ESO 1 Science 1

The Earth in the Universe

What to Learn

  • The Astronomy across time.
  • Dimensions and distances in Astronomy.
  • Galaxies and clusters. The Milky Way and the Local Group.
  • The Stars and the constellations.
  • The Solar System: the Sun, the planets, the dwarf planets and the SSSBs.
  • The movements of the Earth and their effects.
  • The Moon and its phases.
  • The eclipses.
  • The Ecosphere.

Key Information

Vocabulary
GravityEvery object in the Universe exerts a force of attraction upon the objects around it. This force is known as gravity. The Earth is retained by the Sun because of the Sun's gravity; the Moon is retained by the Earth because of the Earth's gravity, etc.
BillionIn most English-speaking countries a billion equals one thousand million; you can write it as 109. Likewise, a trillion equals one million millions, and you can write it as 1012.
Light yearDistances in the Universe are huge, and so they are measured in huge units. A light year is a distance unit that equals about 9.5 trillion km. It is the distance covered by the light in one year.
Astronomical unitIt is another distance unit. It is the distance between the Sun and the Earth, and equals some 150 million km.
Galaxies and Clusters

The Universe is about 14 billion years old, and is formed by more than 100 billion galaxies. A galaxy is a huge system of stars, interstellar gas and dust. Typical galaxies contain from ten million to one trillion stars, all orbiting a common centre of gravity. Some galaxies are elliptical shape, some are spiral, others are irregular. Galaxies are usually separated from others by distances on the order of millions of light years. Groups of galaxies gravitationally attracted between themselves are called galactic clusters.

The Solar System is located in the Milky Way galaxy, a spiral galaxy with a diameter estimated at about 100,000 light years, containing approximately 200 billion stars. The Milky Way belongs in a cluster of over 30 galaxies known as the Local Group. The galaxy of Andromeda is the nearest to the Milky Way and the biggest one in the Local Group.

The Solar System resides in one of the Milky Way's spiral arms, known as the Orion Arm, at about 27,000 light years from the galactic centre. Its speed is about 220 kilometres per second, and it completes one revolution every 226 million years.

Stars

Stars are massive, glowing balls of hot gases, mostly hydrogen and helium. Some stars are alone in the sky (the Sun, the North Star), others have companions (Sirius, which is a binary star system, and Alpha Centauri, which is a ternary star system). The nearest star to the Sun is Alpha Centauri C or Proxima Centauri. The brightest star in the Northern hemisphere's night sky is Sirius.

Not all stars are the same: stars come in all sizes, brightnesses, temperatures and colours:

  • The colour of a star is due to its temperature. A blue or white star is hotter than a yellow star, which is hotter than a red star.
  • The brightness of a star depends on two factors: (a) its distance from us and (b) its luminosity: how much energy it puts out in a given time, which, in turn, depends on its size. Think on a street lamp, which puts out more light than a hand torch. That is, the street lamp is more luminous. But if that street lamp is 1 km away from you, it will not be as bright, because light intensity decreases with distance. In this case, a hand torch held 10 m away from you would be brighter than the street lamp. The same is true for stars.
Constellations

Constellations are groups of stars visibly related to each other in a particular pattern. Some well known constellations contain familiar patterns of bright stars. Examples are Ursa Major (containing the Big Dipper or Plough), Orion (that resembles the figure of a hunter) and Cassiopeia (with the shape of a "W"). The stars of a constellation, although appearing to be very near, may be millions LY away one to another.

The Solar System

The Solar System is the stellar system formed by the Sun and the group of celestial objects gravitationally bound to it:

  • the eight planets and their 162 known moons,
  • five dwarf planets and their six known moons, and
  • thousands of small solar system bodies (SSSB).

The Sun is the main component of the Solar System, a star that contains 99.9% of the Solar System's mass. The Sun releases enormous amounts of energy in the form of electromagnetic radiation, which includes visible radiation (light), ultraviolet radiation and infrared radiation.

The planets are the biggest objects orbiting the Sun. Their orbit is almost circular. In order of their distances from the Sun, the planets are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. The four inner planets are small and rocky planets; the four outer planets are gaseous giant planets with a small rocky core. All planets but the two first are orbited by natural satellites (usually called "moons"). The planets, with the exception of Earth, are named after gods and goddesses from Greco-Roman mythology. The following table shows some major magnitudes measured relative to the Earth:

Diameter (relative to the Earth)Mass (relative to the Earth)Distance to the Sun (in AU)Revolution period (in Earth's years)Rotation period (in Earth's days)Moons
Mercury0.40.060.40.24590
Venus0.950.80.70.62430
Earth111111
Mars0.50.11.51.912
Jupiter11.23185.211.90.3865
Saturn9.4959.529.50.462
Uranus41519840.727
Neptune3.817301650.713

The dwarf planets are also rocky objects orbiting the Sun, smaller than the planets, but bigger than asteroids. There are currently (20-sep-2008) five dwarf planets in the Solar System; the two best known of which are:

  • Ceres, formerly considered the Solar System's biggest asteroid;
  • Pluto, a trans-neptunian object formerly considered the Solar System's ninth planet;

The SSSBs comprise several types of celestial bodies, the best known of which are:

  • Asteroids = planetoids = minor planets. They're the smallest rocky bodies orbiting the Sun. Unlike planets and dwarf planets, they are not spherical, but irregularly shaped. Most of them occupy orbits between the ones of Mars and Jupiter, and make up the asteroid belt. The biggest asteroid is called Vesta.
  • Comets, very small icy trans-neptunian objects that orbit the Sun in very eccentric orbits. When a comet approaches the Sun, its icy surface begins to boil away, creating two long tails, one of gas and another of dust, which are often visible with the naked eye. Two well known comets are Halley and Hale-Bopp.
Presentation: Why the Moon?
[Source]

Google Maps

The Earth

Movies, Animations and Audios

Exploring the Universe
Sputnik news reel

Sputnik news reel

Watch this news reel from Universal Studios on the launch of Sputnik in 1957, the first man-made satellite ever put into orbit.

