IB Physics

Option F - Astrophsyics

Introduction to the Universe

solar system / stellar objects / stellar sizes

The Solar System

The solar system is comprised of the star Sol, and eight planets as well as numerous moons, planetoids and other material left over from the construction of the solar system, such as comets. It is positioned on the unfashionable western spiral of the galaxy, which is of course why the rest of the sentient beings in the galaxy have never bothered to visit our solar system, much less our planet, making the ideal position for a research facility or a hyperspace bypass, the two of which may or may not be connected, but nobody ís saying.

Relative sizes of stellar objects

Our sun, Sol, is about 4.6 billion years old, and has the classification of a Yellow Dwarf Star, or Average Joe Blow. The eight identified planets are Mercury, Venus, Earth and Mars, as the 4 terrestrial planets, and Jupiter, Saturn, Uranus and Neptune as the Gas Giants of the solar system, all of which follow similar elliptical orbits. Jupiter, Saturn, Uranus and Neptune all have many moons, of varying sizes; notable moons are Jupiter's Io, Europa, Callisto and Ganymede, as well as Saturn's Titan. Mars and Earth, too possess two and a single moon respectively, however, Earth's moon is an anomaly, and Phobos and Deimous of Mars are simply captured asteroids, rather than true moons. The other notable features of our solar system are the asteroid belt present between the planets and Jupiter, as well as the two Kuiper belts beyond Neptune, of which Pluto is the largest near object, and second largest overal, since its reclassification from a planet to a dwarf planet, also known as, too hard to justify and kicked out of the club, or oops we got caught up in the moment, and no, that wasn't the discovery of a new planet after all.

The formation of the Solar System is generally accorded to the 'nebular hypothesis'. This theory was proposed in 1755 by Immanuel Kant, but was also independently conceived of by Pierre-Simon Laplace. This theory consists of the idea that the solar system started life some 4.6 billion years ago as a nebula, which then started to condense and spin, under the influence of gravity. Material gravitated to the core of the nebula disc, and was compacted until critical mass was achieved. This was the birth of the sun.

With the birth of the sun, the nebula disc started to become violent. Solar winds, coming from the newly form star, Sol, ravaged the now planetary disc, and blew material away from the center. Only the heavier elements, such as iron, carbon and oxygen remained in the central section of the disc. All the lighter elements, such as hydrogen and helium, were blown out the outer part of the disc. As the planetary disc spun, the material within the disc began to collect into clumps. As these clumps grew larger, they attracted increasing amounts of the surrounding material, soon the planetary disc became world where it was dog eat dog, or rather, planetoid eat planetoid.

However, eventually most of the available material was taken up and, for the most part the planetary disc was once again calm and recognizable as the one we have today. However, even now there are clear testaments to the violence of the solar system's younger days; Earth, with its tilted axis and moon clearly had some sort of impact with a Uranus, spinning on its side after being knocked there by a similar, though evidently larger impact, and Pluto, flung out as a moon in to the disc to take up its strange orbit that we see today. The asteroid belt and the Kupier belt, similarly, are a glimpse back into the violent youth of our solar system.

Categories Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune Pluto
Mean Distance From Sun
(millions of km)
57.9
108.2
149.6
227.9
778.3
1427
2871
4497
5914
Period of Revoution
88
days
224.7
days
365.3 days
687 days
11.86 years
29.46
years
84
years
165
years
248
years
Equatorial Diameter (km)
4880
12100
12756
6786.8
143200
120000
51800
49528
2330
Atmosphere (main components)
virtually none
carbon
dioxide
nitrogen oxygen
carbon dioxide
hydrogen helium
hydrogen helium
hydrogen helium
methane
hydrogen helium
methane
methane + ?
Satellites
0
0
1
2
16
18
15
8
1
Rings
0
0
0
0
3
1000 (?)
11
4
0
Rotational Period
59 days
243 days
retrograde

23 hours 56 min.

