1” “Sky-Notes” of the Open University Astronomy Club. April 2006




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Sky-Notes” of the Open University Astronomy Club.
April 2006.

1. Solar system.
Note that all times shown are UT, remember to adjust for BST as necessary.
Earth.

The Sun transits the meridian at 12h 00m on the 15 and 16. After this transit will occur earlier until mid-June. Has anyone tried to plot the Analemma – the figure-of-eight shape that results from plotting the Sun’s position at the same time of day throughout the year?


Meetings.

21st - 23rd April. Liverpool A.S. is celebrating their 125th Anniversary and hosting the BAA Out of London Weekend.


22nd April. “Astroblast”. Institute of Astronomy, Madingley Road, Cambridge. 10am – 4pm. An Astronomy and Space Extravaganza for all ages and levels of experience. Free admission. Details: www.astroblast.org.uk

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.


Although approaching the minimum of the current solar cycle it is always worthwhile to carry out regular observations for activity. Hours of darkness still provide the opportunity for observing aurora.
Moon.

Phases:

First quarter 05d 12h 01m

Full 13d 16h 40m

Last quarter 21d 03h 28m

New 27d 19h 44m
Apsides: Apogee 09d 13h Diameter. 29’ 28” Distance. 405,548km.

Perigee 25d 10h Diameter. 32’ 51” Distance. 363,736km.


Moon continued.

Spring evenings provide the opportunity to observe (at social hours for many) the waxing crescent Moon from thin crescent through first quarter. Observe the regions along the terminator (sunrise on the Moon) where the low angle of the Sun highlights lunar topography. A basic lunar map is all you need to get started. If you are starting out on photography and/or imaging the Moon will provide an excellent target.


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.

Apl. 04 1008 5.1 21h 36.2m

06 1251 5.9 19h 38.9m

08 1464 7.6 21h 01.6m

09 1562 7.3 29h 38.1m

30 773 6.9 20h 05.6m
Mercury.

Greatest elongation W (28O) is reached on 8th April. Lost in the morning twilight week of the month it will is unlikely to be spotted with naked eye low in the dawn skies. Brightness increases from +0.5 (diameter 8.2” phase 0.43) on the 5th to –0.4 (diameter 5.7” phase 0.78) on the 30th.

4O south of the thin crescent Moon on the 26th.
Venus.

Brilliant at magnitude –4.2 fading to –4.0 during the month Venus is an unmistakeable object low in the SE dawn skies. The diameter decreases from 21.9” (phase 0.55) on the 5th to 18.2” (phase 0.64) on the 25th.


Mars.

High in the western evening sky Mars moves from Taurus into Gemini. Greatest declination north of just over +25O is attained mid-month. Magnitude fades from +1.2 to +1.4 and decreases in size (5.6” to 5.0”) during the month as the Earth – Mars distance increases. The planet presents a distinct gibbous phase of about 0.91 but the small disc will now require moderate or larger aperture telescopes to observe detail.


Jupiter.

Rising mid-evening Jupiter is well placed for observation after mid-night. Opposition is reached on 4th May. Brilliant at magnitude –2.4 with the diameter increasing from 43.0” to 44.5”. The current low declination will adversely affect seeing conditions for observers in the northern hemisphere. Jupiter is an excellent target for Webcam imaging. See separate observing sheet for Jupiter and Saturn.



Saturn.

Saturn is well placed for evening observation. Located just west of the star cluster M44 Praesepe in Cancer making an attractive view in binoculars and low power on small telescopes. A fine target for the camera. Brightness fades slightly from +0.1 (diameter 17.1”) to +0.2 (diameter 16.5”) during the month. The rings are slowly closing but still present a magnificent view in any telescope. Saturn is an excellent target for Webcam imaging. See separate observing sheet.

Cassini continues to return staggering images and data of the planet and its extensive satellite system. The NASA website warrants a daily visit at: http://saturn.jpl.nasa.gov and http://ciclops.org
Uranus.

Lost in the morning twilight. Not observable this month.


Neptune.

May be glimpsed low down in the SE predawn sky towards the end of April.


Pluto.

