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Time Before Clocks
and exoplanets
Mercury - its history
- its transit
Venus - its history
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Venus Express
Mars - its history
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Uranus - its history
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History of Siberia
Part One

the geology and
early history
mammoth hunters
Chukchi Directions
Directions of Time
and feng shui origins
bronze and iron age
civilizations from Siberia
Shamans and Time
Medieval Siberian
British and Russians
discover Siberia
16th century Yakutia:
origin of the Sakha
17th century Yakutia
and the Russian Invasion
18th century Yakutia
the explorers: part one
18th century Yakutia
the explorers: part two
Russian America
18th and 19th centuries
Yakutia 1820 to 1890
extreme tourism
Japan attacks Russia
Siberia 1890-1912
and a British gold mine
starts a revolution
Tunguska event
As seen by
shamans and scientists
Siberia: 1917 to present
The Great Bear
and the Cosmic Hunt

the ancient sky
calendar and myths.
(More being added.)
The Moon
The Moon and Calendars
Origins of modern calendar
Moon and Eclipses
and history links
and Winter Solstice
Spring Equinox
The Cosmic Mill
Iron Age astronomy:
the mathematicians.
The Ptolemy Effect
Medieval astronomy.
Hampton Court Clock
Latest updated booklet
on the Hampton Court Clock
full story so far.

Tudor Bastard
King Edward VI's
Defence of
Lady Jane Grey's Clocks
Astronomy in the
17th century

The impact of the
new observatories
France, China and
other places.
More on John Harrison
and the
Problem of Longitude

in this book which also
has information on
Harrison's scientific work.
18th century astronomy
drinking song
and fuzzy blobs
space travel
- its history
in the 19th to
21st centuries

red shift and big bang
problems with Big Bang
and dark matter.
Story of the
Westminster Clock
only clock
used as sewer
ventilation shaft
The First Batteries.

taking part
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and other
scientific discoveries.

astronomy data
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of the world
summary of
past publications

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Astronomy Data

Big and Small Numbers

Numbers over 1 can be written in terms of powers of 10:


so 1032 is 1 followed by 32 noughts

the mass of the Milky Way is about 2 x 1044 grams

where the total number of grams is 2 followed by 44 noughts.

the luminosity of the Milky Way is 3 x 1037 Watts

which is 3 x 1035 100W. old light bulbs, or 20W modern bulbs.

the Sun is as bright as 4 x 1024 100W.light bulbs or 20W modern bulbs.

The Milky Way is 30 Kpc across which is 6 x 1017 miles

which is 600,000 million million miles.

The lifetime of a proton is at least 6.5 x 1031 years where the total number of years is 6 followed by 5 and then 30 noughts - the 5 takes the place of a nought.

Numbers under 1 can be expressed as negative powers of 10:


so 10-31 is a decimal point followed by 30 noughts and then a 1 or 1/1031 or 1/1+31 noughts

The mass of an electron is 9.1 x 10-31 Kilograms.

Scale of the Universe

Size of Solar System:

If you made a scale model of the solar system on the length of a football pitch -

The Sun - would be a glowing pingpong ball (about 1 inch diameter) on one goal line -

you wouldn't be able to see anything else

Jupiter would be the size of a pea

Earth would be smaller than a grain of sand.

Size of the Universe:

If the Milky Way, our home galaxy, was the size of the Earth, the Earth would be about the size of a virus.

If you depicted the Milky Way by a grain of rice about 2 millimetres long - then M31, the Andromeda galaxy would be about the same size and 6 centimetres away - it is about two million light years away which is around 40 million million miles.

M67 which is an active galaxy in the Virgo cluster, which is the nearest large cluster to which our local cluster of galaxies is being drawn towards, would be the same size and just over a metre away - it is about 33 million light years away from us.

The Hercules cluster of galaxies would have the diameter of a golf ball and lie about 10 metres from the Milky Way.

The horizon of the observable universe would be more than 100 metres from the model of the Milky Way.

There is more than a million stars for every grain of sand on the Earth.

Size of Hydrogen Atom:
If the nucleus of a hydrogen atom is represented by a taxi in the centre of London - then the electron would be a telephone somewhere on the M25 motorway.

The Light-Year

Light in a vacuum would travel one metre in 1/299 792 458 th of a second, which is approximately 3 x 108 metres per second or 300,000 kilometres per second (300,000 km/s.)

Light travels at different speeds in different mediums and can be deflected and bent by gravitational forces. However it can be assumed to be a constant for calculations.

It takes 8.3 minutes for the light from the Sun to reach us - so we see the Sun as it was nearly 9 minutes ago.

It takes four years for light to reach us from the nearest star to our Sun. It takes 60,000 years for light to cross from one side of our Milky Way galaxy to the other. It takes two million years for light to reach us from the Andromeda Nebula (M31) the nearest large galaxy similar to our own, in our cluster of galaxies. Light has taken 33 million years to reach us from one of the nearest clusters of galaxies to ours, the Virgo Cluster.

In one year light travels 9.5 million million kilometres or 5.9 (nearly 6) million million miles. The distance travelled by light (and all electromagnetic radiation) through space in one year is called one light year and is used to measure distances of stars.

By assuming electromagnetic waves travel at constant velocity, RADAR can be used to measure distances of local objects in the Solar system. A radio telescopes transmits a pulse to the surface of the planet. This is reflected back from its surface so some minutes after transmission we get an echo. By timing the delay between transmission and echo we can find the distance. Radar has been used to measure the rotation of Mercury and Venus and to map the surface of Venus - the mountains being nearer than the valleys.

The Astronomical Unit

The Astronomical Unit (AU) is the mean radius of the Earth's orbit about the Sun. This is 150 million kilometres. 1 AU = 1.49578 x 1011metres

Edmund Halley recognized the importance of observing the transits of Mercury and Venus - the rare occasions when one of these planets gets in line of sight between the Earth and the Sun, and appeared to the observer, using a telescope as the lens of a camera obscura, (never look directly at the Sun through a telescope) as a black dot crossing the surface of the Sun.

By timing the exact moments that the planet entered and left the Sun's disk, from different places on Earth, it was thought possible, by using parallax, to determine the distance of the Earth from the Sun, and use that as a baseline, the Astronomical Unit, to find the distance of other objects in the Solar System, and the nearest stars.

Once the distance of the Earth to the Sun was known, the comparative distances of other bodies in the solar System and nearby stars could be calculated.

See also: The Parsec - how it was calculated and used to measure distances in space.

It would also be possible to determine the longitude of the position of the observer. For example observations of the transit of Mercury in 1677, were used to determine the longitude of Port Royal, Jamaica. This is because the transit would be seen differently from different places on Earth.

Major international preparations were made for scientists (regardless of political differences or even war - there was war between Britain and France) to travel to remote parts of the world to observe the transits of Venus in 1761 and 1769. They knew a similar opportunity would not reoccur again until 1874 and 1882 (the next transit was in 2004 and we watched and photographed it from our back garden!). The astronomers had some horrendous adventures on their travels to their destinations in Canada, Tahiti, South Africa, Central Siberia, India, Mexico, and other places.

The method was to time the moment Venus entered in front of the Sun's disk and the moment it left. These times will be different for each observer in each place. The results were then collected together and from then the distance from the Earth to the Sun would be calculated.

The results were disappointing. One reason was the time-keepers. Pendulum clocks were the most accurate at the time, and they had to be reassembled after arduous journeys.

The other reason was that it was difficult to see the precise moment the transit began, there was a "black drop" effect. Astronomers rightly concluded this meant Venus had an atmosphere.

In September 1959, there was the first attempt to find the AU by using radar. Radar signals were bounced off the surface of Venus. The radio telescope at Jodrell Bank was used first as the transmitter and then as the receiver for the echoes. This attempt failed.

In April 1961 came a second international attempt. This used as well as Jodrell Bank (and R.V.Jones), equipment in the USSR, MIT near Boston USA, the JPL, Pasadena, California. By measuring the time delay of the echo they found the distance of Venus and also that they had got the mean distance of the Earth to the Sun too small, and this was why they failed before to detect the echo, they had been looking in the wrong place. They now had more precise clocks - hydrogen masers. There was still a discrepancy of 60,000 km between the radar value of the AU and the best of the conventional values. Eventually the average radar value of 149,600,000 kilometres was accepted.

Astronomers' Time

The solar year is the time taken for the Earth to make a complete orbit of the sun from noon - 00.00 hours on March 21st the Spring Equinox, back again.

