APRIL fromHermanus 2022 - SKY CHARTS - The Hermanus Astronomy Centre

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APRIL fromHermanus 2022 - SKY CHARTS - The Hermanus Astronomy Centre
APRIL
from Hermanus                    2022
                                 SKY CHARTS

 E V E N I N G S K Y 2 8 t h AP R I L a t 2 1 h 3 0 ( N O R T H D O W N )

 E V E N I N G S K Y 2 8 t h AP R I L a t 2 1 h 3 0 ( S O U T H D O W N )

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APRIL fromHermanus 2022 - SKY CHARTS - The Hermanus Astronomy Centre
THE SOLAR SYSTEM
  PLEASE NOTE: All events predicted are as observed from Hermanus, Western Cape, South
  Africa. Times are South African Standard Time (UTC +2).

                       HIGHLIGHTS FROM THE SKY GUIDE
                                          April 2022

Date   Time                Item
  1          08h24         New Moon
             02h44         Moon crosses equator
             01h11         Mercury at superior conjunction
  7          21h12         Moon at apogee (404 437 km)
  8          21h12         Moon northernmost (+26.9º)
  9          08h47         First quarter Moon
             19h51         Moon less than 2º from Pollux at dusk end
                           Mercury crosses the ecliptic
 10                        Venus crosses the ecliptic
 13          00h27         Mercury at perihelion (0.308 AU)
 15          13h34         Moon crosses the equator
 16          20h54         Full Moon (367 076 km, diameter 32.6’)
 18          05h30         Moon (98%) passes 27’ north of Zubenelgenubi (α Librae)
 19          20h19         Moon (88%) rises 16 minutes after Antares (α Sco) (3.8º)
             17h17         Moon at perigee (365 142 km)
 21          19h38         Moon southernmost (-26.9º)
 22          22h21         Moon (68%) rises 9 minutes (1.9º) before Nunki (σ Sgr)
 23          13h56         Moon last quarter
 24                        Mercury northernmost
                           Moon (22%) grouped within 33º of Mars, Venus, Saturn and Jupiter
 27
                           before sunrise
 28          09h50         Moon crosses equator
 29                        Mercury at eastern elongation (20º 36’)
 30          22h28         New Moon
                           Venus near Jupiter

                   SUGGESTED EVENING OBSERVATION WINDOWS
                        (Lunar observations notwithstanding)
                 Date                     Moon               Dusk end
              24rd March          Rises      23h13 (61%)                20h13
               4th April          Sets        20h27 (9%)                19h57
              22nd April          Rises      23h12 (61%)                19h35
               4th May            Sets       20H22 (14%)                19h24

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APRIL fromHermanus 2022 - SKY CHARTS - The Hermanus Astronomy Centre
SOLAR SYSTEM VISIBILITY
                                                             1st        1st
                    APRIL 2022                                                             Visibility
                                                             April      May
                                             Rises:         06h55       0718         Never look at the
Sun           Pisces - Taurus                                                          sun without
Length of                                    Transit:       12h47      12h40
              11.43 to 10.00                                                          SUITABLE EYE
day                                          Sets:          18h38      18h02          PROTECTION!
Mercury       Pisces to Taurus               Rises:         06h47      09h05
Magnitude     +1.9 to +2.6                                                            Behind the Sun
                                             Transit:       12h43      14h00
Phase         100% to 10%                                                            then after sunset
Diameter      5” to 11”                      Sets:          18h38      18h55
Venus         Capricornus to Aries           Rises:         03h17      03h55
Magnitude     -4.3 to -4.0                   Transit:       09h54      10h03              Morning
Phase         56% to 78%
Diameter      22” to 14”                     Sets:          16h31      16h10
Mars          Capricornus to Pisces          Rises:         02h46      02h37
Magnitude     +1.1 to +0.7
                                             Transit:       09h34      09h03              Morning
Phase         92% to 87%
Diameter      5” to 6”                       Sets:          16h22      15h29
Jupiter       Aquarius to Pisces             Rises:         05h20      02h19
Magnitude      -2.0 to -2.3                  Transit:       11h34      08h20              Morning
Diameter      33” to 37”
                                             Sets:          17h48      14h21
Saturn    Capricornus                        Rises:         02h59      23h11
Magnitude +0.8 to +0.7                       Transit:       09h43      05h56              Morning
Diameter 16” to 17”
                                             Sets:          16h28      12h38
Uranus    Aries                              Rises:         09h27      05h44          Evening then
Magnitude +5.8                               Transit:       14h46     11h00           moving behind
Diameter 3”
                                             Sets:          20h05      16h15            the Sun
Neptune Aquarius to Pisces                   Rises:         05h31      01h39
Magnitude +8.0 to +7.9
                                             Transit:       11h42      07h49              Morning
Diameter 2”
                                             Sets:          17h54      13h59
Pluto     Sagittarius                        Rises:         01h01      20h57
Magnitude +14.4 to +14.3
                                             Transit:       08h08      14h09              Morning
                                             Sets:          15h16      11h16

 Phase: In a telescope, the inner planets (Mercury, Venus and Mars) appear to us in phases, depending on
the angle of the Sun’s illumination, as does the Moon. The angular diameter is given in arc seconds (“). This
is the apparent size of the object as we see it from Earth.