Transits the meridian in the dark predawn sky. At 14th magnitude it will require a large aperture telescope to observe visually. Good target for CCD imaging.


Asteroids.

The following asteroid can be located with binoculars and small telescopes using a suitable star chart.



Vesta (4). An 8th magnitude object in Gemini. Fading slowly. Well worth a series of images to track its slow movement across the background stars.

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


Comets.

Comet 73P/Schwassmann-Wachmann. A fragmented small comet due to make a “close” approach to the Earth during May. It will be worth following through April to June. Data for fragments B, C and E are giving in the BAA handbook although magnitudes are uncertain. See BAA comet webpage for updates.

Up to date details of comets may be found on a number of astronomy web sites such as the BAA Comet Section web page at www.ast.cam.ac.uk/-jds.


Meteor Showers.

The Lyrids are active between 19th – 25th April with maximum activity on the 22nd with a ZHR of about 10.

Don’t forget sporadic events and the chance of a brilliant fireball. The latter should be recorded and reported.
Eclipses.

No eclipses this month.



Total Solar Eclipse on March 29. Reports please from those fortunate to have travelled to observe totality.

Through broken cloud I was able to observe brief glimpses of the partial eclipse of 29th March. Any other observations from the UK?



Observing Jupiter & Saturn.
Keep for future reference.
Jupiter. The disc appears distinctly flattened - equatorial diameter greater than the polar diameter. The equatorial bulge is due to Jupiter's very rapid rotation of under 10 hours. Even a short observing session of half an hour will show the rapid rotation of surface features. The main cloud belts are easily seen in small telescopes and with increasing aperture and magnification more and more detail is revealed, subject to atmospheric conditions. Watch for the Great Red Spot, smaller white spots, belt detail, satellite shadows etc. Use as high a magnification as seeing conditions allow. The use of coloured filters can enhance features. Try a selection and you will be surprised at their effect.

Following the ever-changing pattern of the four Galilean satellites - Io, Europa, Callisto and Ganymede - is a fascinating exercise over a few hours and subsequent evenings. Plot your observations on a sheet of graph paper and you will produce their orbital patterns. Identifying each of the satellites is straight forward using charts such as those printed in the BAA Handbook or periodicals such as Astronomy Now, Sky and Telescope, etc.


Saturn. The Cassini division in the rings should be easily seen. Moderate apertures and high power may reveal the Encke division and the dusky Crepe ring, seeing conditions allowing. Cloud belts are visible but these are much less prominent than those on Jupiter. On rare occasions large storm systems may be visible as white spots and/or patches. The use of colour filters enhances the detail.

Saturn's largest satellite, Titan (8.3), is easily visible and moderate aperture telescopes should reveal six others: Mimas (12.9), Enceladus (11.7), Tethys (10.2), Dione (10.4), Rhea (9.7), Iapetus (10.2 - 11.9). Iapetus shows decided variations in brightness, probably due to surface features, with western elongations being brighter than eastern elongations. A suitable chart will be necessary to avoid confusion with faint background stars. The BAA Handbook contains charts for Titan and Iapetus and data for the others. Astronomy Now gives a chart for Titan.

Having identified the brighter satellites visually visit the Cassini mission web site to see what remarkable objects these small specks of light really are and the fascinating planet and ring system they inhabit. See http://saturn.jpl.nasa.gov and http://ciclops.org
Photography/CCD/Webcam Imaging of Jupiter and Saturn.

The brightness and large disc size of these planets make them excellent targets for the aspiring and experienced astrophotographer/CCD/webcam imager.

A wide angle, unguided exposure of up to 25 seconds on ASA 200 or 400 slide film will record the planet amongst the background stars of the constellation through which the planet is currently passing.

The main barrier to recording “surface” details will be the prevailing seeing conditions but with patience and a little luck excellent results can be achieved.

There are a number of publications on photography and imaging to which you can refer to as necessary.

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. Recent and current events.

Active galaxy OJ+287 in Cancer. A BL Lac object which may be on the verge of its regular outburst. Requires regular monitoring with reports being submitted to the BAA Variable Star Section. Good ongoing project for the 16”.

