Astronomy and Space
Interactive Web Resources
Interactive server which lets you
view the Earth and Moon, as illuminated by the Sun at the time of your request,
from a variety of viewpoints.
An interactive animation illustrates how orbits around compact
objects such as neutron stars and black holes depart drastically from
Kepler's laws, and explains why.
eliminating the need for Java, and improves graphics rendering. The
original Java version
Solar System Live, an
interactive orrery for the Web, lets you
view the solar system
in a variety of ways for any date between 4713 B.C. and A.D. 8000.
An ephemeris can be displayed for any location on Earth and, given
orbital elements in the form published in the IAU Circulars, the orbit
and position of asteroids and comets can be plotted.
Space Shuttle imagery and interactive Web navigation
combine to allow you to explore Switzerland, home of
www.fourmilab.ch, from orbit.
As life inexorably expands from the home planet throughout the galaxy
and beyond, there will come a time when our descendents render a
new planet habitable every day.
Terranova invites you to visit
the terraformed planet of the day.
New: 2006 update provides larger JPEG images with improved
planet image quality and more realistic star fields including
Your Sky makes custom maps of the
sky for any location on Earth and any date from 4713 B.C. into the
distant future. Maps can include stars as faint as magnitude 6.5,
constellation names, outlines, and boundaries, the Moon and planets,
deep sky objects from a database of more than 500, and a comet or
asteroid whose position is calculated from its orbital elements. A
variety of display options allow customising the map for its intended
shmillennium! Round numbers depend on which calendar you use to keep
score; human cultures have invented dozens of calendars over the
centuries, all equally valid. Our
calendars from various cultures and computer time representations.
Documents and Images
Kerbal Space Program is a computer game in which the player builds
spacecraft, aircraft, and spaceplanes and sends them on various
missions. Not only is the game a great deal of fun, playing it helps
develop an intuitive sense for rocket design and engineering
and orbital mechanics, even among people who already understand these
topics at the mathematical level. The graphics in the game are
superb. This document is a collection of screen captures from
missions I've flown.
The total solar eclipse of July 11th, 2010 made a landfall in Easter
Island, one of the most remote inhabited places on the Earth, and
Fourmilab was there to observe and photograph the eclipse and
explore the enigmatic artefacts of the island. This photo gallery
chronicles the expedition and includes telephoto imagery of the
Between July 19th and August 6th, 2008 I was off to the North
Pole—no, really—and thereafter to observe the
total eclipse of the Sun on August 1st. So how do you get to the
North Pole? Well, there's always the tedious dogsled method, but if
you're in a hurry, nothing beats a Russian nuclear powered
icebreaker. Here is a collection of images from the expedition,
including the ship, landscapes, wildlife, and the eclipse.
Due to the finite speed of light, observers in different locations or
moving with respect to one another may see events as occurring in
different orders—simultaneity depends upon your viewpoint.
You've heard the mission control recording of Apollo 11
landing on the Moon, but what did it sound like on board the
demonstrates the relativity of simultaneity and lets you experience
the Eagle's touchdown from a lunar perspective, providing
an insight about Neil Armstrong's first radio transmission after
More than two months of computer time, nine billion numerical
integration steps, trillions of floating point operations, five
terabytes of intermediate results, and 3.6 gigabytes of output went
into the preparation of this catalogue of every transit of a planet in
front of the Sun as viewed from any other planet in the Solar System
for the years ±125,000. If you missed the recent transits of
here's your guide to coming attractions (as well as what you've
missed), including the simultaneous transit of Mercury and Venus
visible from Earth in July 69163, the triple transit of Venus, Earth,
and the Moon from Saturn in December 23364, and much more--a total of
1,011,793 transits in all. Animations and images illustrate rare
events, and all data and the programs used to produce them may be
downloaded for your own investigations.
In the first few days of July 2004, three unrelated celestial
phenomena happened to coincide: full Moon, lunar perigee, and Earth's
passage through aphelion. This permitted photographing the full Moon
and Sun within one day, showing the difference in their apparent
size. The effect of the Sun and Moon's orbits on the appearance and
duration of solar eclipses is discussed, and an estimate is made of
when the last-ever total solar eclipse will be visible from Earth.
