The night sky in April 2019

posted 30 Mar 2019, 15:23 by Pete Collins   [ updated 31 Mar 2019, 05:02 ]
by Anne Holt

Sunrise   1st:    06.43       30th:   05.37
Sunset    1st:    19.43       30th:   20.36

Astronomical darkness
1st:  21.49   to  04.35        30th:  23.21  to  02.50 

New Moon:    5th at  09.50
Full Moon:    19th at 12.12

Lunar apogee:     1st at  00.15  (405576 km)   28th at 18.21  (404576 km)
Lunar perigee:   16th at  22.06  (364208 km)
Because we have 2 Lunar apogee in April it means that the month includes a complete anomalistic month - the name given to the period between 2 successive perigee or apogee.

April full Moon is known as the Pink Moon, because of the pink flowers which bloom in the spring  (tra la  - for any fans of G&S). Other names are the Sprouting Grass Moon, Hare Moon and Fish Moon. The Old English/Anglo Saxon names are Egg Moon and Paschal Moon, because this is the one used to calculate the date of Easter.

Highlights

What highlights?  It's almost the end of our 2018/19 season and now the clocks have changed it's too light to do any observing before 9pm, even when the sky is clear.  At the start of April we have 6 hours 46 minutes of astronomical darkness, but only half as long by the end of the month. The only planet putting on a good show is Jupiter, shining brightly in the morning sky at mag -2.3.  The downside is that it remains very low.  The first reasonable meteor shower in months will be washed out by the glare of the just past full Moon and we'll probably have a lot of rain - April is known for its showers.

Looking away from the sky, we do have Easter to look forward to, towards the end of the month.  It has an astronomical connection in the way it is calculated, Easter Sunday is the Sunday after the first full Moon on or after the Vernal Equinox, the date of which is always taken as March 21st even when, as in the last few years, it actually occurs on 20th.  The earliest possible date for Easter Sunday, March 22nd, is extremely rare, the last time was in 1818 and the next won't be until 2285. The latest date, April 23rd, is much more frequent, some of us may have been around the last time in 1943, others may still be here for the next in 2038.   The sequence of dates isn't quite as random as it may appear - it will start to repeat itself after 5,700,000 years.  Which got me thinking:  is this why mathematicians keep on calculating pi to more and more decimal places?  Do they hope to eventually find a pattern?  The latest attempt, by a Google employee, has got it to 31,415,926,535,897 decimal places.  I did wonder why they stopped there, rather than adding a few more to make a nice round number   - till I realised that this is the first 14 digits of pi.

Constellations

Now that BST has been forced upon us, we have to wait even longer for the skies to darken each evening. By the time it gets really dark the winter constellations, including the beautiful area around the Winter Hexagon, so rich in bright stars, is sinking slowly in the West.

Ursa Major is now high in the sky with the Plough overhead around midnight in the second half of the month. Follow the curve of the handle down to the orange coloured Arcturus, brightest star in the constellation Bootes the herdsman, and the 4th brightest in the night sky.
The signature constellation of spring, Leo, is still riding high in the south and the Summer Triangle of Vega (in Lyra), Deneb (Cygnus) and Altair (Aquila) is now rising in the east and visible in the early hours.

Planets

Mercury:  in Aquarius, mag 0.8
A morning object this month but very low in the sky throughout. On 1st it rises at 06.07 but is still 3 degrees below the horizon at dawn.  It is at aphelion (furthest point in its orbit from the Sun) on 10th at 08.40 and the following day reaches greatest western elongation at 27.7 degrees west of the Sun but, because of the angle of the ecliptic, is still very low.  On 13th it reaches its highest point in the morning sky, rising at 05.46 but still not managing to clear the horizon before the sky begins to brighten.  On 16th it moves into Pisces and from 23rd spends a few days over the border in Cetus, before returning to Pisces on 27th, brighter at mag -0.2 but still too low to be seen easily.  By month end it rises at 05.17, only 20 minutes before the Sun.

