<s>
Celestia	B-Application
is	O
a	O
real-time	O
3D	O
astronomy	O
software	B-Application
program	I-Application
that	O
was	O
created	O
in	O
2001	O
by	O
Chris	O
Laurel	O
.	O
</s>
<s>
Celestia	B-Application
also	O
doubles	O
as	O
a	O
planetarium	O
,	O
but	O
the	O
user	O
is	O
not	O
restricted	O
to	O
the	O
Earth	O
's	O
surface	O
,	O
like	O
in	O
other	O
planetarium	B-Application
software	I-Application
such	O
as	O
Stellarium	B-Application
.	O
</s>
<s>
To	O
summarize	O
,	O
Celestia	B-Application
is	O
a	O
scientifically	O
accurate	O
3D	O
universe	O
simulator	O
,	O
that	O
is	O
also	O
highly	O
customizable	O
.	O
</s>
<s>
Celestia	B-Application
can	O
display	O
objects	O
of	O
various	O
scales	O
using	O
OpenGL	B-Application
.	O
</s>
<s>
Celestia	B-Application
is	O
available	O
for	O
AmigaOS	B-Application
4	I-Application
,	O
Linux	B-Application
,	O
macOS	B-Application
,	O
Microsoft	B-Application
Windows	I-Application
,	O
iOS	B-Application
,	O
and	O
Android	B-Application
.	O
</s>
<s>
It	O
is	O
free	B-Application
and	I-Application
open	I-Application
source	I-Application
software	I-Application
released	O
under	O
the	O
GNU	B-License
General	I-License
Public	I-License
License	I-License
.	O
</s>
<s>
Celestia	B-Application
's	O
development	O
stopped	O
in	O
2013	O
,	O
with	O
the	O
final	O
release	O
in	O
2011	O
.	O
</s>
<s>
Since	O
then	O
,	O
some	O
of	O
its	O
development	O
team	O
went	O
to	O
work	O
on	O
celestia.Sci	O
,	O
a	O
cosmological	O
visualizer	O
featuring	O
more	O
realistic	O
rendering	O
of	O
galaxies	B-Application
and	O
planets	O
,	O
gravitational	O
lensing	O
,	O
and	O
many	O
other	O
scientifically	O
accurate	O
enhancements	O
.	O
</s>
<s>
The	O
original	O
creator	O
of	O
Celestia	B-Application
,	O
Chris	O
Laurel	O
,	O
created	O
after	O
Celestia	B-Application
's	O
development	O
stopped	O
,	O
and	O
started	O
work	O
on	O
the	O
widely-used	O
iOS	B-Application
app	O
.	O
</s>
<s>
In	O
late	O
2016	O
,	O
the	O
official	O
Celestia	B-Application
forums	O
were	O
restored	O
,	O
and	O
development	O
restarted	O
.	O
</s>
<s>
Celestia	B-Application
was	O
ported	O
to	O
mobile	O
devices	O
in	O
2020	O
,	O
and	O
it	O
continues	O
to	O
receive	O
updates	O
and	O
experimental	O
beta	O
versions	O
.	O
</s>
<s>
Celestia	B-Application
is	O
available	O
for	O
download	O
from	O
its	O
main	O
website	O
,	O
,	O
but	O
it	O
can	O
be	O
obtained	O
from	O
a	O
large	O
multitude	O
of	O
free	B-Application
software	I-Application
websites	O
as	O
well	O
.	O
</s>
<s>
Between	O
2001	O
and	O
May	O
2017	O
,	O
the	O
former	O
central	O
distribution	O
site	O
SourceForge	B-Application
counted	O
approximately	O
12	O
