08/03/2019 | 19:53
The night sky for April 2019
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Northern HemisphereIan Morison tells us what we can see in the Northern Hemisphere night sky during April 2019.
The PlanetsJupiter starts the month rising around 1 a.m. and brightens from magnitude -2.3 to -2.5 as the month progresses, whilst its angular size increases slightly from 40 to 43 arc seconds. By month's end it rises by ~11 pm so will be due south around 3 am. Sadly it is heading towards the southern part of the ecliptic and currently lies in the southern part of Ophiuchus just above Scorpius so, as it crosses the meridian, it will only have an elevation of ~ 14 degrees. Atmospheric dispersion will thus take its toll and an atmospheric dispersion corrector would greatly help to improve our views of the giant planet.
Saturn, shining with a magnitude increasing from +0.6 to +0.5 during the month, rises around 3 am on April 1st but around 1 am by month's end. Its disk is ~17 arc seconds across and its rings - which are still nicely tilted from the line of sight spanning 36 arc seconds across. By the end of April, Saturn will near the meridian just before sunrise so morning twilight is the best time to observe it but, sadly, now in Sagittarius it is at the lowest point of the ecliptic and will only reach an elevation of ~14 degrees. As with Jupiter, an atmospheric dispersion corrector will help improve our view
Mercury passed through inferior conjunction (between us and the Sun) on March 15th and, at the start of the month rises low in the east-southeast about 30 minutes before the Sun but, shining at a magnitude of +0.9 only reaching an elevation of ~4 degrees. Mercury reaches greatest elongation west, some 28 degrees from the Sun, on April 11th. It lies down to the left of Venus as the two inferior planets approach each other as the month progresses. On April 1st, they lie 10 degrees apart and are closest, just over 4 degrees apart on the 16th - the closest for 3 years. One will need a very low horizon and binoculars could well be used to reduce the background glare, but please do not use them after the Sun has risen.
Mars, though fading from +1.5 to +1.6 magnitudes during the month, remains prominent in the south western sky after sunset setting some four hours after the Sun at the start of April but less than 3 and a half hours by month's end. At an elevation of ~34 degrees after sunset it is moving through Taurus passing between the Pleaides and Hyades clusters on the 4th/5th. (If only it could have been at this elevation when at closest approach last year!) On the 16th, it passes 7 degrees north of Aldebaran, the red giant star that lies between us and the Hyades cluster. Its angular size falls from 4.6 arc seconds to 4.2 arc seconds during the month so one will not be able to spot any details on its salmon-pink surface.
Venus begins April with a magnitude of -3.9 with its angular size reducing from 13.1 to 11.6 arc seconds during the month as it moves away from the Earth. However, at the same time, the percentage illuminated disk (its phase) increases from 81% to 86% - which is why the brightness remains constant at 3.9 magnitudes. On the first of April it rises about 5 am - only 30 minutes before the Sun so binoculars may well be needed to spot it through the Sun's glare. A very low horizon just south of east will be needed and binoculars could well be required to cut through the Sun's glare - but please do not use them after the Sun has risen.
HighlightsApril 5th - early evening: Mars lies between the Hyades and Pleiades. In the early evening looking towards the southwest one should, if clear, be easily able to spot Mars lying halfway between the Hyades and Pleiades open clusters.
April 6th - evening: three open clusters. Looking northwest in the evening at an elevation of ~35 degrees should be seen the 'W' shapes constellation of Cassiopeia. Up to its left lies Perseus with its bright star Mirphak. This lies at the heart of the Alpha Persei Cluster - widely spread across the sky and about 600 light years distant having an age of ~60 million years. Between Cassiopeia and Perseus can be seen with binoculars or a small telescope the Perseus Double Cluster - the common name for the two clusters NGC 869 and NGC 884. These are quite young with an age of ~13 million years and lie at a distance of 7,500 light years. There are more than 300 blue-white supergiant stars in each cluster.
April 9th - early evening: Mars and a crescent Moon in Taurus. Looking southwest in early evening if clear, Mars and a thin crescent Moon will be seen lying above the Hyades and Pleaides clusters in Taurus.