Venus:  in Aquarius, mag -4.0
Also very low in the morning sky this month but, because it is so much brighter than Mercury, might be seen in the morning twilight.  On 1st it rises at 05.55, just under an hour before Sunrise, reaching 2 degrees in the ESE by dawn.   On 2nd the crescent Moon passes south of the planet, closest  (2.5 degrees) at 08.11,  about 90 minutes after Sunrise.  Mercury is also quite close to the pair but much harder to see in the dawn sky.  Venus is at aphelion on 18th, then follows the smaller planet into Pisces on 17th, then into Cetus from 27th to 29th. On 30th, when it is back in Pisces, it rises at 05.00 as civil twilight begins.

Mars: in Taurus, mag 1.4
Visible in the evening sky, as it begins to darken, still setting around 00.30 each day. On 1st it is about 32 degrees altitude in the west at 20.30.  During the first few days of the month it moves N eastwards between the Pleiades and the Hyades (the V shaped head of the bull asterism).  On 1st it is 3.5 degrees SSW of the small cluster and on 8th and 9th the Moon joins the party,  at 21.00 on 9th the Moon will be 7 degrees to the SE.  On 31st Mars is 20 degrees above the western horizon as the sky darkens around 21.30, setting 3 hours later. 

Jupiter:  in Ophiuchus, mag -2.3
Very bright in the morning sky but still low. On 1st it rises at 02.17 and culminates, 13 degrees above the southern horizon, at 06.05, just over half an hour before sunrise.  It rises earlier as the month progresses but will remain low for a long time yet.  On the morning of 23rd the 84% Moon passes 6 degrees west of the planet at around 4am.  They are at their closest, less than 2 degrees apart,  around 13.00, in daylight.  On 30th it rises at 00.21 and reaches 13 degrees in the south at 04.09, while the sky is still quite dark but not astronomically so.

Saturn:  in Sagittarius, mag 0.6
Another morning object in the southern part of the Zodiac, so remaining very low in the sky.  On 1st it rises at 04.00 and reaches an altitude of 10 degrees by dawn.  On the morning of 25th, the 67% Moon passes about 6 degrees west of the planet, the following day it is 6.7 degrees to the east.  They are at their closest, only 22 arcminutes, during the day of 25th - if you happen to be in Australia or New Zealand on that day (night on that side of the world) you might see the Moon occult the planet.  On 30th it rises at 02.09 and reaches 13 degrees before the sky gets too bright.

Uranus:  in Aries, mag 5.9
Not visible this month as it approaches Solar conjunction, when it is on the opposite side of the Sun from the Earth.  On 23rd it sets an hour and a half after the Sun but is separated from it by only 20 degrees.  At the end of the month it is a morning object but even closer - on 30th it appears only 6 degrees from the Sun, rising just 9 minutes before it.

Neptune:  in Aquarius, mag 8
Still not visible after last month's Solar conjunction.  On 1st it rises 30 minutes before the Sun but is still 9 degrees below the horizon at dawn.  By 30th it rises at 04.29 but still doesn't reach the horizon before the sky brightens. 

Dwarf Planets and Asteroids

Ceres, in the asteroid belt, is the only dwarf planet which is close enough and bright enough to be seen through a small scope.  In April it is in Ophiuchus at mag 8.2.  On 1st it rises at 00.55 and culminates, 19 degrees in the south, 75 minutes before Sunrise.  It brightens slightly during the month, reaching mag 7.6 by 30th, when it rises at 22.55 and culminates, still at 19 degrees, at 03.25.

The rest, which orbit beyond Neptune, in the Kuiper Belt, are too distant and too faint to be seen even in the best amateur scopes. When well positioned they could possibly be targets for good amateur astrophotographers

Pluto; in Sagittarius, mag 18.8
Too low in the sky to be a reasonable photographic target, never gets higher than 14 degrees above the horizon.