Apollo 11 mission highlights

Apollo 11 mission highlights

Watch that small step for a man, but giant leap for Mankind.

Apollo lunar landings

Apollo lunar landings

The 6 lunar landings of the Apollo Mission seen simultaneously from the same perspective as the astronauts.

Audio file from the Apollo 13 mission

Audio file from the Apollo 13 mission

Listen to one of the most frightening moments ever lived in space.

Stars, Galaxies, Nebulas and Constellations
Milky Way

Milky Way

Find out more about the Milky Way galaxy.

Produced by Cassiopeia Project

Really big stars

Really big stars

Want to see something really big? Well watch this. Check out how our own moon compares to the largest star we currently know about, VY Canis Majoris.

Produced by Cassiopeia Project

Planets and stars to Scale

Planets and stars to Scale

Watch from the smallest planet in the Solar System to the biggest known star.

The known Universe

The known Universe

From the Himalayas through our atmosphere and the inky black of space to the afterglow of the Big Bang.

Source: American Museum of Natural History

The Sun
Sol

Sol

Find out more about the Sun and its future.

Produced by Cassiopeia Project

SSSB
Pluto

Pluto

Find out more about the dwarf planet Pluto.

Produced by Cassiopeia Project

The Planets
Mercury

Mercury

Find out more about the planet Mercury.

Produced by Cassiopeia Project

Venus

Venus

Find out more about the planet Venus.

Produced by Cassiopeia Project

Mars

Mars

Find out more about the planet Mars.

Produced by Cassiopeia Project

Jupiter

Jupiter

Find out more about the planet Jupiter.

Produced by Cassiopeia Project

Saturn

Saturn

Find out more about the planet Saturn.

Produced by Cassiopeia Project

Uranus

Uranus

Find out more about the planet Uranus.

Produced by Cassiopeia Project

Neptune

Neptune

Find out more about the planet Neptune.

Produced by Cassiopeia Project

The Earth
Earth

Earth

Find out more about the planet Earth.

Produced by Cassiopeia Project

Earth rise from the Moon

Earth rise from the Moon

Recorded in April 2008 by the Kaguya (Selene) spaceprobe from the Japan Aerospace Exploration Agency.

Reasons for seasons

Reasons for seasons

Discover why winter and summer have nothing to do with the proximity of the Earth to the Sun in this Uncommon Knowledge podcast.

Streamed from the Uncommon Knowledge podcast

The Moon
Total lunar eclipse

Total lunar eclipse

Total lunar eclipse of February 20, 2008, in slow motion.

Images

Videocasts

Hubble's Universe 
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Podcasts

Star Stuff 
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NASACast 
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Now in the News

Space.com Top Stories 
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Universe Today 
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NASA breaking news 
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Activities

Reading: Astronomers Await a Nova
[Source: Space.com]
The Star of Bethlehem

At this time of year it seems almost traditional for stargazers to ponder the age-old question of the origin of the Star of Bethlehem. The Star's appearance some 2,000 years ago is quite possibly one of the best-known celestial events in all of recorded history.

The topic has universal fascination, and is why Christmas Star shows still play to packed planetarium houses.

Perhaps the simplest answer that can be offered is that the Star might have been a nova: a new star suddenly blazing forth where no star had previously been seen. While for the most part such objects are really dying stars having a final fling of glory before descending the long road to ultimate extinction, there are some stars that go through such contortions more than once.

One such star is long overdue to pop and could do so at anytime.

Stargazing

The star in question is T Pyxidis, in the constellation of Pyxis, the Mariner's Compass. T Pyxidis is about 6,000 light years away and belongs to a small and seemingly exclusive group of cataclysmic variable stars called recurrent novae (NR). Astronomers have been patiently waiting for T Pyxidis's next outburst for more than 20 years.

Normally this star shines at magnitude 14: that's about a thousand times dimmer than the faintest star that can be perceived by most human eyes on a dark, clear night. But on five occasions, in 1890, 1902, 1920, 1944 and 1967, this star brightened dramatically to magnitudes between 6.5 and 7 (a 1,000-fold increase in brightness in the most extreme case) making T Pyxidis just bright enough to be glimpsed without any optical aid. These eruptions came at an average of just over 19 years apart, and the longest stretch of time between them was 24 years.

But this month marks 40 years since the last outburst.

It was back on Dec. 7, 1966 that the most recent eruption was first noticed by New Zealand amateur astronomer, Albert Jones. The star had more than doubled in brightness to magnitude 12.9. Just two nights later it was almost four magnitudes brighter and after a month it was glowing at magnitude 6.3 before slowly fading back to normal.

Nobody knows exactly why T Pyxidis has remained quiet for so long, but the general consensus is that it may have accumulated an extra-thick coating of nuclear fuel on its surface over these past 20 years, which would make it appear extra bright when it finally blows its next surge of gaseous debris out into space.

Who knows? That night could be tonight!

Key vocabulary
  • Stargazer.
  • Outburst.
Analyse the text
  • What are astronomers expecting to happen and to what?
  • What is a nova?