Since the early years of the space age, many spacecraft have visited Mars in the search for signs of life. Mainly composed of dry ice carbon dioxide with ordinary water ice mixed in with it, the polar ice caps are prominent, and grow and shrink due to the season on Mars which are twice the length as those on Earth due to the carbon dioxide ice sublimating vaporizing in the Martian summer, thereby revealing the surface, and freezing again in winter.
Because of its tilt Mars, like the Earth, experiences seasons. The fact that Mars is at a greater distance from the Sun means that the Martian year is around two Earth years long, the consequence of which is that the lengths of the Martian seasons are around twice those of Earth.
These images were obtained just before the forthcoming opposition of Mars on 17 March of that year when the red planet approached to within around 99 million kilometres These pictures were taken during three HST orbits that were separated by about six hours. This sequence of images covers most of the Martian surface, the timing being chosen so that Mars, with its hour minute day, would rotate about 90 degrees between orbits David Crisp and the WFPC2 Science Team.
Much of the Martian highlands, made up of craters, mountain ranges and volcanoes, lie in the southern hemisphere of Mars where the crust thickness is around 62 kilometres 39 miles.
The crust thins out towards the equator, the northern hemisphere being almost entirely lowlands where the crust thickness is about 38 kilometres 24 miles. It is now believed that the Martian oceans, which existed on Mars a million years ago, filled the Martian lowlands. Phobos is the larger and innermost of the two moons, with a mean diameter of 22 kilometres 14 miles and an orbit which carries it around Mars once every 7 hours and 39 minutes at a height of around 6, kilometres 3, miles above the Martian surface.
When Mars is at opposition and at it is closest to us, a telescope of 75 mm 3-inch aperture will show the main surface markings, although a telescope of 20 cm 8-inch and above is needed to do useful work.
Do not be afraid of using high magnifications depending on the seeing conditions but do remember that a small, sharp view of Mars is better than a large, burred one. Remember also that an astronomical telescope will turn the image of Mars upside down so that the South Pole will be uppermost in the field of view. At or around the opposition date, larger instruments may enable you to see the huge volcano Olympus Mons together with several of the larger Martian craters.
Along with the Martian polar ice caps, you should also be able to glimpse dark areas such as Syrtis Major and Acidalia Planitia. It will also be possible to observe the Martian moons, which will be found to lie just a few arc seconds from the Martian disc. The main difficulty in observing Phobos and Deimos is that their feeble glow can easily be overwhelmed by the glare of Mars itself, Phobos appearing as an 11th magnitude point of light, slightly brighter that 12th magnitude Deimos.
Yet with a telescope of at least mm 4-inch aperture and by viewing from a dark observing site with good, clear and moonless skies, you may pull it off. Above anything else, you will need patience and dedication for the search, as did Asaph Hall while he was searching for these visually elusive objects!
It changes direction on 18 August, reversing from retrograde to direct motion, and reaches greatest elongation west on 26 August, shining at magnitude —0. It has already started to lose altitude as seen from the northern hemisphere but it continues to climb when viewed from more southerly latitudes. By the end of the month it approaches magnitude —4.
MARS resumes direct motion on 28 August after two months in retrograde. It is becoming easier to observe from the northern hemisphere and is best seen in the dark skies around midnight.
Mars remains an easy object from southern latitudes, shining at magnitude —2. The interplay of shadows between the planet and its Galilean satellites is at its most pronounced during this time, making for interesting telescopic opportunities. Unfortunately for northern hemisphere observers, the planet is getting nearer to the horizon as astronomical twilight approaches.
It sets around midnight in southern temperate latitudes so it is best seen as soon as the sky darkens. The waxing crescent Moon is found nearby on 17 August. On 21 August, the waxing gibbous Moon passes just north of the planet. URANUS continues to rise higher in the sky for tropical and southern hemisphere observers for whom it now rises around midnight.
