Proc. of the GHOU 2007 in Tokyo

Interstellar spaceship simulator for astronomical education and communications
Tomonori NOMOTO*An interstellar spaceship simulator, “HippLiner” is introduced. “HippLiner” has been developed forvisualization of interstellar traveling and drawing constellations. Because “HippLiner” contains several
catalogues of stars, galaxies and open clusters, operators can enjoy simulated relativistic/superluminalinterstellar traveling, proper motions of stars, and deformation of constellations as they move from one star toanother star. For astronomical education and communications, “HippLiner” is performed in Science Live Show
“UNIVERSE” for five years.
fundamental information of stars around the sun,the Hipparcos catalogue [1] is used. There are117954 stars with right ascension, declination andmagnitude in the Hipparcos catalogue. For radial
velocity of stars, the Hipparcos input catalogue [3]is also used. Simulation of three dimensional propermotions of stars are possible as linear motion
approximation using proper motions and radial
velocity for 15672 stars. For positions and sizes of601 open clusters, New Catalog of Optically Visible
Open Clusters and Candidates [4] is used. Nearby
Galaxies Catalogue [5] is also used for positions
and diameters of 2365 galaxies.
The primary function of HippLiner is interstellar
spaceship simulation and constellation line drawing.
As an interstellar spaceship simulator, operation ofHippLiner is quite simple. Operators just need to
double click the target star and press “move” button
in a panel displayed below the simulation. The
scenery displayed after arrival is the night sky of

1. Introduction
3D visualizations of celestial bodies are powerful
methods for astronomical education because theyexist three dimensionally and quite sparsely in thespace. Three dimensional positions of more thanhundred thousands of stars are available since theHipparcos and Tycho catalogues [1] were publishedin 1997. Astronomical catalogues with three
dimensional positions and sizes of open clusters andgalaxies are also available. Several 3D visualization
programs have been developed using data of the
Hipparcos catalogue and the other catalogues. Theauthor has been developed an astronomical simulator
named HippLiner. In this paper, the author first
introduces HippLiner. Implementation of relativistic
interstellar traveling is then briefly reviewed, andfinally, actual usage of HippLiner in Science LiveShow UNIVERSE (Hereafter abbreviated asUNIVERSE live-show) performed in the ScienceMuseum, Tokyo is described.
2. HippLiner: Interstellar spaceship simulator
HippLiner was originally developed for drawing
constellation lines displayed in Solar System
Simulator [2] in 2001. However, it is now aninterstellar spaceship simulator that enables
superluminal and relativistic interstellar journey to ahundred thousands of stars around the sun. It is also atool for browsing information of stars in theHipparcos catalogues and other celestial bodies.
HippLiner contains three dimensional positionsof stars, open clusters, and galaxies. ForFig.1. A scenery observed from alpha Centaur
simulated by HippLiner. Shape of Orion is not muchchanged while Sirius comes very close to Betelgeuse.

* Department of Chemistry, Kobe University, Japan
info@nomoto.org

1© 2007, Japan Association for Hands-On Universe

Proc. of the GHOU 2007 in Tokyo

was assumed as a point light source.
Change of apparent star positions by aberration isexpressed as

the target star (Fig.1.). In the superluminal mode ofHippLiner, operators can adjust speed of thespaceship with a unit of light year per second.
Drawing of constellations is also simple. After
entering the constellation drawing mode, operators
just need to double click the stars to connect stars
with lines. At the end of the lines, operators need toclick separator button, or space key. To finish
drawing a constellation, operators need to click theend button or return key. In addition to operation
using menus and panels, operation using shortcut
keys are also possible. Several functions are
assigned to each keys, and operators need notaccess panel windows. This function enables
smooth operation of the simulator during
live-shows or presentations. HippLiner is used inUNIVERSE live-show for 5 years with 3D
stereoscopic projection.

cos θ ′ = (cos θ + β ) (1 + β cos θ ) ,where β = v / c is relative speed of spaceship to light
speed [6]. θ and θ’ are colatitude angle from the lineof motion of the spaceship observed from rest frameof stars and spaceship frame respectively (Fig.2c,d).
The energy distribution of black body radiation
observed in rest frame is expressed as

S ( λ, T ) = Aλ−5 [exp(hc λk BT ) − 1] ,−1where T is temperature of stars, A is amplitude ofradiation for obtaining corresponding apparent
magnitude for each star. The distribution of lightintensity is changed to−1S ′(λ′, T ) = AD −2 λ′−5 [exp(hc λ′k B DT ) − 1] ,by angle-dependent Doppler effect [6] where