Magnitude: we are accustomed to hearing stars described in terms of ‘magnitude’. For example the planet
Jupiter at magnitude -1.8 is considerably brighter than the star Antares (in Scorpius) at +1.05. The scale is
‘inverse’; the brighter the object, the lower the number. A ‘good’ human eye on a clear night can see down to
a magnitude of about +6.

Transit: When an object crosses the local meridian it is said to ‘transit’. The local meridian is an imaginary
line from the horizon directly north passing overhead (through zenith, see charts on page 1) to the horizon
directly south.

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APRIL fromHermanus 2022 - SKY CHARTS - The Hermanus Astronomy Centre
THE MOON
CRATER ARZACHEL (the Sky Guide lunar highlight)
Arzachel is remarkably clear in its structure and a favourite telescope viewing subject for amateur
and advanced astronomers.

Coordinates: 18.2ºS 1.9ºW, located in the highlands of the south-central part of the visible Moon,
close to the zero meridian (the visible centre of the Moon). It lies to the south of the crater Alphonsus
and, together with Ptolemaeus further north, the three form a prominent line of craters to the east of
Mare Nubium.
                                                           Below: Oblique view from Apollo 16, facing south above
Best seen: first quarter (9th April) and 6 days
after Full Moon (22nd April).
Type: ancient crater with high terraced walls.
Central mountain with a craterlet on its southern
slope.
Size: 98 km.
Naming: named for Abū Ishāq Ibrāhīm al-
Zarqālī, an 11th century Arab Muslim instrument
maker and astronomer. Like many of the craters
on the Moon's near side, Arzachel was named by Giovanni Riccioli. His 1651 nomenclature system
has become standardized.
Description: a relatively young lunar impact crater. The smaller Alpetragius lies to the north-west
with Thebit to the south-west along the edge of the mare. The rim of Arzachel shows little sign of wear
and has a detailed terrace structure on the interior, especially on the slightly higher eastern rim. There
is a rough outer rampart that joins a ridge running from the north rim to southern rim of Alphonsus.
The rugged central peak of Arzachel is prominent, rising 1.5 km above the floor, and is somewhat
offset to the west with a bowed curve from south- to north-northeast. The floor is relatively flat except
for some irregularities in the south-western quadrant of the crater. There is a rille system, named the
Rimae Arzachel, that runs from the northern wall to the southeast rim. A small crater lies prominently in
the floor to the east of the central peak, with a pair of smaller craterlets located nearby.

     No lunar or solar eclipses will be visible from southern Africa this month.

                     HERMANUS MOON RISE AND SET TIMES FOR APRIL 2022
     date      day    rise    set      date    day        rise     set       date     day       rise      set
    01-Apr     Fri   06h53   08h59    12-Apr   Tue       16h22    02h14     23-Apr    Sat      no rise   14h15
    02-Apr     Sat   07h54   19h27    13-Apr   Wed       16h53    03h17     24-Apr    Sun     00h21      14h58
    03-Apr     Sun   08h55   19h56    14-Apr   Thu       17h22    04h20     25-Apr    Mon     01h30      15h35
    04-Apr     Mon   09h55   20h27    15-Apr   Fri       17h51    05h24     26-Apr    Tue     02h36      16h06
    05-Apr     Tue   10h55   21h02    16-Apr   Sat       18h21    06h30     27-Apr    Wed     03h40      16h35
    06-Apr     Wed   11h53   21h42    17-Apr   Sun       18h53    07h38     28-Apr    Thu     04h42      17h02
    07-Apr     Thu   12h49   22h28    18-Apr   Mon       19h31    08h49     29-Apr    Fri     05h43      17h28
    08-Apr     Fri   13h42   23h19    19-Apr   Tue       20h14    10h01     30-Apr    Sat     06h43      17h56
    09-Apr     Sat   14h29   no set   20-Apr   Wed       21h06    11h14     01-May    Sun     07h44      18h26
    10-Apr     Sun   15h11   00h14    21-Apr   Thu       22h06    12h22     02-May    Mon     08h44      19h00
    11-Apr     Mon   15h49   01h13    22-Apr   Fri       23h12    13h23     03-May    Tue     09h43      19h38

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APRIL fromHermanus 2022 - SKY CHARTS - The Hermanus Astronomy Centre
METEOR SHOWERS
                                                               Observing
    From SGAS             Maximum                                                                      1   Velocity
                                           Duration           Prospects at        Radiant        ZHR
                                                                                                           Km/sec
       2022               Date/Time
                                                                  max
                                                                               10º south-west
                                                            poor, 61%
                          22nd April      16th to 25th                         of Vega (α Lyr)
    April Lyrids                                          moon is up for                          15         49
                        02h00 – 05h00        April                                close to n.
                                                           the duration
                                                                                    horizon
                                                          fair, 50% moon
                          23rd April      15th to 28th                         2.5º south of
    π Puppids                                               is up for the
APRIL fromHermanus 2022 - SKY CHARTS - The Hermanus Astronomy Centre
LOOKING UP

                  CLUB STARGAZING – the possibility of club Stargazing is now back thanks to
                  the relaxation of the COVID restrictions. The calendar on the front page of our
                  website indicates our planned events.