million	O
downloads	O
.	O
</s>
<s>
Celestia	B-Application
versions	O
1.6.3	O
and	O
under	O
display	O
the	O
Hipparcos	O
Catalogue	O
(	O
HIP	O
)	O
of	O
118,322	O
stars	O
and	O
a	O
compiled	O
catalogue	O
of	O
galaxies	B-Application
,	O
while	O
version	O
1.7.0	O
includes	O
stars	O
from	O
the	O
Tycho-2	O
Catalogue	O
alongside	O
the	O
Hipparcos	O
stars	O
,	O
with	O
some	O
data	O
from	O
Gaia	O
,	O
increasing	O
the	O
star	O
count	O
to	O
over	O
2	O
million	O
.	O
</s>
<s>
Celestia	B-Application
uses	O
the	O
VSOP87	O
theory	O
of	O
planetary	O
orbits	O
to	O
provide	O
a	O
solar	B-Application
and	O
lunar	O
eclipse	B-Application
finder	O
and	O
to	O
display	O
the	O
orbital	O
paths	O
of	O
planets	O
(	O
including	O
extrasolar	O
planets	O
)	O
,	O
dwarf	O
planets	O
,	O
moons	O
,	O
asteroids	O
,	O
comets	B-Language
,	O
artificial	O
satellites	B-Application
,	O
and	O
spacecraft	O
.	O
</s>
<s>
Using	O
the	O
installed	O
catalogues	O
,	O
the	O
names	O
of	O
celestial	O
objects	O
can	O
be	O
displayed	O
,	O
including	O
artificial	O
satellites	B-Application
.	O
</s>
<s>
Celestia	B-Application
allows	O
users	O
to	O
navigate	O
at	O
different	O
speeds	O
,	O
and	O
allow	O
users	O
to	O
orbit	O
stars	O
,	O
planets	O
,	O
moons	O
,	O
and	O
other	O
space	O
objects	O
,	O
track	O
space	O
objects	O
such	O
as	O
spacecraft	O
,	O
asteroids	O
,	O
and	O
comets	B-Language
as	O
they	O
fly	O
by	O
,	O
or	O
travel	O
to	O
and/or	O
fly	O
through	O
galaxies	B-Application
.	O
</s>
<s>
Celestia	B-Application
simulates	O
the	O
appearance	O
of	O
atmospheres	O
on	O
planets	O
and	O
moons	O
,	O
planetshine	O
on	O
orbiting	O
satellites	B-Application
,	O
and	O
miscellaneous	O
planetary	O
details	O
such	O
as	O
sunrise	O
and	O
sunset	O
.	O
</s>
<s>
Information	O
about	O
the	O
objects	O
that	O
Celestia	B-Application
draws	O
can	O
also	O
be	O
displayed	O
,	O
such	O
as	O
temperature	O
,	O
distance	O
from	O
observer	O
,	O
radius	O
,	O
rotational	O
period	O
,	O
luminosity	O
,	O
and	O
more	O
.	O
</s>
<s>
The	O
user	O
can	O
change	O
Celestia	B-Application
's	O
field	O
of	O
view	O
,	O
and	O
the	O
window	O
can	O
be	O
split	O
into	O
multiple	O
different	O
panes	O
,	O
meaning	O
that	O
several	O
objects	O
can	O
be	O
displayed	O
on	O
the	O
screen	O
at	O
once	O
.	O
</s>
<s>
Celestia	B-Application
's	O
support	O
for	O
gamepads	O
and	O
joysticks	O
is	O
relatively	O
limited	O
.	O
</s>
<s>
Celestia	B-Application
can	O
be	O
extended	O
with	O
new	O
objects	O
,	O
and	O
has	O
support	O
for	O
third-party	O
,	O
user-created	O
add-ons	O
available	O
for	O
installation	O
,	O
both	O
fictional	O
and	O
realistic	O
.	O
</s>
<s>
These	O
files	O
are	O
