Distance to a star Parallax A place in the universe Commentary

Friedrich Bessel astronomy

Distance to a star

• To determine
• your distance from a star
• you measure the star’s apparent shift in place
• relative to a more distant star or galaxy
• as the earth moves from one side of the sun
• to the other, six months later.
• Very small shifts
• require very fine and stable instruments
• to measure.
• Bessel was the first to succeed
• using a sixteen-centimeter heliometer
• made by Joseph Praunhofer
• in Königsberg.
• Bessel determined that the parallax of 61 Cigni
• was one third of a second of an arc
• and with this was able to calculate
• our galaxy is ten light-years away.

Parallax

• When, looking across the room,
• I move my head to the left
• objects near at hand shift right.
• When I move my head to the right
• objects near at hand shift left.
• When I walk down the hall
• I sway a little from side to side
• and enjoy the complex reverse cycloidal spiraling
• of doorways and trash cans
• as I focus on the window at the far end of the hall
• where, outside, green hills show through the trees.

A place in the universe

• We teach that the universe is infinite
• because whatever we might imagine beyond it
• is also part of it.
• Love is forever, we say.
• We may not understand each other here and now
• but we hope to live in harmony hereafter.
• At least forty-six billion light years away
• beyond the edge of the observable universe
• is the end or the beginning
• or so we think.