On both 3 August and 31 August, Uranus is overtaken by the waning gibbous Moon. Uranus arrives at a stationary point on 7 August and turns to retrograde motion. NEPTUNE is approaching opposition in Aquarius so it is above the horizon most of the night, rising just before midnight in the northern hemisphere and by mid-evening of southern hemisphere viewers.
With a diameter of 3, kilometres 2, miles and orbiting our planet at a mean distance of , kilometres , miles once every Today we know the moon as a lifeless world where the atmosphere is so thin that it provides no protection from either solar radiation or bombardment from meteoroids.
The lack of an effective atmosphere means that heat is not held near the surface, so temperatures vary wildly. However, it was following the invention of the telescope in that some observers began to believe that the Moon must have life on its cratered surface. Image of the Full Moon taken in March The German astronomer Johannes Kepler — believed that the telescope had revealed a living world, with extensive oceans and a dense mantle of air.
By the end of the 17th century, the idea of oceans on the Moon had been abandoned, although the notion that life existed there had not. He reported seeing colour changes on the lunar surface and attributed these to areas under cultivation.
He also considered some of the formations he observed to be artificial. Irwin gives a military a salute while standing beside the deployed U. He reported finding a number of strange dark patches around Eratosthenes which displayed regular variations each lunar day. Although the Moon is lifeless, American astronauts have landed there during the Apollo missions of the s and s.
The first lunar base is sure to follow, and only then will future generations of observers be able to look up at the Moon and describe it as a truly habited world. Observers in the northern hemisphere may be able to witness this event but Mercury quickly vanishes into the solar glare for viewers in southern temperate latitudes, reappearing by the end of the month in the evening sky.
However, even those in the north lose sight of the planet by mid-month as Mercury undergoes superior conjunction the third one this year on 21 September. VENUS is found just over a degree south of the first-magnitude star Spica in the constellation of Virgo on the first day of the month.
Four days later the planet reaches aphelion. Greatest brilliancy, a delicate balance of planetary phase and distance from the Earth, is on 21 September when Venus achieves magnitude —4. This bright object is easily visible from southern temperate latitudes all month but it is getting quite low in the north west as seen from regions farther north.
The Sun is directly over the equator on this day, passing from the northern hemisphere to the south hemisphere, and signalling the beginning of astronomical autumn in the north and astronomical spring in southern latitudes. This year, the Harvest Moon occurs on 25 September. MARS reaches perihelion on 16 September. Observers on Earth can see the waxing gibbous Moon pass near by Mars four days later. It continues to be well-placed for viewing from tropical and southern latitudes, high in Capricornus at sunset.
From the southern hemisphere it appears high in the west at sunset but disappears before midnight. The waxing crescent Moon is close by on 14 September. Jupiter is shining at magnitude —1. The rings of the planet are at their most open as viewed from the Earth on 18 September and one week later, Saturn reaches east quadrature. This should provide excellent viewing and photographic opportunities, especially for observers in tropical and southern latitudes, as the shadows of the planet, rings and moons are cast at their most extreme angles as seen from our vantage point on Earth.
It is usefully placed for observation this month as it approaches its October opposition. The Moon has been making close passes to this planet all year and this month is no exception, with the appulse occurring on 27 September. This is too faint to see with the naked eye, even under dark skies, so binoculars are required. This group was originally called Apparatus Sculptoris, a name which has since been shortened to Sculptor the Sculptor.
Sculptor is situated immediately to the east of the neighbouring constellation Piscis Austrinus, the brightest member of which is Fomalhaut, which is included on the chart as a guide.
Somewhat closer is magnitude 4. For the northern hemisphere, this is a poor apparition, with Mercury never gaining much altitude above the western horizon. VENUS rapidly disappears from northern hemisphere skies but remains visible until mid- month as seen from southern temperate latitudes. Its crescent shape becomes ever thinner until it disappears altogether during inferior conjunction on 26 October. Earlier in the month, on 5 October, Venus changes direction, moving from direct to retrograde motion.
It is low in the south east as night falls in the northern hemisphere and sets around midnight but southern observers can see the planet quite high in the sky during the evening hours.
