Observers, and even the most powerful ground and space telescopes, see
celestial objects (stars and galaxies) in two dimensions. Today, at ESTEC,
the audience at the Space Science Department Colloquium “Our Galaxy — in
Three Dimensions” were treated to a unique three-dimensional view of our

In this colloquium, Dr. Michael Perryman, Hipparcos Project Scientist,
explained the main features of our Galaxy, highlighting the contribution made
by the ESA Hipparcos space astrometry mission to our understanding of the
Galaxy and its components. Hipparcos follows a noble tradition, dating back
more than 2000 years, of painstaking precise measurements of the positions and
motions of stars across the sky.

Dr. Perryman illustrated his talk by combining conventional two-dimensional
representations of the stars (as we see the sky at night) with stunning
three-dimensional images. To view the 3-D effect the audience wore special
polarizing glasses to view the polarized images which were projected onto a
special reflecting screen.

The images of the stars were created using distances, star colours and stellar
motions from The Hipparcos and Tycho Catalogues, and the resulting visual
effect was truly stunning. Stars appeared suspended above the audience in the
auditorium, spanning a range of distances from close-by to infinity. Familiar
views of the night sky took on a new perspective as we saw the relative
positions of the stars along our line-of-sight. Orion’s Belt was no longer a
flat line of bright stars, but rather a buckled trio. Star clusters, already
beautiful in two dimensions, were even more so in three dimensions. This was
particularly evident in the images of young, hot stars in so-called OB
associations (loose groupings of massive, bright stars) which resembled
clusters of brightly coloured jewels.

In one of the most exciting sequences, the star Gliese 710, at a distance of
62 light-years from our Sun (a light-year is the distance that light travels
through space in one year) and approaching us at 14 km/s, approached the
audience from a distance, growing in size and brightness until it appeared
to engulf the audience. (Data from Hipparcos shows that this star will pass
close by the Sun in about 1 million years, disrupting objects in the Oort
cloud and sending debris hurtling towards Earth.)

This novel presentation of scientific results from Hipparcos served to
highlight the pivotal role of astrometric measurements in many of the hot
topics in astronomy and illustrated the unique insight that such accurate
measurements provide. We can only begin to imagine the impact of the ESA
cornerstone mission GAIA, which will extend the work of Hipparcos both in
accuracy (taking the precision from milliarcsecond to microarcsecond
measurements) and in scope (expanding the zone of measurement from our Local
Solar Neighbourhood to the center of our Galaxy and beyond). This unique
view of our Galaxy also emphasized the enormous contribution which the small
Hipparcos mission is making to modern astronomy.

Hipparcos was launched in 1989, and operated until 1993, and its data was
released to the astronomical community in 1997 in the form of The Hipparcos
and Tycho Catalogues. Since then, these catalogues have been used to address
many topics, ranging from Stellar Evolution to the Age of the Universe, from
studies of our Solar System to the search for planets around other stars.


Some of the vivid 3-D images from this presentation can also be viewed on a
smaller scale, using nothing more complicated than paper, a mirror (optional)
and your eyes. Details of these DIY 3-D images are available on the Hipparcos
Science web site and in the Little Books of GAIA.


* Hipparcos 3-D Stereo Images

* Little Books of GAIA

Associations of young, hot stars observed by the Hipparcos mission.