plain	O
text	O
files	O
that	O
are	O
written	O
like	O
code	O
and	O
have	O
specific	O
syntax	O
rules	O
that	O
have	O
to	O
be	O
followed	O
for	O
Celestia	B-Application
to	O
read	O
them	O
,	O
and	O
there	O
are	O
dozens	O
of	O
different	O
use	O
cases	O
and	O
ways	O
to	O
write	O
these	O
files	O
.	O
</s>
<s>
Celestia	B-Application
also	O
uses	O
custom	O
CEL	O
and	O
CELX	O
scripts	O
written	O
in	O
the	O
powerful	O
Lua	B-Language
programming	I-Language
language	I-Language
which	O
can	O
execute	O
a	O
multitude	O
of	O
functions	O
.	O
</s>
<s>
The	O
default	O
setting	O
for	O
Celestia	B-Application
's	O
Earth	O
is	O
a	O
spheroid	O
.	O
</s>
<s>
The	O
irregular	O
surface	O
of	O
the	O
Earth	O
causes	O
low	O
Earth	O
orbit	O
satellites	B-Application
to	O
appear	O
to	O
be	O
in	O
the	O
wrong	O
places	O
in	O
the	O
sky	O
when	O
watched	O
from	O
the	O
surface	O
,	O
even	O
when	O
the	O
Earth	O
's	O
oblateness	O
is	O
specified	O
.	O
</s>
<s>
Many	O
types	O
of	O
astronomical	O
objects	O
are	O
not	O
included	O
with	O
Celestia	B-Application
.	O
</s>
<s>
Variable	O
stars	O
,	O
supernovae	O
,	O
black	B-Application
holes	I-Application
,	O
and	O
nebulae	O
are	O
missing	O
from	O
the	O
standard	O
distribution	O
.	O
</s>
<s>
Although	O
objects	O
that	O
form	O
part	O
of	O
a	O
planetary	O
system	O
move	O
,	O
and	O
stars	O
rotate	O
about	O
their	O
axes	O
and	O
orbit	O
each	O
other	O
in	O
multiple	O
star	O
systems	O
,	O
stellar	O
proper	O
motion	O
is	O
not	O
simulated	O
,	O
and	O
galaxies	B-Application
are	O
at	O
fixed	O
locations	O
.	O
</s>
<s>
As	O
a	O
result	O
,	O
the	O
constellations	O
in	O
Celestia	B-Application
do	O
not	O
gradually	O
change	O
shape	O
as	O
they	O
do	O
in	O
the	O
real	O
world	O
.	O
</s>
<s>
In	O
addition	O
,	O
Celestia	B-Application
's	O
binary	O
star	O
catalogs	O
only	O
describe	O
a	O
few	O
hundred	O
systems	O
of	O
multiple	O
stars	O
.	O
</s>
<s>
Celestia	B-Application
does	O
not	O
include	O
any	O
stars	O
that	O
are	O
more	O
than	O
a	O
few	O
thousand	O
light-years	O
from	O
the	O
Sun	O
because	O
the	O
parallaxes	O
of	O
more	O
distant	O
stars	O
are	O
too	O
small	O
to	O
be	O
accurately	O
measured	O
by	O
the	O
Hipparcos	O
astrometric	O
satellite	B-Application
.	O
</s>
<s>
Finally	O
,	O
Celestia	B-Application
does	O
not	O
consider	O
the	O
wobbling	O
of	O
some	O
stars	O
induced	O
by	O
their	O
planets	O
,	O
unless	O
said	O
wobbling	O
is	O
very	O
noticeable	O
.	O
</s>
<s>
Wavelength	O
filtering	O
is	O
not	O
implemented	O
in	O
Celestia	B-Application
's	O
engine	O
.	O
</s>
<s>
This	O
means	O
false-color	B-Application
maps	O
and	O
multi-color	O
nebulae	O
are	O
not	O
part	O
of	O