On 11 October, it is found near the waxing crescent Moon and on 29 October, it has a close encounter with Mercury. Jupiter is still found in the faint constellation of Libra. However, it is quite high in the west after sunset in the southern hemisphere and sets around midnight. The waxing crescent Moon passes within 1. Look for the ringed planet in Sagittarius.
On 20 October, it is slightly north of the waxing gibbous Moon in Aquarius. Mission to Mercury: BepiColombo.
In spite of the fact that Mercury orbits the Sun at a mean distance of just The BepiColombo mission is extremely challenging due to Mercury being the closest planet to the Sun and constantly bathed in a stream of energetic charged particles the solar-wind constantly streaming out from our parent star.
Fortunately for BepiColombo, the Sun is now going through a quiet phase with sunspot minima expected to occur sometime in Here it will remain for a few days while mission managers carry out instrument checks to ensure that its solar-electric propulsion system is working properly and that the high-gain antenna is communicating correctly.
The spacecraft will then embark on a 7. Four final thruster burns will further reduce the relative velocity to a point in December when the gravitational pull of Mercury will capture the spacecraft and draw it into a polar orbit without an orbit insertion manoeuvre being required. Caloris is indeed huge - the interior smooth plains have an area of 1.
The surface of Mercury is similar in appearance to our Moon in that it is strewn with impact craters and basins. With a diameter of 1, kilometres miles the largest of these, and one of the largest features of its type in the solar system, is Caloris Basin, discovered on images taken by the Mariner 10 probe in Mercury is much smaller than the Earth and its inner regions are not as compressed so, for the planet to have such a high density its core must be large and rich in iron.
What we do not know for certain is whether the core is molten or solid in composition. This is topped off with a crust which, based on a mixture of data received from Mariner 10 and Earth-based observation, is estimated to be around 35 kilometres 22 miles thick.
The relatively thin crust is something of a dilemma for planetary scientists. One computer model. It is hoped that, during its planned encounter with the planet, BepiColombo will provide answers to many of the questions we have about Mercury. In the meantime, backyard astronomers can content themselves simply by catching a fleeting glimpse of Mercury in the twilight sky, either just before sunrise or soon after sunset.
This sometimes-elusive little world can be tracked down by checking out and following the information given in the Monthly Sky Notes. On 9 November, the tiny planet is 1. Mercury changes from direct to retrograde motion on 17 November by which time it has vanished from view for northern viewers. It soon disappears for southern observers too as it undergoes inferior conjunction on 27 November. On 29 November, Mercury goes through its fourth and final perihelion of the year.
VENUS passes into the morning sky, visible in the east before sunrise and appearing higher in the sky every morning, brightening all the while. On 14 November, after a little more than a month in retrograde, Venus reaches another stationary point and resumes direct motion. On this day it appears less than half a degree south of first-magnitude Spica in the constellation of Virgo.
This is close enough for Mars to be occulted by the Moon as seen from the southernmost regions of Argentina and Chile, and most of Antarctica. Northern hemisphere viewers are finding that Mars has gained some useful altitude in the south after the sky is fully dark but it does set before midnight. Southern observers continue to have the best views, with Mars high in the north at nightfall and setting a little after midnight.
On 20 November, it moves from Libra into Scorpius. On 11 November at around UT, it is within 1. URANUS was at opposition last month and is still aloft most of the night in Aries, not setting until morning twilight. It appears just north of the waxing gibbous Moon on 20 November. On 17 November, the waxing gibbous Moon passes close by and on 25 November, Neptune arrives at a stationary point, resuming direct motion amongst the background stars of Aquarius. Edmond Halley: A Question of Pronunciation.
November sees the anniversary of the birth, at Haggerston, near London on 8 November , of the English astronomer, scientist, geophysicist, mathematician and meteorologist Edmond Halley, who is best remembered for computing the orbit, and successfully predicting the return to the inner solar system, of the famous comet that now bears his name.
Although he is remembered primarily as an astronomer including being the second Astronomer Royal, succeeding John Flamsteed in and holding the position until his death in , his achievements embrace a wide range of disciplines and include significant discoveries in the fields of mathematics, physics, navigation, meteorology and geophysics.
