A unique 3-D view of our Galaxy
7 February 2001Observers, and even the most powerful ground and space telescopes, seecelestial objects (stars and galaxies) in two dimensions. Today, atESTEC, the audience at the Space Science Department Colloquium "OurGalaxy - in Three Dimensions" were treated to a uniquethree-dimensional view of our Galaxy.
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.