The night sky in April 2018

posted 30 Mar 2018, 12:40 by Pete Collins   [ updated 30 Mar 2018, 15:24 ]
by Anne Holt

Sunrise:    1st    06.42           30th     05.36
Sunset:     1st    19.44           30th     20.36

Astronomical Darkness
1st:    21.50  to  04.34      30th    23.21  to  02.49

New Moon:  16th at 02.57
Full Moon:   30th at 01.58

This full Moon is known as the Pink Moon because many flowers of this colour bloom in April. No Lunar eclipse this month, so it won't appear pink. In Old English/Anglo Saxon it was known as the Egg Moon.

Highlights - and lowlights

No more HPAG meetings until late September, fewer and fewer hours of darkness, and as for true astronomical darkness only 6hrs 44m on 1st and a measly 3hrs 28m on 30th.  And let's not forget the proverbial April showers which mar many a night's observing.
On the plus side Venus and Jupiter are both shining brightly, their positions still improving as the month goes on.  We have the Lyrid meteor shower peaking on 22nd, the likelihood of bright fireballs and, though there won't be anything to see, Uranus makes a rare move. There are bright mid evening passes of the ISS every evening from 1st to 6th.

On 1st we have Easter Sunday, which could be considered to be an astronomical event because of the way it's calculated - it's the first Sunday after the first full Moon on or after the Vernal equinox. For anyone who may be interested, the earliest possible date for Easter Sunday is March 22nd. This happens only very rarely, the last time was in 1818, the next will be 2038.  The latest is April 23rd, not nearly so uncommon:  last in1943, next time in 2038.  The most common date is April 19th.  And, though the sequence of dates may appear to be completely random, it isn't - it starts to repeat itself after 5,700,000 years.

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  Pisces, mag 5.8. At inferior conjunction on 1st and is not visible, rising only 18 minutes before the Sun. It hardly improves during the month, on 30th it rises at 05.07, only 29 minutes before sunrise.  It will have brightened to mag 0.3 by 30th  but is hardly visible as it is still below the horizon as the sky brightens. 

Venus: in Aries, mag -3.9. An evening object, its position improving throughout April but still to reach its best.  On 1st it sets at 21.11, almost 2 hours after Sunset, and is  12 degrees above the horizon as the sky darkens. It moves into Taurus on 20th and from 22nd to 26th passes south of the Pleiades.  By month end it has moved to the north of the Hyades, is 17 degrees above the horizon at 9pm and sets 2 and a half hours after the Sun.

Mars:  in Sagittarius, mag 0.3. Still quite low in the sky.  On 1st it rises at 03.24 and reaches an altitude of 11 degrees above the horizon before the sky starts to brighten.  It appears close to Saturn, separated by less than 2 degrees on 2nd, when they are both north of the Teapot asterism.  Mars then moves away following a path eastwards between the Teapot and the less obvious Teaspoon asterism.  By month end it will have brightened to mag -0.3, rising half an hour after midnight but still not culminating in darkness.  The distance between Mars and Earth is now decreasing so the planet appears larger when seen through a scope.

Jupiter
:  in Libra, mag -2.4. Dominating the sky for most of the night during April.  On 1st it rises at 23.22, culminating at 03.51, when it will be 19 degrees above the southern horizon.  It is close to the gibbous Moon on 3rd/4th.  It  brightens slightly during the month, mag -2.5 on 30th, when it rises at 21.11 and culminates at 01.46.

Saturn
:  in Sagittarius, mag 0.5. Rises at  03.18 on 1st and reaches an elevation of 12 degrees by the time the sky brightens.  Best seen between 05.0 and 06.00.  On 30th it rises at 01.24 and culminates half an hour before sunrise, reaching an altitude of 13 degrees before the sky brightens.  It will  be slightly brighter at mag 0.4.

Uranus: in Pisces, mag 5.9. Not easy to see this month, even at the beginning - on 1st it sets about 90 minutes after the Sun, a couple of hours before astronomical darkness begins.  Conjunction is on 18th, when the planet appears only 3 degrees from the Sun, so can't be seen.  It then becomes a morning object but still not visible - on 30th it rises only 15 minutes before Sunrise.  However, Uranus does undergo a rare change in April.  Because it takes 84 years to orbit the Sun it remains in each Zodiac sign for an average of 7 years,  On April 28th it moves into Aries, where it will remain until March 2025.

Neptune
: not visible

Minor planets


Ceres
, in Cancer, mag 7.9. Should be visible in good binoculars and small telescopes, especially in early April, but only as a point of light as it is so small. On 1st it culminates at 21.12 and is 67 degrees above the southern horizon. By month end it will have faded to mag 8.4, setting at  04.57.

Haumea
, in Bootes, mag 17.3. Reaches opposition on 14th but is out of reach of most amateur scopes.  However it is a possible photographic target as it moves slowly eastwards below Arcturus.

Makemake, in Coma Betrenices, mag 17.

For more information on planetary positions, see
https://in-the-sky.org/ephemeris.php
Minor planets come under the heading 'Asteroids'.

Meteors

One fairly major shower this month.

Lyrids, active 14th - 30th, peak 22nd,  ZHR 18 - 20. This is the earliest known shower, recorded in 687BC by Chinese astronomers who said that meteors 'fell like rain'.  Not nearly so prolific now but occasionally puts on a spectacular show, the last time in 1982 when a ZHR of 90 was recorded. These are medium paced meteors, average mag around 2.  Their parent comet is C/1801G Thatcher, which we will never see.  It last came close to the Sun in 1861 and won't return until 2276.  The shower is best seen, this year, on the morning of 22nd after the 48.5% lit Moon has set at 02.34.

A few minor showers are mentioned on various sites, however these are not in the International Meteor Organisation calendar,  and sources don't always agree on dates - or anything else.

Gamma Virginids: active 5th - 21st, peak 14/15th  (some sites say there is no definite peak)  ZHR 5

Delta Draconids:  active March 28th to April 12th.  ZHR 5. Very slow moving meteors, leaving trails.  Best seen around midnight.
Some sources give 2 separate showers - Delta Draconids,  March 13 to April 17th, peak March 31st to April 2nd,  and Tau Draconids, March 28th to April 12th, peak April 1st.

Alpha Bootids:  April14th to May 13th, peak April 28th.  Very slow moving leaving fine trails.  This shower could include fireballs.

April fireballs:  Active from 14th -20th,  Meteors of mag -3 or brighter with no specific radiant.  They appear to come from the SE area of the sky.

And the Antihelion source is active in the first half of the month and again near the end.   These are meteors not belonging to any particular shower, having a radiant on the ecliptic, oposite the position of the Sun.


Comets

Again, there are several very faint comets around, none brighter than mag 10.5. One worth mentioning is C2016R2 (panSTARRS)  mag 11.0. moving from Perseus into Auriga,towards Capella.  Notable  for its bright blue tail. For more information, see www.cometwatch.co.uk/current-observable-comets/
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