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Posted: Mar 30 2010, 09:01 AM
Member No.: 128
Joined: 22-January 10
Neill Mc Keown's excellent observing guide reposted here:
(Please note all times are ST unless otherwise stated and are based on an observing location of Belfast and covers the month of April)
At the start of the month, the Sun rises at 06:55 and sets at 20:00. By the end of the month, it rises at 05:50 and sets at 20:55.
Mercury is at greatest eastern elongation on the 9th and is best placed for observation as an evening object in the first week of the month. It is visible after that until around the 20th, but it is moving back towards the sun and fading as it goes. At the start of the month, it is mag -0.9 and sets at 21:45, by the 9th it has faded to mag -0.1 but sets at 22:20. By the 20th, it has faded to mag +3.0 and sets at 22:00. It lies close to Venus in the first week of the month and the gap between the two is three degrees on the 4th.
Venus is an evening object. At the start of the month, it sets at 21:50. By month’s end, it sets at 23:35 and lies near to Mercury in the first week of the month (see above). It passes near to M45 –The Pleiades around the 23rd/24th at a distance of around four degrees. Over the coming months, it will become much more prominent in the evening sky.
Mars is past its best but is still well placed for observation as an evening object. During the whole month, it rises during daylight hours and by month’s end, sets at 03:55. It does however fade during the month from mag +0.2 to mag +0.7. It lies in the Cancer/Gemini region of the sky during the month and moves in an easterly direction. It passes near to M44 –The Beehive Cluster around mid month with closest approach on the 17th when it passes one degree to the North of the cluster.
Jupiter is not well placed for observation this month, rising roughly one hour before the sun by month’s end.
Saturn is well placed for observation as an evening object in Virgo. During the month, it rises during daylight hours and by month’s end, sets at 05:10. It fades from mag +0.6 to mag +0.8 during the month.
Uranus is not well placed for observation this month, rising roughly one hour before the sun by month’s end.
Neptune is also not well placed for observation this month, rising less than two hours before the sun by month’s end.
In April, the last quarter moon is on the 6th with the new moon on the 14th. The first quarter moon is on the 21st with the full moon on the 28th.
On the morning of the 3rd, a 81% illuminated waning gibbous moon lies four degrees to the West of Antares (Alpha Scorpii, mag +0.9) at around 04:00. At the same time M80 lies three degrees to the North of the moon with M4 three degrees to the East of it.
On the morning of the 4th, a 72% illuminated waning gibbous moon lies less than two degrees to the East of M19 at around 04:00. M62 lies five degrees to the South of the moon at the same time.
On the evening of the 15th, a 1 Day old waxing crescent moon lies less than two degrees to the North of Mercury (mag +1.4) at around 21:00. Venus lies eight degrees to the South of the moon at the same time. Sunset is at around 20:30 with moonset at around 22:30.
On the evening of the 16th, a 6% illuminated waxing crescent moon lies eight degrees to the East of Venus at around 21:00. M45-The Pleiades lies eight degrees to the South-East of the moon at the same time.
On the evening of the 17th, a 12% illuminated waxing crescent moon lies seven degrees to the South of M45-The Pleiades at around 21:00.
On the evening of the 18th, a 20% illuminated waxing crescent moon lies five degrees to the North of M1 at around 23:00. NGC 1746 lies four degrees to the North of the moon at the same time.
On the evening of the 19th, a 30% illuminated waxing crescent moon lies four degrees to the South of M35 at around 23:00.
On the morning of the 21st, a 41% illuminated waxing crescent moon lies within less than a degree of NGC 2392–The Eskimo Nebula at around 02:00.
On the evening of the 21st, a 52% illuminated waxing gibbous moon lies eight degrees to the North-West of Mars at around midnight. M44 –The Beehive Cluster lies seven degrees to the South-East of the moon at the same time.
On the evening of the 22nd, a 64% illuminated waxing gibbous moon lies six degrees to the South-East of M67 at around midnight.
On the evening of the 23rd, a 74% illuminated waxing gibbous moon lies seven degrees to the South of Regulus (Alpha Leonis, mag +1.4) at around midnight.