Eris: in Cetus, mag 18.8
Reaches Solar conjunction on 13th, so not visible this month as it appears too close to the Sun.

Haumea:  in Bootes, mag 17.3
A much better bet for any keen astrophotographers who fancy a game of Spot the Difference with images taken a few days apart. On 1st it reaches 53 degrees above the southern horizon at 02.49.  It is at opposition (directly opposite the Sun in the sky) on 16th, and on 30th culminates at 00.54 at around the same altitude.

Makemake:  in Coma Berenices, mag 17.1
Also well positioned for photography.  On 1st it is at 32 degrees in the east at 21.04, just before the start of astro darkness, and 40 degrees in the west by dawn.  On 30th it is at 57 degrees in the SE at 22.15 and 35 degrees west at dawn.

A couple of asteroids reach opposition in April.  They are closer and brighter than the distant dwarf planets, even though they are much smaller, and might be seen in amateur scopes - even in good binoculars from a very dark sky site.  Again the comparison method is best, as they will never appear as anything other than a point of light.

Pallas:  in Bootes, mag 7.9
The second asteroid to be discovered culminates at 02.35 on the 1st, at an altitude of 51 degrees in the south, 5 degrees SW of Arcturus. It moves northwards through Bootes, reaching opposition on 6th.  By 30th it will have faded to mag 8.2, culminating at 00.19, still reaching 51 degrees.

Iris: in Corvus, mag 9.4
The 4th brightest object in the asteroid belt is much lower in the sky.  On 1st it culminates at 01.20, reaching 22 degrees in the south. It is at opposition on 5th, when it gets to 23 degrees at 01.01.  On 17th it moves into Virgo and ends the month at mag 9.9 but slightly higher, culminating 26 degrees above the southern horizon at 22.54.

As always, recommended sites for exact positions and more information on Solar System objects

Meteor Showers

One fairly major shower in April.

The Lyrids, active April 16th to 28th, peak on the night of 22nd/23rd.  ZHR 18.
These medium paced meteors are the earliest recorded shower, in 687 BC Chinese astronomers noted that meteors fell like rain. Nothing like that now but there are occasional outbursts, the last in 1982 when a ZHR of 90 was recorded at the peak.  The parent comet is C/1801G Thatcher, which no one alive now will have seen or ever will see - its last visit was in 1861 and it won't return until 2276. 
The bad news is that this year's shower will be a washout, even if it isn't raining all but the brightest meteors will be washed out by the glare from the just past full Moon.

Minor Showers
A few of these are given in various sites, however none are included in the International Meteor Organisations calendar.

Gamma Virginids, active 5th to 21st, peak 14th.  These could well be considered by the IMO to be part of the Antihelion Source, which has a radiant moving through Virgo in April.

Some sources mention a couple of weak showers with radiants in Draco, active in the first half of the month,  Delta Draconids, peak 31st March to 2nd April and the Tau Draconids, peak April 1st.  Might be worth keeping an eye on the general direction of Draco at the start of the month.

Alpha Bootids:  active April 4th to May 13th, peak 28th. very slow moving meteors leaving trails.  The shower could include fireballs.


Comets 

A couple are still quite high in the sky but have faded considerably, and continue to do so.

46P/Wirtanen:  in Leo Minor, mag 13.3.  On 1st it is 60 degrees above the SE horizon at 21.04, culminating slightly higher, at 22.30.  It moves into Leo on 29th ending the month at mag 15.2, about 60 degrees in the west at 22.14.

38P/ Stephan-Oterma:  in Lynx, mag 12.5.  Also fading but not as fast as Wirtanen.  It's still circumpolar, on 1st it reaches 78 degrees in the south at 21.23. It moves into Leo Minor on 25th and ends the month at mag 13.3, reaching 61 degrees in the SW at 22.14.

Unfortunately the website which I usually recommend for details of current comets, seems to have vanished.
Maybe it will return in time for next month's sky notes. 
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