The sidereal year is measured by the stars. Each day as measured by the stars is nearly 4 minutes (3 minutes, 56.5 seconds) shorter than the solar day. So after one year the sidereal year is a day behind the solar year. This is corrected on September 21st, the autumn Equinox. The sidereal year is measured from September 21st, the autumn equinox to the next September 21st, from 00.00 hours, noon.

Ephemeris time is used to provide accurate timekeeping with reference to the positions of the moon, planets, Jupiter's satellites, etc. An Ephemeris is a table of coordinates which enables the prediction of position and movements of celestial objects.

Ephemeris time is measured by the most efficient clocks available. Since 1984, the precision of clocks has replaced ephemeris time. This is dynamical time, produced by atomic clocks. The most accurate is the hydrogen maser. Rubidium clocks are the cheapest and used most in industry.

The international time standard is set by the Caesium clock, which uses Caesium 133. In 1967 the standard international time unit was set as the hyperfine transition from the ground state upwards of the electrons in a caesium atom which is about 9.92 giga Hertz.

Dates are written with the year first, then month, day, hour, minute, second. or the decimal fraction of the day: eg 2001 January 1d 2h 34m 4.8s or 2001 January 1.107.

Astronomers used the Julian Date. This was invented by Joseph Scaliger, a 16th century French scholar, who named it after his father whose name was Julius Caesar Scaliger.

It is a cycle of time. Scaliger calculated the least common multiple of the 218-year solar cycle, the 19-year Metonic cycle (of the Moon's orbit) and the Roman indiction (based on the Roman Tax system which began with the Emperor Diocletian, on 1st September 297AD). This came to 7,980 Julian years (that is of the Roman Emperor Julius Caesar) of 365.25 days each. Scaliger thought this long enough to cover all human history from the beginning.

The epoch of the Julian Era is the year when the beginning of the four cycles coincided, which is 4713BC. The Julian Day adopted by astronomers began at noon GMT on January 0, 4713BC. The Julian count begins again on January 0, 3267. So...

The Julian date (JD) counts the number of days that have elapsed since Greenwich noon on 4713BC January 1. Any time less than 12h (0.5d) belongs to the Julian day preceding the civil date.

The standard epoch is a set date and time used for comparing star coordinates and other data. Since 1984 the standard epoch has been 2000 January 1.5, or J2000.0 which is the Julian epoch based on the Julian year of exactly 365.25 days. It is exactly one Julian century (36525 days) removed from the standard epoch of 1900 January 0.5.


the Kelvin

Temperature is measured in Kelvin. A Kelvin was defined at the 13th general Conference on Weights and measures 1967 as "The Kelvin, the unit of thermodynamic temperature is the fraction 1/273.16 of the thermodynamic temperature of the triple point of water"*

*The "triple point of water" is a stable condition at 0.01oC/273.16K where it is balanced equally between liquid and ice and vapour.

Kelvin is from William Thompson (1824-1907) born in Belfast, later became Lord Kelvin. Absolute zero was already known by Kelvin's time. The Kelvin thermodynamic scale was formed from the Celsius scale, using the same units, each now called a kelvin.

Anders Celsius
(1701-44), was an astronomer, born in Uppsala, Sweden. He died of TB. He was opposed to theology in science and championed new ideas. He came from a family tradition of astronomers. Became head of the observatory Uppsala. In 1741 he devised a thermometer with the 100 degree scale, but the other way round to the way we do it now with 0 as boiling water and 100 as the freezing point of water. He published this in 1742 in the Transactions of the Swedish Academy of Sciences.

In 1743, French physicist Jean Pierre Christin (1683-1755) from Lyons, produced thermometers using the same scale but reversed with 0 as freezing and 100 is boiling as now. In Sweden, Celsius's successor, Martin Strömer in 1750 reversed Celsius's scale to 0 freezing and 100 boiling on new instruments made by him and Daniel Ekström instrument maker at the Academy of Sciences. This scale came to be known as Centigrade because of the 100 graduations. It was changed officially to Celsius at the 9th General Conference in Weights and Measures 1948.

However neither the Celsius or the other scales used Fahrenheit or Réamur had zero at absolute zero.

Absolute zero was calculated as follows:

Guillaume Amontons


showed in experiments that if a volume of air was heated to the temperature at which water boils, its pressure always rose by one third. He concluded that as pressures dwindled as temperatures were reduced, a point could be reached where both temperature and pressure equal zero.