On the evening of the 26th, a 97% illuminated waxing gibbous moon lies three degrees to the East of M104 –The Sombrero Galaxy at around midnight. At 02:00 on the morning of the 27th, Spica (Alpha Virginis, mag +1.0) joins the scene, lying eight degrees to the East of the moon.
On the morning of the 30th, a 97% illuminated waning gibbous moon lies eight degrees to the West of M80 at around 02:00.
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 for an observer. 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. 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.
There are two showers this month. The first shower is the Virginids which has two peaks. The Alpha Virginids peak on the 10th and the Gamma Virginids which peak on the 14th. Both have a low ZHR of 5 with no lunar interference from the waning crescent moon.
The second shower is the Lyrids. They peak on the 22nd at around 16:00. The predicted ZHR is 18, but the rate can be as high as 90 depending on the year. The radiant is located near to Vega. Although the peak is during the day, you should observe on the evening of the 22nd from about 23:00 when the radiant is above the horizon through to dawn on the 23rd. However will be lunar interference for this shower with a 60% illuminated waxing gibbous moon in Cancer setting at 03:55 on the morning of the 23rd. They are typically average speed meteors with rates of 30 miles/second. This is in comparison with the Perseids who have speeds of 42 miles/second.
Asteroid 2 Pallas is at opposition on the 30th. It will be mag +8.7 in the Northern region of Serpens Caput close to the boundary with Corona Borealis. As an aid to locate it, it forms a right angle triangle with Alphekka (Alpha Coronae Borealis, mag +2.2) and Gamma Coronae Borealis (mag +3.8). Finder charts are available from the RASNZ link in the information section.
Comet 81P/Wild 2 can be observed in Virgo during April. It is visible from 23:00 at the start of the month and should be visible once darkness falls from mid-month onwards. It is currently around mag +9 and is predicted to remain steady at that during April. It lies near to Iota Virginis (mag +4.1) throughout the month, to the West of the star.
Comet C/2009 K5 (McNaught) is currently around mag +9 and is predicted to peak at mag +8 at the end of April. Its track takes it North during the month starting in Vulpucela, moving into Cygnus and ending the month in Cepheus. On the 6th, it lies to the North of the double star Albireo (Beta Cygni, mag+3.1 + 5.1). Around the 26th, it passes near to Eta Cephei (mag +3.4), to the West of the star. By month’s end, it lies near to the combined open cluster + Nebula – NGC 7023 –The Iris Nebula. The cluster actually lies within the nebula which is designated LBN 487; it is the cluster which is NGC 7023. Its brightness is mag +7 and the comet will lie to the West of this DSO and also to the West of Aphirk (Beta Cephei, mag +3.2) at the same time. It is visible from 02:00 at the start of the month and should be visible once darkness falls from mid-month onwards.
On the deep sky front this month, galaxies M81 and M82 can be observed in Ursa Major. 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. Also in Virgo, M104 - the Sombrero Galaxy can be found. In Coma Berenices, there is M64 - the Black-Eye Galaxy. Also 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 Hercules, two globular clusters – M92 and the excellent M13 can be observed and in Lyra – M57 – The Ring Nebula can be observed. Finally there are some excellent open clusters in Cancer - M44 – The Beehive Cluster and M67.
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.
Information Sources Used and Links
www.skyviewcafe.com - Used for the Sun and Planets section. Also partly used for the Moon Section
Sky at Night Magazine Observing Guide and CD
www.aerith.net and http://cometchasing.skyhound.com – Used for the Comet Section for information and finder charts
http://www.ast.cam.ac.uk/%7Ejds/ - BAA and SPA Comet page
http://kometen.fg-vds.de/fgk_hpe.htm - German Comet page
http://www.rasnz.org.nz – Royal Astronomical Society of New Zealand website – good for asteroids
Sky Guide 2010 – South Dublin Astronomical Society
www.heavens-above.com – For the latest ISS passes, Iridium Flares and Shuttle launches
www.irishastronomy.org – Irish Federation of Astronomy Societies Website
www.stronge.org.uk – Excellent weather site including Space Weather
www.irishastro.org.uk – Irish Astronomical Association website
www.eaas.co.uk – Northern Ireland Amateur Astronomy Society