Observing the Universe

The Scale of Things…

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The night sky may appear to be serene and unchanging but… Star-filled skies

Nova “RS Ophiuchi” in February 2006 “New Stars” Nova Stellae

Before the Telescope “Star” of Bethlehem? Far Eastern Star Gazers

Star of Wonder Tycho Brahe (1546 – 1601)Johannes Kepler (1571 – 1630)

Tycho’s Nova “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.” Tycho Brahe noticed a bright star in the constellation of Cassiopeia in 1572…

The Great Debate of 1920 Harlow Shapley Heber Curtis 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. “The scale of the universe”

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

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. YearType 1006I Crab1054II 1181 Tycho1572I Kepler1604I Cas A1667II Over 400 years since last one was actually observed in our galaxy Novae and Supernovae

Composite: X-ray (Chandra), IR (Spitzer) & optical (Calar Alto) The remnant of Tycho’s nova

Supernova 1987A in the Large Magellanic Cloud More Distant Supernovae