February 11 Observing Guide

Hello all,

February's guide is below:

OBSERVING GUIDE
(NB: all times are UT and are based on the location of Belfast and covers February)

The Sun

At the start of the month, the Sun rises at 08:15 and sets at 17:05. By month's end, it rises at 07:15 and sets at 18:00.

The Planets

Mercury is at superior conjunction on the 25th and is not observable this month.

Venus is visible as a morning object during February. It rises at around 05:30 at the start of the month and at 05:50 by month's end. It fades from mag -4.3 to mag -4.1 during the month. It acts as a pointer this month to some of the deep sky objects in Sagittarius. On the morning of the 3rd, it passes 2° to the S of open cluster M23 and on the following morning, M23, Venus, M20 – The Trifid Nebula and M8 – The Lagoon Nebula form a vertical line. A good SE horizon will be needed to see some of these objects.

By the morning of the 9th, it lies half a degree to the S of Asteroid (4) Vesta which will be mag +7.8. The open cluster M25 lies 2° to the NE of Venus on the same morning and all three objects should be visible in the same binocular field of view.

Mars is at conjunction on the 4th and is not observable this month.

Jupiter is now setting well before midnight and will be lost to the evening twilight by mid-March. At the start of the month, it sets at 21:50 and by month's end at 20:40. It lies to the South of the Circlet asterism and is in Pisces, fading from mag -2.2 to mag -2.1 during the month.

Saturn is visible as an evening object during the month, rising at 23:05 at the start of the month and at 21:15 by month's end. It brightens during the month from mag +0.6 to mag +0.5 and can be located in Virgo.

Uranus is lost to the evening twilight by month’s end. At the start of the month, it sets at 21:30. It maintains its brightness at mag +5.9 during the month, lying to the South of the Circlet asterism in Pisces. Don't expect to see much detail - it will be like a green-blue star.

Neptune is at conjunction on the 17th and is not observable this month.

The Moon

The new moon is on the 3rd with the first quarter moon on the 11th and the full moon on the 18th. The last quarter moon is on the 24th.

On the evening of the 4th, a thin waxing crescent moon is visible low in the West after sunset, setting at 18:50.

On the evening of the 6th and 7th, the waxing crescent moon lies near to Jupiter and Uranus. On the 6th, it lies to the W of the two planets. On the 7th, it lies to their N.

On the night of the 11th/ 12th, the first quarter moon lies to the SE of M45 – The Pleiades. At around midnight, the gap between the two is 3°.

On the night of the 12th/13th, the waxing gibbous moon lies to the N of Aldebaran (Alpha (α) Tauri, mag +0.9).

On the nights of 13th/14th and 14th/15th, the waxing gibbous moon lies near to M35. On the first night, it lies to the SW of the open cluster and its NE on the following night.

On the night of the 16th/17th, the waxing gibbous moon lies to the SE of M44 – The Beehive Cluster.

On the nights of the 17th/18th and 18th/19th, the near full moon lies near to Regulus (Alpha (α) Leonis, mag +1.4). On the first night, it lies to the S of the star and then to its E on the following night.

On the mornings of the 21st and 22nd, the waning gibbous moon lies near to Spica (Alpha (α) Virginis, mag +1.0) and Saturn. On the first morning, the three objects form a triangle in the sky with the moon to the W of the other two and Saturn to the N of Spica. On the following morning, they form a line with Saturn to the N of Spica which is to the N of the moon.

On the morning of the 25th, the waning crescent moon lies 4° to the N of Antares (Alpha (α) Scorpii, mag +1.0) and globular cluster M4.

On the morning of the 28th, the waning crescent moon lies to the W of Venus.

Meteors

There are no meteor showers this month.

Asteroids

Asteroid (44) Nysa is at opposition on the 10th, when it is mag +8.7. It can be observed in Leo, near its border with Cancer. Finder charts are available at www.rasnz.org.nz in the source list below.

Comets

There are no bright comets visible this month.

Finder charts and further information about fainter 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 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. In Auriga there are three open clusters M36, M37 and M38 and also M35 in Gemini. Taurus has the excellent Pleiades – M45, the Hyades and also M1 – The Crab Nebula. Orion returns to our skies with M42 – The Great Orion Nebula and also Cancer with M44 – The Beehive Cluster and M67. Check out the constellation Canes Venatici with the globular cluster - M3 and several galaxies including M51 - the Whirlpool Galaxy and M63 - the Sunflower Galaxy. In Leo, we have several galaxies on view including The Leo Triplet - M65, M66 and NGC 3628. M95, M96 and M105 can also be observed in Leo. The place to really find galaxies is in Virgo. The Virgo Super Cluster can be found here with numerous galaxies on view. In Coma Berenices, there is M64 - the Black-Eye Galaxy.

General Notes

Always keep an eye out for Aurorae. 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 2011- South Dublin Astronomical Society; Philip's Stargazing 2011; Patrick Moore's 2011 Yearbook of Astronomy; www.heavens-above.com ; www.spaceweather.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.

Neill

Thanks Neill.