He did many experiments on measuring relative pressure and temperature. Since the pressure exerted by a fixed volume of gas diminished almost in direct proportion to the reduction of its temperature, absolute zero can be calculated. So it was and is: -273.15ºC which equals 0 K.

Changes in the Position of the Earth with Reference to the Stars

1. The Earth Moves:

The Earth orbits the sun in an ellipse at a mean radius of 150 million kilometres (one astronomical unit or A.U.). It is nearest the Sun in January (perihelion) and farthest from the Sun in July (aphelion). The Earth as viewed from the Sun moves faster along that part of the orbit nearest the Sun than at other times. The difference between Apparent Solar Time and Mean Solar Time is called the Equation-of-Time. It has its maximum value early in November when the difference is about 16 minutes.

During the course of 100,000 years the Earth's orbit round the Sun changes from being more elliptical to rounder and back to more elliptical again - thus the distance between the Earth and the Sun is different at certain times of the year.

The oblate (slightly squashed from round) shape of the Sun and the gravitational pull of the other planets are among the factors which cause the Earth's orbit to rotate round the Sun. It shifts at a rate of 5.0 ± 1.2 arc seconds per century. All the planetary orbits show this effect to some extent, greatest nearer the Sun, with Mercury. the sun also moves in an orbit as it is affected by its planets, especially the largest, Jupiter.

The progress of the Sun and its solar system through the spiral arms of the Milky Way causes the relative positions of the stars to change with time. The solar system is presently drifting towards the constellation of Hercules at a speed of about 19.4 km. per second (43,400 miles per hour). It travels 380 million miles each year. The Sun is passing through a cluster of stars which includes five of the stars in the Plough asterism in the northern sky and Sirius which can be seen low in the southern sky in winter in the northern hemisphere. The Sun is orbiting around the centre of our galaxy, the Milky Way at a rate of 230 km/s and is moving at about 26 km/s through the cloud of molecular hydrogen that surrounds it.

The Milky Way is orbiting around a local cluster of about twenty galaxies. This cluster is orbiting the much larger Virgo cluster, and being dragged towards it. It is also being pulled by other large galactic clusters such as the one in Puppis. These large rotating clusters form great chains and sheets around voids around 200 million light years across with hardly anything in them. As we are able to look further, more structure becomes apparent.

If you could travel back in time you might step out into space as the Earth would have moved on and it would be impossible to predict its exact position.

2. the Earth wobbles:
The Earth is a slightly irregular oblate spheroid,12,756 km. radius through the equator and 12,714 km. through the poles. The irregular shape and off-centre centre of gravity affects the orbits of satellites causing them to process, unless they orbit the equator.

The Earth's spin axis or polar tilt is at present at an average 23 degrees 27 minutes, this varies slightly during the course of 40,000 years and within this cycle at periodic and irregular intervals. Changes in the polar tilt mean changes in the apparent position of a star.

Because the Earth is at an angle to the apparent path of the sun, the days, day and night, vary in length during the year. In the north, at the equinoxes (around March 21st and September 21st) day and night are equal in length in the north, at the summer solstice around June 21st, the day is very long and in the far north the sun never sets at all, at the winter solstice, December 21st, the sun barely rises at midday at latitudes above 50 degrees.

The friction caused by the tides caused by the gravitational pull of the Moon and of the Sun is making the Earth's rotation slower at an average rate of a second in a thousand years. This effect was first noticed by Edmund Halley when he studied ancient records of eclipses.

Before the Moon settled into orbit around the Earth, the Earth's rotation was 11 hours - it had an eleven hour day - and its polar tilt varied chaotically, as much as 60 degrees or more. If the Moon was to be knocked out of its present orbit by a passing asteroid (not impossible) then the Earth's tilt and spin would become chaotic again. The day would shorten back to 11 hours and the polar tilt would expand to 60 degrees or more chaotiacally, causing devastating climatic changes.

The Earth's rotation also varies with the changes of melting ice caps, movement of air and in the Earth's core. At present a solar year in Mean Solar Time is 365 days,5 hours, 48 minutes and 45.5 seconds. 300 million years ago fossil records show that there were 400 days in a year.

The Earth's rotation is also subject to seasonal variations due to the distribution of mass caused by the melting of ice and irregular variations. These smaller variations in the Earth's rotation were shown by the caesium clock, on which the time standard since 1967 has been based.

The day as measured by the stars - Sidereal Day - is nearly four minutes shorter - three minutes 56.5 seconds - than the day as measured by the sun - Solar day. It is the time interval between two successive meridian transits of the Vernal (Spring) Equinox. Standard time used to 1/86400 of a sidereal day, but was redefined in 1967 to 9,192,631,770 periods of the radiation from specified energy levels in the caesium 133 atom. Currently, the International System of Units (SI) defines the second as 9,192,631,770 cycles of the radiation, which corresponds to the transition between two hyperfine energy levels of the ground state of the 133Cs atom.


The Earth's poles swing round in a circle during the course of 25,000 years. The Platonic Year. this is called precession. Gravitational influences cause periodic wobbles in the precession causing nutation. The main variation is of 18.6 years caused by the Moon's main cycle in its orbit round the Earth. There are smaller variations within this.

One effect of precession is that the position of the Earth's poles move round in the course of the Platonic Year, but not to exactly the same position again because of changes in polar tilt.

Polaris which is nearly at the North Pole today was 3.5 degrees away in the 16th century and 7 degrees away at the time of the Vikings. 4,000 years ago. In the Bronze Age, α-Draconis was nearest the North Celestial Pole. 8,5000 years ago at the end of the Ice Age, the Pole Star was τ-Hercules. About 14,000 years ago, the bright star Vega was near the Pole and this will be the Pole Star in 13,000 years time.

Northern legends about the Pole Star or "Northern Nail" which fixed the heavens in place, coming out of place, and subsequent disaster, might stem from observations that the pole star had changed position. But since long-term records were mostly oral it is also possible that these stories are attempting to account for the fact that the axis of the heavens is not observed directly overhead.

Precession and Astrology

The other effect of precession is that the Vernal Equinox moves steadily backwards. This was discovered by Hipparcos who published his star tables in 127 BC. Hipparcos was born in Nicea, a resort on the north coast of what is now Turkey. He worked as an astronomer in Rhodes. When he was compiling his star tables, as well as using his own observations he studied the work of other astronomers. This included the astronomical records from the country now called Iraq which had almost continuous records going back for centuries. The earliest records were Sumerian, from the bronze age, then from the 7th century BC this country was part of the Assyrian empire. It then gets called Babylonian from the capital of the empire, and then Chaldean. At the time Hipparcos was compiling his star tables, this region was all part of the Macedonian Greek empire conquered by Alexander the Great. The records were made on clay tablets so many of them have survived. There are some in the British Museum.

The Babylonian astronomers were scanning the sky each night and making careful records because they believed the position of the heavenly bodies revealed a message of the outcome of future events and warnings and portents - the health of the ruler, outcome of wars, good and bad harvests etc. These meanings and the methods of plotting the sky - the constellations, signs of the Zodiac, etc. all become adopted into the system used by astronomers in the Greek empire, later the Roman empire, around the Mediterranean and in the near east.

At this latitude all the ecliptic which is the part of the sky in which the planets can be seen, was visible through the year. Further north, only part of the ecliptic can be seen, so cosmologies were based on the circumpolar stars. Where the planets could be observed and their positions over the years recorded, predictions, astrology, was based on them. We find this in the near East, in India, which had the most influence on astrology, in China and other places in the Far East and in Central America. Modern astrology and astronomy derives from the methods used in the near East, by way of Hipparcos, mainly through the work of Ptolemy who depended heavily upon references to Hipparcos in his star tables published in 141 AD, and Ptolemy's work survived to become a major influence in astronomy in later centuries.

The circle of the ecliptic was divided into 360 degrees, and this was divided into twelve equal parts of 30 degrees each, each part named after a constellation near or within it. In astrology which until the 18th century was a lucrative and import part of the astronomer's work, the position of planets in the zodiac is believed to have significance in each person's life. The signs of the zodiac have retained their names from the time of the Roman Empire:

Aquarius, Pisces, Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpio, there is the large constellation of Ophiuchus between this and the next sign, Sagittarius, Capricorn.

Hipparcos noticed that the Vernal Equinox was in Taurus. It had been in Taurus around 3000-1800 BC so this indicates how old the continuous astronomical records were in Iraq. According to Hipparcos' s calculations the spring equinox was the first point of Aries. Astrology has become frozen in time, for astrologers today who are no longer astronomers and scientists, still place the equinox there although it has moved back through Pisces and is entering Aquarius by 2700 AD. The spring equinox was crossing the Milky Way between Gemini and Taurus 6,500 to 5,000 years ago.

