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October 10 Observing Guide
- Neill
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13 years 7 months ago - 13 years 7 months ago #86409
by Neill
October 10 Observing Guide was created by Neill
Hi all,
October's guide is below. There is a new section at the back of the guide with "technical" explanations of terms used in the guide for beginners etc. Would appreciate feedback on it.
OBSERVING GUIDE
(NB: all times are DST 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 07:25 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 visible as a morning object in the east for the first few days of the month. At the start of the month, it rises at 06:10 with a mag of -1.1. After this, it is too close to the sun and is at superior conjunction on the 17th.
Venus and Mars are not observable this month with Venus at inferior conjunction on the 29th.
Jupiter is well placed for observation this month. It rises during daylight hours throughout the month. It is to the South of the Circlet asterism and moves from Pisces into Aquarius during the month. It fades from mag -2.9 to mag -2.8 during the month. It moves away from the fainter Uranus during the month, heading westward. By month’s end, it sets at 03:10 UT. Currently Jupiter’s South Equatorial Belt has gone missing; also its four Galilean moons are worth a look in a small telescope.
Saturn is at conjunction on the 1st and is visible by month’s end as a morning object, when it rises at 04:40 UT at mag +0.9 in Virgo. It lies near to Porrima (Gamma (γ) Virginis, mag +2.9).
Uranus is well placed for observation this month. It rises during daylight hours throughout the month. It fades from mag +5.7 to mag +5.8 during the month, lying to the South of the Circlet asterism in Pisces. Jupiter moves away from Uranus during the month. By month’s end, it sets at 03:30 UT. Don’t expect to see much detail - it will be like a green-blue star.
Neptune is well placed for observation this month and rises during daylight hours. It fades from mag +7.8 to mag +7.9 during the month and sets at 00:30 UT by month’s end. It lies to the W of Iota (ι) Aquarii (mag +4.3) and to the N of Delta (δ) Capricorni (mag +2.9). You’ll see even less detail than on Uranus: It will appear like a faint bluish star.
The Moon
The last quarter moon is on the 1st with the new moon on the 7th. The first quarter moon is on the 14th with the full moon on the 23rd. The second last quarter moon of the month is on the 30th.
On the morning of the 1st, the last quarter moon lies 6° to the SE of M35 at around 01:00.
On the morning of the 2nd, the waning crescent moon lies 8° to the SW of Pollux (Beta (β) Geminorum, mag +1.1) at around 03:00.
On the morning of the 3rd, the waning crescent moon lies 6° to the SW of M44 –The Beehive Cluster at around 03:00.
On the mornings of the 4th and 5th, the waning crescent moon lies near to Regulus (Alpha (α) Leonis, mag +1.4). It lies to the NW of the star on the 4th and to its S on the 5th. For both mornings, look around 05:00.
On the evening of the 17th, the waxing gibbous moon lies 5° to the N of Neptune at around 23:00.
On the evenings of the 19th and 20th, the waxing gibbous moon lies near to Jupiter and Uranus. It lies to the NW of the two planets on the 19th and to their NE on the 20th. For both evenings, look around midnight.
On the evenings of the 24th and 25th, the waning gibbous moon lies near to M45 –The Pleiades. It lies to the W of the cluster on the 24th and to its SE on the 25th. For both evenings, look around 23:00. Also on the 25th, Aldebaran (Alpha (α) Tauri, mag +0.9) will lie to the S of the moon.
On the evening of the 27th, the waning gibbous moon lies less than 2° to the SW of M35 at around 22:00.
On the morning of the 30th, the waning gibbous moon lies 8° to the NW of M44 –The Beehive Cluster at around 04:00.
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 Delta Aurigids have an ill-defined peak and may be visible for the first three or four days of the month. The ZHR is 3 with the radiant visible from about 23:00. The waning crescent moon rising in the pre-dawn hours may cause some interference, best to observe before the moon rises.
The Draconids peak on the 8th with a variable ZHR and are typically very slow moving meteors. The radiant is circumpolar and thus visible all night and there is no lunar interference, one day after new moon.
The Piscids peak on the 13th with a ZHR of 10. The radiant is visible from about 21:00. The waxing crescent moon sets just after 22:00 on the 13th, creating little interference for this shower.
The Epsilon Geminids peak on the 18th with a ZHR of 3. Lunar conditions are poor with the waxing gibbous moon in Aquarius prominent in the evening sky and only setting at just after 04:00 on the 19th. The radiant is visible from about midnight with the pre-dawn hours the best time to view this shower after the moon has set.
