Analysis of Heat Transfer

The authors then used the preceding data to develop an analysis of the heat transferred through a window. This can be used to do design trades of the number and size of windows. Another study could look at which direction a building or home faces and how many windows are located on the south-facing walls.

Assume a 30-degree incidence of light hitting the window.

Taking this analysis one step further for a large house with six windows that are 2 m², the heat transfer rate would be, at this time of day with this angle of incidence, 6 × 2 × 831 watts, or approximately 10,000 watts. That is a lot of heat entering through those windows.

Adding the reflective coating reduces that to 3000 watts which is a lot less but still quite a bit of energy.

Engineers can use analysis like this to ensure the air-conditioning system is sized properly and provides adequate cooling on hot days.

Radiation Heat Transfer Recap

The preceding data shows how beneficial from a heat transfer perspective using windows with reflective coatings can be to reduce the amount of solar radiation (heat) that enters a window. It can also be utilized to estimate the amount of heat contribution and develop changes to the number and size of windows when designing a building or house.

Assembling the Meade ETX-60AT and Raspberry Pi

The individual pieces (telescope, Raspberry Pi/touchscreen/case, and the shelf) have their own sections later that describe them. The following diagrams in this section show how the major pieces are assembled.

The authors tried to modularize the system so that it can quickly be assembled or disassembled. One unique feature of this design is the Raspberry Pi 3 system can be removed with one screw and set up as its own work station to review and select the pictures remotely from the telescope. Note that in the top view in Figure 7-5, the telescope and support yokes are not shown.

Figure 7-6 shows the assembled system with identification labels for the components.

After all key components are built, the astronomer should follow these seven steps to assemble the system:

1. 1.

   Insert AA batteries into the telescope (Figure 7-7) in accordance with the telescope instructions. Because of their location, under the shelf, the batteries need to be inserted first.

    
2. 2.

   Attach the Raspberry Pi 3 and case to the shelf (Figure 7-8).

    
3. 3.

   Slide the shelf through the telescope yoke (Figure 7-9).

    
4. 4.

   Place the movable clamp against the front of the yoke and screw in the eye bolt through the movable clamp into the RIVNUT angle bracket (Figure 7-9).

    
5. 5.

   Tighten the eye bolt until the clamp secures the shelf in place.

    
6. 6.

   Insert the Raspberry Pi 3 camera case into the telescope eyepiece (Figure 7-10).

    
7. 7.

   Follow the Meade telescope setup instructions to enable star tracking. Now it is ready to start capturing beautiful images!

    

Astrophotography Meade ETX-60AT Setup Recap

The small size of the Meade ETX-60AT with the Raspberry Pi attached to it is perfect for an amateur astronomer as it can be left set up. It has a small footprint, takes a small space, and is ready to go at a moment’s notice!

Components Needed to Assemble the Raspberry Pi 3 Mounting System to the 4 1/2-Inch Telescope

This system is relatively simple and does not require as complex a system to mount the Raspberry Pi 3 as the Meade ETX-60AT telescope; see Figures 7-15 through 7-19 for details on the mounting system and that will allow attaching a Raspberry Pi to this older telescope.

Sighting this telescope on a distant planet like Saturn is a little difficult. The authors found it best to find it first with the eyepiece, then remove it, and insert the Raspberry Pi camera to get the image. Due to the Earth’s rotation, the image moves rather quickly across the telescope’s view, so the astronomer will need to install the Pi camera and take the image quickly.

After adding the Raspberry Pi and camera, the 4 1/2-inch reflector telescope is now set up and ready to take some pictures of the larger planets.

Reflector Telescope Setup Recap

Turning these two older telescopes into modern astrophotography machines was a real joy. The next sections detail first a simple method without programing to start taking images. Later sections detail how to program two GUIs for easy picture and video captures. The final sections provide details on building the complex shelf set up to attach the Raspberry Pi to the Meade ETX-60AT.

