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October 2013 Observing Guide
- Neill
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10 years 7 months ago - 10 years 7 months ago #98785
by Neill
October 2013 Observing Guide was created by Neill
OBSERVING GUIDE
(Please note all times are ST unless otherwise stated and are based on the location of Belfast and covers October)
The Sun
At the start of the month, the Sun rises at 07:30 and sets at 19:00. By month's end, it rises at 07:25 UT and sets at 16:50 UT.
The Planets
Mercury is not visible this month.
Venus is visible in the evening sky this month, albeit it stays very low relative to the horizon. At start of the month, it sets at 20:00 and by month's end at 18:25 UT. It moves from Libra to Scorpius and brightens from mag -4.2 to mag -4.5 during the month.
Mars is visible in the morning sky this month. At the start of the month, it rises at 02:45 and by month's end at 01:35 UT. It moves from Sextans to Leo and brightens from mag +1.6 to mag +1.5 during the month. It is at conjunction with Regulus (Alpha (α) Leonis, mag +1.4) on the morning of the 15th, lying 1° to the N of the star.
Jupiter becomes visible in the evening sky this month in Gemini and is at Eastern Quadrature on the 12th. At the start of the month, it rises at 23:40 and by month's end, it rises at 20:50 UT. It brightens from mag -2.2 to mag -2.4 during the month.
Saturn is not visible this month.
Uranus is at opposition on the 3rd and is visible in the evening sky this month in Pisces. During the month, it rises during daylight hours and sets at 04:45 UT by month’s end. It maintains its brightness at mag +5.7 during the month and lies less than 5° to the S of Kaht (Epsilon (ε) Piscium, mag +4.3) and Linteum (Delta (δ) Piscium, mag +4.4).
Neptune is visible in the evening sky this month in Aquarius. During the month, it rises during daylight hours and sets at 01:05 UT by month’s end. It brightens from mag +7.8 to mag +7.9 during the month and lies between Sigma (ς) Aquarii (mag +4.
and Iota (ι) Aquarii (mag +4.3).
The Moon
The new moon is on the 5th with the first quarter moon on the 12th and the full moon on the 19th. The last quarter moon is on the 27th.
There is a penumbral lunar eclipse on the night of the 18th. At its peak 76% of the moon will lay inside the Earth’s outer shadow with the Southern limb darker than usual. It starts at 22:51 with the peak occurring at 00:50 and the eclipse ending at 02:50.
On the morning of the 2nd, the waning crescent moon lies to the S of Regulus (Alpha (α) Leonis, mag +1.4) at around 06:00.
On the evening of the 8th, the waxing crescent moon lies to the N of Venus at around 19:00.
On the evening of the 14th, the waxing gibbous moon lies to the NW of Neptune at around 20:00.
On the evening of the 17th, the waxing gibbous moon lies 6° to the N of Uranus at around 20:00.
On the evenings of the 21st and 22nd, the waning gibbous moon lies near to Aldebaran (Alpha (α) Tauri, mag +0.9). On the 21st, it lies to the NW of the star and on the following evening, it lies 6° to the E of it. The moon also lies to the S of M45 - The Pleiades on the 21st. On both evenings, look at around 22:00.
On the evening of the 23rd, the waning gibbous moon lies 7° to the W of M35 at around 22:00.
On the evenings of the 24th and 25th, the waning gibbous moon lies near to Jupiter. On the 24th, it lies to the W of the planet. On the following evening, it lies to the SW of it. On both evenings, look at around midnight.
On the morning of the 27th, the last quarter moon lies 8° to the SW of M44 – The Beehive Cluster at around 01:00.
On the mornings of the 29th and 30th, the waning crescent moon lies near to Mars. On the 29th, it lies to the NW of the planet, on the following morning it lies to the S of it. It also lies 8° to the SW of Regulus (Alpha (α) Leonis, mag +1.4) on the 29th. On both mornings, look at around 03:00.
Meteors
The best time to observe meteor showers is when the moon is below the horizon; otherwise its bright glare limits the number you will see especially the fainter ones. Below is a guide to this month's showers.
The Orionids peak on the morning of the 21st with a ZHR of 20. The radiant is visible from 01:00 on the morning of the 21st, but the view is spoilt by a waning gibbous moon in Aries.
