The Night Sky This Month: April 2019

Spring Triangle
Image Credit: Bob King

Prominent constellations in the night sky at this time of the year include Gemini, Leo, Cancer, and Canis Minor. Meanwhile, Virgo is now rising in the southeast, and in the mid-evening hours one of its brightest star Denebola forms the Spring Triangle in the northern sky, together with Arcturus in Boötes, and Regulus in Leo. Also prominent is the north circumpolar constellation Ursa Major, which contains the Plough (Big Dipper) asterism.

The Moon in April 2019

Favourable illumination on the night of the 14th and again on the 26th will offer lunar observers two excellent opportunities to view a pair of major craters on the Moon. The first is Tycho, a 108-million year-old crater that dominates the Southern Lunar Highlands. This crater is thought by most planetary scientists to have been created by a part of the impactor that had created the asteroid Baptistina.

The second major crater is the 800 million year-old crater called Copernicus. It is located in the eastern reaches of the Oceanus Procellarum, which can be found beyond the termination of the Apennine mountain range. Copernicus is a classic terraced crater with a depth of nearly 4000 meters, and a diameter of 93 kilometres. Both craters are readily visible with the naked eye, although binoculars and small telescopes provide much improved views.

The Moon Phases in April 2019

New Moon First Quarter Full Moon Last Quarter
5th
12th 19th 26th

The Planets in April 2019

This year, the month of April is not a particularly good time to view the planets. Some are very low on the horizon, while others rise less than one hour before the Sun. Nonetheless, for observers that have access to atmospheric dispersion correctors, reasonably good views of two outer planets may be possible. Below are some details of what can be seen of the planets during April:

Mercury passed between the Sun and Earth on the 15th of March. It will therefore rise low over the east-south-eastern horizon at the beginning of April. Note that while the little planet will shine at magnitude +0.9, it will reach an elevation of only about 4 degrees. During the month, Mercury will move towards its furthest remove from the Sun, and on the 11th will be 28 degree west of the Sun. Look for Mercury to the leftward of Venus as it rises about 30 minutes before dawn on the 16th. The two planets will subsequently be only four degrees apart, their closest separation for the past three years.

Venus is now receding from us, and its angular diameter will therefore reduce from 13.1 seconds of arc to 11.6 seconds of arc. However, the planets’ illumination will increase from 81% to 86% during the month. This means its brightness will remain fairly constant at magnitude 3.9 throughout April. Note that for much of the month, Venus will rise at around 05:00 AM (BST), which is only 30 minutes or so before sunrise. So take great care not to use optical instruments to view the planet after the Sun has risen.

Mars will dim from magnitude +1.5 to magnitude +1.6 during April. Nevertheless, Mars still dominate the south-western night sky for about four hours after sunset at the start of the month. And for about 3.5 hours after sunset towards month end. The Red Planet remains easy to spot as it passes between the Pleiades and Hyades clusters at an elevation of around 34 degrees on the 4th/5th of April. On the night of the 16th, Mars will pass within about 7 degrees of the red giant star Aldebaran, and even though it remains easy to spot, its angular diameter will reduce from 4.6 seconds of arc to 4.2 seconds of arc. This means it will be impossible to spot even major surface features on the planet.

Jupiter begins April rising about one hour after midnight. Its brightness increases to magnitude -2.5 during the month and its angular diameter grows from 40 to 43 seconds of arc. However, it will not rise above about 14 degrees above the southern horizon when it crosses the meridian. As is the case with the planet Saturn, an atmospheric dispersion corrector will be required to obtain clear or even reasonable views of Jupiter through the murk of the lower atmosphere.

Saturn increases in brightness from magnitude +0.6 to magnitude +0.5 as the month progresses, and its overall angular diameter spans across 36 degrees. However, the planet is now at its lowest point on the ecliptic, and will therefore not rise above about 14 degrees. Look for Saturn in the constellation Sagittarius when it rises close to the meridian just before dawn by month’s end. As is the case with the planet Jupiter, an atmospheric dispersion corrector will required to obtain clear or even reasonable views of Saturn through the murk of the lower atmosphere.

Meteor Showers in April 2019

This year, the Lyrids meteor shower is expected to peak after midnight on the 23rd. The Lyrids is an average shower that rarely produces more than about 20 or so meteors during its peak. However, it does occasionally produce bright meteors that leave extended dust or smoke trails in the atmosphere. This year the waning gibbous Moon will extinguish most of the fainter meteors. But with some patience and perseverance it might still be possible to spot a few exceptionally bright ones. Note that while the radiant of the Lyrids shower is in the constellation Lyra, Lyrids meteors can appear from almost any point in the night sky.

Deep-Sky Objects to Look For In April Night Sky

Below are some deep sky targets that can be observed from the northern hemisphere. Optical equipment, such as a pair of binoculars or small telescopes, will be required to view these beautiful deep sky objects.

Three Open Clusters

Three Star Clusters

The image above shows the positions of three open clusters that can be seen in relatively close proximity to each other on April 6th. The constellation Cassiopeia is prominent in this image; towards its upper left is the bright star Mirphak that marks out the heart of the Alpha Persei star cluster, which is located about 600 light years away. The other pair of clusters is located about midway between the constellations Cassiopeia and Perseus; this pair of clusters are both only 13 million years old, and each cluster in the pair contains more than 300 blue-white supergiant stars. All three clusters are relatively easy targets for large binoculars and small telescopes.

Galaxy NGC 2903

Galaxy NGC 2903

This spectacular type Sb spiral galaxy is found in the constellation Leo. It is remarkable for the fact that even though it has a magnitude of 8.9, it is not included in either the Messier or the Caldwell catalogues. Located about 20.5 million years away, this galaxy was discovered by William Herschel, who listed it as number 2903 in his New General Catalogue. Look for this active star-forming galaxy just below the star Lambda Leonis.

Asteroid Pallas

Asteroid Pallas

While asteroids do not really qualify as deep sky objects, asteroid Pallas is nevertheless a night sky object well worth observing. Pallas, the second asteroid ever to be discovered, becomes readily visible on the night of April 10th. At which time, it will be seen directly on a line between the stars Arcturus and Muphrid where it will shine at magnitude 8.0. This will require a small telescope for the best views.

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