Lithium is a Group 1 (IA) element containing just a single valence electron (1s22s1). Group 1 elements are called "alkali metals". Lithium is a solid only about half as dense as water. A freshly cut chunk of lithium is silvery, but tarnishes in a minute or so in air to give a grey surface.
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Kepler’s Three Laws of Planetary Motion
The laws were formulated between 1609 to 16l9, and are (as usually stated):
<ul> <li> Planets move around the Sun in <strong>ellipses</strong>, with the Sun at one focus </li> <li> The line connecting the Sun to a planet sweeps <strong>equal areas in equal times. </strong></li> <li> The<strong> square</strong> of the orbital period of a planet is proportional to the <strong> cube</strong> (3rd power) of the mean distance from the Sun in (or in other words--of the"semi-major axis" of the ellipse, half the sum of smallest and greatest distance from the Sun) </li> </ul> <ol> </ol> <!--more--> <a href="http://www-spof.gsfc.nasa.gov/stargaze/Kep3laws.htm" target="_blank" rel="noopener noreferrer">Read more . . .</a><br />
From Stargazers to Starships
This high-school level tutorial focuses on three topics: Astronomy of the Earth's motion in space, which includes information, and some experiments and projects that teach concepts about the calendar, seasons, Kepler's laws, building a sundial, and more; Newtonian mechanics, which ha understanding Newton's laws and discussion of mass and motion; and Spaceflight and Spacecraft. Includes a timeline, a list of concepts covered, and a glossary.