New: January 26th, 2005 update adds photos of the
apogean full Moon of January 2005 compared to the Sun with
the Earth near perihelion.
On June 8th, 2004, for the first time since 1882, the planet Venus
passed in front of the Sun as seen from Earth. This spectacle is not
only rare, it's about the only opportunity one ever gets to see
another planet with the unaided eye as a spot, not a
dot. Fourmilab was blessed with almost equally rare
cloudless skies for this event, which permitted capturing the images
presented on this page.
In November 2003 an unusually bright total lunar eclipse
was visible from all continents except Australia. At my
observing site in western Switzerland, the Moon was high in the
sky throughout the eclipse and, astonishingly for November,
the sky was clear for the entire immersion phase and almost
all of totality. This page describes the eclipse and presents
images captured with a telescope and digital camera, including an
animation which shows the Moon's encounter with the Earth's
Only fourteen times in the twenty-first century will
astronomers be treated to the spectacle of Mercury's silhouette
majestically traversing the Sun. This century's first transit
of Mercury occurred on May 7th, 2003, and was the first I ever
managed to observe and photograph. Information and
images of 2003's transit are presented, along with previews of
coming attractions including the spectacular and
extraordinarily rare transits of Venus in 2004 and 2012.
Images of the total solar eclipse of June 21st, 2001, observed near
Lusaka, Zambia, plus wildlife and scenery from Zambia, Zimbabwe,
Botswana, and South Africa.
A Rocket A Day Keeps the High Costs Away asks why it is,
considering that the V2 cost about US$13,000 each (1945
dollars) and could be launched at rates approaching 100 a
week, that today's launchers cost 1000 times as much. A
market-oriented approach to overcome the current cost
barrier to space development is suggested.
Rocket engineering is complicated and demanding, but rocket
science is pretty straightforward. Explore the rocket equation,
which governs the operation of all rockets, and understand why it's so difficult
to get to orbit from the surface of the Earth and why multistage rockets
Manned orbiting battle stations, armed with rapid-fire machine guns!
Bad science fiction? Well, actually, space age history, just
recently revealed. Read all about it, and explore guns in
space: yesterday, today, and tomorrow.
On October 15th, 1991 a proton
with an energy of 3×1020 electron volts slammed into in
the Earth's atmosphere. Let's crunch some numbers…. A
performance comparison with 24th century Galaxy Class
starship technology is presented.
On rare occasions around peaks in the 11 year solar
activity cycle, a sunspot group may appear which is
sufficiently large to be observed without any optical
aid other than a filter for safely viewing the Sun. If
observing this phenomenon interests you, don't count on
quick success; it took me thirty-five years
from the time I started looking until I observed my
first naked-eye sunspot on September 23rd, 2000. This
document contains photos of that enormous sunspot, both
my own and high resolution images from spacecraft and a
solar observatory, and provides tips and resources to
assist in your own quest to view the next "big one".
Images and movies of the total solar eclipse of August 11th, 1999, which
I observed from Esfahan, in central Iran.
Have you ever seen Mercury? A portrait of the three inner planets of our
solar system serves as the point of departure for a discussion
of when and how you can best observe this bright but elusive planet.
The companion Mercury
custom predictions for viewing Mercury, including finder charts
for your observing site and Orrery views of the inner solar system
at maximum elongations of Mercury.
Images of Comet C/1995 O1 (Hale-Bopp), the Great Comet of 1997.
Images of Comet C/1996 B2 (Hyakutake) from its 1996 close encounter with Earth.
Inconstant Moon explores
a universally seen but seldom observed phenomenon: the different
appearance of the Moon at perigee and apogee.
The only reason Einstein's special theory of relativity seems weird to those
learning it is that the velocities we're familiar with are such a tiny
fraction of the speed of light we've never had a chance to
gain an intuitive sense of relativistic effects. If the speed of
light were 100 kilometres per hour, footballers would have no trouble
dealing with relativistic goal shots. C-ship
uses computer image synthesis to put you aboard a starship entirely
consistent with the laws of physics and lets you look out the window to
experience special relativity with your own eyes.
This "basement science" experiment demonstrates the universality of
gravitation, showing the gravitational attraction between masses of
less than a kilogram. Could Archimedes have discovered universal
gravitation nineteen centuries before Newton? Well, let's see....