There are additional minor showers this month, details of which can be found at meteorshowersonline.com/calendar.html or www.imo.net/calendar/2013
Asteroids
Asteroid (42) Isis is at opposition on the morning of the 20th at mag +9.9. It can be found in Cetus and is visible from 22:00 on the evening of the 19th.
Asteroid (20) Massalia is at opposition on the evening of the 31st at mag +8.7. It can be found in Aries and is visible from 18:00 UT on the evening of the 31st.
Finder charts and further information about other fainter asteroids can be found at; britastro.org/computing/charts_asteroid.html in the source list below.
Comets
C/2012 S1 (ISON) has had a lot of publicity. Current information has it peaking in brightness similar to Jupiter, maybe as bright as Venus when it is at perihelion on Nov 28th. There is a high level of uncertainty about how bright this comet will get so the closer to the 28th we get, the more accurate the predictions will become. It passes very close (around 1 million miles) to the Sun’s surface at perihelion so there is a chance it may not survive the encounter, will just have to wait and see!
In October, it is heading through Leo and lies less than 2° to the N of Mars on the morning of the 1st. On the morning of the 15th, it lies 1° to the N of Mars which in turn lies 1° to the N of Regulus (Alpha (α) Leonis, mag +1.4). On the morning of the 30th, it lies less than 1° to the NW of Chi (χ) Leonis (mag+4.6). It is visible from 04:00 at the start of the month with it visible from 04:00 at mid-month and from 03:00 UT by month’s end. Current estimates have the comet at mag +13 and it is expected to brighten during October and November.
2P/Encke is also at perihelion in November (21st) with it expected to peak at mag +7. During October it starts the month in Lynx when it visible from midnight. It then heads into Leo Minor by mid-month, visible from 03:00 and ends the month in Leo, again visible from 03:00 UT. On the morning of the 27th, it lies less than 4° to the N of Denebola (Beta (β) Leonis, mag +2.0). It is expected to be mag +8/9 during October and brightening.
Finder charts and further information about other fainter comets can be found at www.aerith.net , cometchasing.skyhound.com , www.ast.cam.ac.uk/%7Ejds/ , in-the-sky.org , kometen.fg-vds.de/fgk_hpe.htm and www.rasnz.org.nz in the source list below. Any above estimates for predicting a comet's brightness are based on current information at the time of writing the guide and the comet may be brighter/dimmer than the above predictions.
Deep Sky
On the deep sky front this month, galaxies M81 and M82 can be observed in Ursa Major. In Lyra – M57 – The Ring Nebula can be observed and in Vulpecula – M27 – The Dumbbell Nebula can be found. In Andromeda, M31 – The Andromeda galaxy can be observed along with its satellite galaxies M32 and M110. In Perseus, there is the open cluster M34 and the excellent Double Cluster – NGC 869 and 884. In Triangulum, there is the galaxy M33. Auriga reappears with its three open clusters M36, M37 and M38 as does Taurus with the excellent Pleiades – M45 and the Hyades. Orion returns to our skies with M42 – The Great Orion Nebula along with Gemini with the open cluster M35.
General Notes
Always keep an eye out for Aurorae. On the morning of the 27th at 2am, the clocks go back one hour and summer time ends.
Other interesting naked eye phenomena to look out for include the Zodiacal Light and the Gegenschein. Both are caused by sunlight reflecting off dust particles which are present in the solar system. The Zodiacal Light can be seen in the West after evening twilight has disappeared or in the East before the morning twilight. The best time of year to see the phenomenon is late-Feb to early-April in the evening sky and September/October in the morning sky - it's then that the ecliptic, along which the cone of the zodiacal light lies, is steepest in our skies. The Gegenschein can be seen in the area of the sky opposite the sun. To view either, you must get yourself to a very dark site to cut out the light pollution. When trying to observe either of these phenomena, it is best to do so when the moon is below the horizon. A new appendix has been added explaining some of the more technical terms used in the guide.