The Orionids peak on the morning of the 22nd with a ZHR of 25. The shower is noted for fast meteors with persistent trains and the radiant is visible from about 01:00 on the 22nd. However a waxing gibbous moon in Pisces washes this shower out.
The Leo Minorids peak on the 23rd with a ZHR of 2. The radiant is visible from about 02:00, but the full moon in Pisces washes this shower out.
Comets
Comet 103P/Hartley is predicted to reach mag +4 towards the end of October, starting the month at mag +6 if it is as bright as predicted. However comets don’t always perform in line with predictions so it may not be as bright as the predictions – current observations bear this out with the comet at least three magnitudes dimmer than predictions. At the start of the month it is circumpolar and lies less than 2° to the S of Schedar (Alpha (α) Cassiopeiae, mag +2.2). It then moves into Perseus and passes close to the Double Cluster (NGC 884 and 869) around the 7th/8th. On the morning of the 10th, it passes close to Eta (η) Persei (mag +3.
and on the 13th; it passes to the N of Mirphak (Alpha (α) Persei, mag +1.. On the evening of the 14th, it passes to the N of Lambda (λ) Persei (mag +4.3).
It then moves into Auriga and is visible from about 21:00 around mid-month. It passes to the SW of Capella (Alpha (α) Aurgia, mag +0.1) on the evening of the 18th and to the NE of the open clusters M36, M37 and M38 around the 22nd/23rd. By month’s end it is Gemini, visible from about 22:00 and lying to the N of the winter triangle (Procyon, (Alpha (α) Canis Minoris, mag +0.4), Sirius, (Alpha (α) Canis Majoris, mag -1.5) and Betelgeuse, (Alpha (α) Orionis, mag +0.4)). Although the comet is at its closest to the Earth on the 20th, it is best observed in the first half of the month before the moon dominates the night sky.
Finder charts and further information about the above and other comets can be found at www.aerith.net , cometchasing.skyhound.com , www.ast.cam.ac.uk/%7Ejds/ , kometen.fg-vds.de/fgk_hpe.htm and www.rasnz.org.nz in the source list below.
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 31st at 1am, 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;
Sky Guide 2010 – South Dublin Astronomical Society; Philip’s Stargazing 2010;
Patrick Moore’s 2010 Yearbook of Astronomy; www.heavens-above.com ;
seds.org/messier/ - 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.
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.
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 above pictorial guide should hopefully help in this.
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 its 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.
October's guide is below. There is a new section at the back of the guide with "technical" explanations of terms used in the guide for beginners etc. Would appreciate feedback on it.
OBSERVING GUIDE
(NB: all times are DST 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 07:25 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 visible as a morning object in the east for the first few days of the month. At the start of the month, it rises at 06:10 with a mag of -1.1. After this, it is too close to the sun and is at superior conjunction on the 17th.
Venus and Mars are not observable this month with Venus at inferior conjunction on the 29th.
Jupiter is well placed for observation this month. It rises during daylight hours throughout the month. It is to the South of the Circlet asterism and moves from Pisces into Aquarius during the month. It fades from mag -2.9 to mag -2.8 during the month. It moves away from the fainter Uranus during the month, heading westward. By month’s end, it sets at 03:10 UT. Currently Jupiter’s South Equatorial Belt has gone missing; also its four Galilean moons are worth a look in a small telescope.
Saturn is at conjunction on the 1st and is visible by month’s end as a morning object, when it rises at 04:40 UT at mag +0.9 in Virgo. It lies near to Porrima (Gamma (γ) Virginis, mag +2.9).
Uranus is well placed for observation this month. It rises during daylight hours throughout the month. It fades from mag +5.7 to mag +5.8 during the month, lying to the South of the Circlet asterism in Pisces. Jupiter moves away from Uranus during the month. By month’s end, it sets at 03:30 UT. Don’t expect to see much detail - it will be like a green-blue star.
Neptune is well placed for observation this month and rises during daylight hours. It fades from mag +7.8 to mag +7.9 during the month and sets at 00:30 UT by month’s end. It lies to the W of Iota (ι) Aquarii (mag +4.3) and to the N of Delta (δ) Capricorni (mag +2.9). You’ll see even less detail than on Uranus: It will appear like a faint bluish star.
The Moon
The last quarter moon is on the 1st with the new moon on the 7th. The first quarter moon is on the 14th with the full moon on the 23rd. The second last quarter moon of the month is on the 30th.
On the morning of the 1st, the last quarter moon lies 6° to the SE of M35 at around 01:00.
On the morning of the 2nd, the waning crescent moon lies 8° to the SW of Pollux (Beta (β) Geminorum, mag +1.1) at around 03:00.
