# The Reproduction and Evaluation of Star Fields with the Milky Way in a Planetarium
## 2 Experiment
### Experimental Procedure  
The observers evaluated the results compared with those of the recalled actual Milky Way using opposite word pairs (\"faithful\"/\"non-faithful\") and five integer levels from \(-2\) to \(+2\), and wrote their evaluation values down on answer cards based on a 5-point Likert scale. The meanings of each evaluation level were \(-2\) (not faithful), \(-1\) (slightly not faithful), 0 (neither), \(+1\) (slightly faithful), and \(+2\) (faithful). In the preference and depth feeling evaluations, the observers performed evaluations using another opposite word pair (\"preference\"/\"non-preference,\" \"deep\"/\"shallow\") with the same five integer levels from \(-2\) to \(+2\) without a comparison target. The answer task was conducted in darkness with only the projected star images in order to maintain dark adaptation. However, there was no other bias to discriminate against particular answers. In the evaluation, there was no designated fixation point, and the observers were able to observe the star image freely. Therefore, they could judge the total appearance of all projection stimuli based on foveal vision with the cones and peripheral vision with the rods [15]. Snapshot images of the experimental environment are shown in Figure 3. Each star pattern was projected onto the position of the oval mark in the figure. The diameter of the dome screen was 23 m, and the zenith of the dome screen was slanted 15\({}^{\circ}\) frontward. There was no other illumination in the space where the experiment was conducted than the projected starry sky image. The room appeared completely dark. It was not possible to verify the low light level using the spectroradiometer, as it was too dark to measure (\(<\)0.003 cd/m\({}^{2}\)). The viewing angle of the projected star image was 37.3\({}^{\circ}\). The projectors were surrounded with partitions to prevent leakage from the light source from reaching the observers. From the experimental stimuli (star field image), it was realized that the observers could see from both the right and left sides. All observers had a cushion-reclining seat and observed the projected star image in a relaxed posture. The dome was maintained at a suitable temperature, and the conditions remained comfortable and uniform throughout the experiment. A total of 37 observers (22 males and 15 females aged 20-50 and older) participated in this experiment, as shown in Table 2. All experiments were conducted according to the principles outlined in the Helsinki Declaration. Written informed consent was obtained from all participants. As a result of previous experiments [8], evaluation bias was independent of astronomical observation experience. To confirm this tendency for star fields with the Milky Way, we collected experienced/inexperienced observers, each group half the total observers; 19 were experienced and 18 were inexperienced. Furthermore, in this study, the condition for selecting the observers considered general customers who visited a planetarium. Therefore, the observers were randomly gathered without bias to their characteristics such as age, gender, or experience of astronomical observation. This means that if observers do not have enough experience observing the Milky Way in the actual starry sky, they answered the faithfulness evaluation compared to the imagination of actual Milky Way. This psychometric experiment was conducted using the dome of the planetarium. After the observers had taken their seats in the dome, the illumination in the dome was turned off. At the beginning of this psychometric experiment, the observers received instructions for the evaluation experiment and performed exercises using all 12 patterns. In the experimental instructions, the observers heard the entire process of the experiment, rating methods including definitions of the three indices and time management for each evaluation, and a questionnaire for their personal information such as age, gender, and experience of astronomical observation in a planetarium and an actual sky.