Reports - 2010
Astronomy Benalla Meeting Presentations - Wednesday 18th August 2010
Astronomer of the Month - Presenter: Anne Sumner
Johannes Hevelius
A scientist, astronomer and brewer, Hevelius lived in Danzig, Poland but came from a German speaking family of
Bohemian origin. He built an observatory on the roofs of 3 connecting houses overlooking the river Vistula, the
longest river in Poland. The Englishman Edmund Halley of Halley’s Comet fame and various European royalty
visited him. Hevelius made observations of sunspots, discovered four comets and seven current constellation
names are attributed to him.
Hevelius was granted membership of the Royal Society in London for his astronomical work. Basically, and
unbelievably- he did most of his astronomical work with a quadrant and a strange instrument called an alidade of
his own design. While his equipment ultimately included a large Keplerian telescope of 45 m (150 ft) focal length,
with a wood and wire tube he constructed himself, he is thus considered the last astronomer to do major work
without the use of a telescope. He spent a lot of time charting the lunar surface and is often called the founder of
lunar topography. Fire ripped through his observatory unfortunately in 1679 but he had the energy somehow to
rebuild to enable him to observe the great comet of December 1680. His second wife Elizabeth supported him
compiling a monster catalogue of stars and their positions, publishing two of his works after his death, and she is
considered the first female astronomer.
A plaque in Danzig city hall points out that Johannes Hevelius was an astronomer & city mayor.
The H-R Diagram - Presenter: Patrick Watson
The Hertzsprung-Russell Diagram
Named for the two scientists who created it, Ejnar Hertzsprung and Henry Norris Russell, the diagram plots a
measure of the brightness of stars against a measure of their temperature. Absolute and apparent magnitude were
reviewed, along with the history behind the spectral classes from their sequencing according to the strength of
certain hydrogen absorption lines, to the ultimate recognition of a colour and hence a temperature sequence, that
led to the Harvard OBAFGKM sequence.
Hertzsprung noted that where two stars of the same spectral class have different magnitudes, the more luminous
star must be the larger one and termed the brighter stars giants.
Independently, Russell came to the same conclusion, using the same term to describe the luminous stars and the
term dwarf stars for their dimmer counterparts.
Plots revealed the majority of stars lie on a ‘diagonal’ band that extends from hot stars of high luminosity in the
upper left corner to cool stars of low luminosity in the lower right corner, called the Main Sequence.
A star is said to be on the main sequence at the stage in its life when it is converting hydrogen to helium at its
centre. As you move up the main sequence from the lower right to the upper left of the H-R diagram, the mass,
luminosity, and surface temperature of main-sequence stars all increase. To this plot was later added a further
dimension – luminosity classes introduced by Morgan and Keenan most of which covered giant stars.
An overview was then given of the pre-main sequence evolutionary track, and the critical importance of mass in a
stars position on the main sequence and its further evolution. H-R diagram plots were also shown for open and
globular star clusters where turn-off points can indicate cluster ages. The instability strip and areas of long and short
period variable stars were also shown.
Woodcut illustration of a 45 meter long An azimuthal quadrant. A range of alidades. Item E
astronomical refracting telescope built was designed by Hevelius.
by Hevelius.