The precession of the equinoxes accounts for some early Christian symbolism and was used to determine the date of Christ's birth. The sacrificed lamb symbol stood for the passing Aries the Ram sign. The P for Pisces and the new Spring sign of the fish - a symbol for what followers saw as the "New Age".

The degrees used today in astronomical charts, came from Iraq. 360 days of the year is easier to cope with mathematically and to divide into twelve. The Chinese astronomers divided the celestial equator into 3651/4 degrees, the right number of days in a year. The Maya of Central America, and other Central American nations, had 360 days in the year, which meant there were five days left over. The astrologers coped with these by making them "unlucky" days in which no new enterprises should be undertaken.

The twelve divisions of the zodiac was not only to coincide with the months of the year, (which do not quite fit in as there is a third left over, so that is why they became fixed lengths in the Roman Calendar) but also coincides with the orbit of twelve years for Jupiter. This explains why Jupiter appears in a different zodiac sign each year.

The system may have originated in India, or at least India and the near East influenced each other. Another zodiac system came from India and spread to Central Asia and China and other countries in the Far East. It was also used for horoscopes as well as the calendar and the times of the day: TIGER HARE DRAGON SERPENT HORSE SHEEP MONKEY COCK DOG BOAR RAT OX.

The Brightness of Stars


originated with Hipparcos. In 127BC he classified stars in his star catalogue according to their magnitude. As he believed all the stars to be the same distance from the Earth, fixed to a sphere, he thought the brighter the star, the bigger. The brightest in his catalogue were first magnitude and the dimmest were 6th magnitude.

Since then some stars have been classified brighter than first magnitude so they can be zero or a negative magnitude. Also the term is now applied to all objects in the sky like planets, comets and the moon. The telescope has enabled stars far fainter than sixth magnitude to be seen. Most people cannot see objects dimmer than 5th magnitude without a telescope, more usually it is not possible to see dimmer than third magnitude.

When it was accepted that stars are of variable distances from us a method of calculating absolute magnitude had to be found. This is done by calculating the magnitude a star would have at 10 parsecs from us. eg the absolute magnitude of our Sun is +5, and of Sirius is +1.4 (30 times brighter).

Since telescopes now operate at different wavelengths a new measure of the total brightness (luminosity) of the object in the electromagnetic spectrum is used. This is:

the Jansky

one Jansky equals 10-26 watts per square metre per Hertz of frequency bandwidth, which is equivalent to a 9th magnitude star in the optical region of the spectrum eg Sirius has an apparent magnitude of -1 and an apparent optical flux of 10,000 janskys Our Sun has an apparent magnitude of -26 which is 1014 janskys.


of stars are defined in terms of the difference in their magnitudes at different wave lengths. eg. the difference between the magnitudes of a star in the blue (B) waveband, centered on 440nm. and the visual (V) waveband centered at 550 nm. This colour index or colour (B-V) is a measure of how blue or red the star is. Blue stars are hot, red stars cool. This statement is qualified by working in terms of colours such as B-V.

Astronomical Measures of Flux Density:

Astronomers work in terms of magnitudes (=m.) which are negative logarithmic measures of flux density defined by m = constant -2.5log10S where S is the flux density of the object. Thus a difference of five magnitudes corresponds to a difference in flux density of a factory of 100.

The magnitude system is normalized so that the standard star, chosen to be the bright star Vega (±-Lyrae) in the constellation of Lyra, has zero magnitude at all wavelengths. In this way magnitudes can be defined at all wavelengths.

The faintest stars which can be seen with the naked eye have m=5, the faintest stars which could have be observed with a 4-metre telescope in a 5 minute observation using a CCD camera have m-25, but the latest space telescopes can produce images of clusters of galaxies which if the current "Big Bang" theory was correct, would be at the edge of the universe and just after the "Big Bang".

To measure the intrinsic luminosities of celestial objects astronomers use:

absolute magnitudes (M)
the magnitude which the object would have if it were placed at a distance of ten parsecs.

