The night sky in April 2016

posted 31 Mar 2016, 06:06 by Pete Collins
by Anne Holt

Sunset:   1st    19-45     30th:   20-38

New moon:  7th     Full moon;  22nd

This month's highlights are a lunar occultation of Venus and the oldest recorded meteor shower.
However, conditions are not good for viewing either of these. Also, a good month to try to spot elusive Mercury.


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 beautiful area round the Winter Hexagon, so rich in bright stars, is sinking slowly in the West.

Winter Hexagon

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 Aries, mag -1.5. This will be the best month this year to spot the elusive planet Mercury, which can never be seen in a dark sky as it is so close to the Sun. The best way of spotting it is to scan the western horizon with binoculars after the sun has set. In early April it sets about an hour after the sun so should be visible about 20 minutes after sunset from a site with a good clear western horizon. On 8th it is 6 degrees to the right of the 2% lit moon. It reaches greatest eastern elongation on 18th, when it sets 2 hours after the sun, but will have faded to mag 0.3.   It continues to fade rapidly and by month end will be at mag 2.9.

Venus:  in Pisces, mag -3.9. Not easy to see this month, despite its brightness, as it rises only a short time before the sun.
On 6th, it is occulted by the 2% lit moon.  Unfortunately, this is in daylight - the planet moves behind the much fainter moon at 8.37am and reappears after about 20 minutes. 

Mars:  in Ophiuchus,  mag -0.5. Rising soon after 2am in early April and around midnight by month end, when it will have brightened to -1.5 as it moves towards opposition in May. Moving eastward against the background stars until 17th, when it appears to stand still before changing to retrograde motion, ending the month just slightly south of its position at the start of April. Mars, Saturn and red giant Antares form a fairly close triangle throughout April, with Antares at the base, but rather low in the southern sky.

Jupiter:  in Leo, mag -2.4. Still shining brightly for most of the night, throughout April. By month end it will have faded slightly to -2.3 and will be setting not long after sunrise.

Saturn:  in Ophiuchus, mag 0.4. Visible very low in the south west in the later part of the night, rising about 30 minutes after Mars.Maximum elevation 16 degrees but worth having a look if location and conditions permit.  The planet's south pole is tilted towards us and the rings very wide open.

Uranus and Neptune are not visible this month. 

Meteor Showers

One major shower - the April Lyrids. Active 16th to 25th, peak 22nd/23rd.  ZHR 10.  This shower used to be much more proific than it is now. Mag around 2 but could be occasional fireballs. Medium fast moving, about 28 miles per second. These are particles from comet C/1861G1 Thatcher.  It is the strongest shower known to come from a long period comet - albeit at the shorter end of long, with a period of 415 years. It has the distinction of being the oldest known shower, having been  recorded by Chinese astronomers in 687BC. The bad news is that, as you may have realised, the peak coincides with the full moon this year, so it won't be a good show.

Several very minor showers.

Librids:  active 15th to 30th April,  several peaks. 

Alpha Bootids:  April 25th to May 13th,  there is no definite peak, it is sometime around 25th.
Slow moving metors leaving fine trails.

Delta Draconids:  March 28th to April 17th, no definite peak, very slow moving, leaving conspicuous trails.
This shower was only discovered in 1971, so is probably not very prolific or obvious.

I also found mention of something called the April Fireballs, active from April 15th to 30th .  These are said to have no specific radiant but appear to emanate from the south eastern part of the sky.  They have sometimes been known to reach the ground as meteorites.

Several minor showers, with their radiant in Virgo,  are also active in April.

The combined ZHR of these minor showers is said to be around 4.
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