Clear Skies
Neill McKeown
Information Sources Used and Links
www.skyviewcafe.com ; Sky at Night Magazine Observing Guide and CD; www.aerith.net ; cometchasing.skyhound.com ; www.ast.cam.ac.uk/%7Ejds/ ; kometen.fg-vds.de/fgk_hpe.htm ; www.rasnz.org.nz ; Stardust Magazine; britastro.org/computing/charts_asteroid.html ; in-the-sky.org ;
Philip's Stargazing 2013; Patrick Moore's 2013 Yearbook of Astronomy; www.heavens-above.com ; www.spaceweather.com ;meteorshowersonline.com/calendar.html ; www.timeanddate.com/astronomy/ ; www.imo.net/calendar/2013 - International Meteor Organisation;messier.seds.org/ - The Messier Catalogue website; www.seds.org/messier/xtra/ngc/ngc.html - NGC Catalogue website; www.irishastronomy.org - Irish Federation of Astronomy Societies Website; irishastro.org.uk - Irish Astronomical Association website; www.eaas.co.uk - Northern Ireland Amateur Astronomy Society;
Appendix
The ZHR or Zenithal Hourly Rate is the number of meteors an observer would see in one hour under a clear, dark sky with a limiting apparent magnitude of 6.5 and if the radiant of the shower were in the zenith. The rate that can effectively be seen is nearly always lower and decreases as the radiant is closer to the horizon. The Zenith is the overhead point in the sky.
The radiant is the point in the sky, from which (to a planetary observer) meteors appear to originate, i.e. the Perseids, for example, are meteors which appear to come from a point within the constellation of Perseus. When the radiant is quoted as "circumpolar", it is never below the horizon and visible all night, otherwise the times quoted are when the constellation in which the radiant lies rises above the horizon in the East.
A fireball is defined by the International Astronomical Union as a meteor brighter than any of the planets, i.e. magnitude -4 or brighter. The International Meteor Organisation alternatively defines it as a meteor which would have a magnitude of -3 or brighter at the zenith.
The ° symbol in the guide is that for degrees. A degree is two full moon widths to give an idea for judging any distances quoted in the guide. There are 60 arcminutes in a degree.
An asterism is a collection of stars seen in Earth's sky which form simple patterns which are easy to identify, i.e. the Big Dipper. They can be formed from stars within the same constellation or by stars from more than one constellation. Like the constellations, they are a line of sight phenomenon and the stars whilst visible in the same general direction, are not physically related and are often at significantly different distances from Earth.
Mag is short for magnitude which is the measure of an object's brightness. The smaller the number, the brighter the object. The brightest object in the sky is the Sun at mag -26, the full moon is mag -12 and Venus the brightest planet is mag -4. The brightest stars are mag -1. If there is a 1 mag difference between two objects - there is a difference in brightness of a factor of 2.5 between the two objects. For example the full moon is eight magnitudes brighter than Venus on average which means it is 1,526 times brighter than Venus. Objects down to mag +6 can be seen with the naked eye under very dark skies.
Local time is always quoted in the guide and this means for November - February - universal time (UT)/GMT is used and for April to September - daylight savings time (DST, = GMT+1). For the months of March and October when the clocks go forward/back respectively, both times will be used and attention should be paid to any times at the end of these months for that change.
Deep Sky Objects such as galaxies, nebulae and star clusters are classified in catalogues such as the Messier catalogue for objects like M44 - M for Messier. Another example of a catalogue would the New General catalogue whose objects have the prefix NGC. There are links for websites to both catalogues in the section above.
Perihelion is the point in the orbit of a planet, asteroid or comet where it is nearest to the sun. It is the opposite of Aphelion, which is when the object is at the farthest point in its orbit from the sun.
The Planets
From Earth - Mercury and Venus are the inner planets in the solar system and Mars, Jupiter, Saturn, Uranus and Neptune are the outer planets. Below is a short guide as to how both the inner and outer planets move around the sun.
The Inner Planets
These are best seen when at Greatest Eastern/Western elongation and are not visible when at either Inferior/Superior conjunction. Greatest Eastern elongation is when the inner planet is at its furthest point east from the sun as seen from Earth and visible in the evening sky in the West after sunset, Western elongation is when it’s at its furthest point west from the sun as seen from Earth and visible in the morning sky in the East before sunset. Inferior conjunction occurs when the inner planet is between the Sun and the Earth. Superior conjunction occurs when the inner planet is on the other side of the Sun as seen from Earth.
From our Northerly latitudes, the ecliptic, along which the planets move, lies at a very shallow angle to the horizon after sunset in the autumn and before sunrise in the spring. This means that any of the planets will be difficult to see when fairly close to the Sun in the evening sky in the autumn or in the morning sky in the spring. In particular, Mercury is more or less invisible from here when at Eastern elongation in the autumn or at Western elongation in the spring, because it lies so close to the horizon and is never above the horizon except in daylight or bright twilight.
