July
2010
Updated: 1 July 2010
Welcome to the night skies of Winter, featuring
Carina, Southern Cross, Centaurus, Scorpius and Saturn
Explanatory Notes
:Rise and
set times are given for the theoretical horizon, which is a flat horizon all the
way round the compass, with no mountains, hills, trees or buildings to obscure
the view. Observers will have to make allowance for their own actual
horizon.
Transient phenomena are provided for the current month and the next. In the list of geocentric events, the nearer object is given first.
When a planet is referred to as ‘stationary’, it means
that its movement across the stellar background appears to have ceased, not that
the planet itself has stopped. With inferior planets (those inside the Earth’s
orbit, Mercury and Venus), this is caused by the planet heading either directly
towards or directly away from the Earth. With superior planets (Mars out to
Pluto), this phenomenon is caused by the planet either beginning or ending its
retrograde loop due to the Earth’s overtaking it.
Apogee and perigee: Maximum and minimum distances of the
Moon or artificial satellite from the Earth.
Aphelion and perihelion: Maximum and minimum distances of a
planet, asteroid or comet from the Sun.
A handspan at arm's length covers
an angle of approximately 20 degrees.
mv = visual magnitude
or brightness. Magnitude 1 stars are very bright, magnitude 2 less so, and
magnitude 6 stars are so faint that the unaided eye can only just detect them
under good, dark conditions. Binoculars will allow us to see down to magnitude
8, and the Observatory telescope can reach magnitude 15. The world's biggest
telescopes have detected stars and galaxies as faint as magnitude 30. The
sixteen very brightest stars are assigned magnitudes of 0 or even -1. The
brightest star, Sirius, has a magnitude of -1.44. Jupiter can reach -2.4, and
Venus can be more than 6 times brighter at magnitude -4.7, bright enough to cast
shadows. The Full Moon can reach magnitude -12 and the Sun magnitude -27. Each
magnitude step is 2.51 times brighter or fainter than the next one, i.e. a
magnitude 3.0 star is 2.51 times brighter than a magnitude 4.0. Magnitude 1.0
stars are exactly 100 times brighter than magnitude 6.0 (5 steps each of 2.51
times, 2.51x2.51x2.51x2.51x2.51 = 2.515 = 100).
Solar
System Sun:
Partial solar eclipse:
On the morning of July 12 next, there will be an eclipse of the Sun in which two-thirds of the Sun will be obscured. Unfortunately, the eclipse will not be visible from the Sunshine Coast, as it will end at 5:08 am, an hour and a half before sunrise.
Moon Phases: Lunations this month: #1082, 1083
Last Quarter:
July 5
0:36 hrs
diameter = 29.9'
New Moon:
July 12
5:40 hrs
diameter = 32.9' Partial
solar eclipse
First Quarter: July 18
20:10 hrs
diameter = 31.8'
Full Moon:
July 26 11:37 hrs
diameter = 29.7'
Last Quarter: August 3
14:59 hrs
diameter = 30.4'
New Moon:
August 10 13:08 hrs
diameter = 33.4'
First Quarter: August 17 4:14 hrs
diameter = 31.3'
Full Moon:
August 25 3:05 hrs
diameter = 29.4'
Lunar Orbital Elements:
July
1:
Moon at apogee (405 063 km) at 20:10 hrs, diameter = 29.5'
July 11: Moon at descending node at
17:28 hrs, diameter = 32.7'
July 13:
Moon at perigee (361 122 km) at 21:22 hrs, diameter = 33.1'
July
24:
Moon at ascending node at 17:59 hrs, diameter = 30.0'
July 29:
Moon at apogee (405 958 km) at 10:20 hrs, diameter = 29.4'
August
8: Moon at descending
node at 3:23 hrs, diameter = 32.6'
August
11: Moon at perigee (357
869 km) at
3:59 hrs, diameter = 33.4'
August
20:
Moon at ascending node at 22:15 hrs, diameter = 30.0'
August
25:
Moon at apogee (406 370 km) at 15:58 hrs, diameter = 29.4'
Moon at 8 days after New, as on July 19
Moon at 9 days after New, as on July 20
The two photographs above show the Mare Imbrium area in the Moon's northern hemisphere. They were taken a day apart, just after First Quarter. Mare Imbrium (the Sea of Rains) is a large lava flow caused by the Imbrium Event - a cataclysmic collision of an asteroid with the Moon many millions of years ago. A comparison of the two photographs will show how the appearance of lunar features changes with the angle of the Sun.