On the morning of the 3rd, the waning crescent moon lies 6° to the SW of M44 –The Beehive Cluster at around 03:00.
On the mornings of the 4th and 5th, the waning crescent moon lies near to Regulus (Alpha (α) Leonis, mag +1.4). It lies to the NW of the star on the 4th and to its S on the 5th. For both mornings, look around 05:00.
On the evening of the 17th, the waxing gibbous moon lies 5° to the N of Neptune at around 23:00.
On the evenings of the 19th and 20th, the waxing gibbous moon lies near to Jupiter and Uranus. It lies to the NW of the two planets on the 19th and to their NE on the 20th. For both evenings, look around midnight.
On the evenings of the 24th and 25th, the waning gibbous moon lies near to M45 –The Pleiades. It lies to the W of the cluster on the 24th and to its SE on the 25th. For both evenings, look around 23:00. Also on the 25th, Aldebaran (Alpha (α) Tauri, mag +0.9) will lie to the S of the moon.
On the evening of the 27th, the waning gibbous moon lies less than 2° to the SW of M35 at around 22:00.
On the morning of the 30th, the waning gibbous moon lies 8° to the NW of M44 –The Beehive Cluster at around 04:00.
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 Delta Aurigids have an ill-defined peak and may be visible for the first three or four days of the month. The ZHR is 3 with the radiant visible from about 23:00. The waning crescent moon rising in the pre-dawn hours may cause some interference, best to observe before the moon rises.
The Draconids peak on the 8th with a variable ZHR and are typically very slow moving meteors. The radiant is circumpolar and thus visible all night and there is no lunar interference, one day after new moon.
The Piscids peak on the 13th with a ZHR of 10. The radiant is visible from about 21:00. The waxing crescent moon sets just after 22:00 on the 13th, creating little interference for this shower.
The Epsilon Geminids peak on the 18th with a ZHR of 3. Lunar conditions are poor with the waxing gibbous moon in Aquarius prominent in the evening sky and only setting at just after 04:00 on the 19th. The radiant is visible from about midnight with the pre-dawn hours the best time to view this shower after the moon has set.
The Orionids peak on the morning of the 22nd with a ZHR of 25. The shower is noted for fast meteors with persistent trains and the radiant is visible from about 01:00 on the 22nd. However a waxing gibbous moon in Pisces washes this shower out.
The Leo Minorids peak on the 23rd with a ZHR of 2. The radiant is visible from about 02:00, but the full moon in Pisces washes this shower out.
Comets
Comet 103P/Hartley is predicted to reach mag +4 towards the end of October, starting the month at mag +6 if it is as bright as predicted. However comets don’t always perform in line with predictions so it may not be as bright as the predictions – current observations bear this out with the comet at least three magnitudes dimmer than predictions. At the start of the month it is circumpolar and lies less than 2° to the S of Schedar (Alpha (α) Cassiopeiae, mag +2.2). It then moves into Perseus and passes close to the Double Cluster (NGC 884 and 869) around the 7th/8th. On the morning of the 10th, it passes close to Eta (η) Persei (mag +3.
and on the 13th; it passes to the N of Mirphak (Alpha (α) Persei, mag +1.. On the evening of the 14th, it passes to the N of Lambda (λ) Persei (mag +4.3).It then moves into Auriga and is visible from about 21:00 around mid-month. It passes to the SW of Capella (Alpha (α) Aurgia, mag +0.1) on the evening of the 18th and to the NE of the open clusters M36, M37 and M38 around the 22nd/23rd. By month’s end it is Gemini, visible from about 22:00 and lying to the N of the winter triangle (Procyon, (Alpha (α) Canis Minoris, mag +0.4), Sirius, (Alpha (α) Canis Majoris, mag -1.5) and Betelgeuse, (Alpha (α) Orionis, mag +0.4)). Although the comet is at its closest to the Earth on the 20th, it is best observed in the first half of the month before the moon dominates the night sky.
Finder charts and further information about the above and other comets can be found at www.aerith.net , cometchasing.skyhound.com , www.ast.cam.ac.uk/%7Ejds/ , kometen.fg-vds.de/fgk_hpe.htm and www.rasnz.org.nz in the source list below.
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 31st at 1am, 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;
Sky Guide 2010 – South Dublin Astronomical Society; Philip’s Stargazing 2010;
Patrick Moore’s 2010 Yearbook of Astronomy; www.heavens-above.com ;
seds.org/messier/ - 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.
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.
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 above pictorial guide should hopefully help in this.
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 its 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: 13 years 7 months ago by Neill.
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