1” “Sky-Notes” of the Open University Astronomy Club. December 2005. All times shown are ut




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Sky-Notes” of the Open University Astronomy Club.
December 2005.
All times shown are UT.
1. Solar system.
Earth.

The December Solstice (Winter for Northern Hemisphere), is reached at 18h 35m on 21st December marking the lowest southern declination of the Sun. Not everyone is aware that the earliest sunset occurs in mid-December and latest sunrise in early January. This is due to the elliptical orbit of the Earth and associated variation in orbital speed.


The Earth reaches perihelion (closest point to the Sun) (147 million km) on 4 January 2006.
Meetings.

Saturday 17th December. BAA Christmas Meeting. 14:30 – 18:00. English Heritage Lecture Theatre, Savile Row, Piccadilly, London W1.

See BAA website www.britastro.org for full details.



Sun.

To prevent permanent damage to your eyes avoid looking at the Sun directly and never with binoculars or a telescope unless special (expensive!) filters are used. The safest way is the simplest – project the image of the Sun onto grey or white card.


It is always worthwhile to carry out regular observations for activity.
Moon.

Phases: New 01d 15h 01m

First quarter 08d 09h 36m

Full 15d 16h 16m

Last quarter 23d 19h 36m

New 31d 03h 12m
Apsides: Perigee 05d 04h Diameter. 32’ 31” Distance. 367,400km

Apogee 21d 03h Diameter. 29’ 31” Distance. 405,000km



Lunar Occultations.

Unlike the gradual disappearance of a planet (small disc) a star vanishes instantly demonstrating that it is a point source of light as viewed from the Earth. For all occultation events start observing 10 to 15 minutes before the predicted time to identify the required star and to allow for slightly different time if you are not at Greenwich. Use an accurate watch to record the time that you observe the occultation remembering that times are UT not BST. Disappearance is behind the dark limb of the Moon unless otherwise stated. Enter details in your observing log.


Predictions are for Greenwich, (E 0o.0, N 51o.5) from the BAA Handbook 2005.
Date. ZC No. Mag. Time.

Dec. 7 3327 6.8 18h 31.5m

9 38 7.9 16h 42.7m

9 50 6.0 21h 21.8m

11 309 7.9 22h 18.7m
Observing the Moon.

The decreasing altitude of the Sun means that the thin waxing crescent Moon is not well placed for observation. First quarter through to last quarter provide the best conditions apart from the days around Full Moon when there is little contrast on the lunar surface. Observe along or near to the terminator where long shadows show greater detail of the Moon’s topography. Use a basic “Moonmap” to familiarize yourself with the major features i.e. the Maria and larger craters. Note that the orientation of a feature on a map may differ from that of the observed image of the Moon depending on the type of telescope used. If you find the Moon too bright use a filter to reduce the glare. The Moon is also an excellent object to start photography and/or imaging especially with webcams and digital cameras.


Mercury.

Mercury reaches Greatest Elongation W (21o) on the 12th. Although not high in the dawn skies it should be spotted with the naked eye around this time. Magnitude increases from +1.3 (diameter 9.0”, phase 0.16) on the 1st to –0.5 (diameter 6.2”, phase 0.72) on the 16th.


Venus.

Although low in the sky after sunset December provides the opportunity to follow the rapidly waning crescent phase of Venus as it heads for inferior conjunction on 13th January 2006. Magnitude increases from at –4.5 (diameter 38.8”, phase 0.29) on the 6th to –4.6 (diameter 45.7”, phase 0.20) on the 16th and then decreases to –4.2 (diameter 60.4”, phase 0.03) on the 31st. If observing during the latter part of December take great care that the Sun does not accidentally enter your field of view.


Mars.

Mars is well placed for observation throughout the evening. However the disc is now rapidly shrinking as the Earth – Mars distance increases. Make the most of this month as magnitude decreases from –1.5 (diameter 17”) to –0.5 (diameter 11.6”).