the	O
official	O
distribution	O
,	O
but	O
some	O
are	O
available	O
as	O
add-ons	O
.	O
</s>
<s>
Celestia	B-Application
also	O
does	O
not	O
simulate	O
gravity	O
.	O
</s>
<s>
For	O
example	O
,	O
a	O
near-Earth	O
object	O
approaching	O
the	O
Earth	O
will	O
not	O
be	O
deflected	O
by	O
the	O
Earth	O
's	O
gravity	O
unless	O
the	O
person	O
who	O
defined	O
the	O
NEO	O
's	O
trajectory	O
for	O
Celestia	B-Application
included	O
that	O
effect	O
.	O
</s>
<s>
Some	O
moons	O
do	O
not	O
cast	O
shadows	O
on	O
their	O
planet	O
during	O
eclipses	B-Application
.	O
</s>
<s>
This	O
is	O
because	O
irregularly	O
shaped	O
objects	O
do	O
not	O
cast	O
shadows	O
in	O
the	O
current	O
version	O
of	O
Celestia	B-Application
,	O
although	O
this	O
is	O
planned	O
for	O
future	O
versions	O
.	O
</s>
<s>
Most	O
real-world	O
spacecraft	O
such	O
as	O
Voyager	O
2	O
are	O
not	O
available	O
in	O
Celestia	B-Application
but	O
are	O
provided	O
as	O
add-ons	O
by	O
users	O
.	O
</s>
<s>
Additionally	O
,	O
most	O
of	O
the	O
spacecraft	O
included	O
with	O
standard	O
Celestia	B-Application
use	O
outdated	O
or	O
low-quality	O
models	O
,	O
such	O
as	O
the	O
stock	O
Mir	O
which	O
uses	O
extremely	O
low-quality	O
textures	O
and	O
models	O
,	O
and	O
the	O
stock	O
ISS	O
which	O
has	O
n't	O
had	O
an	O
update	O
since	O
around	O
2007	O
,	O
but	O
there	O
are	O
add-ons	O
on	O
the	O
Celestia	B-Application
Forums	O
which	O
add	O
more	O
accurate	O
and	O
higher-quality	O
models	O
.	O
</s>
<s>
Celestia	B-Application
uses	O
the	O
Julian	O
calendar	O
and	O
cannot	O
go	O
back	O
or	O
forward	O
more	O
than	O
2	O
billion	O
years	O
,	O
and	O
the	O
default	O
time-setting	O
system	O
cannot	O
go	O
further	O
than	O
the	O
years	O
-9999	O
or	O
9999	O
.	O
</s>
<s>
Higher	O
resolution	O
surface	O
textures	O
are	O
available	O
for	O
most	O
Solar	B-Application
System	O
bodies	O
,	O
including	O
Virtual	O
Textures	O
with	O
coverage	O
up	O
to	O
32768	O
pixels	O
wide	O
(	O
1.25km/pixel	O
at	O
the	O
Earth	O
's	O
equator	O
)	O
,	O
with	O
selected	O
coverage	O
at	O
higher	O
resolutions	O
.	O
</s>
<s>
3D	O
models	O
of	O
historical	O
and	O
existing	O
spacecraft	O
are	O
available	O
flying	O
in	O
reasonably	O
accurate	O
trajectories	O
,	O
such	O
as	O
Sputnik	O
1	O
,	O
Voyager	O
2	O
,	O
the	O
Hubble	O
Space	O
Telescope	O
,	O
and	O
the	O
International	O
Space	O
Station	O
,	O
as	O
are	O
extended	O
data	B-Application
plots	I-Application
for	O
stars	O
(	O
2	O
million	O
with	O
correct	O
spatial	O
coordinates	O
)	O
,	O
DSOs	O
(	O
nebulae	O
,	O
galaxies	B-Application
,	O
open	O
clusters	O
,	O
etc	O
.	O
</s>
<s>
)	O
,	O
as	O
well	O
as	O
catalogs	O
of	O