3. Relativistic mode of HippLiner

D = (1 + β cos θ )Quite recently, the author added a relativisticmode of interstellar spaceship simulation. Previously,
HippLiner supported only superluminal spaceshipsimulation which allows exceeding light speed suchas several light years per second. However, in theprinciple of physics, it is impossible to exceed lightspeed. Hence, more realistic interstellar spaceshipsimulation requires relativistic theory. According to
the relativistic theory, we need to simulate aberration,
Doppler effect and proper time. First, apparent
positions of stars change to the direction of motion
as speed of spaceship becomes close to light speed.
Doppler effect results in changes of colors andmagnitudes of the stars to blue-shifted or red-shiftedwith brightening or darkening dependent on
spaceship speed. Approximation of proper time isalso necessary because progression of time in thespaceship becomes slower as spaceship becomes
faster. As a result, all the sky view is converged tothe direction of motion, and the brightness of stars
also becomes brighter.
The above relativistic effects are implemented in
HippLiner. Positions of stars observed in simulator
become different as the spaceship becomes faster(Fig.2a,b). Colors of stars are also changed to bluishor reddish dependent on the speed of spaceship. For
simulation of colors of stars, black body radiation

1 − β 2 , λ and λ’ are wavelength

(a)

(b)

β=0.0(c)θ=0°θ

β=0.6(d)30°60°

θ'=0° 15°
θ=0° 30° 32° θ'
60°
53°
θ 90°
120° 82°

90°

β=0.0
180°

150°

120°

β=0.6

150°
124°

180°

Fig.2. Examples of relativistic effects simulated byHippLiner. (a) Original night sky on the earth with
0 % of light speed (β =0.0). (b) The same direction
observed from the position of the earth with 60 % oflight speed (β =0.6). Shapes of constellations andmagnitudes of stars are changed. (c), (d) Changes ofapparent position on the sky by aberration dependent
on the relative speed of the spaceship. Lines in (c) areoriginal angle of the stars in rest frame while lines in(b) are aberrated angle of the stars in starship frame.
2© 2007, Japan Association for Hands-On Universe

Proc. of the GHOU 2007 in Tokyo

space and interstellar journey. Using stereoscopic 3D
projection of HippLiner, interstellar travel and thedistribution of stars near the sun are shown in
UNIVERSE live-show. Usually, the host speaker first
explains about that the stars in the sky is not attachedto the sphere above us, and exist at different position
with different distances. In the 3D stereoscopic
theater, alpha Centaur can be seen as popped out
when the spaceship is on the sun because it is thenearest star from the sun. The spaceship withaudience is then moved to alpha Centaur in several
seconds. The scenery of the celestial sphere is notmuch changed because of close distance from the sun.
However, there are also some differences in alphaCentaur. When we see Orion, bright star is shining atvery close to Betelgeuse. The host speaker asks theaudiences like “Where is the bright star from?”, andthen the simulator comes back to the sun. The brightstar moves to downward to Orion’s hound during
travel, and finally we know that the bright star near
Betelgeuse was Sirius. Alnilam (ε Ori) also often
becomes the target star to go because it is the farthest
star in Orion. Hyades or Pleiades are also major
showplaces to go. After showing shapes ofconstellations changing by observer’s position, oneof the volunteer audiences can choose the star where
he/she wants to go. The scenery viewed from the starchosen is printed out and given to the audience as asouvenir.
Because the sceneries from the other stars were
not possible to simulate before the Hipparcos
catalogue, showplaces where are worth going aretotally unexplored yet. Double stars or stars whichhave exoplanets are possible showplaces of theinterstellar journey. For visualization of theshowplaces more impressive, an extension programof HippLiner is developed by Kuniaki Koike. Theextension program, named “Wakusei-guruguru” isan exoplanet simulator [11]. Effective representation
and usages of simulation of interstellar space is still
under investigation. The author is welcome to hear
about impressive usages or requests of newfunctions.

