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Transcript
SKY DIARY
Last quarter
23 Sep, 10:56
22 Oct, 20:14
Moon phases
Apsides
Date
Apsis
06 Sep, 20h Apogee
18 Sep, 18h Perigee
Occultations
Date
18-Sep
20-Sep
21-Sep
21-Sep
21-Sep
23-Sep
24-Sep
17-Oct
19-Oct
19-Oct
19-Oct
19-Oct
20-Oct
25-Oct
26-Oct
Object
nu Piscium
mu Ceti
89 Tauri, NSV
16124
sigma 1 Tauri
sigma 2 Tauri
130 Tauri
26 Geminorum
Hyadum I,
gamma Tauri,
NSV 01553
71 Tauri, V777
Tauri
theta 2 Tauri
theta 1 Tauri,
NSV 16016
111 Tauri
31 Leonis
56 Leonis,
VY Leonis
A summary of the main sky events,
September to October 2016 (UT times)
New
01 Sep, 10:03
01 Oct, 01:11
Dist (km) Size
405,055 km 29’ 31”
361,896 km 33’ 00”
Date
04 Oct, 12h
17 Oct, 01h
Bright limb
Disappearance
Reappearance
Dark limb
First quarter
Ma 09 Sep, 12:49
09 Oct, 05:33
Apsis
Apogee
Perigee
Full
16 Sep, 20:05
16 Oct, 05:23
Dist (km)
406,096
357,861
Size
29’ 26”
33’ 23”
The position angle (PA) of the
occultations given below is
measured anticlockwise from the
northpoint of the Moon’s disc (use
the Moon’s north pole as a guide).
0°
270°
90°
180°
ZC
249
405
699
Mag
4.4
4.3
5.8
Phase
RD
RD
RD
Data for Greenwich
Time
PA⁰
Alt⁰
22:01
201
24
00:29
165
40
22:55
273
16
Az⁰
114
133
84
Data for Edinburgh
Time
PA⁰
Alt⁰
22:10
211
22
00:49
196
38
23:01
282
15
Az⁰
115
137
84
702
704
878
1029
5.1
4.7
5.5
5.2
RD
RD
RD
RD
23:05
23:19
03:44
01:59
208
237
267
243
17
19
49
28
86
88
136
96
23:16
23:27
03:44
02:06
220
246
280
256
17
19
45
26
87
89
135
97
462
635
6
3.7
RD
RD
20:27
00:12
240
272
19
45
95
130
20:34
00:12
248
286
18
41
95
130
661
4.5
RD
03:11
203
49
189
671
669
3.4
3.8
RD
RD
04:41
04:45
229
250
47
46
226
228
04:39
04:39
244
263
45
45
218
219
806
1486
1589
5
4.4
5.9
RD
RD
RD
01:39
03:35
03:18
238
302
233
50
24
11
137
104
94
01:42
03:34
03:30
252
317
252
45
21
11
137
103
95
These are the only occultation for this period, based on the following criteria: Mag: Visual magnitude. Phase: (R)eappearance, (D)isappearance or
(G)raze at (D)ark or (B)right lunar limb. Alt: Altitude. The Moon’s height. Az: The angular position along the horizon measured clockwise from
true north (through E, S, W back to N). PA: Position Angle, measured anticlockwise from the direction of the celestial North Pole. This listing
shows lunar occultations of stars brighter than mag +6, observable with small telescopes in a sky dark enough to be seen without difficulty. For
data specific to your own locality or details of fainter occultations, contact Occultation Section Director Mell Jeffery (address on p46).
A
s mentioned in previous editions of
Popular Astronomy, during this two
month period 16 occultations can be
observed, in fact if you are in the far
south west of England (Devon/Dorset)
you can add an extra one to the list!
On 20 September mu Ceti is occulted.
For much of the country the
reappearance takes place at the dark
limb of the 85% illuminated waning
gibbous Moon. However, further south,
e.g. Greenwich, you are more likely to
see the event take place at the lit portion
of the Moons southern cusp.
