Download The Ever Expanding Universe

The Ever Expanding Universe
The distances to stars and galaxies are approximate measures that are often revised
especially if they are far away. Our understanding of the Universe depends upon
accurate mapping of every structure in the Universe and was begun by the Greeks,
Persians and Indians thousand of years ago! Measuring the distance to the first star was a
Herculean task that involved over 2000 years of work! The Greeks knew how to do it
using their mathematical invention trigonometry (the mathematics of right triangles), but
a telescope precise enough to measure extremely tiny angles was not available until the
19th century when Friedrich Bessel successfully measured the first absolute distance to a
star 11 light years away. Bessel’s technique, based on Greek trigonometry, was known
as parallax and involved measuring the tiny angle a star makes when the Earth is 6
months apart as it journeys around the Sun. With Bessel’s determination of the distance
to a star in the 19th century, astronomers thought all the stars in the sky would soon be
measured, but 100 years later only a handful of star distances were discovered. Most
stars were too far away to be measured by parallax. In fact the average star in the night
sky is 2000 light years away, far too vast a distance to measure even a fraction of a
parallax angle! New techniques would have to be found for measuring distance
throughout the Milky Way. In 1912 Henrietta Leavitt, working at the Harvard College
Observatory discovered a type of star whose light output (luminosity) varied over a
regular period that could determine its absolute magnitude. Recall that some stars
brighten and dim over time for various reasons. Leavitt’s star, discovered in the
constellation Cephus, brightens and dims as gasses expand and contract in the star. Once
astronomers know a stars absolute magnitude they can determine its distance because
luminosity is directly related to the square of the distance to a star. There are about 700
Cepheid variable type stars in the Milky Way galaxy, the North Star Polaris being the
most famous. Cepheids became crucial in determining distance throughout the Milky
Way. And Cepheids would have a starring role in making the first measurement to a
Galaxy. Meanwhile, as astronomers built larger and larger telescopes throughout the 18th
and 19th century, they began observing fuzzy objects that were neither stars nor planets.
These “nebulae”, for nebulous, or mysterious, were catalogued by astronomers like
William Herschel and Charles Messier who speculated on their origin and distance.
Herschel built a massive reflector telescope that required assistants who would lower and
raise it with pulleys and levers while Herschel stood on a ladder of scaffolding fighting
the chilly night air to make his observations. Messier was looking for comets but will
always be remembered for finding the most interesting deep sky targets for amateur
astronomers worldwide. But what were these fuzzy objects and were they inside or
beyond the Milky Way? Recall how human understanding of the size of the Universe
was expanding since the time of the Greeks. And by the 19th century the Universe was a
large as the farthest stars measured in our galaxy. But like people today that wonder
what is beyond our Universe the question remained was there anything beyond the Milk
Way?
In the 20th century Edwin Hubble would answer the “nebulae” question and
expand the Universe to unimaginable dimensions. Edwin Hubble returned to the U.S.
from college in England landing the dream of a lifetime job working at the largest
telescope ever built. Staring through the eyepiece of the 100 inch reflector built atop Mt.
Wilson in Los Angeles, Hubble began observing the mysterious “nebulae” in the
constellation Andromeda. Working over many nights Hubble discovered a Cepheid in
the nebulae and was able to determine its distance as millions of light years away.
Hubble’s fuzzy object was the Andromeda galaxy millions of light years beyond the
Milky Way! Hubble quickly began observing other galaxies throughout the Universe and
by applying Einstein’s new equations about mass, light, and energy, Hubble determined
that the further a galaxy is the faster it’s moving away from Earth. In fact the observable
Universe of billions of galaxies is accelerating outward in all directions and extends an
incredible 14 billion light years at least. Hubble’s discovery of the ever expanding
physical Universe perfectly complemented the expansion of the human mind to
understand the growing boundaries of our world whose dimensions were fought and won
over thousands of years of scientific work! In the time of the Classical Greeks the
Universe was thought to extend out to where Jupiter is today, about 5 AU's. But today
that boundary is now known to be approaching infinit proportions! It is truly a marvel
how far and wide science has opened our understanding of the physical world, and along
with it, our realizations of the true dimensions of the Universe within the minds of Homo
sapiens!
Answer the following questions.
1. What is the name of the technique that was first used to measure the distance to stars?
Who (which culture) first knew how to do this? Why did it take over 2000 years to
finally measure the distance to the first star? Who first successfully measured the
distance to a star? How far away is the average star in the Milky Way from Earth?
Describe a Cepheid variable type star. Why are they important to astronomers? Who
discovered them? Name one that is commonly known. Where does the name Cepheid
come from? Can you remember who Cephus was in the Andromeda story?
2. What did Herschel and Messier catalogue in the 18th and 19th century? Where does
the word nebula come from? What was Messier looking for?
3. Where did Edwin Hubble work? What did Hubble's "nebulas" turn out to be? What
do we use the word nebula for today? What did he discover about the relationship
between galaxies and distance? What is happening to the Universe today? How big is it
known to be today? What was the size of the Universe thought to be in the times of the
Classical Greeks?