Star Mapper: A visualisation based on data from the European Space Agency's Hipparcos star mapper

The visualisation tour is divided into five sections: Apparent Magnitude, Absolute Magnitude, Hertzsprung-Russell, Motion, and Explore.

Apparent Magnitude
The apparent magnitude is a measure of the brightness of a star or celestial object as seen from Earth or a telescope in space (near Earth). The value depends on the object’s true brightness (its luminosity), its distance, and the amount of light that is absorbed between the star and the viewer. The scale is logarithmic, with larger magnitudes corresponding to fainter stars.

Absolute Magnitude
The absolute magnitude of a star or celestial object is the apparent magnitude it would have if placed at a distance of 10 parsecs (32.6 light years) from Earth. Absolute magnitude is used to compare the true brightness of celestial objects, regardless of their distance from us.

The Hertzsprung-Russell diagram is used by astronomers to study how stars evolve. The colour of stars - an indication of their surface temperature - is plotted on the horizontal axis, and their absolute magnitude on the vertical axis. The location of a star on the graph indicates what stage in its life cycle the star is at.

Despite appearances, the stars do move, but by tiny amounts on human timescales. A star’s velocity in space is a combination of its proper motion, the velocity perpendicular to the line of sight, and its radial velocity, the velocity along the line of sight. Proper motion can be obtained by monitoring the change in a star’s position over time. Radial velocity comes from the Doppler shift in the lines of a star’s spectrum.

Star Mapper:  A visualisation based on data from the European Space Agency's Hipparcos star mapper

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Alex E

“Maps are like campfires – everyone gathers around them, because they allow people to understand complex issues at a glance, and find agreement about how to help the land.”