His fame is reflected in the fact that at least two pubs now bear reference to his name along with several streets and roads, an Antarctic research station, a crater on the Moon and one on Mars and a mountain here on Earth. However, his legacy may be said to include a particular area of controversy in that his surname is one of the most commonly mispronounced words in astronomy.
For example, the early registers of Halifax Parish Church in the West Riding of Yorkshire contain a dozen or more different spellings of the now- standardised name Greenwood. These reflect the way the name was pronounced at the time and the way that the parish officials heard, and subsequently recorded, that pronunciation. Nowadays, of course, the spelling of this and other names have been standardised.
However, the problem has not really gone away. For example, ask anyone who lives in Shrewsbury, Leominster or Bicester how often the names of their towns come across verbally and you will realise this! Anyway, to get back to the issue in hand… the surname Halley, when applied to the astronomer, is a victim of two particularly common mispronunciations. This is an obvious allusion to the rock and roll singer Bill Haley and his backing group The Comets.
Logically, and taking into account the basic spelling of the name, this pronunciation would appear to be the correct one. As noted above, prior to the early 19th century, names were often written down and recorded the way they sounded. In other words, and importantly in this context, the way they were pronounced by the people themselves. In the case of Edmond Halley, perhaps the most famous examples of contemporary sources are the diaries of Samuel Pepys — This is clear evidence, from a reliable contemporary source, of the correct pronunciation of the surname of Edmond Halley.
This is a true and accurate reflection of the pronunciation that Halley himself preferred and which, out of respect to him, the one that we should certainly use today. Best observed from northern temperate latitudes, it is 1. The following day Mercury reaches a stationary point, resuming direct motion. On 15 December, it reaches greatest elongation west.
By this time, it is starting to lose altitude above the eastern horizon. Shining at magnitude —0. VENUS rules the morning sky, reaching greatest brilliancy of magnitude —4. The waning crescent Moon is in close proximity on 3 December and Venus reaches its second perihelion of the year on 26 December. This is the shortest day of the year in the northern hemisphere and the longest day south of the equator, exactly opposite to the June solstice.
Astronomical summer begins in the southern hemisphere and astronomical winter arrives in the north. MARS reaches east quadrature on 3 December, and four days later, it is within half a degree of Neptune.
Although Mars appears higher in the sky from southern temperate latitudes, viewers in both hemispheres have a good chance to see the red planet this month. On 21 December, Mars moves from Aquarius into Pisces. Northern viewers will find it difficult to catch a glimpse of this planet this month.
On 13 December, Jupiter moves from Scorpius to the non-zodiacal constellation of Ophiuchus. Jupiter, shining at magnitude —1.
Saturn is soon lost in the glare of our parent star and is unobservable for most of the month. On 18 December, it encounters the waxing gibbous Moon. The planet is well-placed for viewing in the evening sky, not setting until the early morning hours. On 5 December, the planet is at east quadrature and two days later, it is less than half a degree away from the much brighter planet Mars. Neptune is only eighth magnitude so binoculars or a small telescope will be necessary to observe this appulse in the constellation of Aquarius.
The European spacecraft Gaia is scheduled to end its five-year mission in or around late after successfully mapping the positions of more than a billion stars in the Milky Way Galaxy and Local Group.
The name of the Gaia mission was originally derived as an acronym from Global Astrometric Interferometer for Astrophysics GAIA reflecting the technique of optical interferometry that was originally intended for use on the spacecraft. Although the acronym GAIA no longer applies, the name remains to provide mission continuity. The primary goal of the Gaia mission was to obtain data to allow and facilitate further study of the composition, formation and evolution of the Milky Way Galaxy. During its time in space Gaia has performed an all sky survey, mapping the three dimensional position and velocity of all objects down to 20th magnitude and measuring the positions of more than one billion stars with accuracy down to 24 micro-arc-seconds.