Gamma Virginis. This interesting binary is best placed for observation from late evening through the early hours star. Now past periastron it should be possible to split visually with the 16” under good seeing conditions and worth trying with smaller apertures to record when it can be resolved. Another object that requires regular monitoring over the next months. The unexpected motion detected at the last periastron passage in the 1930’s has again been observed indicating the presence of an unseen companion in the system, hence the need for continuing observations.


    1. Variable Stars.

Beta () Persei, Algol. +2.2 to +3.4, period 2.7 days. Favourable evening minima occur on 10d 19.9h and 30d 21.7h.

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 very successful “mentor” system where novices to variable star observation are given guidance and support.

2.2 Double Stars/Star Clusters/Nebulae/Galaxies.

Coma Berenices (Com).

To the east of Leo a closer inspection of what at first appears to a casual glance to be a large hazy patch reveals a beautiful scattering of moderate to faint stars. This is the Coma star cluster (Mel 111) best seen in binoculars and well worth a photograph.

2 Com ds (6.0, 7.5) separation 3.6". Use high power when seeing is good.

24 Com ds. (5.0,6.5) separation 20.3" Wide contrasting yellow and blue pair.

35 Com ds. (5.1,7,2) separation 1.2”. Yellow and purple (deep blue).

Coma is a fine hunting ground for galaxies plus a very fine globular cluster.

Start your search from the second magnitude star  Leo (Denebola). Move about 6o east to reach a 5th magnitude star.

NGC4192 (M98) (10.1) sg. Appears just before reaching the 5th magnitude star. Seen almost edge-on. Low surface brightness so can easily be missed on first inspection.

NGC4254 (M99) (9.8) sg. Slightly southeast of the 5th magnitude near M98. Bright nucleus surrounded by an outer haze.

NGC4321 (M100) (9.4) sg. From the 5th magnitude star move 5o northeast. Seen almost face on.

NGC4501 (M88) (9.5) sg. Located 4o east of M99. Inclined to our line of sight. Broad central glow surrounded by fainter envelope. Stands high magnification well.

Now examine the rest of Coma.

NGC4559 (10.5) sg. Bright oval smudge. Mottled appearance in large telescopes.

NGC4565 (10.5) sg. One of the finest "edge-on" spiral galaxies. Appears as a thin needle of light with the hint of a central bulge. Moderate apertures begin to show a dark dust lane. The North Galactic Pole is located a few degrees to the East.

NGC4826 (M64) (8.6) sg. This bright galaxy is located almost halfway between M53 and NGC4565. Nicknamed the "Black-eye galaxy" because of its appearance due to a dust lane which is visible in 6" and larger telescopes.

NGC5024 (M53) (7.7) gc. Locate  Com in the southeast corner of the constellation and move just a little to the northeast. Binoculars will show a fuzzy blob. Moderate aperture telescopes will begin to resolve the cluster into individual stars. A excellent object to finish with, but before packing up try to locate:-

NGC5053 (8.7) gc. Rather sparse globular cluster located 1o to the ESE of M53. Not an easy object in smaller telescopes which provides the challenge.
Canes Venatici (CVn).

 CVn ds, (2.9,5.5) separation 19.6". Cor Coroli (Heart of Charles), A fine bluish-white and white double star.

NGC4151 (11.2) sg. Barred spiral with a bright nucleus.

NGC4215 (10.5) ir. Located south and slightly west of NGC4244.

NGC4244 (10.7) sg. Spiral galaxy seen edge-on appearing as a needle of faint light. Fine object whose appearance brightens with increasing aperture.

NGC4258 (M106) (8.3) sg. Large inclined galaxy located about 5o east of UMa on the borders of Canes Venatici and Ursa Major.

NGC4395 (11.0) sg. Bright core with a low surface brightness circular halo.

NGC4449 (10.5) ir. Appears almost rectangular making it an unusual object to view.

NGC4485 (12.5) ir and NGC4490 (10.1) sg. Interacting pair of galaxies.

Canes Venatici continued.

NGC4631 (9.7) sg and NG4656 (10.4) pc. are a fine example of a pair of interacting galaxies, both edge-on to our view, located mid-way between Cor Coroli and the Coma star cluster. One end of NGC4656 has a distinct hook which may be glimpsed in 8" telescopes under good seeing conditions.