of radiation observed in rest frame of stars andspaceship frame respectively. The relationship of λand λ’ is λ’ = λ / D. Apparent magnitude is calculated
from above distribution. RGB values of standard
RGB (sRGB) color space [7] are also transformedvia CIE (1931) XYZ color space [8]. The resulting
color still corresponds to that of black body radiation
with temperature DT in starship frame. Dark stars
below an adjustable threshold can be drawn ingrayscale to simulate scotopic vision.
HippLiner adopted uniform motion for each stepof drawing frame during flight from one star toanother star. The distance from the starting position
in rest frame becomes summation of length ofprogression at each drawing frame as

distance = ∑ β step Δt'2
1 − β step ,step

where βstep is relative speed to light speed for eachframe of 3D rendering, and Δt’ is fixed interval of
3D renderings in proper time of starship frame. After
starting journey to the stars, βstep gradually increases
to the maximum speed and it decreases to zero
before arrival. The total time becomes at least several
years if we apply maximum β < 0.9. For example,
even if we apply uniform motion to alpha Centaur at
99.9999% of light speed, it takes 40 hours to arrivethat is not preferable for lives-show and users. It isalso not preferable to accelerate speed to much fasterbecause the simulation itself becomes incorrect. Thisis because the most dominant celestial bodies
observed by human’s eyes become those with strong
infrared irradiation when we apply faster speed,
whereas the Hipparcos catalogue does not containthose objects. On this account, a parameter: time
acceleration ratio between starship time andoperator’s time was introduced to make the journey
within minutes. As a result, actual time of thejourney for operator is adjustable as total time. Thus,
HippLiner enables the relativistic journey ofspaceship in limited time of live show.
4. Usage of HippLiner in a liveshow
UNIVERSE live-show is a popular attraction ofthe Science Museum, Tokyo which started in 1996
[9-10]. Since 2002, HippLiner is used in a part of
UNIVERSE live-show that is about the interstellar

5. Conclusion
HippLiner is a free superluminal/relativistic
interstellar spaceship simulator with more than3© 2007, Japan Association for Hands-On Universe

Proc. of the GHOU 2007 in Tokyo

the Internet, pp.117 - 123.
[10] Handa T., 2007, "A science liveshow
UNIVERSE, which will go beyond the horizon",Proc. of the GHOU 2007 in Tokyo.
[11] Koike K. & Handa T., 2007, "Softwares toexpand “UNIVERSE Liveshow” Raytrace simulation& Wakusei-guruguru (exoplanet simulator)", Proc. ofthe GHOU 2007 in Tokyo.

hundred thousands of celestial bodies. It has been
performed in a part of UNIVERSE live-show for five
years, and is freely downloadable from the following
URL.
http://T.NOMOTO.org/HippLiner/index-e.html
By using HippLiner, users can access many
visualization parameters manually for adding
flexibility to live-shows or finding ideas for
astronomical studies or writing science fictions. Theauthor is pleased when users can improve theirinspirations or ideas by using HippLiner.
6. Acknowledgement
The author acknowledges Dr. Toshihiro Handa,
Dr. Toshikazu Ebisuzaki and members of Team
Chimons for their suggestions and feedbacks, Mr.
Kuniaki Koike for extension program and drawing
3D constellations, and Ms. Sachiko Onodera, Mr.
Kyo Matsuura, Mr. Seiichiro Naitoh, Ms. Akiko
Nakano, and Mr. Yasuhide Yodo for drawing 3D
constellations attached to the software.
References[1] ESA, 1997, "The Hipparcos and Tycho
Catalogues", ESA SP-1200.
[2] Solar System Simulator Project, 1997, Solar
System Simulator series (http://www.sssim.com/).
[3] Turon C., et al., 1992, "The Hipparcos Input
Catalogue", ESA SP-1136.
[4] Dias W. S., et al., 2002, "New Catalog of
Optically Visible Open Clusters and Candidates",
A&A 389, 871.
[5] Tully R. B., 1988, "Nearby Galaxies Catalogue",
Cambridge, Cambridge University Press.
[6] McKinkey J. M. & Doherty P., 1979, "In searchof the "starbow": The appearance of the starfieldfrom a relativistic spaceship", Am. J. Phys. 47, 309.
[7] Stokes M., et al., 1996, "A Standard Default
Color Space for the Internet - sRGB"(http://www.w3.org/Graphics/Color/sRGB).
[8] Commission Internationale de l’Eclairage, 1932,"CIE Proceedings 1931", Cambridge UniversityPress.
[9] Nomoto T., et al., 1998, "Scientific Live Show in
Computerized Theater: Universe", Frontiers Science
Series No. 27, Proc. of the Misato International
Symposium 1998 on Astronomical Education with4© 2007, Japan Association for Hands-On Universe