24 hours 37 min.
9 hours 55 min.
10 hours 40 min.
17 hours 12 min.
16 hours
7 min.
retrograde
6 days 9 hours 18 min.
retrograde
Inclination of Axis Degrees (tilt)
near 0
177.2
23, 27'
25, 12'
3, 5'
26, 44'
97, 55'
28, 48'
120
Temperature at surface (degrees celcius)
-173
to
427
480
-90
to
58
-143 to
17
-150
-180
-210
-214
-220
Mass
(Earth=1)
0.055
0.814
1.000
0.107
317.8
95.16
14.55
17.23
0.0026(?)
Density
(water=1)
5.43
5.24
5.52
3.93
1.33
0.71
1.31
1.77
1.1

 

For all you ever wanted to know about the solar, the nine planets website below.

http://www.solarsystem.org.uk/

Stellar Objects

The primary consistency, of which the universe is composed, is, well, empty space. Vast amounts of empty space. However, every so often if one ís to travel across an infinitely empty universe, there will be a hotspot of matter. Sort of like the odd service station or McDonalds that is encountered upon a long country road, with the occasional country town.

Single Stars are like the lonely fruit stands or cattle stations of the universe. Alternatively, they could also be considered as the family units of the universe, coming together to build a greater community. The quintessential cold fusion nuclear family.

Binary Stars are the more torrid versions of the Single Star, otherwise known as the fast food store/ petrol station combo, or the shared house that ís too gravitationally dysfunctional to be able to really support anyone other than the two stars, ejecting any other members of the household to an outer orbit, or the couch/bathroom/garden.

Clusters are the small country villages, where Single or Binary Stars all gather together to create a community. Generally, star clusters can be separated into two types; globular, and open. The importance of clusters is their demographic; like a village, all the stars are more or less the same age and type, although it is debatable whether or not they share the same apparent tendencies as an Agatha Christe village in being a den of iniquity.

A stellar cluster and a constellation are quite different from one another. Stellar (or star) clusters are groups of stars which are gravitationally bound. Two distinct types of star cluster can be distinguished: globular clusters are tight groups of hundreds of thousands of very old stars, while open clusters generally contain less than a few hundred members, and are often very young. Constellations, on the other hand, are any one of the 88 areas into which the sky - or the celestial sphere - is divided. The term is also often used less formally to denote a group of stars visibly related to each other in a particular configuration or pattern.

Some well-known constellations contain striking and familiar patterns of bright stars. Examples are Ursa Major (containing the Big Dipper), Orion (containing a figure of a hunter), Leo (containing bright stars outlining the form of a lion) and Scorpius (a scorpion). Other constellations do not encompass any discernible star patterns, and contain only faint stars.

The constellation of Orion

Galaxies on the other hand are the island nations of the universe. They are composed of many individual clusters of varying sizes, types and ages. Galaxies come in several different forms, and although on a much larger scale than a cluster; a village community can hardly be compared to a country, however small, also vary drastically in size. There are of three archetypes of galaxies; spiral, elliptical and irregular. They also, not unlike countries usually have some sort of central core of elder star; and usually a super-massive black hole at the very centre. Galaxies themselves also belong to galactic clusters, much like a continent or archipelago. Our own galaxy, the Milky Way is a bar spiral. The biggest galaxy in our local cluster is Andromeda, another bar spiral galaxy.

Andromeda - the Milky Way's galactic neighbour

Nebulae are the nurseries, or maternal wards come childcare centers of the universe. Essentially a nebula is a cloud of cold gas. Under the influence of gravity, the nebula condenses to from protostar, then stars and a solar system. More than one star or solar system can appear in a large nebula.

The Horsehead Nebulae

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Stellar Distances

Imagine this; if the Sun were a table in the Centerpoint tower, then Mercury would be a tic-tac lying in Pitt Street mall. Earth would be another bottle cap floating in the Hyde Park fountain. Mars would be a jellybean dropped in St Mary's Cathedral. In the Opera House would be a dinner plate known as Jupiter, and Saturn would appear as an entree plate in the Sydney Cricket Ground. Uranus would be a teacup on the Royal Randwick Racecourse, and finally, Neptune would be another teacup left on South Head.

Now, consider that Neptune is 5.47 light hours from the sun, while the closest star to the sun, Alpha Proxima (part of the Alpha Centauri system) is 4 light years away from our sun. The definition of a light year is the distance that light travels in a vacuum in one year.

Having considered that, think about the fact that our galaxy is 100,000 light years in diameter, and the distance from our sun to the center of the Milky Way is estimated at anywhere from 26,000 to 35,000 light years. The bar of the Galaxy is about 27,000 light years across.

Andromeda is approximately 2.5 to 2.9 million light years away from our galaxy and about 220,000 light years across. Our local group of galaxies is approximately 5 million light years across.

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