In the first photograph, Mare Imbrium (left) is separated from Mare Serenitatis (right) by two ranges of mountains, the Alps to the north and the Apennines to the south. Two large craters at upper right are Aristoteles and Eudoxus. The straight Alpine Valley may be seen cutting through the Alps. Mt Piton (height 2000 metres) is visible as a bright spot with a shadow, due south of the southern end of the Alpine Valley. Archimedes is the large crater at left. It is a walled plain 80 kilometres in diameter with a flat floor. To its right are two bowl-shaped craters, Aristillus and Autolycus. These craters are all formed by impact with large meteors. Apollo 15 landed close by the Apennines, in a small enclosed area to the right and below Archimedes, on the picture's central vertical axis.
In the second photograph, the sunrise line (called the 'terminator') has moved to the left, revealing a large walled plain in the Alps, known as Plato. South of Plato, an isolated mountain protruding through the lava flow is called Mt Pico. Ripples in the lava, called 'wrinkle ridges', are visible. The crater at lower left is Timocharis, 42 kilometres in diameter.
A detailed map of the Moon's near side is available here.
A rotatable view of the Moon, with ability to zoom in close to the surface, and giving detailed information on each feature, may be downloaded here.Click
here for a photographic animation showing the lunar phases. It also shows the Moon's wobble or libration, and how its apparent size changes as it moves from perigee to apogee each month. It takes a little while to load, but once running is very cool !
Geocentric Events:
July 4:
Moon 6º
north
of Uranus at 0:29 hrs
July 4:
Earth at perihelion at 0:31 hrs
July 4:
Moon
7º
north of Jupiter at 5:06
hrs
July 5:
Uranus at western stationary point at 23:43 hrs (diameter = 3.5")
July 8:
Moon occults some stars in the Pleiades star cluster between 18:08 and 19:21hrs
(not visible from Nambour)
July 10:
Venus
1º
north of the star Regulus (Alpha
Leonis, mv
= 1.36)
at 21:48 hrs
July 11:
Moon
2.1º
north of the star Mu
Geminorum, (mv=
2.87) at
6:54 hrs
July 11: Moon 1.4º
south
of the star Mebsuta (Epsilon Geminorum, mv=
3.06)
at 13:59 hrs
July 13:
Moon
3.2º
south
of Mercury at 8:06 hrs
July 15:
Moon
4.8º
south
of Venus at 6:35 hrs
July 16:
Moon
4.8º
south
of Mars at 10:05 hrs
July 17:
Moon
7.2º
south of Saturn at
1:35 hrs
July 22:
Waxing gibbous Moon occults the star Omicron Scorpii (mv
= 4.55)
between 1:07 and 2:06 hrs
July 22:
Moon
1.3º
north of the star Sigma Scorpii (mv=
2.9)
at 0:27 hrs
July 22: Moon 2.3º
north of the star Antares (Alpha
Scorpii, mv
= 1.06)
at 3:53 hrs
July 23:
Jupiter at western stationary point at 21:17 hrs
July 24:
Moon 5.6º
south
of Pluto at 2:12 hrs
July 24: Moon 2.3º
north
of the star Kaus Borealis (Lambda Sagittarii, mv= 2.82)
at 6:47 hrs
July 25: Limb
of Moon 21 arcminutes south
of the star Pi Sagittarii (mv=
2.88)
at 2:51 hrs
July 25:
Mars 8.5 arcminutes south of the star Zavijava (Beta Virginis, mv=
3.59
) at 17:21 hrs
July 28:
Moon
4.7º
north of Neptune at 13:09
hrs
July 31:
Moon
6.6º
north of Uranus at 6:57 hrs
July 31:
Moon
7º
north of Jupiter at 13:09
hrs
July 31:
Mars
1.8º
south of Saturn at 16:44
hrs
August 4:
Venus 51.5 arcminutes south of the star Zavijava (Beta Virginis, mv=
3.59
) at 22:05 hrs
August 5: Moon occults
stars in the Pleiades star cluster between 00:41 hrs and 2:47 am
August 7: Mercury at
Greatest Elongation East (27.2º)
at 6:16 hrs (diameter = 7.6")
August 7: Moon
1.4º
north of the star Mu Geminorum (mv=
2.87) at
17:13 hrs
August 8: Moon 1.7º
south
of the star Mebsuta (Epsilon Geminorum, mv=
3.06)
at 00:24 hrs
August 8: Mercury at
aphelion at 20:07 hrs (diameter = 7.8")
August 8: Venus
2.7º
south of Saturn at 20:40
hrs
August 12: Moon
1.5º
south of Mercury at 9:54
hrs
August 13: Moon
4.2º
south of Venus at 18:48 hrs
August 13: Moon
5.1º
south of Mars at 23:11 hrs
August 17: Moon 27 arcminutes south of
the star Dschubba (Delta Scorpii, mv=
2.29)
at 22:29 hrs
August 18: Moon
1.9º
north
of the star Sigma Scorpii (mv=
2.9)
at 6:06 hrs
August 18: Moon
2.6º
north
of the star Antares (Alpha
Scorpii, mv
= 1.06)
at 9:31 hrs
August 19: Venus
1.9º
south of Mars at 14:36 hrs