The normal cycle for an inner planet is Superior Conjunction - Greatest Eastern Elongation - Inferior Conjunction - Greatest Western Elongation - Superior Conjunction. After superior conjunction, the planet moves away from the Sun as seen from Earth and becomes visible in the evening sky after a period of time. It then moves past the point of Greatest Eastern Elongation and moves back towards the Sun as seen from Earth until a point when it is not visible and at Inferior Conjunction. After this the planet appears in the morning sky for a time, before again slipping into the Sun's glare as seen from Earth. The duration of this cycle will depend on the planet's closeness to the Sun, i.e. Mercury completes the above cycle in around 4 months.
The Outer Planets
These are best seen when at opposition and are not visible when at conjunction. Opposition occurs when the earth is between the sun and the outer planet. It is the best time to observe them because the planet is visible all through the night and it is due South and at its highest at about midnight. The planet is also at its closest point in its orbit to Earth - making it appear brighter. Conjunction occurs when the outer planet is on the other side of the Sun as seen from Earth.
If the planet is at or near it furthest point South along the ecliptic, then it won't get very high in the sky even at opposition - just as the Sun never gets high in the sky in midwinter. This happens when opposition occurs near midsummer when the planet is opposite the Sun in the sky and in midsummer the Sun is high, so the planet will be low. The opposite of course applies in winter.
The normal cycle for an outer planet is Conjunction - Western Quadrature - Opposition - Eastern Quadrature - Conjunction. After conjunction, the planet moves away from the Sun as seen from Earth and becomes visible again. The planet from this point on rises earlier and earlier in the morning sky and eventually becomes visible in the evening sky. At Western Quadrature it is at its highest at sunrise and by opposition it is in the same position by midnight. By Eastern Quadrature, it is past its best and is at its highest at sunset, meaning it is rising in daytime and setting earlier and earlier until a point when it sets too close to the Sun as seen from Earth and is no longer visible. The duration of this cycle will depend on the planet's closeness to the Sun, i.e. Jupiter completes the above cycle in around 13-14 months.
(Please note all times are ST unless otherwise stated and are based on the location of Belfast and covers October)
The Sun
At the start of the month, the Sun rises at 07:30 and sets at 19:00. By month's end, it rises at 07:25 UT and sets at 16:50 UT.
The Planets
Mercury is not visible this month.
Venus is visible in the evening sky this month, albeit it stays very low relative to the horizon. At start of the month, it sets at 20:00 and by month's end at 18:25 UT. It moves from Libra to Scorpius and brightens from mag -4.2 to mag -4.5 during the month.
Mars is visible in the morning sky this month. At the start of the month, it rises at 02:45 and by month's end at 01:35 UT. It moves from Sextans to Leo and brightens from mag +1.6 to mag +1.5 during the month. It is at conjunction with Regulus (Alpha (α) Leonis, mag +1.4) on the morning of the 15th, lying 1° to the N of the star.
Jupiter becomes visible in the evening sky this month in Gemini and is at Eastern Quadrature on the 12th. At the start of the month, it rises at 23:40 and by month's end, it rises at 20:50 UT. It brightens from mag -2.2 to mag -2.4 during the month.
Saturn is not visible this month.
Uranus is at opposition on the 3rd and is visible in the evening sky this month in Pisces. During the month, it rises during daylight hours and sets at 04:45 UT by month’s end. It maintains its brightness at mag +5.7 during the month and lies less than 5° to the S of Kaht (Epsilon (ε) Piscium, mag +4.3) and Linteum (Delta (δ) Piscium, mag +4.4).
Neptune is visible in the evening sky this month in Aquarius. During the month, it rises during daylight hours and sets at 01:05 UT by month’s end. It brightens from mag +7.8 to mag +7.9 during the month and lies between Sigma (ς) Aquarii (mag +4.
and Iota (ι) Aquarii (mag +4.3).The Moon
The new moon is on the 5th with the first quarter moon on the 12th and the full moon on the 19th. The last quarter moon is on the 27th.
There is a penumbral lunar eclipse on the night of the 18th. At its peak 76% of the moon will lay inside the Earth’s outer shadow with the Southern limb darker than usual. It starts at 22:51 with the peak occurring at 00:50 and the eclipse ending at 02:50.