A light year is the distance that a beam of light, travelling at around , kilometres , miles per second, would travel in a year and is equivalent to some 10 trillion kilometres around 6 trillion miles. When the first set of positional data was released in , it became clear that many of the published constellation books and star charts we have come to rely on now need to be revised, many stars having been found to be either further away or closer to us than previously measured.
This image of the galaxy M33 NGC , also known as the Triangulum Spiral, shows tens of thousands of stars detected by Gaia, including a small stellar census in its star-forming region NGC Many of these stars turn out to be further away that previously believed, the best example being Alnilam which is now known to lie more than light years beyond former estimates.
Mintaka, on the other hand, is over light years closer to us than earlier measurements suggested. The Gaia spacecraft has also provided astronomers with a large dataset of measurements to help them in their search for exoplanets — planets that orbit stars other than the Sun.
With access to the high-precision results delivered by Gaia, scientists forecast that it will now be possible to detect some tens of thousands of exoplanets out to around 1, light-years from the Sun. Comets in The year may well be remembered as the year of the periodic comet because of the 72 comets expected to return to perihelion, no fewer than 57 come within the periodic category, having orbital periods of less than 20 years, and consequently having made many perihelion passages over the years.
This is a problem for the backyard observer who does not possess state-of-the-art equipment because, as a rule, these comets do not become much brighter than 12th magnitude, which means that either a large telescope or CCD equipment is required. They do not become bright targets unless they either have an outburst event such as Comet Holmes of or they make close passes to Earth … … and luckily for us, later this year will see a close pass by two of these comets.
This being said, it is worth remembering that comets are being discovered on a regular basis and the next Hale-Bopp or Hyakutake could be discovered at any time!
You can keep up to date with these discoveries by checking out the British Astronomical Association Comet Section page www. The comets listed here should put on a good show, but do remember that comets are very unpredictable and so can either exceed expectations, or fail to live up to expected potential. During January this long-period comet will be at its best, hovering at around magnitude 10, and will be well placed for observers in the northern hemisphere.
The comet reaches perihelion on 9 May at a distance from the Sun of 2. The comet remains well placed throughout the rest of the year and remains at around magnitude 10 or The period for this comet is in the order of 20, years.
Orbital calculations confirmed it to be a periodic comet and it was believed the following two returns would be unfavourable, and indeed it was not until October that it was recovered, by Ernst Zinner of the Bamberg Observatory, Germany. The orbit was refined and the period was determined as 6.
The comet was then linked to the October Draconid meteor shower and, although the comet is at perihelion this year, no significant activity regarding the meteor shower is expected. This apparition is very favourable as the comet is at perihelion on 10 September and just a day later makes its closest approach to Earth at 0. Visually, the comet should be picked up in June, and by the end of August it may have become a naked eye object. This is expected to continue throughout September although it begins to sink southwards soon after, but experienced observers can hope to follow it until the end of October.
This object was initially discovered by the French. It was not until that it was seen again, this by the Finnish astronomer Liisi Oterma, and identified as the comet first discovered by Coggia in It was later found to have an orbital period of The comet brightened rapidly, attaining a magnitude of 8 in early December, and was followed until April With a period between 20 and years, this comet fits the classic Halley-type family of comets. The orbit is also very interesting in that the perihelion point for the comet sits perfectly at the orbit of Mars and its aphelion point very close to the orbit of Uranus which means that close approaches to the aforementioned planets often occur, as was the case in when the comet passed within 1.
One such pass occurs this year as the comet will get down to The comet begins moving rapidly north in November when it should be within binocular range and will remain well placed for northern hemisphere observers in December, when it may attain a magnitude of around 3 and become a naked eye object. We currently know of more than , minor planets and of these some , have been allotted a permanent number, due to their orbits being well defined, and of these over 16, have been given names ranging from musicians to scientists to mythological characters.
The vast majority of these objects lie within the main asteroid belt, located between the orbits of Mars and Jupiter. However, some of these rocky travellers, known as Potentially Hazardous Asteroids PHAs , travel around the Sun in larger elliptical orbits that often bring them into close encounters with the planets.