August 20: Venus at Greatest
Elongation East (46º)
at 2:34 hrs (diameter = 24.3")
August 20: Moon
5º
south of Pluto at 6:57 hrs
August 20: Moon
2.2º
north
of the star Kaus Borealis (Lambda Sagittarii, mv= 2.82)
at 12:29 hrs
August 20: Neptune at opposition at
19:55 hrs (diameter = 2.3")
August 21: Mercury at eastern
stationary point at 6:02 hrs (diameter = 9.6")
August 21: Moon 2 arcminutes south of
the star Pi Sagittarii (mv=
2.88)
at 8:34 hrs
August 24: Moon
4.2º
north
of Neptune at 17:52 hrs
August 27: Moon
6.1º
north
of Uranus at 11:48 hrs
August 27: Moon
6.7º
north
of Jupiter at 15:39 hrs
The Planets for this month:
Mercury: The innermost planet passed behind the Sun (superior conjunction) on June 28, and this month will re-appear in the evening sky, between Venus and the north-western horizon at dusk. Mercury will be easiest to see in the first week of August.
V
enus: The brightest planet is now dominating the twilight sky, and can be easily seen above the north-western horizon as daylight begins to fade. The waxing crescent Moon will be close to Venus on July 14 and 15. At mid-month, the magnitude (brightness) of Venus will be -4.1 and its angular diameter will be 17 arcseconds. Its phase will be 65%.(The coloured fringes to the first and third images below are due to refractive effects in our own atmosphere, and are not intrinsic to Venus. The planet was closer to the horizon when these images were taken than it was for the second photograph, which was taken when Venus was at its greatest elongation from the Sun).
Click
here for a photographic animation showing the Venusian phases. Venus is always far brighter than anything else in the sky except for the Sun and Moon. Up until last December, Venus appeared as a 'Morning Star', but now it is an 'Evening Star' once again. Each of these appearances lasts about eight to nine months.Because Venus was visible as the 'Evening Star' and as the 'Morning Star', astronomers of ancient times believed that it was two different objects. They called it Hesperus when it appeared in the evening sky and Phosphorus when it was seen before dawn. They also realised that these objects moved with respect to the so-called 'fixed stars' and so were not really stars themselves, but planets (from the Greek word for 'wanderers'). When it was finally realised that the two objects were one and the same, the two names were dropped and the Greeks applied a new name Aphrodite (Goddess of Love) to the planet, to counter Ares (God of War). We use the Roman versions of these names, Venus and Mars, for these two planets.
Mars:
Mars has now been left far behind by the Earth, and this month presents a disc only 5 arcseconds in diameter. During July its magnitude is only 1.5, a little fainter than the stars Regulus and Spica, but brighter than the stars Denebola and Porrima. All four stars are not far from Mars this month. In mid-July, Mars will be about two handspans above the north-western horizon at 6 pm.Watch Mars as it heads through Leo this month. It will across into Virgo on July 20 and will reach Saturn on July 31. They will be joined by Venus on August 5, and the crescent Moon will pass by the three planets on August 13. Mercury will also be close by.
In this image, the south polar cap of Mars is easily seen. Above it is a dark triangular area known as Syrtis Major. Dark Sinus Sabaeus runs off to the left, just south of the equator. Between the south polar cap and the equator is a large desert called Hellas. The desert to upper left is known as Aeria, and that to the north-east of Syrtis Major is called Isidis Regio. Photograph taken in 1971.
Jupiter:
The giant planet is now dominating the eastern pre-dawn sky, in the constellation Pisces. At the beginning of July it rises due east a little after 11:15 pm. Jupiter passed Uranus at an angular distance of only 26 arcminutes on June 8. It will continue to move away from Uranus until July 23, when it will cease its easterly movement and begin its retrograde loop, back towards Uranus. It will pass Uranus again, moving in the opposite direction, on September 19, when the two planets will be 48 arcminutes apart. Two days later, both planets will be at opposition.
