The planets, stars and beyond.... Nicola Loaring, SAAO

What’s the difference between stars and planets? Whether or not they burn hydrogen in their cores. Stars do this; planets don't. In order to have high enough temperatures in the core to burn hydrogen, an object needs to have a mass of at least 75 or so times that of Jupiter. Anything more massive than that is automatically considered a star.

Where are stars born? In giant molecular clouds

Formation of the solar system Formed when a cloud of gas and dust in space was disturbed Gravity pulled the gas and dust together, forming a solar nebula The cloud began to spin as it collapsed As the disk got thinner particles began to stick together and form clumps eventually forming planets or moons As the cloud continued to fall in, the center eventually got so hot that it became a star, the Sun

The Sun, our closest star EUV imaging telescope image showing the Sun’s atmosphere at 60,000C. This is hot, but the core is even hotter at ~15 million C!

Multiwavelength views of the Sun

Solar Structure Radiative zone – 0.8R Convective zone – 0.2R

Sunspots on the Photosphere Each granule is ~1000km across (CT to JoBurg!) and lasts 3-10 mins, like bubbles of boiling water. Sunspot temperature ~3500C (cf ~5400C)

Prominences and Flares

Prominences

The rocky planets’ composition composition

The gas giants’ composition

The Solar Cycle Maunder minimum – little ice age 11 year cycle in sunspot numbers 22 year total solar cycle

The inner rocky Planets -Venus Venus is a similar size to the Earth, and is called our twin It atmosphere is mainly Carbon dioxide and Nitrogen, with clouds of sulphuric acid! Its very hot there due to the ‘Green house effect’ a whopping 462C

Our home the Earth Earth is the 3rd planet from the Sun at a distance of 150 million km. It has a diameter of 12,756 km only a few hundred km larger than that of Venus. Our atmosphere is composed of 78 percent nitrogen, 21 percent oxygen and 1 percent other constituents. 71% of the Earth’s surface is covered by water! Earth is the only planet in the solar system known to harbour life. Picture taken by Apollo 17 astronauts

The Moon Orbits the Earth, completing one orbit every 29.5 days

The inner rocky Planets - Mars Mars is 1/10 th the mass of Earth Average temp is –63C Rock are made of silicates (like sand) and also a dash of iron oxides to give it that reddish colour (Mars is rusty!) No liquid water present now, but evidence for water in the past (3-4 billion years ago!)

The gas giants - Jupiter Jupiter is the largest planet in the solar system – diameter is 11x the Earth’s diameter, mass is 318x the Earth’s mass. Jupiter takes about 12 years to orbit the sun and is the fastest spinner in the solar system! Its day is about 10 hours. Jupiter has faint rings and 63 moons. Jupiter has the strongest magnetic field of all the planets, 14x that of the Earth. Jupiter is famous for the Great Red Spot. This storm has been raging for ~350 years and is twice the size of Earth!

Saturn Saturn is 9.5 times farther from the Sun than the Earth. 95 times the Earth’s mass but rotates on its axis in 10 hr 39 min! Because it is so far from the sun it takes 29.5 years to orbit the Sun. Saturn would float on water. Famous for its rings, it also has 62 moons.

Saturn’s rings The rings extend from 6630 km to 120,700 km above Saturn's equator Approximately 20 m thick Composed of 93% water ice with some impurities The particles that make up the rings range in size from specks of dust to the size of a small automobile

Neptune Neptune has the fastest winds in the solar system, over 2000km/hr! Cloud tops are extremely cold at -218C

Pluto Pluto has been down-graded from a planet to a “dwarf planet”! In 2006 astronomers decided it didnt meet all 3 of the criteria for it to be defined as a planet. These are: 1. Must orbit the Sun 2. Must be big enough that its own gravity squashes it into a round ball. 3.Must clear out other things from its orbit.

23 Dwarf Planets

1pc =3x10 13 km = 3.2 light years = 206,000AU Have 100s of billions of stars Stars gather together by mutual gravitational attraction Gas and dust are intermixed with the stars 70% spiral, 30% elliptical Size ~9kpc (~30,000 LY) Galaxies

You should now know! The difference between stars and planets. How many planets are in our solar system. What a galaxy is..