Zoomer Applet
Zoomer is a modest attempt to show earth's place in the universe. Slide the scrollbar
to zoom in and out, or use the buttons for smooth, continuous zooming.
Zoomer displays the following objects:
- The planet earth
(sorry about the lack of detail).
- Orbits of three classes of artificial earth satellites. Most satellites (including
all spacecraft that have carried humans except for the Apollo moon missions) fly in
low
earth orbit, just high enough to avoid significant drag from earth's atmosphere. At this
altitude the required orbital speed takes them around in about 90 minutes.
GPS (Global Positioning System) satellites
are higher and move more slowly, orbiting
once every 12 hours. Most communication satellites are higher still, in
geosynchronous orbits
that take exactly one day; these satellites appear stationary in earth's sky as earth rotates.
- Our moon and its
orbital path.
The moon is drawn approximately to scale, only a few pixels
across when it first appears at the edge of our view.
- The L1 and L2 Lagrangian points,
where earth's gravity allows spacecraft to orbit the sun synchronously with the earth.
- Orbits of the eight major planets, including earth,
around the sun. By the time the other
planets' orbits appear in our view, the planets themselves would be much smaller than one pixel
across. (The orbits of a few of the moons of the outer planets could have been shown,
but are omitted for simplicity.)
- The sun, drawn to scale when it first appears
near the edge of our view, but then drawn much larger to emphasize its great brightness.
- The asteroid belt, which contains thousands
of minor planets orbiting between Mars and Jupiter,
and the Kuiper belt, which also contains
a large number of minor planets including Pluto.
- The four spacecraft that are leaving
the solar system, all launched in the 1970's (shown at their approximate locations as of early
2008).
- A reference "box" whose width is 5000 times the
distance from the earth to the sun. At this
scale there are no major astronomical objects to draw, although this region is thought to contain
large numbers of small icy objects,
some destined to become
comets if they fall toward the inner
solar system.
- More than 60 stars, including all of the
brightest
stars in our night sky plus a few other
near neighbors.
No attempt is made to represent the physical
sizes of stars, which
at this scale would typically be less than a millionth of a pixel in diameter. Multiple pixels
are used, however, to better represent the variation in brightness among stars
(using code borrowed from Kerry Shetline's AstroPlotPanel
class). In the real universe, however, the stars vary much more in relative brightness than
shown here.
- A few of the most prominent bright
emission nebulae (glowing hydrogen gas clouds) in our portion of the Milky Way.
- The Milky Way galaxy,
which contains roughly 100 billion stars.
- Neighboring galaxies including the
Large and
Small
Magellanic Clouds,
the Andromeda Galaxy
(M31), and a few dozen others, as far out as the
Virgo Cluster. (Beyond these galaxies,
try to imagine millions more.)
- Several of the
brightest quasars.
Though their distance from earth makes them far too faint to see with the naked eye,
quasars have enormous luminosities,
far out-shining their host
galaxies. They are thought to consist of heated matter falling into massive black holes. Though
they are rare today, we see great numbers of them as we look out to cosmic distances, from which
light has taken billions of years to reach earth.
- The
hot early universe, at our
cosmic horizon. The universe became transparent to light
only when it cooled below about 3000 K. The abundant light from that era reaches us today as
the cosmic background radiation,
cooled by the thousand-fold expansion of the universe since
the time the light was emitted. This is the most distant and ancient electromagnetic signal
we can detect. At the scale shown, it essentially coincides with the beginning of the universe
as we know it, 13.7 billion years ago. Zoomer shows nothing beyond the cosmic horizon not
because there is nothing there, but because the universe is not yet old enough for light to
have reached us from more distant locations.
Zoomer is intended mainly to show the relative distances from earth to various astronomical objects.
This two-dimensional "cartoon" view does not attempt to correctly depict the objects themselves
or their relations to each other
in three-dimensional space. Stars, galaxies, and quasars are plotted according to their approximate
distances and
right ascensions (longitudes)
in our sky, ignoring their
declinations (latitudes).
No attempt has been made to show the detailed structure of the
Milky Way or of the
large-scale distribution of galaxies
and quasars.
Please explore the links on this page to view images of the various objects and to learn more
about them.
The scale displayed by Zoomer is calibrated in units of time--the time for light to travel
the indicated distance. At cosmological scales the
relation between time and distance
becomes complex and confusing, due to the expansion of the universe and the need to
distinguish between the present distance and the distance when the light was emitted.
By using a scale of "lookback time" rather than distance, Zoomer tries to avoid these complications.
Zoomer was inspired by Powers of Ten, a short
film and related book that
zoom in and out on the universe. Zoomer, however, is limited to astronomical length
scales--from the earth on up. Here are some links to other web sites and resources that
complement Zoomer in various ways:
