Download 1” “Sky-Notes” of the Open University Astronomy Club. April 2005

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“Sky-Notes” of the Open University Astronomy Club.
April 2005.
All times shown are UT.
1. Solar system.
Earth.
For a few weeks around the equinox the Zodiacal Light may be visible from dark
sites with a clear east and/or west horizon. Look for it in the predawn or darkening
twilight evening skies where it should appear as a thin cone of light stretching up
from the horizon. The ZC is due to sunlight being scattered by dust along the plane of
the Solar System.
Meetings.
No major meetings this month.
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. Although hours
of darkness are decreasing opportunities are still presented for observing aurora from
dark sites.
Moon.
Phases:
Last quarter
New
First quarter
Full
02d
08d
16d
24d
Apsides:
Perigee 04d 11h
Apogee 16d 19h
Perigee 29d 10h
00h
20h
14h
10h
50m
32m
37m
06m
Diameter. 32’ 26”
Diameter. 29’ 33”
Diameter. 32’ 23”
Distance. 368,500km
Distance. 404,300km
Distance. 369,000km
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.
Apr. 12
12
13
14
15
17
20
20
ZC No.
683
698
812
979
1108
1348
1645
1648
Mag.
7.3
7.6
7.8
7.7
6.9
7.7
6.6
7.0
Time.
19h 29.5m
21h 52.5m
19h 31.8m
20h 44.6m
20h 58.4m
21h 09.7m
20h 44.7m
21h 43.1m
Observing the Moon.
Spring provides an excellent opportunity for evening observation of the Moon. From
the thin waxing crescent (particularly favourable) to near Full the Moon has a
northerly declination. 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 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. At times features along different parts of the limb are better presented due the
effect of libration – an apparent wobbling of the Moon about its axis – that allows us
to see about 59% of its surface. The BAA Handbook and some monthly magazines
(Sky & Telescope) give details of the magnitude and direction of libration. The Moon
is also an excellent object to start photography/imaging especially with webcams and
digital cameras.
Mercury.
Mercury passed through inferior conjunction on March 29th becoming a morning
object. Greatest Elongation W (27) is reached on April 26th. However it will never be
very high in the sky so that observation from the northern hemisphere I less
favourable. During the month brightness increases from +3.2 (diameter 11.3” phase
0.05) on the 5th to +0.3 (diameter 7.5” phase 0.50) on the 30th.
Vague surface markings may be seen. Members are encouraged to capture the change
in size and phase during the apparition especially using a webcam.
Venus.
Low down in evening twilight Venus is not an easy object. Magnitude –3.8 (diameter
9.7”, phase 0.99 phase). At present a fairly mundane object.
Mars.
Mars is a difficult object to observe low down in the dawn skies. During the month
brightness increases from +0.9 (Diameter 5.8”, phase 0.90) to +0.6 (diameter 6.7”,
phase 0.87).
Jupiter.
Opposition reached on April 3rd providing opportunity for all night observation.
Unmistakeable at magnitude –2.4 the disc shrinks from 44.1” to 43.2” by the end of
the month.
An excellent target for Webcam imaging. See separate observing sheet.
Saturn.
Saturn is still well placed for observation throughout the evening. Magnitude
decreases from +0.1 (diameter 18.7”) to +0.2 (diameter 17.7”) during the month. The
rings are still well open presenting a magnificent view in any telescope. Like Jupiter
Saturn presents an excellent target for Webcam imaging. See separate observing
sheet.
Uranus.
A morning object low down in the morning twilight. Unlikely to be observed this
month.
Neptune.
Beginning to emerge into the predawn skies but not an easy object to observe.
Pluto.
An early morning object requiring at least an 8” (200mm) diameter telescope and a
dark site to locate. A suitable target for CCD imaging.
Asteroids.
The following asteroids can be located with binoculars and small telescopes using a
suitable star chart.
Pallas (2). Fades from 7th to 8th magnitude during the month. Crosses from Virgo into
Coma an area rich in moderately bright galaxies. Worth imaging.
See monthly periodicals/BAA Handbook for details of other asteroids.
Comets.
Comet/2004 Q2 (Machholz). At 8th magnitude, fading slowly it is still a good
binocular object. Although not a spectacular object Machholz has provide four
months of easy observation. Moving through Draco towards the Plough.
Any images?
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.
A minor shower the Virginids is active between April 7th – 18th with peak activity on
the 10th.
The Lyrids are active between April 19th – 25th with peak activity on the 22nd.
Unfortunately this coincides with a nearly Full Moon.
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.