Saturn: The ringed planet
is in the constellation Virgo, and passed through opposition on March 22. Saturn is still observable in July, and the Ring system is opening up once again. It appears as a bright cream-coloured object a little less than three handspans above the north-western horizon at 7 pm on July 1.Sa
turn is presently midway between the first magnitude stars Regulus and Spica, and brighter than either. It is less than two degrees from the third magnitude star Zavijava. Slow-moving Saturn passed from Leo into Virgo on September 2 last year, and will take three and a quarter years to move right across Virgo into Libra.Saturn’s rings are always a magnificent sight, but at present they are very narrow, slowly widening. In early October 2009 a new, large ring around Saturn was discovered by the Spitzer Infrared Space Telescope. Although the new ring cannot be seen by ordinary telescopes, the familiar ring system seen in visible-light images can be detected in even the smallest telescope.
Uranus:
This planet reached conjunction on March 17, and at mid-month rises at about 10:15 pm. Its magnitude is 5.8 and its diameter is 4 arcseconds. Its proximity to Jupiter makes it easy to locate with binoculars.
Neptune: The icy blue planet passed through conjunction on February 15, and reached western quadrature on May 20. On July 1 it rises in the constellation Aquarius a little before 9 pm. It currently nearly two handspans above Jupiter, but a telescope is needed to observe it. It reaches opposition on August 20.
Neptune, photographed from Nambour on October 31, 2008
Pluto:
The erstwhile ninth and most distant planet is a faint 14.1 magnitude object in the constellation Sagittarius, near the boundary with Scutum (The Shield). It is currently passing through the great Sagittarius star cloud, close to the cluster M24, and about 2 degrees south of the Omega (or Swan) Nebula, M17. A powerful telescope is needed to detect Pluto, which even under excellent seeing conditions appears as a very faint star-like object. It is now observable for all of the night, and reached opposition on June 26. Its angular diameter is 0.13 arcseconds, less than one twentieth of the size of Neptune.
The movement of Pluto in two days, between 13 and 15 September, 2008. Pluto is
the one object that has moved.
Width of field: 200 arcseconds
Meteor Showers:
Pegasids July 10 Waning crescent Moon, 6% sunlit
ZHR = 8S Delta Aquarids
July 29
Waning gibbous Moon, 91%
sunlit ZHR = 20 Alpha Capricornids
July 30
Waning gibbous Moon, 86% sunlit ZHR =
8
Radiant:
Between the stars Skat and Deneb Algedi
Radiant: Near the star Algedi
Use this Fluxtimator to calculate the number of meteors predicted per hour for any meteor swarm on any date, for any place in the world.
Although most meteors are found in swarms associated with debris from comets, there are numerous 'loners', meteors travelling on solitary paths through space. When these enter our atmosphere, unannounced and at any time, they are known as 'sporadics'. Oan average clear and dark evening, an observer can expect to see about ten meteors per hour. They burn up to ash in their passage through our atmosphere. The ash slowly settles to the ground as meteoric dust. The Earth gains about 80 tonnes of such dust every day, so a percentage of the soil we walk on is actually interplanetary in origin. If a meteor survives its passage through the air and reaches the ground, it is called a 'meteorite'. One caused great alarm in Canada recently, being recorded on a camera mounted on the dashboard of a police cruiser. In the past, large meteorites (possibly comet nuclei or small asteroids) collided with the Earth and produced huge craters which still exist today. These craters are called 'astroblemes'. Two famous ones in Australia are Wolfe Creek Crater and Gosse's Bluff. The Moon and Mercury are covered with such astroblemes, and craters are also found on Venus, Mars, planetary satellites, minor planets, asteroids and even comets.
Comets
Comet Lulin
This comet, (C/2007 N3), discovered in 2007 at Lulin Observatory by a collaborative team of Taiwanese and Chinese astronomers, is now heading towards the outer Solar System, and has faded below magnitude 12.
.
T
he LINEAR robotic telescope operated by Lincoln Near Earth Asteroid Research is used to photograph the night skies, searching for asteroids which may be on a collision course with Earth. It has also proved very successful in discovering comets, all of which are named ‘Comet LINEAR’ after the centre's initials. This name is followed by further identifying letters and numbers. Generally though, comets are named after their discoverer, or joint discoverers. There are a number of other comet and near-Earth asteroid search programs using robotic telescopes and observatory telescopes, such as:Nearly all of these programs are based in the northern hemisphere, leaving gaps in the coverage of the southern sky. These gaps are the areas of sky where amateur astronomers look for comets from their backyard observatories.
To find out more about current comets, including finder charts showing exact positions and magnitudes, click
here. To see pictures of these comets, click here.