Using Raspistill to Capture an Image

Raspberry Pi 3 saves an image with the name cam.jpg. The following site provides additional information regarding using Raspistill including how to add a time stamp to the image captured:

www.raspberrypi.org/documentation/usage/camera/raspicam/raspistill.md

More Advanced Raspistill Input Without a Keyboard

The authors also came up with a way to input the commands using only a mouse. This is a lot less awkward outside at night during an observation session. It requires some setup time prior to the observation session. The astronomer uses either the simple text editor or a program on the Pi called Libre Word Processor. Use these programs to set up the Raspistill commands in a file. Using only a mouse, the astronomer can open the document file and then highlight, copy, and paste the text command into the command line. This capability simplifies and reduces commanding time. The no-keyboard configuration may also make it easier to operate outside during an observation session.

The results of these steps can be seen in Figure 7-21.

The first two of these commands turn the preview on for 10,000 or 70,000 milliseconds, which is equivalent to 10 or 70 seconds. The 70 seconds is probably needed to focus the object. The 10 seconds is enough to look quickly before taking a picture and to ensure the object is still in view or in focus. The next two commands take a picture. It names the file image pic20.jpg or pic30.jpg.

The astronomer will need to change the file name or move these files from the Raspberry Pi, or the Raspistill will overwrite them the next time you run these lines of code.

The astronomer can insert his/her own code into the command file if some other name is desired.

Raspistill Image Capture Recap

Since the Raspberry Pi is a full-blown computer, there are already built-in tools that the reader can access and use. If the reader would like to automate taking images, the next section provides code to develop a GUI using the built-in Tkinter module.

Initiating the GUI

The authors learned these tips and tricks while developing this code.

sets the location of the GUI at 200 × 1100 pixel sizes. It is the window size, and +0+0 is the x–y position using pixels again. The code may need to be adjusted to move the location to a different one. The authors wrote this code to match the 7-inch touchscreen. For other monitor sizes, the programmer may need to change the position and size to fit.

The authors found that the touchscreen can be used to take a picture, but it might set up a vibration and potentially blur the image. Using a wireless mouse prevented that from happening.

PI_SN003 Raspberry PI GUI Recap

This program PI_SN003 is very easy to use during an observation session. It lets you observe the object constantly, and then when the perfect image appears, with a simple click of the mouse you capture a fantastic image!

Raspberry Pi, Touchscreen, and Case

This section describes the assembly of the Raspberry Pi, touchscreen, and housing for them. One of the key features for this project is the touchscreen to show the image to ensure it is in focus. The 7-inch screen is an excellent choice for this application, as it is large with good contrast and definition. The authors found a case they liked that nicely integrated the touchscreen and the Raspberry Pi 3. It was also easy to modify the case with a single hole and add a RIVNUT to attach it to the shelf.

Total cost ≈ $185

For remote operations where there is no power, the reader may want to use a power inverter. It is a device that plugs into a lighter connection in a car and changes the DC to AC and can power the Raspberry Pi and touchscreen. The authors needed this device to capture the eclipse images. The model used was the remote operations power inverter ($35), Wagan Tech part number: SmartAC 200 USB+.

Modification of the Case and Assembly

The authors made two modifications to the Raspberry Pi 3 case. The first is drilling a hole so that the RIVNUT could be attached. A RIVNUT, as seen in Figure 7-23, is a unique device which is installed like a rivet and therefore is locked to the housing. Internally, it has female threads so that a screw can be threaded into it. The installation procedure is shown in Figure 7-24.

Figure 7-25 shows it installed in the Raspberry Pi touchscreen case.

An alternative to the RIVNUT approach is to simply glue a small nut inside the case using epoxy. This should be adequate to apply enough torque to secure the Raspberry Pi to the shelf.

One other important aspect is to apply tape over the end of the RIVNUT. This will catch any potential metal shavings when the screw is threaded into the case, clamping it down. Metal shavings could potentially short out circuit paths or connections which could damage the Raspberry Pi.

The second modification was gluing a small piece of plastic to the inside of the case to aid in restraining the ribbon cable as it twists to exit the case; this can be seen in Figure 7-26.

The case comes with instructions regarding this modification to the Raspberry Pi 3 setup.

Components and Assembly of the Raspberry Pi Case Recap

This case was perfect for this application; it had a great place to use for mounting to the shelf and contained the touchscreen and the Raspberry Pi. It has been used on many observation outings with no issues.

Camera Modifications

It is a little tricky, because two tools are needed to carefully remove the lens. One set of pliers holds the outside of the camera, and then the lens must be rotated out with forceps or another small tool (Figure 7-27).