asteroids	O
and	O
comets	B-Language
,	O
and	O
more	O
than	O
96,000	O
locations	O
on	O
the	O
Earth	O
can	O
be	O
drawn	O
by	O
the	O
program	O
.	O
</s>
<s>
Add-ons	O
also	O
include	O
other	O
objects	O
such	O
as	O
red	O
and	O
blue	O
supergiants	O
,	O
red	O
and	O
brown	O
dwarfs	O
,	O
neutron	O
stars	O
,	O
spinning	O
pulsars	O
,	O
rotating	O
black	B-Application
holes	I-Application
with	O
accretion	O
disks	O
,	O
protostars	O
,	O
Wolf-Rayet	O
stars	O
,	O
star	O
nursery	O
nebulae	O
,	O
supernova	B-Application
remnants	O
,	O
planetary	O
nebulae	O
,	O
galactic	O
redshifts	O
,	O
geological	O
planetary	O
displays	O
(	O
e.g.	O
</s>
<s>
3D	O
interiors	O
,	O
topographic	O
and	O
bathymetric	O
maps	O
,	O
paleogeography	O
)	O
,	O
planetary	O
aurorae	O
,	O
rotating	O
magnetic	O
fields	O
,	O
animated	O
solar	B-Application
prominences	O
,	O
3D	O
craters	O
and	O
mountains	O
,	O
and	O
historic	O
collision	O
events	O
(	O
Either	O
spacecraft	O
such	O
as	O
Deep	O
Impact	O
and	O
DART	O
,	O
or	O
meteoric	O
impacts	O
such	O
as	O
the	O
Chelyabinsk	O
meteor	O
)	O
.	O
</s>
<s>
These	O
include	O
simple	O
tours	O
,	O
reconstructions	O
of	O
complex	O
space	O
missions	O
such	O
as	O
Cassini	O
–	O
Huygens	O
and	O
Deep	O
Impact	O
,	O
and	O
scripts	O
showing	O
useful	O
information	O
,	O
like	O
size	O
comparisons	O
,	O
or	O
particular	O
events	O
such	O
as	O
multiple	O
simultaneous	O
eclipses	B-Application
of	O
Jupiter	O
's	O
moons	O
or	O
the	O
evolution	O
of	O
a	O
star	O
.	O
</s>
<s>
Fictional	O
universes	O
can	O
be	O
depicted	O
,	O
with	O
planetary	O
systems	O
and	O
3D	O
models	O
—	O
films	O
such	O
as	O
2001	O
:	O
A	O
Space	O
Odyssey	O
,	O
Star	B-Operating_System
Trek	I-Operating_System
and	O
Star	B-Application
Wars	I-Application
,	O
and	O
TV	O
shows	O
including	O
Stargate	O
SG-1	O
and	O
Babylon	O
5	O
.	O
</s>
<s>
Add-ons	O
illustrating	O
less	O
well-known	O
internet	O
fiction	O
,	O
like	O
Orion	O
's	O
Arm	O
,	O
or	O
role-playing	O
games	O
,	O
like	O
2300	O
AD	O
,	O
and	O
personal	O
works	O
by	O
members	O
of	O
the	O
Celestia	B-Application
community	O
depicting	O
fictional	O
planetary	O
systems	O
with	O
inhabited	O
worlds	O
,	O
spacecraft	O
,	O
cities	O
,	O
and	O
special	O
effects	O
can	O
also	O
be	O
added	O
.	O
</s>
<s>
These	O
activities	O
provide	O
approximately	O
40	O
hours	O
of	O
space	O
journeys	O
and	O
astronomical	O
lessons	O
to	O
include	O
extensive	O
tours	O
of	O
the	O
Celestia	B-Application
universe	O
,	O
the	O
complete	O
life	O
cycle	O
of	O
stars	O
,	O
the	O
Solar	B-Application
System	O
,	O
the	O
human	O
space	O
program	O
,	O
the	O
Search	O
for	O
Extraterrestrial	O
Intelligence	O