Jupiter.

Jupiter is available for early morning observation low in the southeast. Magnitude increases from –1.7 (diameter 31.5”) to –1.6 (diameter 33.6”) during the month.


Saturn.

Saturn is beginning to take over from Mars as the prime planet for observing. Rising about 21.00 at the beginning of the month and 19.00 at the end of the month. Magnitude increases from +0.2 (diameter 19.2”) to -0.1 (diameter 20.2”) during the month. Saturn is a fine visual target in any telescope and provides an ideal target for webcam imaging. Spectacular images and data continue to be returned from the Cassini spaceprobe.


Uranus.

Well placed in the early evening sky. At magnitude +5.7 (diameter of nearly 4”) it is easily located in binoculars using a suitable star chart.


Neptune.

Located further west than Uranus. At magnitude 7.8 (diameter 2.5”) it may be located in binoculars using a suitable star chart.


Pluto.

Not observable this month. In conjunction with the Sun on the 16th.


Asteroids.

The following asteroid can be located with binoculars and small telescopes using a suitable star chart. Both are bright enough for photography.



Vesta (4). A 7th magnitude object in Gemini.

Juno (3). Located in Orion at magnitude 7.5 in mid-month.

To confirm the correct identity of the asteroid observe the suspected object over a period of nights to follow its slow motion across the background stars.

See monthly periodicals/BAA Handbook for details of other asteroids.
Comets.

No bright comets are visible at present. Several fainter ones may be located using data available on a number of astronomy web sites such as the BAA Comet Section web page at www.ast.cam.ac.uk/-jds.


Meteor Showers.

One of the best meteor showers the Geminids are active from the 7th to 16th with peak activity on 13th at 22h and ZHR of about 100. Unfortunately a 12 day old Moon interferes but still worth observing as this shower regularly produces “bright events”.

Don’t forget the potential spectacle of bright sporadic events. If you are fortunate enough to observe a very fireball record the time, direction, observed start and finish points, colour, if fragmenting and any other description. These can then be reported to a collation point such as the BAA. Analysis of reports may lead to the location of a “landfall” and possible recovery of meteoritic debris.
Eclipses. No eclipses this month.

2. Deep Sky.

Abbreviations used.



M = Messier object. (Shown in bold).

NGC = New General Catalogue. IC = Index Catalogue. (Extension of the NGC).

ds = double star. ms = multiple star. gc = globular cluster.

oc = open cluster. pn = planetary nebula. en = emission nebula.

rn = reflection nebula. sg = spiral galaxy. eg = elliptical galaxy.

lg = lenticular galaxy. ir = irregular galaxy. pg = peculiar galaxy.

snr = super nova remnant. ly = light year.

The magnitude of an object is shown in brackets e.g. (6.5).




    1. Variable Stars.

Beta () Persei, Algol. +2.2 to +3.4, period 2.7 days. Favourable evening minima this month occur on the 19h, 22nd and 25th.

Delta () Cephei. +3.5 to +4.4, period 5.37 days. The prototype for the Cepheid class of variable stars. Their period-luminosity relationship has lead them to being used as “standard candles” in measuring distances to nearby galaxies.

Maximum brightness occurs on 4th, 10th, 15th, 20th, 26th and 31st.



Mu () Cephei. +3.7 to +5.0, approximate period 755 days. A semi-regular variable star famous for its striking red colour being fittingly called “Herschel’s Garnet Star”. It is the reddest naked eye star visible from the northern hemisphere. Its colour may show signs of variability.
To become a regular variable star observer it is advisable to have your own detailed star charts or those such as available from the Variable Star Section of the BAA. The Section operates a “mentor” system where novices to variable star observation are given guidance and support.


    1. Double Stars/Star Clusters/Nebulae/Galaxies.

Camelopardalis (Cam).

390 (5.1/9.5) ds. Separation 14.8". White primary with a purple secondary.

