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Observing the Universe
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The Scale of Things…
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You are Here -
Star-filled skies
The night sky may appear to be serene and unchanging but…
Nova Stellae
“New Stars”
Nova “RS Ophiuchi” in February 2006
Before the Telescope
“Star” of Bethlehem?
Far Eastern Star Gazers
Star of Wonder
Tycho Brahe (1546 – 1601)
Johannes Kepler (1571 – 1630)
Tycho’s Nova
Tycho Brahe noticed a bright
star in the constellation of
Cassiopeia in 1572…
“On the 11th day of November in the evening after
sunset, I was contemplating the stars in a clear sky. I
noticed that a new and unusual star, surpassing the
other stars in brilliancy, was shining almost directly
above my head; and since I had, from boyhood,
known all the stars of the heavens perfectly, it was
quite evident to me that there had never been any
star in that place of the sky, even the smallest, to say
nothing of a star so conspicuous and bright as this…
A miracle indeed, one that has never been previously
seen before our time, in any age since the beginning
of the world.”
The Great Debate of 1920
Harlow
Shapley
Heber
Curtis
“The scale of the universe”
Shapley argued that “spiral nebulae” (like Andromeda)
were just nearby gas clouds inside our own Galaxy.
Curtis believed them to be galaxies in their own right
lying far outside our own Galaxy.
Novae part of the problem
1885: S And, a nova in the
Andromeda Nebula. “Standard
Candle” led to distance
estimate within our Galaxy,
the Milky Way.
1920’s: Edwin Hubble used these Standard Candles
(Cepheid Variable stars) to get a much larger
distance to Andromeda.
Hence S And was 20,000 times brighter than a
“normal” nova…
Baade therefore dubbed these objects “super-novae”.
Supernovae
Two main classes:
Type II
Explosion of massive stars at
end of their lives
Type Ia
Explosion of white dwarf star
near its limiting mass of 1.4x
the mass of the Sun
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Novae and Supernovae
We see a few ordinary novae per year in our galaxy.
Supernovae are much rarer, a typical galaxy may only have one
every 30 years.
We know of 6 Supernovae in our galaxy
in the last 1000 years.
Year
Type
1006
I
Crab
1054
II
1181
Tycho
1572
I
Kepler
1604
I
Cas A
1667
II
Over 400 years since last one was actually observed in our galaxy
The remnant of Tycho’s nova
Composite: X-ray (Chandra), IR (Spitzer) & optical (Calar Alto)
Supernova
1987A in the
Large Magellanic
Cloud
More Distant
Supernovae