Astronomy: Planets

Astronomy: Planets

Beginning of our Solar System • Cloud of dust and gas collapses. • Nebula’s densest part grows larger and hotter; forms proto-sun. • Small bodies called planetesimals form. • Planetesimals clump together to form proto-planets. • Eight planets & a dwarf planet emerge.

The planets

Keeping it all in perspective

Keeping it all in perspective Antares is the 15th brightest star in the sky. It is more than 1000 light years away.

The inner planets are called terrestrial planets. • A terrestrial planet is one of the highly dense planets nearest to the sun; Mercury, Venus, Earth, and Mars. • Distances in the solar system are often measured in terms of the distance from Earth to the sun, which is one astronomical unit (AU), or 150 million km. • Mercury has extreme temperatures. • Its day is 58 Earth days; its year is 0.24 Earth years. • It has almost no atmosphere and no water. The Inner Planets

Between Mars and Jupiter is a band of asteroids – rocky or matallic fragments that never formed a planet. Asteroids range in size from a few feet in diameter to hundreds of miles. A collision with an asteroid would be catastrophic to Earth, creating tidal waves, huge forest fires, or great clouds of ash and dust that could block out the sun for months at a time. The asteroid belt

The planets most distant from the sun are Jupiter, Saturn, Uranus, and Neptune. • These large planets are called the gas giants. • A gas giant is a planet that has a deep, massive atmosphere and no solid surface. • Neptune was first discovered in 1846 • Its period of rotation is 16 hours, 7 minutes. • Its period of revolution is 163 years, 263 days. The Outer Planets

Pluto • Discovered in 1930, Pluto is very small and icy, unlike either the rocky planets or gas giants. • Some scientists belive Pluto to be an “icy planetesimal” formed in the Kuiper Belt, a region beyond the orbit of Neptune.

Space Observatories 1962 – The first of many space telescopes, the Orbiting Solar Observatory, was launched. In 1990 NASA launched the first of 4 “Great Observatories” including: • Hubble Space Telescope (visible, ultraviolet and part of the infrared) • Chandra X-ray Observatory • Compton Gamma-ray Observatory • Spitzer Space Telescope (long wave – infrared)

Sending humans into space is a very complex taskthat takes years of engineering to prepare for. There are numerous considerations involved ranging from how to get the craft where it needs to be to what the craft needs to be able to do when it gets there, including supporting the life it carries. Visiting Space

In 1957, Soviet Yuri Gagarin orbited Earth In 1968, the Apollo 8 mission allowed 3 American astronauts to orbit the moon. In 1969 the Apollo 11 mission landed the first humans on the moon. Since the 1980’s there have been numerous space shuttles and space stations orbitting earth. Visiting Space

To explore beyond the moon, scientists have relied on robot probes. Some probes are orbiters and some are Landers. Launching a spacecraft at a distant planet is extremely difficult. Both earth and the planet are moving. It’s like threading a needle from across the room. Probing Space

All 8 planets have been visited by at least one probe. Pluto has not yet, but the New Horizons probe launched on 19 January 2006. It flew past Jupiter on 28 February of this year, getting a kick from the planet's gravity to help it reach Pluto in 2015. • Voyager 1 is more than 9 billion miles from Earth. Launched in 1977, it visited Jupiter and Saturn in 1979-1980 and is now heading toward the edge of the solar system. It is expected to send back data until at least 2020. Probing Space

Astronomy: Planets