1 Introduction
Tactile star charts are educational aids to help the visually impaired students learn about astronomy. They are useful for learning about constellation lines and the arrangement of constellations. The Multi-modal Book “An Introduction to Astronomy” is an astronomical textbook that includes tactile star charts. Because this is a printed book, however, users cannot change the settings of the tactile star charts. Whenever tactile star charts with different settings are required, the teachers have no option but to create them by hand. These take a tremendous amount of time and effort to complete. Therefore the authors decided to develop an automated system for creating tactile star charts based on settings specified by the user.
2 Tactile star charts
Tactile star charts created by this system allow stars, constellation lines and constellation boundaries in a given starfield to be observed by touch. Stars are expressed as points, constellation lines as solid lines and constellation boundaries as dotted lines.
2.1 Starfields
A starfield is an arbitrarily fixed area of the night sky.
2.2 Constellation lines
Constellation lines are lines drawn to link up stars, often forming human or animal shapes after which the constellations are named. Many of these originate in Greek myth.
2.3 Constellation boundaries
Constellation boundaries are lines showing the boundaries between constellations. The entire night sky is divided into 88 constellations enclosed by constellation boundaries in polygonal shapes, each with its own name.
3 Tactile star chart automatic creation system
This system is built as a Web application. Users input the constellation name and star chart settings to get the original star chart. The star chart is printed on microcapsule paper and passed through a developer. The tactile star chart is completed in this way.
3.1 How the system works
-
User inputs star chart settings – The settings of the targeted tactile star chart are designated on the Web page.
-
Decide the central coordinates of the chart – When using constellation names to designate starfields, the central coordinates of the targeted constellation are extracted from the constellation database. When designated by rectascension and declination, these values are used as they are.
-
Write into text file – The settings obtained are written into a text file, which is saved in PP3 format.
-
Execute using PP3 – The text file created in step 4 is read, data are captured from three sources (the star database, the constellation line database and the constellation boundary database), and a star chart image is created in PDF format using the star chart creation program PP3.
-
Return the PDF file – The PDF file is returned to the users.
3.2 Tactile star chart settings
To create a tactile star chart which is easy to observe by touch, the following three points must be taken into account.
-
If the lines are too wide they will overlap with nearby stars; if too narrow, they will be difficult to observe by touch. Therefore, the width of the lines has to be set appropriately.
-
Stars and lines are hard to distinguish if they are too close to each other. Therefore, the space between them must be made sufficiently wide.
-
A surfeit of objects makes observation difficult. Therefore, objects have to be selected.
Based on the above, this system allows the user to set the following five parameters on Web page.
The brackets show which of the above requirements is satisfied in each case.
-
Width of constellation lines and constellation boundaries (1)
-
Space between stars and constellation lines (2)
-
Constellation boundaries on / off (3)
-
Magnitude of displayed stars (3)
-
Scale (3)
3.3 How to designate starfields
In this system, constellation names can be used to designate starfields. The starfield may also be designated by specifying rectascension and declination.
3.4 Star chart creation program PP3
The star chart creation program uses the PP3 (Parvum Planetarium, version 3) developed by Torsten Bronger. This is operated by loading the text file with star chart specifications into PP3. Once the text file is loaded, PP3 creates and automatically compiles a TeX file and generates EPS, DVI and PDF files.
3.5 Databases
This system uses four databases.
-
Star database – Uses BSC (Bright Star Catalog), a catalog of stars compiled • at Yale University. The coordinates and magnitude of stars is extracted from this database.
-
Constellation line database – PP3 includes a original database created by • Bronger himself. However, this database has too few constellation lines. Therefore, a separate constellation line database was created for this system.
-
Constellation boundary database – Uses the Constellation Boundary Data • created by A.C. Davenhall, based on constellation boundaries determined by the International Astronomical Union in 1928.
-
Constellation database – Holds constellation names and the central coor• dinates of those constellations.
3.6 Printing and development
The star chart is printed on microcapsule paper and passed through a developer. The parts coated black absorb the heat and swell, causing the stars, constellation lines and constellation boundaries to lift up in relief. The tactile star chart is completed in this way.
4 Conclusion
The authors set out to develop a tactile star chart automatic creation system enabling users to create tactile star charts with various settings quickly and simply. In the future, experiments will be conducted to find the settings most suited to tactile observation.