Because of the inverse square law, an object of intrinsic luminosity L has flux density S=L/4pr2 and therefore for any object M = m -5 log10 (r/10) where the distance r is measured in parsecs for stars of different luminosities

M = M(Sun) -2.5 log10 (L/LU)

The absolute bolometric magnitude of the Sun is M(sun) = 4.75 and hence in general we can write M = 4.75 -2.5 log10 (L/LU).

The Electron Volt

Used for sub atomic particles.

An electron-volt (eV) is the energy an electron (or proton or anything of unit charge) gains when it is accelerated across a voltage difference of one volt.

The mass of an electron is 510 thousand electron volts

The mass of a proton is 935 million electron volts

It weighs 1.7 x 10-27 kilogramme

and produces 1.5 x 10-10 joules energy

1019 protons, that is 17 micrograms, converted every second would fuel a power station.

The e-m spectrum (see chart) of electro-magnetic radiation is a strong force made of photons with a maximum speed of 3x108 m/s.

Ions and Isotopes

INSIDE ATOMS: chart showing parts

The Helium atom:
proton proton
neutron neutron

if the two electrons are lost, the helium atom becomes a HELIUM ION or ALPHA (α) PARTICLE, with a positive charge


is an atom with a particular number of protons and neutrons. The element's name is based on the number of protons only so one element may have a number of possible isotopes. Some isotopes are more unstable than others. Electrons may be detached by heating. They may then be directed by a positive anode and forced into a narrow beam by magnets.

IN RADIOACTIVE DECAY, the isotope disintegrates producing new isotopes and α, β (beta), and γ (gamma) radiation. Gamma radiation is very short wave high frequency electromagnetic radiation. The atom is changed to another element. The rate of decay is measured by the time it takes for half the atoms in any sample of the element to decay. This is its half-life.

Watching them watching us

You may in the early evening or early morning before daybreak, see what looks like a star travelling across the sky. This is probably a low orbit satellite, or the space station.

For a satellite to escape the gravitational pull of the Earth sufficiently to remain in orbit or "free-fall" without falling back onto the Earth, it must be launched at a speed of at least 11 kilometres a second (7 miles a second). Since the friction of the atmosphere would cause it to slow down and fall back to Earth, it must be launched to a height of at least about 200 miles. Then it must keep travelling at a speed of at least 28,000 kilometres per hour. (17,000 miles per hour).

Then it is in "free-fall" round the Earth, and could continue orbiting for ever if it were not disturbed by, the Earth's irregular shape and its changing magnetic field, making its path drift, the tidal pull of the Moon and the Sun, the Solar Wind and the Sun's magnetic field with sudden flares which shoot out from the Sun's surface past the Earth, interfering with satellite equipment. (Such a flare caused the Salyut 7 space station to crash). There is also danger from impacts with other objects both natural and increasingly, debris left from earlier launching.

The first low orbit satellite, Sputnik, was launched in October 1957, and since then so many satellites and crewed space craft have been launched that the space between 150 and 400 miles above the Earth's surface has become dangerously polluted with all sorts of junk. A cosmonaut working outside the Space Station could be killed if hit by only a tiny particle.

It takes the Space Station (ISS) or a low-orbit satellite, about one and a half hours to orbit the Earth, so you can see it for less than 45 minutes. One and a half hours later it will rise over the horizon from a different position as the Earth will have rotated 22 degrees.

Low orbits are used for for the Space Station, for satellites scanning the Earth, telling us where we are, broadcasting television and scanning the Earth so you can even see your own home on the internet, and for telescopes scanning the universe in different wavelengths, such as Hubble. These can be serviced from the space station or a shuttle.

Communications satellites and other satellites which are required to stay over the same place on the Earth's surface are launched to a height of 22,000 miles into a position over the equator, at a speed of 7,000 mph. They will orbit the Earth in 24 hours and so appear stationary from the Earth's surface. You will not be able to see these from Lincoln although you can receive the programmes from the television satellites. Communication satellites for the far north, have to take an elliptical orbit over the poles. This way people by the shores of the Arctic Ocean can still watch television.

More Facts About the Universe

There are 4 Forces:
is a weak force – it exerts pressure on every body.


Electromagnetic force
is a strong force - it holds the atoms together.

The particles in the nucleus of the atom are held together by the

Strong Force
Weak Force
comes into play when they fall apart as when neutrons break up into protons, electrons and neutrinos.