On the morning of the 2nd, the waning crescent moon lies to the S of Regulus (Alpha (α) Leonis, mag +1.4) at around 06:00.
On the evening of the 8th, the waxing crescent moon lies to the N of Venus at around 19:00.
On the evening of the 14th, the waxing gibbous moon lies to the NW of Neptune at around 20:00.
On the evening of the 17th, the waxing gibbous moon lies 6° to the N of Uranus at around 20:00.
On the evenings of the 21st and 22nd, the waning gibbous moon lies near to Aldebaran (Alpha (α) Tauri, mag +0.9). On the 21st, it lies to the NW of the star and on the following evening, it lies 6° to the E of it. The moon also lies to the S of M45 - The Pleiades on the 21st. On both evenings, look at around 22:00.
On the evening of the 23rd, the waning gibbous moon lies 7° to the W of M35 at around 22:00.
On the evenings of the 24th and 25th, the waning gibbous moon lies near to Jupiter. On the 24th, it lies to the W of the planet. On the following evening, it lies to the SW of it. On both evenings, look at around midnight.
On the morning of the 27th, the last quarter moon lies 8° to the SW of M44 – The Beehive Cluster at around 01:00.
On the mornings of the 29th and 30th, the waning crescent moon lies near to Mars. On the 29th, it lies to the NW of the planet, on the following morning it lies to the S of it. It also lies 8° to the SW of Regulus (Alpha (α) Leonis, mag +1.4) on the 29th. On both mornings, look at around 03:00.
Meteors
The best time to observe meteor showers is when the moon is below the horizon; otherwise its bright glare limits the number you will see especially the fainter ones. Below is a guide to this month's showers.
The Orionids peak on the morning of the 21st with a ZHR of 20. The radiant is visible from 01:00 on the morning of the 21st, but the view is spoilt by a waning gibbous moon in Aries.
There are additional minor showers this month, details of which can be found at meteorshowersonline.com/calendar.html or www.imo.net/calendar/2013
Asteroids
Asteroid (42) Isis is at opposition on the morning of the 20th at mag +9.9. It can be found in Cetus and is visible from 22:00 on the evening of the 19th.
Asteroid (20) Massalia is at opposition on the evening of the 31st at mag +8.7. It can be found in Aries and is visible from 18:00 UT on the evening of the 31st.
Finder charts and further information about other fainter asteroids can be found at; britastro.org/computing/charts_asteroid.html in the source list below.
Comets
C/2012 S1 (ISON) has had a lot of publicity. Current information has it peaking in brightness similar to Jupiter, maybe as bright as Venus when it is at perihelion on Nov 28th. There is a high level of uncertainty about how bright this comet will get so the closer to the 28th we get, the more accurate the predictions will become. It passes very close (around 1 million miles) to the Sun’s surface at perihelion so there is a chance it may not survive the encounter, will just have to wait and see!
In October, it is heading through Leo and lies less than 2° to the N of Mars on the morning of the 1st. On the morning of the 15th, it lies 1° to the N of Mars which in turn lies 1° to the N of Regulus (Alpha (α) Leonis, mag +1.4). On the morning of the 30th, it lies less than 1° to the NW of Chi (χ) Leonis (mag+4.6). It is visible from 04:00 at the start of the month with it visible from 04:00 at mid-month and from 03:00 UT by month’s end. Current estimates have the comet at mag +13 and it is expected to brighten during October and November.
2P/Encke is also at perihelion in November (21st) with it expected to peak at mag +7. During October it starts the month in Lynx when it visible from midnight. It then heads into Leo Minor by mid-month, visible from 03:00 and ends the month in Leo, again visible from 03:00 UT. On the morning of the 27th, it lies less than 4° to the N of Denebola (Beta (β) Leonis, mag +2.0). It is expected to be mag +8/9 during October and brightening.
Finder charts and further information about other fainter comets can be found at www.aerith.net , cometchasing.skyhound.com , www.ast.cam.ac.uk/%7Ejds/ , in-the-sky.org , kometen.fg-vds.de/fgk_hpe.htm and www.rasnz.org.nz in the source list below. Any above estimates for predicting a comet's brightness are based on current information at the time of writing the guide and the comet may be brighter/dimmer than the above predictions.