April 10th - evening: Spot Asteroid 2, Pallas. In the evening after dark, the bright star Arcturus will be seen rising in the east. Up to its right is the star Muphrid. Exactly on the line between them and just to the lower left of Muphrid one should spot Pallas, the second asteroid to be discovered, shining at magnitude 8. Binoculars or a small telescope will be needed.
April 15th - evening: the Moon below Leo. If clear in the evening and looking south, the waxing Moon just after first quarter will be seen lying below the constellation Leo. Up to the left of Leo lies the Coma Star Cluster - well seen in binoculars.
April 24th - before dawn: Jupiter, Saturn and a waxing gibbous Moon. If clear before dawn, and given a low horizon towards the south, one should easily see Jupiter and Saturn lying on either side of the waxing Gibbous Moon.
April 14th/26th: Two Great Lunar Craters. These are two great nights to observe two of the greatest craters on the Moon, Tycho and Copernicus, as the terminator is nearby. Tycho is towards the bottom of Moon in a densely cratered area called the Southern Lunar Highlands. It is a relatively young crater which is about 108 million years old. It is interesting in that it is thought to have been formed by the impact of one of the remnants of an asteroid that gave rise to the asteroid Baptistina. Another asteroid originating from the same breakup may well have caused the Chicxulub crater 65 million years ago. It has a diameter of 85 km and is nearly 5 km deep. At full Moon - seen in the image below - the rays of material that were ejected when it was formed can be see arcing across the surface. Copernicus is about 800 million years old and lies in the eastern Oceanus Procellarum beyond the end of the Apennine Mountains. It is 93 km wide and nearly 4 km deep and is a classic "terraced" crater. Both can be seen with binoculars.
Haritina Mogosanu and Samuel Leske from the Carter Science Centre in New Zealand speaks about the Southern Hemisphere night sky during April 2019.
Global Astronomy Month First of all, April is the Global Astronomy Month (GAM). But wait, it gets even better than that! From Sunday, March 31 to Sunday, April 7 is the 2019 International Dark Sky Week! It was created in 2003 by high-school student Jennifer Barlow. International Dark Sky Week has grown to become a worldwide event and a key component of Global Astronomy Month. Each year it is held in April around Astronomy Day. Brights stars adorn the evening sky, Sirius, Canopus and Alpha Centauri are visible in one go and the Galactic Centre starts making a reappearance in the Southern Sky, rising about 10:30pm by the end of the month. The Milky Way looks fantastic in April as it stretches almost horizon to horizon and as the dense star fields and dust lanes of the Galactic Centre become more visible, our galaxy creates quite a spectacle throughout the month. Those of you with a keen eye will be able to spot the Milky Way Kiwi rising in the early morning at the start of the month.
A bit about April - Here is autumn again, the grapes have been harvested and awaiting to be transmuted into wine and while we wait, we prepare for the long beautiful nights in which the galactic centre climbs to the Zenith. April is a Latin name, Aprilis, or maybe the mispronounced name of Greek goddess Aphrodite, since the first of April was dedicated to Venus, the ancient Romans were celebrating Veneralia. Maybe it has a common root with aperire, (Latin to open, as in opening buds and blossoms) since in Europe is the month of the first blossoms on the trees. Whereas here we also get the first taste of Winter as the odd southerly front roars up from the Southern Ocean to remind everyone what's on the way. Those closer to the tropics start seeing a bit less humidity as the dry season starts. The roaring southerly fronts also remind us of the super clear, cool and stable air that often sits behind those fronts and makes for cool evenings of amazing seeing.
What's the Sun up to? The Sun rises from 7:00 to 7:40AM throughout the month and sets the morning and sets from around quarter past seven in the evening to half past five. Yes that is correct - April is also the month when we get rid of daylight saving. So towards the end of the month we would be enjoying a beautiful and long night - that is if the sky will stay clear.
April is more or less the month of the zodiacal constellation of the fish, Pisces, with the Sun moving into the Ram (Aries) only the 20th of April. That means the Sun is transiting both the constellations of Pisces and Aries and so we cannot see them because of two reasons: (1) the stars that make them are well behind the Sun and (2) it's dangerous to look into the Sun. Of course, if you have solar telescope, that is well maintained and is designed for looking at the sun, then you can look at the Sun.