1 Cam. (550). (5.7/6.8) ds. Separation 10.3". White primary with light blue secondary.

11 & 12 Cam. (5.4/6.5) ds. Separation 108.5". White primary/deep yellow secondary. Fine binocular object.

Beta () Cam. (4.0/8.6) ds. Separation 80.8". Yellow primary/blue secondary. A third component (11.2) is visible in moderate aperture telescopes.

NGC1501 (11.5) pn. Bright, large with a blue tint located about 2 degrees south of the open star cluster NGC1502. Resembles the "Eskimo Nebula" in Gemini.

NGC1502 (5.7) oc. A fine open cluster. Extending NW of this cluster is a line of 9th and 10th magnitude stars which form "Kemble's Cascade". A beautiful sight in binoculars or a low power wide-field eyepiece on small telescopes.

NGC2403 (8.4) sg. Visible in large binoculars. It lies at a distance of 8m light years and is possibly a member of the M81/M82 group.

IC342 (12.0) sg. Once considered to be a member of the Local Group of galaxies. Its low surface brightness makes it a challenge for moderate apertures. This face on spiral galaxy would be an impressive object if it were further away from the plane of the Milky Way.

Cassiopeia (Cas).

Sigma (). (5.0/7.1) ds. Separation 3.0”. Blue-white primary/yellow secondary. Fine object.

Alpha ().(2.2/7.5) ds. Separation 64.4". Orange primary/blue secondary. Brightest stars of a multiple system.

Eta (). (3.4/7.5) ds. Separation 12.9". Observers report different colours for this pair ranging from gold, yellow or topaz for the primary and orange, red and garnet for the secondary. What do you see?

NGC129 (6.5) oc. Loose cluster of stars.

NGC147 (9.3) eg. A satellite galaxy of M31.

NGC185 (9.2) eg. A satellite galaxy of M31.

NGC278 (10.9) eg. Located a few degrees SE of NGC185.

NGC457 (6.4) oc.

NGC581 (M103) (7.4) oc. Fine object.

IC1805 (6.5) oc.

IC1848 (6.5) oc.

NGC7654 (M52) (6.9) oc. Fine object.

NGC7789 (6.7) oc. Fine object, surprisingly not in Messier’s catalogue.


Perseus (Per).

Beta () Algol. An eclipsing binary star magnitude range 2.1 - 3.4, period 2.7 days.

Eta () (3.8/8.5) ds. separation 28.3". Fine gold and blue contrast.

Theta () (4.1/9.9 ds. separation 20.0". Yellow primary with blue companion.

NGC650/1 (M76) (11.0) pn. the "Little Dumbbell". One of the faintest Messier objects.

NGC869/NGC884 (4.4/4.7) oc's. The famous "Sword handle" double cluster. Magnificent object in binoculars and small telescopes.

NGC957 (7.2) oc.

NGC1023 (11.0) eg.

NGC1039 (M34) (5.5) oc. Fine object.

NGC1245 (6.9) oc.

NGC1499 (4.0) en. The "California Nebula". Very low surface brightness making this a notoriously difficult object visually. Shows well on photographs.

NGC1528 (6.0) oc.



Taurus (Tau).

422 (5.9/.8) ds. separation 6.6". Yellow primary/blue-white secondary.

30 Tau. (5.1/10.2) ds. separation 9.0"). Blue-white primary/reddish secondary.

Lambda (). Variable star magnitude 3.3 - 3.8, period 3.95 days. Naked eye eclipsing binary.



M45 oc - "The Pleiades" or "Seven Sisters". Probably the most famous star cluster. Test your eyesight from a dark site by counting the number of naked eye stars that are visible. Seven should readily be seen. Keen vision will lead you into double figures. A test for moderate apertures is the nebulosity around some of the other brighter stars of the group, especially Merope. Nebula/UHC filters will help.