(	O
SETI	O
)	O
,	O
and	O
depictions	O
of	O
astronomical	O
events	O
such	O
as	O
the	O
formation	O
of	O
the	O
Moon	O
billions	O
of	O
years	O
ago	O
,	O
and	O
the	O
possible	O
terraforming	O
of	O
Mars	O
in	O
the	O
future	O
.	O
</s>
<s>
In	O
mid	O
2016	O
,	O
a	O
large	O
addon	O
pack	O
project	O
called	O
Celestia	B-Application
Origin	O
was	O
created	O
,	O
which	O
replaces	O
all	O
vanilla	O
textures	O
and	O
graphics	O
with	O
higher-quality	O
renderings	O
,	O
adds	O
more	O
minor	O
objects	O
such	O
as	O
TNOs	O
and	O
asteroids	O
,	O
while	O
also	O
adding	O
more	O
extrasolar	O
planets	O
with	O
custom	O
textures	O
,	O
more	O
nebulae	O
with	O
full	O
3D	O
and	O
accurate	O
models	O
,	O
more	O
stars	O
and	O
galaxies	B-Application
,	O
more	O
star	O
clusters	O
,	O
more	O
spacecraft	O
,	O
and	O
a	O
ton	O
of	O
more	O
enhancements	O
.	O
</s>
<s>
In	O
2019	O
,	O
Celestia	B-Application
Forum	O
member	O
FarGetaNik	O
created	O
an	O
addon	O
pack	O
called	O
Project	O
Echoes	O
,	O
featuring	O
higher-quality	O
renderings	O
that	O
replace	O
all	O
vanilla	O
textures	O
.	O
</s>
<s>
Celestia	B-Application
1.7.0	O
appears	O
to	O
use	O
Project	O
Echoes	O
as	O
inspiration	O
for	O
its	O
textures	O
.	O
</s>
<s>
NASA	O
and	O
ESA	O
have	O
used	O
Celestia	B-Application
in	O
their	O
educational	O
and	O
outreach	O
programs	O
,	O
as	O
well	O
as	O
for	O
interfacing	O
to	O
trajectory	O
analysis	O
software	O
.	O
</s>
<s>
The	O
French	O
Space	O
Agency	O
(	O
CNES	O
)	O
created	O
a	O
heavily	O
modified	O
version	O
of	O
Celestia	B-Application
in	O
2016	O
,	O
called	O
VTS	O
Timeloop	O
,	O
and	O
it	O
has	O
since	O
been	O
used	O
by	O
multiple	O
space	O
agencies	O
,	O
including	O
ESA	O
and	O
CNES	O
themselves	O
.	O
</s>
<s>
Celestia	B-Application
was	O
used	O
in	O
the	O
media	O
by	O
the	O
CBS	O
television	O
show	O
NCIS	O
(	O
Season	O
4	O
,	O
Episode	O
22	O
:	O
"	O
In	O
the	O
Dark	O
"	O
)	O
.	O
</s>
<s>
Character	O
Timothy	O
McGee	O
explains	O
what	O
Celestia	B-Application
is	O
and	O
how	O
an	O
add-on	O
can	O
allow	O
the	O
user	O
to	O
store	O
a	O
diary	O
within	O
the	O
program	O
,	O
as	O
well	O
.	O
</s>
<s>
Textures	O
designed	O
by	O
Celestia	B-Application
graphic	O
artists	O
were	O
used	O
in	O
the	O
movie	O
The	O
Day	O
After	O
Tomorrow	O
and	O
the	O
2008	O
miniseries	O
The	O
Andromeda	B-Application
Strain	O
.	O
</s>
<s>
Celestia	B-Application
has	O
also	O
appeared	O
on	O
the	O
Science	O
Channel	O
's	O
Through	O
the	O
Wormhole	O
.	O
</s>
<s>
Eurogamer	O
's	O
Jim	O
Rossignol	O
named	O
Celestia	B-Application
among	O
a	O
top	O
20	O
list	O
of	O
Summer	O
of	O
PC	O
Freeware	B-License
games	O
in	O
2006	O
.	O
</s>