                  Please consult our website for updates: http://www.hermanusastronomy.co.za

                                       THE JEWEL BOX
                           NGC 4755, Kappa Crucis cluster, Caldwell 94

The following details are applicable to 28th April 2022 at 21H30
Description        Open cluster                              Visibility on 28th April 2022
Constellation      Crux
Distance           6.4 kly, 1.95 kpc                 Rises            Transits           Sets
Magnitude          +4.19 (integrated)            Does not rise         23h11          Does not set
Absolute mag.      -7.29 visual
Apparent size      10 arcmin
Alt/Az             +59º 23’ 15” / 155º 40’ 16”   Naked Eye            Yes, resembling a fuzzy star
J2000 lat/long     -60º 20’ 00” / 12h 53m 36s    Binoculars                 Yes, some detail
Diameter           18.7 ly, 5.7 pc               Telescopes                 Yes, more detail

NGC 4755 - Jewel Box Cluster
NGC 4755 is a stunning open cluster in the constellation Crux, the Southern Cross. It is known as
both the Jewel Box and the Kappa Crucis cluster (after its most prominent member).
Discovery : The cluster is one of the finest objects discovered by
Nicolas Louis de Lacaille during his visit to South Africa in 1751-
1752. John Herschel described this famous group of bright
young stars as "a casket of variously coloured precious stones"
and "...a superb piece of fancy jewellery", hence the name "the
Jewel Box" cluster.
Location: The Jewel Box is only visible from southern latitudes
and appears close to Mimosa (Beta Crucis), the easternmost star
of the Southern Cross.
Properties: an A-shaped asterism with an apparent magnitude of
4.2. It looks like a single fuzzy star to the unaided eye. The cluster
contains around 100 stars within a 10' diameter area. Most are
blue giants, the brightest of which is Kappa Crucis (Bayer star
designation), a blue supergiant of visual magnitude +5.9 and spectral type B5 1a, surface
temperature 13 600 Kelvin. The fourth-brightest is a magnitude +7.6 red supergiant of class M2
that contrasts strongly against its hot, blue companions. Distance estimates for the Jewel Box
range from 6,400 to 8,150 light years. This cluster is one of the youngest known with an estimated
age of only 7.1 million years.
The Coal Sack, a huge dark area within the band of the Milky Way, appears close to NGC 4755 to
its south-west. This dark nebula is probably much closer than the cluster at only 500 to 600 light
years distance.

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Observation

                                                                 the Jewel Box Cluster - Steve Crouch base

Prominent members
The central part of the cluster is framed by bright stars
making up an "A"-shaped asterism. The bar of the "A"
consists of a line of four stars. On the right (south) is BU
Cru, a magnitude +6.92 B2 supergiant and eclipsing
binary. Next to it is BV Cru, a magnitude +8.7 B0.5 giant
and Beta Cepheid variable. Next in line is DU Cru, an M2
red supergiant that varies irregularly between magnitude
7.1 and 7.6. The last of the four is CC Cru, a magnitude
7.83 B2 giant and ellipsoidal variable.
Each leg of the base of the asterism's outline is marked
by a blue supergiant star. HD 111990 (HIP 62953) is
magnitude 6.77 and B1/2. The star κ Cru itself is
magnitude 5.98 and B3.
Physical characteristics
The Jewel Box cluster is one of the youngest known open clusters. The mean radial velocity of the
Jewel Box cluster is 21 kilometres per second (13 mi/s). The brightest stars in the Jewel Box
include some of the brightest stars in the Milky Way galaxy.
Calculating its distance is difficult due to the proximity of the Coalsack Nebula, which obscures
some of its light.

Please keep in touch...
Have a look at our excellent website, edited by Derek Duckitt.
http://www.hermanusastronomy.co.za/
Contact ASSA - Get in touch with officers of the Society - we're real people with a passion for astronomy,
so contact us and let's talk!
You can find us on Facebook, Twitter, the
ASSAInfo mailing list and the ASSADiscussion               Grateful thanks to the following:
mailing list.
                                                           ASSA
ASSA website http://assa.saao.ac.za
                                                           Sky Guide Africa South 2022
ASSA Deep-Sky Section
                                                           Sky Safari
Whatsappchat group: [ 074 100 7237 ]                       Skywatchers’ Handbook
MNASSAhttp://assa.saao.ac.za/about/publications/           Stellarium
mnassa/                                                    Wikipedia
Nightfall https://assa.saao.ac.za/?s=Nightfall
Official Big 5 of the African Sky web page                 Edited by Peter Harvey -
Official Big 5 Facebook group                              petermh@hermanus.co.za –
ASSA Deep-Sky Section mailing list                         Tel: +27 (0) 81 212 9481

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