However, because the Sun is in Aries, it means that 180 degrees on the other side of the zodiacal band, is Scorpius. This means, Scorpius is opposite the Sun and it will be visible in the night sky. Scorpius's is quite high in the late evening by the end of the month - meaning that Sagittarius and the galactic centre will also be not far behind.
The Milky Way - the most spectacular feature of the Southern Hemisphere's sky... and to say this is such an understatement. The Milky Way is so striking here in New Zealand, that in the absence of a polar star, people could and should orient themselves by it. For two reasons: one is because we think it is so amazing, and also because when it's at its highest, the Milky Way stretches here from North to South through the zenith. What else is better than that? Plus it might remind people to be more sensible about lighting so we can preserve dark skies.
Back in 2011 was the first time ever when I really saw the Milky Way. Not that I thought I didn't see it before. I thought I did. But no... it was in the Wairarapa back in 2011 and it is a sight I will never forget. I like to call the Milky Way my City of Stars. Or the leg of the Octopus, since its centre is almost on the horizon at sunset. From the rising core, all the way to its setting edge - from Scorpius to Taurus is one glorious panorama. The City of Stars stretches through the night sky southeast to northwest. Here in Aotearoa, the M?ori have three names for the same asterisms (groupings of stars) at different times of the year. What we know as Scorpius is, at this time of the year, called Manaia Ki Te Rangi, the guardian of the skies.
It is a great time of the year to get the telescope out in the early evening, now that daylight saving has finished, and just browse the star fields, catching glimpses of nebulae and star clusters.
So what can we see? - Ropes of Stars. Imagine two arches, one smaller running though the Northern part of the sky, that is the ecliptic, the other one larger, running through the zenith - that is the Galaxy.
Bright stars on the Ecliptic - the smaller arch. Through the northeastern sky runs the ecliptic, in a lower arch, which marks the plane of our solar system, bearing the zodiacal constellations. They intersect the Milky Way right on the horizon at the start of the month in the late evening. To see things on the ecliptic one should simply turn towards that part of the sky that carries the memory of the path of the Sun or of the Moon, for that matter. Let's swipe them from west to east:
Setting first in the evening at visually towards the outskirts of the galaxy, as we can see it from Earth, and at about 65 light years away, is the red giant Aldebaran, very low on the horizon and setting at about 8:30pm by the middle of the month, in Taurus at 0.86 magnitudes. Then hot white Castor and orange Pollux - in Gemini at 1.93 and 1.14 mag, followed by blue-white Regulus at 1.36 in Leo - almost due North, and blue-white Spica at magnitude 0.98 in Virgo, in the North East. Just rising near the centre of the Galaxy, is another red giant, Antares, at mag 1.06 and at 604 light years from us.
Other bright stars throughout the Galaxy - the larger arch. Outside of the ecliptic are a bunch of other bright stars including the famous Betelgeuse, a red giant at 0.42 mag and Rigel, a blue giant at mag 0.13, both in Orion. Then the Dogs of the Celestial River, because they are guarding it each from one side of it, are yellowish-white Procyon - in the Small Dog at 0.34 and Sirius - in the Big Dog, at mag -1.46. Sirius, a blue giant, is the brightest star in the sky. The big dog constellation finally looks the right way up heading also to the western horizon too. From it, turn your gaze left.
Nearby comes Canopus -0.72, the second brightest star in the sky. Canopus is not in the white band of the Milky Way. Standing tall, Canopus is high in the sky as it likes to be at this time of the year after sunset. Canopus is a circumpolar star from Wellington. This means that it goes around in circles in 23 hours and 56 minutes, riding something that is like a celestial Ferris Wheel of the Southern Skies, a giant wheel that never stops, with the South Celestial Pole at the centre and a bunch of other stars that look like a circle.
