Astronomy, like other fields of study, is not immune from nonsense ideas. Some of these are born of simple ignorance or misunderstanding that the sad state of public knowledge of the sciences allows to flourish. Other nonsense is created by rumor (spread easily on the web), or by outright lying for profit (witness the many books sold by promoters of pseudoscience and conspiracy theories). Sadly, any fool can create a website or blog to promote his particular foolishness or lunacy. This page is my humble contribution to debunking some of this silliness. If I were to suggest one thing to people it would be this: Check your sources and their qualifications before you even consider accepting what they claim!
Don Yeomans is a close as you are likely to find to an expert on Earth threat objects.
These are the facts.
I would encourage people to listen to real science and real scientists
like Don, not to the hoardes of ingnorant, unqualified, and uninformed (but very loud)
woo-woo and conspiracy peddlers.
Other Astronomical Nonsense
1) Misunderstood Definitions
Astronomy (definition from Wikipedia) is a natural science that deals with the study of celestial objects (such as stars, planets, comets, nebulae, star clusters and galaxies) and phenomena that originate outside the atmosphere of Earth (such as the cosmic background radiation). It is concerned with the evolution, physics, chemistry, meteorology, and motion of celestial objects, as well as the formation and development of the universe.
Astrology (definition also from Wikipedia) "consists of a number of belief systems which hold that there is a relationship between visible astronomical phenomena and events in the human world. In the West, astrology most often consists of a system of horoscopes that claim to predict aspects of an individual's personality or life history based on the positions of the sun, moon, and planetary objects at the time of their birth. While astrology may bear a superficial resemblance to science, it is a pseudoscience because it makes little attempt to develop solutions to its problems, shows no concern for the evaluation of competing theories, and is selective in considering confirmations and dis-confirmations."
IMHO, one humorist was dead on when he said that the difference between Astronomy and Astrology was "about 50 IQ points"!
Cosmology is the discipline that deals with the nature of the Universe as a whole. Cosmologists seek to understand the origin, evolution, structure, and ultimate fate of the Universe at large, as well as the natural laws that keep it in order. Modern cosmology is dominated by the Big Bang theory, which brings together observational astronomy and particle physics.
Cosmetology is the study and application of beauty treatment. Branches of specialty including hairstyling, skin care, cosmetics, manicures/pedicures, and electrology.
In other words, both of the above are largely unrelated pursuits whose names in English just happen to sound similar.
2) The "Mars will appear as big as the full moon" email
This silliness comes from an email that seems to never stop circulating. A small amount of knowledge
about the size and scale of the planets and the solar system will show you that this is utter nonsense.
The origins of the myth are explained at Snopes as well as at Bad Astronomy.