The Moon moves by the asterism of the
Hyades during 21 September. The +5.1
and +4.7 mag. stars sigma 1 and sigma
2, are occulted with a 10 to 14 minute
gap between the events, late in the
night, with the waning gibbous Moon
still rising in the east.
During the morning of 19 October, the
Moon passes through the Hyades,
occulting the stars theta 1 and 2 Tauri.
44 Popular Astronomy
For observers in the south of the country
there is a four minute interval between
the two occultations. For those further
north, e.g. in Edinburgh, the events take
place within 50 seconds of each other.
A little over an hour prior to the theta
1 and 2 Tauri event, there is a graze of
the +4.5 mag. star 71 Tauri. The graze
path for this event runs from the Welsh
coastline between Llangrannog and New
Quay, passes across country between
Walsall and West Bromwich, to the
north of Leicester, cuts across the Wash
and out to sea on the Anglian coast just
north of Cromer. North of this graze line
an occultation is visible.
Later that morning, approximately
07:41 UT, the Moon occults the +1.0
mag. star alpha Tauri, Aldebaran.
However this event is only visible from
the far south western area of England.
The 86% illuminated waning gibbous
Moon is at a reasonable altitude but the
Sun is just rising in the east, so this is a
www.popastro.com
daylight event.
The graze line for the event runs from
the north Devon coast, just south of
Croyde, clips the very north of
Barnstaple and cuts across the country
to the southern coastline, between the
entrance to Poole Harbour and Swanage,
in Dorset. South of this graze line an
occultation is visible, north, a
conjunction (07:42 UT for Greenwich).
The next event involving Aldebaran
takes place in December and is a
country-wide event.
Please see page 43 for maps showing
the graze path for the occultations 71
Tauri and Aldebaran.
For further information regarding any
of the events mentioned, or others listed
in the table, please contact me.
Observations of events, listed or
otherwise, are more than welcome.
Mell Jeffery
September - October 2016
SKY DIARY
Planets
T
his period offers an excellent opportunity to observe the
outer “ice giants”, which are very well placed and Mercury
gives its best morning show of the year for UK latitudes.
Mercury starts the period in inferior conjunction, between
the Earth and the Sun, on 13 September, but rapidly moves
into the morning sky becoming noticeable as a bright spark
above the eastern horizon. Climbing higher each morning, it
reaches its greatest elongation to the west of the Sun on 28
September, when it will lead the Sun by 18 degrees. On that
date Mercury will be obvious, due east, around 10 degrees
above the horizon at 05:25 UT, some 35 minutes before sunrise
and shining at a magnitude of -0.5. Mercury can be followed
each morning into the second week of October, its altitude
steadily reducing. Its brightness changes noticeably through
this period: being +1.1 on 22 September, reaching -0.6 by
month’s end, and -1.1 by 14 October. This is due to the steadily
increasing visible phase being just 28% illuminated four days
before greatest elongation, 50% on the day, and 94%
illuminated by mid-October.
Venus will be hard to see from UK latitudes during
September and October as it first appears close to the setting
Sun in the western evening sky. As the period progresses
Venus increases its separation to the east of the Sun but the
reducing angle of the ecliptic at this time of year places Venus
lower in the sky. From the UK the best time to glimpse Venus
is towards the end of October shortly before sunset, when it
will appear as a bright magnitude -4.0 spark around southwest, just above the horizon and slightly below much dimmer
Saturn (mag +0.5).
Mars keeps company with Saturn, at least from the start of
September, the pair being briefly visible as darkness falls, low
in the SSW. Mars has a prograde (eastern) motion against the
background stars in this period and will rapidly separate from
Saturn, appearing very slightly further south each night as
darkness falls. Sadly Mars also suffers from the declining
position of the ecliptic, being around 10 degrees up as darkness
falls throughout the period. Just like Venus and Saturn, Mars
improves in visibility the further south your location is. Its
apparent size falls below 10 seconds of arc in early September,
so really detailed observation will be very difficult by the end
of October.