Deep Sky
On the deep sky front this month, galaxies M81 and M82 can be observed in Ursa Major. In Lyra – M57 – The Ring Nebula can be observed and in Vulpecula – M27 – The Dumbbell Nebula can be found. In Andromeda, M31 – The Andromeda galaxy can be observed along with its satellite galaxies M32 and M110. In Perseus, there is the open cluster M34 and the excellent Double Cluster – NGC 869 and 884. In Triangulum, there is the galaxy M33. Auriga reappears with its three open clusters M36, M37 and M38 as does Taurus with the excellent Pleiades – M45 and the Hyades. Orion returns to our skies with M42 – The Great Orion Nebula along with Gemini with the open cluster M35.
General Notes
Always keep an eye out for Aurorae. On the morning of the 27th at 2am, the clocks go back one hour and summer time ends.
Other interesting naked eye phenomena to look out for include the Zodiacal Light and the Gegenschein. Both are caused by sunlight reflecting off dust particles which are present in the solar system. The Zodiacal Light can be seen in the West after evening twilight has disappeared or in the East before the morning twilight. The best time of year to see the phenomenon is late-Feb to early-April in the evening sky and September/October in the morning sky - it's then that the ecliptic, along which the cone of the zodiacal light lies, is steepest in our skies. The Gegenschein can be seen in the area of the sky opposite the sun. To view either, you must get yourself to a very dark site to cut out the light pollution. When trying to observe either of these phenomena, it is best to do so when the moon is below the horizon. A new appendix has been added explaining some of the more technical terms used in the guide.
Clear Skies
Neill McKeown
Information Sources Used and Links
www.skyviewcafe.com ; Sky at Night Magazine Observing Guide and CD; www.aerith.net ; cometchasing.skyhound.com ; www.ast.cam.ac.uk/%7Ejds/ ; kometen.fg-vds.de/fgk_hpe.htm ; www.rasnz.org.nz ; Stardust Magazine; britastro.org/computing/charts_asteroid.html ; in-the-sky.org ;
Philip's Stargazing 2013; Patrick Moore's 2013 Yearbook of Astronomy; www.heavens-above.com ; www.spaceweather.com ;meteorshowersonline.com/calendar.html ; www.timeanddate.com/astronomy/ ; www.imo.net/calendar/2013 - International Meteor Organisation;messier.seds.org/ - The Messier Catalogue website; www.seds.org/messier/xtra/ngc/ngc.html - NGC Catalogue website; www.irishastronomy.org - Irish Federation of Astronomy Societies Website; irishastro.org.uk - Irish Astronomical Association website; www.eaas.co.uk - Northern Ireland Amateur Astronomy Society;
Appendix
The ZHR or Zenithal Hourly Rate is the number of meteors an observer would see in one hour under a clear, dark sky with a limiting apparent magnitude of 6.5 and if the radiant of the shower were in the zenith. The rate that can effectively be seen is nearly always lower and decreases as the radiant is closer to the horizon. The Zenith is the overhead point in the sky.
The radiant is the point in the sky, from which (to a planetary observer) meteors appear to originate, i.e. the Perseids, for example, are meteors which appear to come from a point within the constellation of Perseus. When the radiant is quoted as "circumpolar", it is never below the horizon and visible all night, otherwise the times quoted are when the constellation in which the radiant lies rises above the horizon in the East.
A fireball is defined by the International Astronomical Union as a meteor brighter than any of the planets, i.e. magnitude -4 or brighter. The International Meteor Organisation alternatively defines it as a meteor which would have a magnitude of -3 or brighter at the zenith.
The ° symbol in the guide is that for degrees. A degree is two full moon widths to give an idea for judging any distances quoted in the guide. There are 60 arcminutes in a degree.
An asterism is a collection of stars seen in Earth's sky which form simple patterns which are easy to identify, i.e. the Big Dipper. They can be formed from stars within the same constellation or by stars from more than one constellation. Like the constellations, they are a line of sight phenomenon and the stars whilst visible in the same general direction, are not physically related and are often at significantly different distances from Earth.
