Skip to content
Science, Maths & Technology

The Hipparcos Spacecraft

Updated Tuesday 1st June 2004

The spacecraft Hipparcos produced a range of staggering stereoscopic star maps, as Dr Alan Cooper explains

Hipparchus deserves to be called the first astronomer. Over many years between 146 and 127 BC he carefully logged and measured the positions of stars in a thoroughly scientific way, and was rewarded by discovering and measuring the precession of the Earth's axis. He was the first to have some understanding of spherical trigonometry, and for that alone claims the respect of students up to the present day! The European Space Agency (ESA) launched a spacecraft in 1989 with the sole aim of making the best star catalogue possible - what better name for it than Hipparcos?

The design of Hipparcos depends entirely on the advantages of being in space: it would not work on Earth. In the absence of atmospheric distortions, no telescope is needed. Hipparcos has a set of masks, rotating with a constant speed in the absence of friction. Its photometers record the times of appearance and disappearance of stars through these masks. Over many months the whole sky is covered, and many millions of timings recorded. A huge calculation identifies the stars (with reference to existing catalogues) and finds improved "least squares" estimates of their positions and luminosities. This is also the prelude to applying the method of parallax used by Bessel to estimate distances of the nearer stars - but the Hipparcos results reach out much further, surveying a substantial part of the Galaxy. The final results are available for anyone to use, in the form of a CD. For the layperson, the results for the brightest stars are available in a form which re-uses parallax. With the distance known, it is possible to calculate what the sky would look like if the separation of our eyes was not 65mm but 200,000 AU (or 100,000 times the diameter of the Earth's orbit). This is shown as a stereoscopic pair of images, one red and one green. Viewed through red/green spectacles, the Galaxy appears, truly for the first time on this planet, in full 3 dimensional depth. Stereoscopy, after all, is just parallax by another name.

This huge database has proved so useful that a new spacecraft, GAIA, is planned (for 2009) to reach ten times further than Hipparcos - about 1000 times as many stars. This is still within our Galaxy, and quite different methods (not directly AU based) are needed to get to other galaxies, and hence into the realm of cosmology.

 

For further information, take a look at our frequently asked questions which may give you the support you need.

Have a question?

Other content you may like

60 Second Adventures In Astronomy: Supernovae video icon

Science, Maths & Technology 

60 Second Adventures In Astronomy: Supernovae

Learn how all the elements in the Universe were formed, and where, exactly, your favourite silver necklace comes.

Video
Explore the Solar System Copyrighted image Icon Copyright: photos.com activity icon

Science, Maths & Technology 

Explore the Solar System

Explore the planets in our Solar System with our interactive guide.

Activity
Pluto comes into sharp focus – but it’s still not a planet Copyrighted image Icon Copyright: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute article icon

Science, Maths & Technology 

Pluto comes into sharp focus – but it’s still not a planet

New Horizons is giving us the chance to see Pluto, close-up, for the first time. But familiarity won't restore Pluto's planet status.

Article
You are here Copyrighted image Icon Copyright: Used with permission activity icon

Science, Maths & Technology 

You are here

Get to know the neighbourhood, with our interactive guide to our position in space – find out more about the Milky Way, the 30 or so galaxies that make up our local group and much more

Activity
How we found gravitational waves Copyright free image Icon Copyright free: NASA/JPL-Caltech/DSS - Full description of image video icon

Science, Maths & Technology 

How we found gravitational waves

Martin Hendry, part of the team that discovered gravitational waves, explains how they made their historic discovery.

Video
10 mins
Discover Mercury: Introduction Creative commons image Icon NASA Goddard Space Flight Center under Creative Commons BY 4.0 license article icon

Science, Maths & Technology 

Discover Mercury: Introduction

Messenger has just visited Mercury; BepiColombo is about to head out - and 2016 sees a Transit of Mercury. Get to know the planet we're starting to find out a whole lot more about. 

Article
Sky notes: July Copyrighted image Icon Copyright: OU image library article icon

Science, Maths & Technology 

Sky notes: July

A guide to the what's happening in the night sky in July.

Article
New Horizons finally gets up close with Pluto – for 15 minutes Copyrighted image Icon Copyright: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute article icon

Science, Maths & Technology 

New Horizons finally gets up close with Pluto – for 15 minutes

After a journey of over four and a half billion miles, New Horizons gets some face time with Pluto. But not too much.

Article
SuperWASP: Search for Extrasolar Planets Copyrighted image Icon Copyright: SuperWASP article icon

Science, Maths & Technology 

SuperWASP: Search for Extrasolar Planets

The Transit Of Venus was focused on our Solar System. But there are projects which are looking far, far further afield - and the SuperWASP is just one.

Article