The apparent proximity of both Saturn and Jupiter to the
Sun means that they too are lost to detailed night time
observation but, Saturn in particular, may be found and
observed in daylight as long as sensible precautions are taken
to ensure the Sun can never enter the field of view of either
the telescope or the finder-scope. Jupiter is just too close to the
Sun for this to be safely attempted.
Which brings us to the outer ice giant planets of Uranus
and Neptune: Neptune reaches opposition, due south at
midnight UT, on 2 September and Uranus reaches opposition
on 15 October. This means that both planets are visible during
nearly all of the available darkness on any night in the period,
with Neptune up first and Uranus following on. Neptune will
be a telescopic object, little more than 2 seconds of arc in
apparent size, shining at a faint +7.8 magnitude against the
background stars of Aquarius. In small telescopes it will
appear as a defocused pale-blue or blue-green “star” but larger
instruments and high magnification will start to show a visible
disc. From mid-UK latitudes Neptune will be around 28
degrees above the southern horizon as it transits due-south
and will be worth seeking out if the seeing is steady. On the
evening of 15 September, the Moon and Neptune are in a very
close conjunction and from mid UK latitudes Neptune will be
hidden behind the nearly full Moon until around 19:54 UT,
when it will appear from behind the mountains on the southeastern limb – an interesting observational challenge.
Uranus will be even better placed than Neptune, transiting
some 2 hours and 40 minutes later and noticeably higher,
around 46 degrees up throughout the period. Uranus will also
appear both slightly larger and considerably brighter, on the
edge of naked eye-visibility at magnitude +5.7, against the
background stars of Pisces, the planet should appear as a bluegrey disc in visible light under steady seeing conditions.
Alan Clitherow
Meteor notes
September: Although background sporadic and minor shower rates are quite good during September, there are no major
meteor showers active.
October: The highlight of October is the broad peak of the Orionid meteor shower during 20-24 Ocober. A good number of
Orionids are bright and leave persistent trains. Be aware that the Orionid radiant actually lies midway between the main
patterns of Orion and Gemini, rather than within the main stars of Orion itself, and doesn’t rise above the horizon until around
21:00 UT (22:00 BST). The disappointing news for 2016 is that a waning gibbous moon will be rising soon after this. Activity
from the Taurid meteor shower can also be seen throughout October, typically producing a few meteors per hour, rising as the
month progresses. For additional information, see www.popastro.com/meteor/reference/meteorshowers/index.php
Tracie Heywood
Variable Star notes
Eclipsing Variables: RZ Cassiopeiae can be seen in eclipse during the evenings of 3, 9 and 15 September, with the first
eclipse being centred near 22:00 BST (21:00 UT) and each successive eclipse in the sequence occurring approx. 35 minutes
earlier. Another series of evening eclipses occurs on 4, 10, 16, 22 and 28 October, with the 4 October eclipse being centred just
before midnight BST (23:00 UT). Eclipses last for just under five hours.
The most favourable eclipses of Algol (Beta Persei) will be centred at the following times (UT): 6 September 22:42, 9
September 19:54, 29 September 21:12, 19 October 23:00, 22 October 19:48. Eclipses last for approximately. ten hours.
Mira type variables: Best placed for observation is Chi Cygni, which is due at maximum in mid-September and should be
readily visible in binoculars during September and October. It may also be visible with the naked eye for a while from good
observing sites. R Ursae Majoris is due at maximum in early September and is usually just below magnitude +7.0 at maximum.
T Ursae Majoris should reach maximum in early October, with its average peak brightness being around magnitude +7.7. Mira
(Omicron Ceti) will be closing in on its 9th magnitude minimum, but should be visible in larger binoculars.
Finder charts for these and other variable stars on the SPA VSS programme can be found by clicking on the name of the star in
the section’s programme listing: www.popastro.com/variablestar/observingprogramme/index.php
Tracie Heywood
September - October 2016
www.popastro.com
Popular Astronomy 45