Building the Camera Case

3D printing is an awesome technique that provides a unique way to create many different shaped parts. This is similar to the replicators in the original Star Trek series. Many creator spaces online can help a person develop parts using the 3D printing process. Mitch Long was very helpful in showing the authors how to create these camera cases.

The first step is to use computer-aided design (CAD) software to create a virtual model. The next step is to load that model in the correct format into the 3D printer, which uses a device that heats a material so that it flows easily. It precisely controls laying the melted material, layer upon layer, leaving voids in accordance with the input model, and gradually shaping the object until completion in each dimension. Hence, the process actually creates a 3D hardware object using a procedure that is partially analogous to ordinary paper printing.

The authors used a CAD program (see Appendix) to design and build the Raspberry Pi camera case. They output it in an STL format and took that (Figures 7-28 to 7-31) to a local library that had a 3D printer (MakerBot Replicator2). In about an hour, the basic part was completed.

The authors then drilled and tapped four holes for a flat cover plate as illustrated in Figures 7-32, 7-33, and 7-34, and the camera case was nearly ready to be used.

The authors have uploaded their Pi camera case to Thingiverse, which is a repository of 3D files. The authors created both a version for the Meade ETX-60AT (1 ¼-inch diameter) and the 4 ½-inch telescope (1-inch diameter). The files are located at the following site:

www.thingiverse.com/thing:2885450

Figure 7-28 shows the image of the camera case in the CAD program.

The dimensions for the camera case are shown in Figure 7-29.

The camera case is starting to take shape in Figure 7-30.

The material used to print the camera case was standard black PLA (polylactic acid) which is a common material for 3D printers. The MakerBot slicer software sets up the file for 3D printing. The slicer software used by the authors is CURA. A few parameters are set that relate to the fill and the supports. To minimize material, the shape is mostly hollow. The fill percentage creates a honeycomb structure inside the shape. The authors set it at 20% since it will be drilled and tapped. Typically the fill is set at 10%. Another setting that was selected is to add supports; these keep a section with nothing under it from collapsing as it cools. The supports will need to be removed after the shape is finished printing as seen in Figure 7-31.

If the reader does not have access to a 3D printer, there are several companies that will (for a fee) print out an object. Shapeways is one: www.shapeways.com.

Figure 7-31 shows how the case comes from the printer and the items that need to removed. The first step is to remove what is called the raft. It is the plate that the 3D printer puts down first and ensures the print has a solid base to prevent warping. The next step is to remove the supports which were located in the square box of the camera case.

To finish the camera case, cut a small styrene sheet (0.030 inches thick) of plastic 1 ½ × 1 ½ inches square (Figure 7-32). Draw lines that guide where the holes will be drilled. If you use the authors’ 3D case on Thingiverse, the holes should be approximately 0.095 inches in from the edge.

Tape the cover in place on the camera case (Figure 7-33) and drill through the cover plate, keeping the drill bit perpendicular to the plate. When the drill penetrates the cover plate, it leaves a mark where the hole will be drilled in the case. The reader can use extra 2-56 tap drill bits to help with alignment by placing them in each hole as it is drilled to keep the parts lined up. Otherwise, make sure the tape keeps the plate from shifting when drilling the next hole.

The authors cut a small notch in the cover and the case to guide the assembly. This is done while the tape is still in place and helps to ensure the cover can be placed in the correct orientation later, so that the holes line up properly after the tape is removed. Tap the holes using a 2-56 tap. Then the last modification is to file a slight gap for the camera cable to pass through. See Figures 7-33 and 7-34.

Final Assembly of the Camera in the Case

Finally, add two pieces of double-sided foam tape to help prevent the camera from shifting in the case (Figures 7-35 and 7-36). Then insert the camera into the case and tighten the screws. Make sure the camera does not shift out of the hole. The foam tape may not be tall enough to adhere to the case, so you may need two layers or put it on the cover plate.

However, if the astronomer does not want to utilize 3D printing for the camera case, the following web site describes a unique way to build up a similar case using a large modified SD card case and a piece of PVC pipe to construct it:

www.instructables.com/id/Raspberry-Pi-Astro-Cam/

Power Cord Combination

The final aspect is a modification the authors made to the Raspberry Pi astrophotography system after using it for a short time. There are two power cables: one for the Raspberry Pi and the other for the touchscreen. They were constantly getting tangled up. The authors decided to wrap the two power cables with the slit cable wrap. This effectively created one power cable. See Figure 7-37. It significantly improved setup and cord entanglement issues.