Did you know that when the planet Venus is bright and far from
the Sun it can be glimpsed with the unaided eye in broad
daylight? This page provides tips for viewing Venus in the
daytime, plus a calculator which shows the best opportunities
for any year and produces finder charts for your observing site.
Here's an opportunity to see something that's up in the sky for
anybody to spot but which few ever do: a planet shining in the
blue sky at midday.
Fast interstellar travel will never be possible with any kind of
rocket, regardless of the energy source (be it chemical, nuclear, or
antimatter), due to the need to carry the rocket's
reaction mass on board. How can a person who coined the maxim
"Never invest in something that violates a conservation law" seriously
entertain the possibility of "propellantless propulsion"? This
brief document speculates on how a "Vacuum Propeller" might be
built which violates no law of physics.
This directory contains the file
poss.zip, a Zipped archive
which extracts into the file
poss.xls. This is a Microsoft
Excel 5.0 (or above) workbook which contains a catalogue of the
Palomar Observatory Sky Survey plates, including the mapping
between the original plates and the MicroSky microfiche edition
published by Deen Publications, Inc.
Windows Applications and Screen Savers
Home Planet is a Microsoft Windows 3.1, 95/98/Me, and
NT/2000/XP application which puts a somewhat different spin on the
usual astronomical or planetarium program. Home Planet places the
Earth in its place in the universe, allowing one to look up toward the
stars or down upon the Earth from a variety of perspectives.
Comprehensive documentation is included in a hypertext help file. For
additional information and instructions on how to download and install
the software, please see the
updated for Windows XP dual screen and registry-based individual
settings, and to use the
cloudless Earth image.
What better way to protect your monitor's phosphor than by smashing
rocks into it at dozens of kilometres per second? The
Craters Screen Saver
simulates cratering of initially flat terrain, obeying the same
power-law relating crater size to number observed on airless solar
system bodies. New version 3.0 is compatible with dual screen
configurations on Windows XP and saves preferences in the registry
individually for each user. This is a minimalist screen saver
originally released in 1994 which
appeared in the November 2000
issue of Sky & Telescope magazine.
Retro-computing enthusiasts may
download the original version for Windows 3.1 which runs fine on a 20
Mhz 80386 and will probably work on a PC/AT with an EGA.
Microsoft Windows tool which displays the current phase of the Moon in
an icon and other information when opened. The program is in the
public domain and complete source code is available. New
1999 release includes a 32-bit version which supports the Windows
95/98/NT time zone setting, works for all non-negative Julian
day numbers, minimises to the system tray, and includes a Help file.
For old time's sake, an updated
16-bit version compatible
with Windows 3.0 and above is also available.
The Earth Screen Saver
(for 32-bit systems such as Windows 95/98/Me and NT/2000/XP only)
shows the Earth with the correct illumination based on the date and
time. You can view the Earth from the Sun (day side), Moon, night
side, or at a given altitude above any location specified by latitude
and longitude. New version 3.1 is compatible with dual screen
configurations on Windows XP and saves preferences in the
registry individually for each user.
Now you never need to go outside again!
Sky Screen Saver
shows the sky as it presently appears including stars
from the more than 9000 star Yale Bright Star Catalogue, the Sun, Moon
(with the correct phase), and planets, deep sky objects drawn from a
database of more than 500 prominent objects including all Messier objects,
constellation names, boundaries, and outlines, and ecliptic and equatorial
co-ordinates. All of these items can be individually selected to customise
the display. The screen saver can be configured for any time zone and any
location on Earth. This program is based on the more comprehensive star
map window of Home Planet,
adapted to be a self-contained and well-behaved screen saver. Like Home
Planet, this program is in the public domain.
New version 3.1 (July 2006) saves preferences in the registry
individually for each user.
Displays an icon with the current phase of the Moon on an
OpenLook or SunView screen. When opened,
is displayed about the Sun and Moon.
OpenWindows utility which shows you,
as an icon or resizeable
portion of the Earth
currently day and night. In
conjunction with the "Two Line Elements" posted to the space
newsgroups periodically or obtained by FTP, lets you track
Earth satellites, with the current satellite position shown on