The Hyades oc is another naked eye star cluster although more spread out than the Pleiades. The first magnitude star Aldebaran (0.9) is not a member of the cluster and appears brighter as it is closer to us, 21 parsecs - about halfway to the clusters centre. Aldebaran has a faint companion (13.4) separation 30.4". Spotting the companion is not easy even in moderate telescopes.

NGC1952 (M1)(8.5) - snr - "The Crab Nebula". One of the most studied astronomical objects in recent decades. A "new star" appeared in 1054 and over a few months faded from view. Centuries later the faint oval patch was discovered by Dr John Bevis in 1731 and independently by Charles Messier on 12th September 1758 while observing the comet of that year. Its true nature was not recognized until much later.

NGC1952 (M1)(8.5) - snr - "The Crab Nebula". One of the most studied astronomical objects in recent decades. A "new star" appeared in 1054 and over a few months faded from view. Centuries later the faint oval patch was discovered by Dr John Bevis in 1731 and independently by Charles Messier on 12th September 1758 while observing the comet of that year. Its true nature was not recognized until much later. In 1942 astronomers had speculated that a peculiar star in the nebula might be a neutron star. In 1968 radio astronomers discovered that the central star was a pulsar spinning at 30 times a second ie. pulsing every 33 milliseconds. The "Crab" is also a strong emitter of X-rays. A fascinating object enhanced by the current proximity of Saturn!

NGC1647 (6.4) oc. rich cluster.

NGC1746 (6.1) oc. poorer than 1647

NGC1808/1817 (7.0/7.7) oc. a pleasant "double cluster when observed at low powers.

NGC1514 (10.0) pn. Not easy in small instruments.

NGC1554/1555 is a faint variable reflection nebula. The source of illumination is the very young star T Tauri which varies between magnitudes 9.4 and 13 over an irregular period and therefore well worth observing.

Other interesting variable stars worth observing:-

Lambda eclipsing binary, range 3.4 to 4.1, period 3.95d.

RV irregular variable, range 9.5 to 13, period 79d.

RR irregular variable, range 9.9 to 13, period "chaotic".

P.V.H.

Useful symbols.



o b

Aries (Ari).

Gamma () (4.8/4.8) ds. Separation 7.8". Fine pair of bluish-white stars.

Lambda (ds. Separation 37.4”. Attractive yellow/white and pale blue stars.

Epsilon () (5.2/5.5) ds. Separation 1.5". Fine pair of white stars requiring good seeing conditions and moderate apertures to split.

1 Ari. (6.2/7.2) ds. Separation 2.8”. Fine contrast of yellow and pale blue stars.

30 Ari. (6.6/7.4) ds. Separation 38.6”. Fine pair of yellow stars.

33 Ari. (5.5/8.4) ds. Separation 28.6”. Fine pair of yellow/white and pale blue stars.

326 (7.6/9.8) ds. Separation 5.9”. Beautiful pair of orange and dull red stars.

NGC772 (10.2) sg. Small bright core with diffuse halo.

NGC877 (11.9) sg. Faint and elongated. Try locating a number of fainter galaxies in the same field of view.

NGC972 (11.4) sg. Faint and elongated with brightening towards its centre.

Cetus (Cet).

Gamma () (3.5/7.3) ds. Separation 2.8".

Omicron () Cet. Mira the classic long period variable star is currently approaching minimum (9.3).

NGC45 (10.4) sg. Located about 8o SW of . Faint oval with a brighter centre.

NGC157 (10.4) sg. Slightly oval shape.

NGC246 (8.0) pn. Located about 6o north of . One of the largest pn in the sky. Appears as an incomplete ring structure with a 12th magnitude central star.

NGC247 (8.2) sg. Located about 4o SSE . Highly inclined to our line of sight. Low surface brightness. A great shame that it never rises high in the sky from UK.

NGC578 (11.5) sg. Roundish mottled haze.

