Anyone who conducts an argument by appealing to Authority is not using his intelligence, he is just using his memory.
– Leonardo da Vinci

Irrationally held truths may be more harmful than reasoned errors
– T.H. Huxley

What Is Science?

• In short: An organized, logical method to obtain knowledge about the natural world; Uses careful observation, reasoning, and/or experiment; Produces models ("explanations"), predictions (which must be falsifiable, so they test the models and may lead to their revision), and applications.
• Tools: Observation (collecting facts as objectively as possible; not always obvious!); Logic and math; Intuition, "insight", dialogue, luck; Guided by paradigms and "fashions".
• Stages: A common pattern is Observation –> Model / Hypothesis –> Predictions –> Test / Experiment; Experiments are new observations that can lead to changes in the models; The pattern refers to the logical development of science, sometimes to what scientists actually do in their work; It is not possible to reduce that to a set of steps, and in that sense "doing science" is a creative activity, but one that must follow rules of logic.
• Theories: After repeated testing of its predictions, a theory becomes accepted; While a theory can never be proven "true", a successful one is an overarching explanation that accounts well for known facts, hypotheses, and observations whithin its range of applicability; in this sense, a scientific theory is not "just a theory"; It must also include ways of disproving it, and almost every theory is eventually superseded by a better one.

Development of Science

• Historically: Developed over many centuries, with different key contributions.
• Ancient Greece: Greek culture was superstitious and had a large irrational component, but it also developed a naturalistic philosophy and interpretation of the universe (as opposed to mystic), in which knowledge of geometry played a prominent role; We can describe nature by using conceptual models.
• Modern view: Started in the XV century, with Renaissance Europeans assimilating Eastern and Arabic knowledge and accumulated observational records; We can understand nature by using physical laws.
• Technological advances: We can reach out and become more actively involved, manipulate nature.
• Today's debates: We can push our reliance on our intellect all the way to questioning the reason for our existence and the origin of the universe.
• Role of astronomy: Astronomy has been one of the disciplines with the greatest impact on the development of science, because of its strong ties to practical aspects human life from ancient times, as reflected for example in our calendar, and to the Big Questions (which it can't really answer, but it can provide a context to them).

What Kinds of Statements Does Science Make?

• Observed facts: The fact that a planet has (at least) a certain number of moons.
• Interpreted facts: Jupiter has dark cloud "belts" and lighter "zones"; For decades, it was (apparently) falsely believed that the belts were made of sinking gas, and the zones of rising gas, by analogy with Earth features.
• Is science objective? Facts do "speak for themselves", but we don't always understand what they say, and scientists often cannot help being influenced by cognitive barriers that cloud our judgment.
• Scientific statements: They are not really to be taken as "bits of the truth"; Science is more like a search for laws and descriptions that work, and reflects our best ability to understand and model natural phenomena.
• Limits of science: Any scientific statement may need to be replaced if it turns out that the assumptions it used are not correct, or better data become available. But we do not always replace a scientific statement whose limits of validity are known. A theory can be very useful even if we know it is wrong, provided we use it in a context where it provides a good approximation; For example, planets do not really orbit the Sun along ellipses.
• Science and religion: For an example of a point in which the approaches differ, read the responses to a question on scientific dating vs Biblical dating posted by Earth & Sky.

Compared to Pseudocience and Nonscience

• Pseudoscience: Makes non-scientific claims but tries to pass them off as science, in an attempt to convince people of their truth. Similar to bad science, which makes scientific claims which contradict the facts (either by mistake, or as the result of a deliberate attempt to mislead). Both are a problem; they are relatively easy to uncover (for example, psychics' predictions are almost always wrong), if one knows about them, but it is difficult to stop people from making claims or believing in those claims (37% of Americans believe that "houses can be haunted"!). Education is the best answer.
• Nonscience: Does not deal with testable predictions, but faith and tradition. Science and nonscience do not contradict each other, since they deal with different questions, and can live alongside each other.
• Examples: Canals on Mars, ESP, UFO's; Bending of spoons, magnetic bracelets, and the like; But what about the anthropic principle, or the multiverse idea? Distinctions can be blurry at times.

Astrology

• What it is: The belief that the positions of celestial objects like the planets and stars can affect lives of individuals, or can be interpreted as indications of future events.
• Historically: Centuries ago the monitoring of positions of stars and planets, and their use in predicting effects on human lives, was a popular activity. Many decisions were taken based on them (assassination of Caesar, ...). Many astronomers, Kepler included, were also astrologers.
• Examples: Position of stars and planets at birth; Planetary alignments.
• Today: Considered pseudoscience, or non-science if it does not try to make predictions.
• Fact: Astrology holds little, if any, predictive power. Not a shred of evidence (other than indirectly through weather, ...) that star and planet positions or alignments have ever had any consequences, and many reasons to doubt it. (The position of the doctor and nurse at your birth are far more important than those of the planets!)

Examples

• Titius-Bode law: The distances of the planets (and asteroid belt) from the Sun, in astronomical units, can be obtained from the sequence of numbers 0, 3, 6, 12, 24 by adding 4 and dividing the result by 10.
• Kepler's Period Law: The distances of the planets (and asteroid belt) from the Sun, in astronomical units, can be obtained by taking the third power of the periods of their orbits, in Earth years, and taking the square root of he result.
• Assessment: What does science make of statements like these? What is a good model for the Solar System?
• Conclusion: Our brains have evolved pattern-recognition machines; Science is an attempt to systematically pursue the fruitful ones, and it requires training; Scientists do have their prejudices, however; Up to the 1920's everybody "knew" the universe was static, and until the 1990's that its expansion was slowing down; But eventually...