Mag is short for magnitude which is the measure of an object's brightness. The smaller the number, the brighter the object. The brightest object in the sky is the Sun at mag -26, the full moon is mag -12 and Venus the brightest planet is mag -4. The brightest stars are mag -1. If there is a 1 mag difference between two objects - there is a difference in brightness of a factor of 2.5 between the two objects. For example the full moon is eight magnitudes brighter than Venus on average which means it is 1,526 times brighter than Venus. Objects down to mag +6 can be seen with the naked eye under very dark skies.
Local time is always quoted in the guide and this means for November - February - universal time (UT)/GMT is used and for April to September - daylight savings time (DST, = GMT+1). For the months of March and October when the clocks go forward/back respectively, both times will be used and attention should be paid to any times at the end of these months for that change.
Deep Sky Objects such as galaxies, nebulae and star clusters are classified in catalogues such as the Messier catalogue for objects like M44 - M for Messier. Another example of a catalogue would the New General catalogue whose objects have the prefix NGC. There are links for websites to both catalogues in the section above.
Perihelion is the point in the orbit of a planet, asteroid or comet where it is nearest to the sun. It is the opposite of Aphelion, which is when the object is at the farthest point in its orbit from the sun.
The Planets
From Earth - Mercury and Venus are the inner planets in the solar system and Mars, Jupiter, Saturn, Uranus and Neptune are the outer planets. Below is a short guide as to how both the inner and outer planets move around the sun.
The Inner Planets
These are best seen when at Greatest Eastern/Western elongation and are not visible when at either Inferior/Superior conjunction. Greatest Eastern elongation is when the inner planet is at its furthest point east from the sun as seen from Earth and visible in the evening sky in the West after sunset, Western elongation is when it’s at its furthest point west from the sun as seen from Earth and visible in the morning sky in the East before sunset. Inferior conjunction occurs when the inner planet is between the Sun and the Earth. Superior conjunction occurs when the inner planet is on the other side of the Sun as seen from Earth.
From our Northerly latitudes, the ecliptic, along which the planets move, lies at a very shallow angle to the horizon after sunset in the autumn and before sunrise in the spring. This means that any of the planets will be difficult to see when fairly close to the Sun in the evening sky in the autumn or in the morning sky in the spring. In particular, Mercury is more or less invisible from here when at Eastern elongation in the autumn or at Western elongation in the spring, because it lies so close to the horizon and is never above the horizon except in daylight or bright twilight.
The normal cycle for an inner planet is Superior Conjunction - Greatest Eastern Elongation - Inferior Conjunction - Greatest Western Elongation - Superior Conjunction. After superior conjunction, the planet moves away from the Sun as seen from Earth and becomes visible in the evening sky after a period of time. It then moves past the point of Greatest Eastern Elongation and moves back towards the Sun as seen from Earth until a point when it is not visible and at Inferior Conjunction. After this the planet appears in the morning sky for a time, before again slipping into the Sun's glare as seen from Earth. The duration of this cycle will depend on the planet's closeness to the Sun, i.e. Mercury completes the above cycle in around 4 months.
The Outer Planets
These are best seen when at opposition and are not visible when at conjunction. Opposition occurs when the earth is between the sun and the outer planet. It is the best time to observe them because the planet is visible all through the night and it is due South and at its highest at about midnight. The planet is also at its closest point in its orbit to Earth - making it appear brighter. Conjunction occurs when the outer planet is on the other side of the Sun as seen from Earth.
If the planet is at or near it furthest point South along the ecliptic, then it won't get very high in the sky even at opposition - just as the Sun never gets high in the sky in midwinter. This happens when opposition occurs near midsummer when the planet is opposite the Sun in the sky and in midsummer the Sun is high, so the planet will be low. The opposite of course applies in winter.
The normal cycle for an outer planet is Conjunction - Western Quadrature - Opposition - Eastern Quadrature - Conjunction. After conjunction, the planet moves away from the Sun as seen from Earth and becomes visible again. The planet from this point on rises earlier and earlier in the morning sky and eventually becomes visible in the evening sky. At Western Quadrature it is at its highest at sunrise and by opposition it is in the same position by midnight. By Eastern Quadrature, it is past its best and is at its highest at sunset, meaning it is rising in daytime and setting earlier and earlier until a point when it sets too close to the Sun as seen from Earth and is no longer visible. The duration of this cycle will depend on the planet's closeness to the Sun, i.e. Jupiter completes the above cycle in around 13-14 months.
Last edit: 10 years 7 months ago by Neill. Reason: New Info
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