Crux, the Southern Cross, is no stranger to the northern hemisphere and it was entirely visible as far north as Britain in the fourth millennium BC. The Greeks could see it too but since then, the precession of the equinoxes, the wobble of Earth, its gyroscopic dance on the orbit has changed the skies a lot so that now Crux is only visible in the Northern Hemisphere from as far south as 25 degrees latitude north. Florida Keys, Puerto Rico, the islands of the Caribbean, as well as Hawaii are its northern limit of visibility. Near the Southern Cross, there is a dark patch of dust that masks the light that comes from the stars behind it and that is known as the coalsack. Inside the coalsack, the Jewel Box is one of my favourite sights that I visit over and over with the telescope.
Lower down on the path of the Milky Way the two pointers look now as if they are hanging from the Southern Cross. First comes Beta Centauri (the genitive for Centaurus, the name of the constellation) then the famous Alpha Centauri.
Binocular objects in AprilM44 - the beehive cluster and the surroundings in Cancer
M42 - in Orion
Omega Centauri - these are all really high around the South Celestial Circle
Telescope Objects in April M83 - southern Pinwheel
Sombrero Galaxy - M 104
M68 (a lovely globular cluster)
M80, M4, M7 in Scorpius
Planets. The good news for April is that the planets are coming back, not all of them, and nothing like last year but still in their spectacular glory that we've become used to. For those who live on mountain tops with a nice clear view of the South Eastern horizon, you will see Jupiter rise just before 11pm at the start of the month and by the end of the month Jupiter will be starting to appear around 8pm. Of course to actually get a reasonable view of Jupiter you need to wait a couple of hours after it rises which is still a quite reasonable time by the end of the month. Jupiter is exceptionally easy to find because it's right there in the middle of the Milky Way Kiwi, quite close to the galactic centre just between Scorpius and Sagittarius.
Jupiter is huge and bright with a magnitude of -2.2, this is because it really is huge with a diameter of 142,984 kilometres, just over 11 Earth diameters. Its huge distance from us of around 750 million kilometres means that even this massive planet won't out shine Venus at -4 magnitude. Jupiter is a great sight in binoculars as the Galilean Moons are clearly visible, depending on their positions.
Saturn is about 2 hours behind Jupiter in the march along the ecliptic, so it's very much an early morning planet for most of the month before being visible at a good altitude by midnight at the end of the month. Saturn is a bit further away from the Milky Way between Sagittarius and Capricornus. Of course, by a bit further away we mean the angular distance. In distance terms it is 1.449 billion kilometres away with an angular dimension of 17.1 arcseconds in diameter. The distance doesn't change much during the month, only about 70 million kilometres.
Saturn's crowning jewel is its rings, which look fantastic. I think every astronomer I have ever spoken to can remember the first time they saw Saturn. To see the rings of Saturn you need to have a telescope or be about 1.1 billion kilometres closer to the gas giant. Clearly it's not that easy to be 1.1 billion kilometres closer so let's think about why we can't see them with the naked eye. The human eye has a range of angular resolution of between 1 and 4 arcminutes, depending on the eye and atmospheric conditions. The size of Saturn's rings are about 46 arcseconds when they are at their biggest, so significantly smaller than what the best human eye in the best conditions can resolve. The best you can see of Saturn with the naked eye is its beautiful golden colour.
Mars - unfortunately Mars doesn't do much during the month other than skirt along across Taurus to Gemini, and given it's now about 344 million kilometres away and only 4.1 arcseconds in diameter, it's not going to be much to look at anyway. In New Zealand we also miss out on the conjunction of Venus and Neptune on 10 Apr when the two planets get to within 18 arcminutes of each other. At the same time Venus and Mercury get very close as well at about 5 degrees apart. Northern hemisphere observers will have to get up early and have a good view of the horizon to see it, maybe you could send us a picture?
The Moon is new on the 5 Apr and full on 19 Apr. It's still quite close to the Earth during the Full Moon at about 368,000 kilometres, not quite the over-hyped super moon that gets people excited but not far off it.
So Clear and dark skies from Space Place at Carter Observatory here in the southern hemisphere. Special Thanks go to the amazing Rhian Sheehan, Space Place at Carter Observatory.