NGC4736 (M94) (8.2) sg. Locate B CVn and move 3o east to locate the tightly wound spiral galaxy which has a very bright core. 16" (40cm) telescopes reveal a hazy ring infilled with dusky mottling surrounding the core.

NGC5005 (10.8) sg. Located to the SE of  CVn.

NGC5033 (11.0) sg. Appears in the same low power wide field as NGC5005.

NGC5055 (M63) (8.6) sg. Easily located 5o east and slightly north of M94. Oval patch with brighter core.

NGC5194 (M51) (8.4), sg and NGC5195 (9.3). Interacting pair of galaxies. Aptly named the Whirlpool galaxy M51 was the first galaxy to have its spiral structure recognized. (Lord Rosse 1845). To locate the pair use the bright star  UMa at the end of the Plough and move about 4o SW. Both objects are easily visible in binoculars. A 12" (30cm) telescope will begin to show the subtle spiral structure and the tenuous bridge between the two galaxies.

NGC5272 (M3) (6.4) gc. Superb globular cluster easily seen as a fuzzy spot in binoculars. 12" telescopes will almost resolve this cluster to its core. To locate move about half the distance between Cor Coroli and the first magnitude star Arcturus (0.0). A fine end to your tour of this constellation.


Virgo (Vir).

The Virgo supercluster of galaxies, which extends into the neighbouring constellation of Coma Berenices, contains in excess of a thousand galaxies.

Our own Local Group of galaxies is probably an outlying "village" of this "Grand Metropolis".

Virgo and Coma provide the chance to collect a "hatful" of Messier objects in the same area of the sky. Star hopping skills will be well exercised. One note of caution though - there are numerous other galaxies bright enough to be detected in small and moderate instruments to cause confusion if care is not taken! Correct identification of objects in a crowded field presents a very rewarding challenge.

If at any time you get lost in your exploration don't panic or become dejected. Simply return to a known reference point and start again. Confidence is only gained through practice.

Locate B (Denebola) Leo and move 5 east to reach a 5th magnitude star. Move about a degree SE to reach NGC (M99) and then move 2o southeast to reach NGC4374 (M84) (9.3) and NGC4406 (M86) (9.2) easily visible in the same field of view. Scan this field carefully to locate other non-Messier galaxies. Note their positions and sketch the field, then use a suitable star chart to identify them.

About 1o southeast of M84 & M86 is NGC4486 (M87) (8.6) also known as "Virgo A" a powerful radio source. M87 is a giant elliptical galaxy and high resolution images reveal a huge jet of material being ejected from its core. There is evidence for an anti-jet. Radio maps reveal huge structure not detected at visual wavelengths. Current theory for the highly active nature of M87 points to a massive black hole at heart of the galaxy.

Virgo continued.

From M87 move about 1o east to locate NGC4552 (M89) (9.8) and then half a degree northeast to locate NGC4569 (M90) (9.5).

Return to M89 and move 2o eastsoutheast to locate NGC4579 (M58) (9.8). From M58 sweep just over a degree east to locate NGC4621 (M59) (9.8) & NGC4649 (M60) (8.8) visible in the same low-power field.

Return to M87 and move about 4o south to NGC4472 (M49) (8.4). 4o southwest of M49 is NGC4303 (M61) (9.7).

To complete our exploration of Virgo Locate the first magnitude star Spica and sweep almost 10o west to locate NGC4594 (M104) (8.3) the "Sombrero Hat". The visual effect is caused by the dark dust lane(s) of this galaxy.

For moderate and larger aperture telescopes a final challenge is to locate two “bright” quasars both variable in brightness. A detailed star chart of the areas will be required.



3C273 (11.7 – 13.3) at R.A. 12h 26m. Dec. +2.3o

3C279 (11.5 – 17.0) at R.A. 12h 56m. Dec. -5.8o

NGC3430 (11.5) Spiral galaxy.

NGC(3432 (11.2) Spiral galaxy seen nearly edge-on.

NGC3486 (10.3) Spiral galaxy seen nearly edge-on.

NGC3504 (11.1) Spiral galaxy.

P.V.H.
Useful symbols.



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