Camera, Camera Case, and Power Cord Assembly Recap

This section outlines all of the changes needed to set up and assemble these key components for the Raspberry Pi astrophotography system.

Building the Shelf for the Meade ETX-60AT

This section describes the steps needed to construct the shelf assembly which contains the clamping device that provides a secure mounting place for the Raspberry Pi to the Meade ETX-60AT telescope. The shelf assembly makes a self-contained, easily transported setup for the telescope and Raspberry Pi combination. This shelf requires a bit of woodworking skills, but each step is described. It provides the base for mounting the Raspberry Pi on and then using a clamp system that attaches it to Meade ETX-60AT. Building this requires a bit of engineering skills, using mathematics to lay out the hole patterns, and some manufacturing skills to fabricate the parts. Each section shows the steps required to build each part. There are four main parts: the shelf, fixed clamp, movable clamp, and eye screw/bracket (see Figures 7-38 and 7-39).

The shelf assembly is made up of the subassemblies shown in Figure 7-39. Each component will be described in detail in the next few sections. It may look somewhat complex, but it is really straightforward.

As always, safety first when using saws and tools, especially if the reader is not familiar with their operation. Remember to use hearing protection and safety glasses when using power tools such as saws and drills. Inexperienced young astronomers should get assistance from an adult or visit a maker group. These are groups around the country and are set up to aid people who want to learn how to make things.

Figure 7-40 shows the two areas that due to rotation of the scope to the vertical (overhead viewing) position may need some clearance added to the shelf and the fixed clamp. The authors did this, but the reader may find it unnecessary.

Plywood shelf base

Material: 3/16-inch-thick plywood, 3 5/8 inches wide by 13 inches long

After the shelf is cut to size, the astronomer must modify it slightly by milling out a small area for clearance of the end of the telescope. The authors used a Dremel grinder to grind or mill out the clearance area. Figure 7-41 shows the top and bottom views of the shelf base along with the dimensions for the features and holes including the required milled-out area. A summary of the modifications is shown in Figure 7-41.

The authors used flat head screws so the holes must be countersunk on the shelf bottom.

Using the Dremel grinder tool, grind or mill out the clearance area, which is approximately 2 1/8 inches square and approximately 1/16–3/32 inches deep.

Fixed clamp (Figure 7-42)

Material: 1/2-inch square wood that is 5 1/2 inches long

Movable clamp (Figure 7-43)

Material: 1 ½ × 2 ½ × 5 ½-inch wood

The hole needs to be positioned so the movable clamp is slightly above and not resting on the shelf, so it does not drag when the eye bolt is tightened.

Bracket and RIVNUT (Figure 7-44)

Material: 1 inch × 1 inch angle bracket and RIVNUT

Shelf Components and Assembly Recap

This section provides details on how to fabricate and assemble the shelf and the interfaces between the telescope and the Raspberry Pi. It makes a nice integrated package and is easy to assemble.

Lessons Learned Recap

After several observation sessions, the authors learned several lessons they wanted to pass on to the reader. These items help to make a fun successful observation session and can improve the experience for everyone involved.

Example Images Taken with the Upgraded Meade ETX-60AT Astrophotography System

The image in Figure 7-45 was taken when the temperature outside was 32 degrees Fahrenheit, and the Raspberry Pi 3 worked well. The crater details near the terminator are fascinating. With a little math, the astronomer might be able to determine a rough height for the crater wall given the known diameter of the moon.

Figure 7-46, taken early morning on January 29, 2018, clearly shows Jupiter and three of its moons. One unique historical fact regarding the Jovian moons is that Galileo used them to reason that the Earth orbited the sun. Over time he observed the paths of Jupiter’s moons with respect to the planet. They were not stationary, and the only way he could explain those positional changes was orbital paths around Jupiter. Once he understood the orbital hierarchy of objects in the solar system, he reasoned that a similar orbital path existed in the Earth/sun relationship.

