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Introduction. Contents and Structure of the Universe. 12,756 km. Planets. Earth. 1.52 AU. 1 AU. 0.39 AU. 0.72 AU. Rough Scale Drawing of the Orbits of the Terrestrial Planets. Mercury. Venus. Mercury.

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rough scale drawing of the orbits of the terrestrial planets

1.52 AU

1 AU

0.39 AU

0.72 AU

Rough Scale Drawing of the Orbits of the Terrestrial Planets




The average distance from Sun to Earth is about 150 million kilometers (93 million miles. This distance is called the astronomical unit and abbreviated AU.



scientific notation
Scientific Notation

Very small and very large numbers are most conveniently expressed as the product of a number between 1 and 10 with the appropriate power of 10. This way of writing a number is called “scientific notation”. Some examples are given below.


Example 1 The diameter of Earth is 12,756 km. Express this distance in light-seconds.

Earth’s diameter is 0.0425 light-seconds

Example 2 The average distance between Earth and the Moon is 384,000 km. If a message is sent from Earth to the an observer on the Moon, what is the smallest time interval between sending the message and receiving a reply?


The Sun

1.392×106 km

This is and X-ray picture of the Sun.

Diameter = 4.64 light-seconds


150,000 light years


The Andromeda Galaxy

About 2.6 million light years away

The Milky Way Galaxy (our galaxy), is similar to this one, and its diameter is about 80,000 ly.

hubble deep field

A Cluster of Galaxies in the Hubble Deep Field

Hubble Deep Field

We see these galaxies as they were 8 billion years ago.

The universe is about 13.7 billion years old.

walls filaments and voids
Walls, Filaments, and Voids

This picture is a map of more than 11,000 galaxies. The empty appearing areas are called voids. They are enclosed by walls and filaments made up of superclusters of galaxies. These structures are the largest in the universe.

900 million light-years

outline of the history of the universe
Outline of the History of the Universe

t = 0 (the “Big Bang”)

The sudden appearance of an expanding hot and dense distribution of exotic particles and energy

t = 10-12 s

The formation of neutrons and protons.

t = 10-2 s

The formation of electrons.

t = 180 s

The formation of atomic nuclei (mainly hydrogen and helium).

t = 300,000 years

The formation of neutral atoms. The universe became transparent.

t = 109 years

The formation of stars and galaxies.

t = 11109 years

The emergence of life on Earth.


“The physical species Homo may count for nothing, but the existence of mind in some organism on some planet in the universe is surely a fact of fundamental significance. Through conscious beings the universe has generated self-awareness. This can be no trivial detail, no minor byproduct of mindless, purposeless forces. We are truly meant to be here.”

Paul Davies, “The Mind of God: The Scientific Basis for a Rational World”

“The most incomprehensible thing about the universe is that it’s comprehensible.”

Albert Einstein

“The more the universe seems comprehensible, the more it also seems pointless.”

Steven Weinberg, “The First Three Minutes”


“Once an idea is declared to be ‘truth’, then all progress stops.”

21st Century Astronomy, page 11

“The scientist’s creed is that nature, through observation, is the final arbiter of the only thing worthy of the term objective truth.”

21st Century Astronomy, page 12

“This choice of funding channels the directions in which scientific knowledge advances and can lead to serious ethical issues. For example, moral judgments about nontraditional lifestyles greatly restricted the funding available for AIDS during the decade or so after its discovery.”

21st Century Astronomy, page 12


“More recently, progress in stem cell research and solutions to human-caused climate change have been hindered by widely distributed misinformation on the Web and by constant political bickering.”

21st Century Astronomy, page 12

Is it ethical to destroy human embryos in order to harvest their stem cells for medical research?

Is it ethical to destroy human embryos in order to harvest their stem cells for medical research?

Should the government fund research that involves the destruction of human embryos to harvest their stem cells for scientific research?

In what way can the scientific method be used to answer questions like these?

political climatology

We have to offer up scary scenarios, make simplified, dramatic statements, and make little mention of any doubts we may have. Each of us has to decide what the right balance is between being effective and being honest.

Dr. Stephen Schneider (Discover magazine Oct 1989)

Political Climatology

Nobody is interested in solutions if they don't think there's a problem. Given that starting point, I believe it is appropriate to have an over-representation of factual presentationson how dangerous it is, as a predicate for opening up the audience to listen to what the solutions are, and how hopeful it is that we are going to solve this crisis.Al Gore(Grist magazine May 2006)

Elements of a "perfect storm," a global cataclysm, are assembled.

Dr James Hansen. (Huffington Post)


Slow increase of CO2 concentration

Faster increase of CO2 concentration

Large increase in annual temperature around 1998  PANIC!