Introduction

Dutch physicist, astronomer, and mathematican Willebrord Snell (1580-1626) made significant advances in the fields of trigonometry, optics (the study of light), and map making. Snell is best remembered today for Snell's law, which explains the angle of refraction (bending) of light. He used a large quandrant (a circular arc divided into 90-degree angles) to measure angles of separation of two points, and in this way could calculate the distance between them. He arrived at a figure for the radius of the Earth, a figure we know today to be very accurate.

The measurement of Earth also occupied German mathematican Carl Friedrich Gauss (1777-1855). As director of the Gottingen Observatory from 1807 until his death forty-eight years later, Gauss became interested in geodesy, the study of the size and shape of the Earth. To his end, in 1821 he invented the heliotrope. The heliotrope is an instrument that reflects sunlight over great distances to mark the positions of participants in a land survey.

How does a planet hang on to its atmosphere?

A planet's ability to retain an atmosphere is determined by its gravitational field. A gravitational field, in turn, depends on a planet's mass. In the case of our planet, Earth's mass is great enough to keep most gases (except for very light gases like hydrogen and helium) from escaping.

What does the Earth's atmosphere consist of?

The Earth's atmosphere is made up of 78 percent nitrogen, 21 percent oxygen, and 1 percent argon, with minute quantities of water vapour, carbon dioxide, and other gases.

How did the Earth form its atmosphere?

Various theories try to explain the origin of these gases. One theory states that when the Earth was formed, the gases were trapped in layers of rock beneath the surface. They eventually escaped, primarily through volcanic eruptions, to form the atmosphere. Water vapour was the most plentiful substance to spew out, and it condensed to form the oceans. Carbon dioxide was second in terms of quantity, but most of it disolved in the water or was altered chemically through reactions with other substances in the rocks. Nitrogen came out on smaller amounts, but has always remained in its present form because it never underwent reactions or condensation. For that reason, it is the most abundrant gas in the atmosphere today.

Has oxygen always been part of the Earth's atmosphere?

According to the prevailing theor, oxygen only became part of our atmosphere when green plants came into being. Green plant, through photosynthesis, produce oxygen by converting carbon dioxide. The other gases in the atmosphere were probably released from underground by volcanic activity- a process that began long before green plants came into being. Oxygen is also removed from the atmosphere when green plants, as well as animals, die. As they decay, they oxidize- a process that uses up oxygen.

How does Earth's atmosphere compare to the rest of the solar system?

The Earth's atmosphere is unique within the solar system. Inparticular, it stands out as the only planetary atmosphere capable of sustaining life. By way of comparsion, Saturn, and Neptune, on the other hand, are each more massive than the entire Earth. And while our atmosphere is mainly made of nitrogen, those of Mars and Venus are dominated by carbon dioxide.

Could our atmosphere have come from space?
A fairly recent theory proposes that the elements found in the Earth's atmosphere were deposited here by comets. Deris from comets is shown to have carbon and nitrogen in roughly the same proportion as found in our atmosphere. And scientists have identified numerous impact craters on Earth from past collisions with comets.

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