A Hybrid Solar Eclipse takes place on April 8th. Visible from Central America and the
Pacific Ocean. A Hybrid eclipse occurs when the eclipse moves from the partial phase
to annular, to total, to annular and returns to partial.
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).
2.1
Variable Stars.
Beta () Persei, Algol. +2.2 to +3.4, period 2.7 days. Favourable evening minima
occurs on 8d 19.5h and 28d 21.2h.
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 1st, 6th, 12th, 17th, 23rd and 28th.
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. This
Section operates a “mentor” system where novices to variable star observation are
given guidance and support.
2.2
Double Stars/Star Clusters/Nebulae/Galaxies.
Leo (Leo).
This easily recognized constellation is also a fine hunting ground for many
moderately bright galaxies providing an excellent area to practice "star-hopping"
skills as there are many bright reference stars should you go astray.
Leo contains some fine double stars.
Alpha (Regulus) (1.4, 7.7) separation 176.9”. Regulus is blue/white, the
companion is yellowish.
Gamma () (2.2, 3.5) separation 4.4”. Deep yellow/pale yellow.
54 Leonis (4.5,6.3) separation 6.5”. Pale yellow/bluey-green.
90 Leonis (6.0,7.3) separation 3.3”. Both bluish-white. A third member of the system
(8.7) sepation 63” in p.a. 234o, deeper blue.
A "route" of exploration I enjoy is to start with NGC2903 at the eastern end of the
"Sickle" and follow the curve of the sickle until Regulus is reached, then move to the
"underbelly" containing M95/M96 and then to the tail where M65/M66 are located.
Finally drop down the hind leg to the bright but rather isolated NGC 3521. Following
the above route will lead you to encounter numerous moderately bright galaxies some
of which make pleasing groups in the same low power/wide field of moderate
aperture telescopes. Don't be afraid to use high magnification once you have located
an object.
Leo (Leo) cont.
NGC2903 (8.9) sg. A spiral galaxy inclined to our line of sight. One of the brightest
galaxies in Leo it is surprisingly not a Messier object.
NGC3190 (11.0) sg and NGC3193 (10.9) eg. Pair of galaxies located mid-way
between and .
NGC3226 (11.4) and NGC3227 (10.8) about 1o east of  form a close interacting pair
of galaxies.
NGC3351 (M95) (9.7) sg, NGC 3368 (M96) (9.2) sg and NGC 3379 (M105) (9.3) eg.
An excellent trio in the same low power field located about 3o south of 52 Leo. Close
to M105 is NGC 3384 (10.0) eg.
NGC3623 (M65) (9.3) sg, NGC3627 (M66) (9.0) sg and NGC3628 (9.5) sg. Located
about 3o SSE of  form another fine trio in a low power field. NGC3628 is seen edgeon and begins to reveal a dark dust lane at higher power with moderate apertures.
NGC3596 (11.0) sg. Located about a degree east of the M65/M66 group.
NGC3607 (10.0) eg. and NGC3608 (11.0) eg. A close pair of galaxies midway
between  and .
NGC3626 (10.9) sg. Located about one degree east of NGC3607.
NGC3655 (11.9) sg. Located about two degrees southeast of NGC3607.
NGC3686 (11.4) sg. Located about one degree NNE of NGC3655.
NGC3521 (8.9) sg. "Star-hop" southwards from the M65/M66 group to locate this
bright spiral galaxy which is often overlooked as it lies some way south of the main
body of Leo. Another object overlooked by Messier?
Two objects belonging to the "Local Group" of galaxies are located in Leo. Both are
dwarf galaxies and are extremely difficult to view visually but make excellent targets
for CCD imagers.
Leo I is located a mere third of a degree north of Regulus whose light drowns the
feeble glow of the small stellar system.
Leo II is located two degrees north of . It is smaller and fainter than Leo I.
Leo Minor (LMi).
A small constellation providing an opportunity to develop your “star-hopping” skills.
NGC3003 (11.7) and NGC3021 (12.1) form a close pair. Take care when identifying
the identity of this pair as NGC3021 has a higher surface brightness.
NGC3184 (9.7) although just over the border in neighbouring Ursa Major this spiral
galaxy is easily located about 1o west of  UMa.
NGC3245 (10.8) Elliptical galaxy.
NGC3254 (11.5) Spiral galaxy seen almost edge-on.
NGC3294 (11.7) Spiral galaxy.
NGC3344 (9.9) Spiral galaxy. It is the largest and brightest galaxy in Leo Minor. A
ninth magnitude double star lies 1' to the east which interferes with the view.
NGC3395 (12.1) and NGC3396(12.2) Interacting Spiral and Peculiar galaxies.
NGC3414 (10.7) Spiral galaxy.
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.
o b