute long exposures.

The basic idea of astrophotography is just like any other type of photography. Light goes in, hits the camera sensor, and an image is recorded. The telescope and everything else in between the first piece of glass and the image sensor acts as a big camera lens. The particular refractor that I use isn't actually that much more "zoomed in" than a decently sized camera lens. The following list describes the path the light takes through the imaging train.

• Telescope : a doublet apochromatic lens focuses the light through multiple refractive lens elements and a focal reducer. The focal length of the telescope is one main factor that determines

• Adapters : these don't change anything with the light coming through, they just connect the various elements together. It is generally better to have threaded adapters. These adapters also serve to make sure the distance between the lens elements and the sensor is correct.

• Filter Wheel : the electronic filter wheel has seven slots for high grade astronomy filters. The typical seven are L, R, G, B, Sii, Ha, and Oiii. These block certain wavelengths of light for reasons that are discussed further down this page.

• Camera : a dedicated cooled monochrome astronomy camera registers the photons from the imaging train and sends them to the computer. The size of the sensor and its pixels are the other main factors that affect the scale of an image.

Nearly every part of a modern astrophotography rig is controlled by software on a computer. A wide variety of programs are used to tell the telescope where to point, tell the camera when to take images, how long the images should be, what filter to use, and so on. One result of this automation is that a with the right software working together, the rig can take images over a whole night with little to no input from the user. The following list describes some important software and how it operates.

• N.I.N.A : the control center for most actions, NINA connects to the mount and both cameras, displays captured images, and most importantly, controls the sequence of events that the rig must take. The sequencer in NINA allows the user to give a set order of events such as "slew to target" or "take x images" and combinations of all the available functions can automate a whole night's worth of imaging.

• Cartes du Ciel : a sky map. This makes it easy to find the location of targets, see what is up in the sky at any given time, and also connects to the mount and can slew to any target on the map.

• PHD2 : guiding software. Locks onto guide star in image from mini camera and sends continuous tiny corrections to the mount based on the movement of the guide star to ensure extremely precise tracking.

• Pocket Power Box : also the physical power box on the rig, distributes and measures the power going from the battery to each part of the rig.

Because modern astrophotography relies so heavily on technology and automation, the rig obviously requires a certain amount of power to last through a whole night of imaging. The two largest sources of power usage are the mount tracking and the camera cooling, but various other things such as dew heaters and the controlling laptop require power as well. When available the rig is connected directly to power from an outlet, but astrophotography often takes place in very remote locations that don't have easily accessible power outlets. In this case, the rig is powered by large batteries.