With the Raspberry Pi attached to the telescope, you too can capture sequential images over time and observe phenomena such as the motion of Jupiter’s moons as they orbit the planet just like Galileo.

This set of images (Figure 7-47) of the lunar eclipse was taken on January 31, 2018, just as the moon was setting. It exemplifies time-lapse photography as it shows the progression of the eclipse in approximately 10-minute increments. One item of note that can be seen in the images is the terminator line is not very sharp. Compared to normal phased moon images, the terminator here appears “fuzzy.” In a lunar eclipse, as the Earth passes between the sun and moon, particles in the Earth’s atmosphere degrade the sun’s light before it strikes the moon and produce the fuzzy nature of the terminator.

The next photo is of a full moon that occurred on March 1, 2018 (See Figure 7-48). It is pieced together from individual sections, as the whole moon does not fit in the screen.

Using an image such as this, the astronomer can start finding and labeling craters and features on the moon they observe.

Finally, one more image, Figure 7-49, taken with the Meade ATX-60AT, was of a full moon on April 19, 2019. It shows the southern region very nicely and the crater Tycho.

Making an Astronomical Video and Creating Enhanced Images

The following images (Figures 7-50 to 7-52) are repeated to demonstrate how an image can be enhanced using the video GUI Python program and the steps outlined later in this section.

Figure 7-50 is unenhanced image and 7-51 is after enhancement.

Figures 7-51 and 7-52 are enhanced images using the techniques outlined in this section.

Figure 7-52 is the enhanced image taken with the 4 1/2-inch reflector showing the red spot and bands of Jupiter. This was the first time using this telescope the authors had seen the red spot and it was because of the enhancement techniques!

The following Raspberry Pi code (Listing 7-3) was used to capture the videos that created single images which were then enhanced to create the preceding images. The faint numbers are line numbers for the code; they need to be deleted if the reader copies this code. Be sure that the indention for the program is identical to what is shown in the following. The indention is how the Python compiler knows what is in scope or not.

0  #Code Developed by Paul Bradt

1  import tkinter as tk

2  import picamera

3  import os

4  import traceback

5  import datetime

6  import time

7  import sys

8  import subprocess

9  from subprocess import Popen, PIPE, CalledProcessError

10  pwd = os.getcwd()

11  root = tk.Tk() #makes the window

12  root.geometry('200x1100+0+0')

13  camera = picamera.PiCamera()

14  root.wm_title("Camera GUI Program") #Makes the title that will appear in the top left

15  root.config(background = "#FFFFFF") #Sets background color to  white

16  global now

17  #put widgets here

18  def picapture():

19       try:

20                global now

21                debugLog.insert(0.0, "Date Initialization Done ")

22                now = datetime.datetime.now().strftime("%F_%X")

23                debugLog.insert(0.0, now + " ")

24                camera.start_preview (fullscreen=False,window = (200,0,1100,640))

25               camera.start_recording('/home/pi/' + now + '.h264')

26       except:

27                print(traceback.format_exc(

limit=10))

28  def stopcapture():

29                camera.stop_recording()

30               camera.stop_preview()

31  #Main Frame and its contents

32  mainFrame = tk.Frame(root, width=200, height = 900)

33  mainFrame.grid(row=0, column=1, padx=10, pady=2)

34  btnFrame = tk.Frame(mainFrame, width=200, height = 200)

35  btnFrame.grid(row=1, column=0, padx=10, pady=2)

26  debugLog = tk.Text(mainFrame, width = 20, height = 10, takefocus=0)

27  debugLog.grid(row=3, column=0, padx=10, pady=2)

28  cameraBtn = tk.Button(btnFrame, text="Start recording", command=picapture)

29  cameraBtn.grid(row=1, column=0, padx=10, pady=2)

30  stopBtn = tk.Button(btnFrame, text="Stop recording", command=stopcapture)

31  stopBtn.grid(row=2, column=0, padx=10, pady=2)

32  root.mainloop() #start monitoring and updating the GUI. Nothing  below here runs.

Listing 7-3

Raspberry Pi Code PI_SN004_Astrophotograhy_Video Capture

Recap of Example Images and Enhancement Techniques

This section shows a few images captured by the authors and provides a high-level overview of some of the tools and techniques used to enhance and create some spectacular images of the two largest planets in the Solar System.