NGC908 (10.9) sg. Similar appearance to NGC578 but slightly brighter.

NGC936 (10.1) sg. Fine barred spiral. Nebulous knot surrounded by a faint haze.

The following are located in the same area of sky as NGC936.

NGC1055 (10.6) sg. Almost edge-on. Large amateur telescopes reveal broad equatorial dust lane.

NGC1068 (M77) (8.8) sg. Located about a degree SW of . Worth locating as it is the brightest Seyfert galaxy - a class of active galaxy. Same area of sky as Mira.

NGC1073 (11.0) sg. Seen face-on and hence low surface brightness.

NGC1087 (11.1) sg. Slightly elongated. Appears brighter than NGC 1073.
Pisces (Psc).

Alpha () (4.2/5.1) ds. Separation 1.8”. Bright bluish-white pair not easily split.

Psi-one () (5.6/5.8) ds. Separation 30.0”. Fine almost equal pair of bluish-white stars.

42 Psc. (6.2/10.1) ds. Separation 28.5”. Fine orange and blue pair.

51 Psc. (5.7/9.5) ds. Separation 27.5”. Very fine blue-white and greenish pair.

55 Psc. (5.4/8.7) ds. Separation 6.5”. Very fine yellowish-orange and blue stars.

65 Psc. (6.3/6.3) ds. Separation 4.4”. Fine equal yellowish pair.

Wolf 28 (12.3) White Dwarf. One of the few white dwarf stars visible in amateur telescopes.

NGC128 (11.6) sg. Stellar nucleus in moderately bright halo.

NGC488 (10.3) sg. Fairly bright elongated object.

NGC628 (M74) (9.4) sg. Face on hence low surface brightness making this one of the more difficult Messier objects.

NGC7541 (11.7) sg. Bright core with moderately bright halo.


Triangulum (Tri).

NGC598 (M33) (5.7) sg. Viewed face-on and hence has a low surface brightness making it an elusive object. From dark sites and under good seeing conditions it is just visible to the naked eye and vies with M31 as the most distant object visible to the naked eye. With 8"+ scopes try to locate the a vast star cloud NGC604.

NGC672 (11.6) sg. A bright barred spiral galaxy seen somewhat edge-on.

NGC925 (12.0) sg. Steeply inclined to our line of sight makes it fairly bright.



Mars.

Mars reaches opposition on the 7th although closest approach to the Earth occurs a few days earlier. At magnitude –2.3 the fiery orange-red colour makes it unmistakeable. Make the most of the next few weeks as this is best apparition for the next 14 years.

Magnitude fades from –2.3 on the 6th (diameter 20.0”, phase 1.00) to –1.8 (diameter 17.7” phase 0.98) on the 26th.

The disc is large enough for major surface features to be visible in small telescopes, subject to seeing conditions. Use as high a magnification as conditions allow.

Mars is an excellent target for webcam imaging but use an IR block or IR-Uv blocking filters.

The use of colour filters will enhance different aspects of the disc. Examples are given below. The number in brackets refers to the Wratten filter number. Filters may be purchase in sets, normally four per set, with a number of sets being available.


Orange (21). Increases contrast of dark surface markings such as maria and desert areas. Well suited for small to moderate aperture telescopes.

Red (25). As above and improves enhancement of polar-capsand dust storms. Well suited for larger aperture telescopes.

Green (58). Enhances details of surface fogs, frost patches and polar-caps.

Blue (80A). Enhances details of water vapour clouds and polar hoods.


The rotation of Mars is about half an hour slower than that of the Earth so that observations made at the same time on successive nights show only a small change in surface features presented. Therefore it takes almost three weeks to follow one rotation. Recent dust storm activity has been reported.

If drawing the planet record what you see. If uncertain add a qualifying note. If you want to practice drawing the disc take an image of Mars from a magazine and try drawing it from a distance.



Current astronomy periodicals carry a number of articles on observing and imaging The Red Planet.


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