The 3.9 metre Anglo-Australian Telescope (AAT) at the Australian Astronomical Observatory near Coonabarabran, NSW
Deep Space
Sky Charts and Maps available on-line
There are some useful representations of the sky available here. The sky charts linked below show the sky as it appears to the unaided eye. Stars rise four minutes earlier each night, so at the end of a week the stars have gained about half an hour. After a month they have gained two hours. In other words, the stars that were positioned in the sky at 8 pm at the beginning of a month will have the same positions at 6 pm by the end of that month. After 12 months the stars have gained 12 x 2 hours = 24 hours = 1 day, so after a year the stars have returned to their original positions for the chosen time. This accounts for the slow changing of the starry sky as the seasons progress.
The following interactive sky charts are courtesy of Sky and Telescope magazine. They can simulate a view of the sky from any location on Earth at any time of day or night between the years 1600 and 2400. You can also print an all-sky map. A Java-enabled web browser is required. You will need to specify the location, date and time before the charts are generated. The accuracy of the charts will depend on your computer’s clock being set to the correct time and date.
To produce a real-time sky chart (i.e. a chart showing the sky at the instant the chart is generated), enter the name of your nearest city and the country. You will also need to enter the approximate latitude and longitude of your observing site. For the Sunshine Coast, these are:
latitude: 26.6o South longitude: 153o East
Then enter your time, by scrolling down through the list of cities to "Brisbane: UT + 10 hours". Enter this one if you are located near this city, as Nambour is. The code means that Brisbane is ten hours ahead of Universal Time (UT), which is related to Greenwich Mean Time (GMT), the time observed at longitude 0o, which passes through London, England.
Click here to generate these charts._____________________________________
The first, circular chart will show the full hemisphere of sky overhead. The zenith is at the centre of the circle, and the cardinal points are shown around the circumference, which marks the horizon. The chart also shows the positions of the Moon and planets at that time. As the chart is rather cluttered, click on a part of it to show that section of the sky in greater detail. Also, click on Update to make the screen concurrent with the ever-moving sky.
The stars and constellations around the horizon to an elevation of about 40o
can be examined by clicking onView horizon at this observing site
.The view can be panned around the horizon, 45 degrees at a time. Scrolling down the screen will reveal tables showing setup and customising options, and an Ephemeris showing the positions of the Sun, Moon and planets, and whether they are visible at the time or not. These charts and data are from YourSky, produced by John Walker.
The charts above and the descriptions below assume that the observer has a good observing site with a low, flat horizon that is not too much obscured by buildings or trees. Detection of fainter sky objects is greatly assisted if the observer can avoid bright lights, or, ideally, travel to a dark sky site. On the Sunshine Coast, one merely has to travel a few kilometres west of the coastal strip to enjoy magnificent sky views. On the Blackall Range, simply avoid streetlights. Allow your eyes about 15 minutes to become dark-adapted, a little longer if you have been watching television. Small binoculars can provide some amazing views, and with a small telescope, the sky’s the limit.
The Eta Carinae Nebula, to the right of the Southern Cross tonight
The
The
se descriptions of the night sky are for 8 pm on July 1 and 6 pm on July 31. They start at the western horizon.Close to the western horizon is the second magnitude star Alphard. This is an orange star that was known by Arabs in ancient times as 'The Solitary One’, as it lies in an area of sky with no bright stars nearby.
In the north-west, Leo the Lion is preparing to set. It will have completely disappeared by 10.30 pm. The bright star Regulus (Alpha Leonis) marks the Lion’s heart. A handspan to the right and above Regulus is Denebola, a white star marking the tip of the lion's tail. It is about 30 degrees above the north-western horizon. We see the lion upside-down from the Southern Hemisphere. Regulus is the western-most star in a pattern called 'The Sickle' (or reaping-hook). It marks the end of the Sickle's handle, with the other end of the handle, the star Eta Leonis, below and to the right. The blade of the Sickle curves around clockwise from Eta Leonis to the horizon. The Sickle forms the mane and head of the lion, when observed right-way-up. The Sickle is just touching the theoretical horizon at this time tonight. The planet Venus passes through the stars of the Sickle in the first half of the month. Mars begins July between Leo's front and hind legs. It crosses into Virgo on July 19.
The constellation Leo, as we see it from Australia. Regulus is above centre left, and Denebola above centre right. The Sickle curves down from Regulus.
High in the north, (about 43 degrees above the horizon, and about 10 degrees west of the meridian or north-south line) we can find the fourth brightest star in the night sky, Arcturus. It is outshone only by Sirius, Canopus and Alpha Centauri. Arcturus differs from those just named, for it is an obvious orange colour, a K2 star of zero magnitude.