To date there are 1, known PHAs and around of these are believed to be more than a kilometre in diameter. To qualify as a PHA these objects must have the capability to pass within 8 million km 5 million miles of Earth and to be larger than metres across. A large number of smaller asteroids pass close to the Earth on a regular basis.
These asteroids can be anything from just a few meters in diameter to several tens of meters wide, and of course, much smaller ones enter the Earths atmosphere on a daily basis and burn up harmlessly as meteors. The more serious astronomers interested in following these objects should go to the home page of the Minor Planet Center, whose job it is to keep track of these objects and determine orbits for them.
This page can be accessed by going to www. At the top of the page is a search box that you can use to find information on any object that you are interested in, and from this you can obtain ephemeredes of the chosen subject. Compiled with the help of over 20 expert contributors under the editorship of renowned author and broadcaster Ian Ridpath, the third edition of A Dictionary of Astronomy covers everything from space exploration and the equipment involved, to astrophysics, cosmology, and the concept of time, in over 4, entries.
The dictionary. A Complete System of Astronomy. This accessible and entertaining biography chronicles the life and triumphs of astronomer Jan Hendrik Oort, who helped lay the foundations of modern astronomy in the 20th century.
The book puts into context some of Oort's most significant achievements, including his discovery that the Milky Way rotates, as well as his.
A History of Optical Telescopes in Astronomy. This book is uniquely about the relationship between the optical telescope and astronomy as they developed together. It covers the time between the telescope's pivotal invention in the 's up to the modern era of space-based telescopes. We only index and link to content provided by other sites.
Please contact the content providers to delete copyright contents if any and email us, we'll remove relevant links or contents immediately. Popular ebooks. The Yearbook of Astronomy is the Diamond Jubilee edition of this iconic publication, the annual appearance of which has been eagerly anticipated by astronomers, both amateur and professional, ever since this invaluable book first appeared in As the preface to the edition informed its readers, the post-war years had seen a tremendous growth of interest in astronomy and space research.
Doubtless fuelled by the dawn of the Space Age, the launch of Sputnik 1 in October marked a significant change in the course of history. This epoch-making event, coupled with the subsequent flights of Soviet cosmonaut Yuri Gagarin April and American astronaut Alan Shepard May , served to engender a public interest in astronomy and space that has continued to grow and expand to this day.
To supplement all this is a variety of entertaining and informative articles, a feature for which the Yearbook of Astronomy is known. The Yearbook of Astronomy continues to be essential reading for anyone lured and fascinated by the magic of astronomy. It remains an inspiration to amateur and professional astronomers alike, and warrants a place on the bookshelf of all stargazers and watchers of the Universe.
Bursting with up-to-the-minute information, the Yearbook of Astronomy is, as ever, essential reading for anyone fascinated by the night sky. Yearbook of Astronomy was released on 30 October It is also available at Amazon and at other online book retailers. Maintaining its appealing style and presentation, the Yearbook of Astronomy contains comprehensive jargon-free monthly sky notes and an authoritative set of sky charts to enable backyard astronomers and sky gazers everywhere to plan their viewing of the year's eclipses, comets, meteor showers and minor planets as well as detailing the phases of the Moon and visibility and locations of the planets throughout the year.
The ongoing process of improving and updating what the Yearbook of Astronom y offers to its readers is continued in the edition with the introduction of apparition charts for Mars, Jupiter and Saturn, which ensures that charts are now included for all the major planets in our solar system.
The edition of the Yearbook of Astronomy now includes diagrams showing the positions of Mercury and Venus at sunrise or sunset throughout each apparition, as well as finder charts for Uranus and Neptune. It is also available online at Amazon and at other online book retailers. The edition of the Yearbook of Astronomy will include finder charts showing the positions of Mars, Jupiter and Saturn throughout the year.
To give readers of the edition a preview of these charts, we have prepared downloadable PDF files for these planets in There are two charts for Mars. The red planet slows down as it approaches opposition in October , and the second chart is a close-up view of the region of Pisces and Cetus where Mars may be found between July and December
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