What we see as

is a small part of the electromagnetic spectrum (em) made up of photons. In a total vacuum these would travel one metre in 1/299 792 458 th of a second, which is approximately 3 x 108 metres per second or 300,000 kilometres per second (300,000 km/s.) called c. But normally photons are not travelling in a vacuum and their speed varies, and they can be deflected and bent by gravitational forces. Looking deep into space we can see reflections of far off galaxies distorted into arcs. This is caused by nearer large galaxies bending the light from those behind them, and acting like lenses.

In one year light would travel 9.5 million million kilometres or 5.9 million million miles (that is nearly six million million miles), this is called the light year (ly) and is used to measure the vast distances in the universe.

Another measure is the

The Parsec
. One parsec (1 pc) is 3.26 ly which is 31 million million kilometres or 19 million million miles. 1 Kpc is 1000 pc. The nearest stars to ours are just over a parsec away, or 4 ly.

The Milky Way our home galaxy is 30 Kpc across which is 600,000 million million miles or 6 x 1017 miles.


Luminosity (brightness at all wave lengths) of the Milky Way
is 3 x 1037 Watts which is equivalent to 3 x 1035 100-Watt old light bulbs (3 followed by 35 0s)

The mass of the Milky Way is about 2 x 1044 grams.

Our Sun, is about 10 Kpcs from the centre of the Milky Way

Absolute zero
is 0 Kelvin which is - 273.15 degrees Celsius Nothing can exist at absolute zero, but many things are just above it. The background temperature of space is about 2.7 K.

The Sun is 15 million K. in its centre, and 5,800 K. on its surface. At this temperature it is in the temperature range we see as light – we have developed eyes to make use of this part of the spectrum. Many living things can respond to more of the spectrum than we can – for example, snakes have additional simple eyes which can see in the infra-red which we only perceive as heat. The surface temperature of the Sun is in the green light part of the em spectrum which we see as yellow. Stars with a cooler surface temperature look red, those with a hotter surface temperature are bright blue. The Density of Water is 1. The Earth is about 5. Saturn is less than 1. Our Sun is only slightly denser overall than water, you would have to go a long way into the centre before it became as dense as our atmosphere.

There are approximately 100 billion stars in the Milky Way and they rotate around the centre hub of the Milky Way at a speed of about 200 - 500 kilometres a second. Some stars go much faster, especially near the central engine - the black hole Sag.A*.

The galaxies are part of clusters which are about 5 x 106 that is five mega parsecs, across and which rotate around each other. These clusters are in superclusters of around 10 mega parsecs across and they are lumped together forming voids between.

Data on the Universe

One light year (1 ly) is 9.5 million million kilometres or 5.9 million million miles (that is nearly six million million miles)

One parsec (1 pc) is 3.26 ly which is 31 million million kilometres or 19 million million miles

1 Kpc is 1000 pc. The Milky Way our home galaxy is 30 Kpc across which is 600,000 million million miles or 6 x 1017 miles.

The Luminosity (brightness at all wave lengths) of the Milky Way is 3 x 1037 Watts which is equivalent to 3 x 1035 100 Watt light bulbs

The mass of the Milky Way is about 2 x 1044 grams.

The Sun, is about 10 Kpcs from the centre of the Milky Way

Absolute zero is 0 Kelvin = -273.15 degrees Celsius

Water freezes at -273.15 K. = 0 degrees C.

and boils at - 373.15 K. = 100 degrees C.

The Sun is 15,000 million K. in its centre

5,800 K. on its surface

The Density of Water is 1.

The Sun is only slightly denser overall than water, you would have to go a long way into the centre before it became as dense as our atmosphere.

There are approximately 100,000 million stars in the Milky Way and they rotate around the centre of the Milky Way at a speed of about 200 - 500 kilometres a second.

The galaxies are part of clusters which are about 5 x 106 that is five mega parsecs, across and which rotate around each other

These clusters are in superclusters of around 10 mega parsecs across and they are lumped together forming voids between - the clusters form sheets and strings across the universe. The further we are able to look out in the universe the more we see of the same galaxies -

Either there is just one infinite universe

or (current belief) we are living in one of infinite numbers of universes

This chart last updated in 2000 shows briefly the history of our changing views of the universe with developing technology.

The Cosmicelk website is designed and maintained
by Heather Hobden
The Cosmic Elk

Copyright Heather Hobden and the Cosmic Elk