As declared by the Astronomers Without Borders (AWB), April is the Global Astronomy Month (GAM). But wait, it gets even better than that! Also in April, there is an Astronomy Day and around that date is the International Dark Sky Week!
April is full of stars.
It might as well be, since brights stars adorn the evening sky, Sirius, Canopus and Alpha Centauri are visible in one go. The Galactic Centre starts making a reappearance in the Southern Sky, rising about 10:30 PM 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 this time of the year here in the Southern Hemisphere. Those of you with a keen eye will be able to spot the dark silhouette of the Milky Way Kiwi rising in the early morning at the start of the month.
A bit about April
Is autumn again in New Zealand, the grapes have been harvested, awaiting to be transmuted into wine and while we wait, among wine festivals and winery days we finally can enjoy 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. What we know is that the first of April was dedicated by the ancient Romans to Venus and around now they were celebrating Veneralia. Maybe April 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. In the meantime Zeelandia might 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. Not always a bad omen, 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. Those closer to the tropics start seeing a bit less humidity as the dry season starts.
What’s the Sun up to?
The Sun rises from 7 to 7:40AM throughout the month and sets from around 7:15 to 5:30 PM. Yes that is correct – in April we get rid of daylight saving. Towards the end of the month beautiful and long nights await.
In April, the Sun transits first the zodiacal constellations of the fish, Pisces, and later, after 20th of April, the Ram (Aries). And it doesn’t matter which side of the world you are for this one, we are looking at the same stars, albeit their figures in the sky are upside down here in the south. That throws Orion’s legs in the air. In this hemisphere night sky he’s always performing a cartwheel through the night. Orion is not a zodiacal constellation but is neighbouring them and also marks the edge of our galaxy. Zodiacal constellations are stars that are visible behind the plane of our solar system, and form a band in the sky, called the Zodiacal Band. What’s a constellation?
Since the Sun is transiting both the space we call Pisces and Aries it means we cannot see the stars in these constellations, behind the Sun they are washed out by it besides 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.
The Sun in Aries means only one thing: opposite the Sun (that 180 degrees on the other side of the zodiacal band) is Scorpius. This means, Scorpius will be visible all night long! 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, I tell everyone that we can and should find directions by it.
When it’s at its highest, the Milky Way stretches here from North to South through Zenith. And, even better, when that happens, it is the centre of the Milky Way that climbs at Zenith in this hemisphere. In the other hemisphere, Cygnus climbs at Zenith, that’s the edge of it and so it has less stars. There, our beloved galaxy does look rather like a river or a road – via lactea which is the Latin name that gave it the translation Milky Way. Shaped like a disk we are looking at it from inside and thus it looks like a band on the sky. Unless you come to the Southern Hemisphere where it looks like many things, an arm of the octopus – I would say, right now in April.
When you visit the southern hemisphere for the first time, make sure you pay attention to the Milky Way. Follow it South, you bump into the Southern Cross – that is in the wake of the Milky Way. That’s how you find directions by following the Galaxy. This time of the year this octopus arm, and who knows maybe it was Te Feke the legendary, that brought people to Aotearoa, stretches from southeast to northwest. From the rising core, all the way to its setting edge — from Scorpius to Taurus is all one glorious panorama.
Scorpius and Orion
Mortal enemies in ancient Greece, hence they’ve been placed in opposite parts of the sky – or at least that was their mnemonic, Scorpius and Orion look here like noting that would indicate they can symbolise a scorpion or a human.
At the antipodes, Scorpius is a scorpion, slithering around the horizon. Because of Earth’s tilt, the constellation only rises 30 degrees or so above the horizon. Just like a scorpion, it’s just crawling due south and then disappears into Mother Earth again, like scorpions would do in the desert. For the same reason, Sagittarius is a teapot there.
In Aotearoa, the Māori names for Scorpius are usually Te Matau A Maui – the fishhook of Maui, and this time of the year, also Manaia Ki Te Rangi – the guardian of the heavens.
Out of all constellations, Scorpius is probably the most spectacular, it can be anything. Check out the November sky to see what it is then for Māori.
Orion the hunter is upside down to what you’d be accustomed at the antipodes. Perhaps that’s why everyone’s calling it a pot here. Talking about calling names… But you can see why, the stars resemble to a pot that you put on a stove.
So what can we see? – Ropes of Stars
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. I imagine two arches, one smaller running though the Northern part of the sky, that is the ecliptic, the other one larger, running through Zenith, that is the Galaxy.
Bright stars on the Ecliptic
Through the northeastern sky runs the ecliptic, which marks the plane of our solar system, bearing the zodiacal constellations. These intersect the Milky Way in Scorpius and Sagittarius, which are either side of the centre of the Milky Way and Taurus and Gemini, which flank the edge. The ecliptic is “a great circle on the celestial sphere representing the Sun’s apparent path during the year, so called because lunar and solar eclipses can only occur when the moon crosses it.”
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:
- Red giant, about 65 light years away from Earth
- visually towards the outskirts of the galaxy, as we can see it from Earth, one of the ancient Royal Stars
- setting at about 8:30pm by the middle of the month, in Taurus @0.86 magnitude.
Castor & Pollux
- hot white Castor and orange Pollux are in Gemeni @ 1.93 / 1.14 mag,
- blue-white Regulus @1.36 is in Leo – almost due North,
- Is one of the ancient Royal Stars
- blue-white Spica @0.98 is in Virgo, in North East.
- Rising near the centre of the Galaxy, red giant, Antares, @1.06 M, lays at 604 light years from us in Scorpius
- Antares is the third Royal Star
Stars in the Milky Way
Outside of the Ecliptic are a bunch of other bright stars including the famous Betelgeuse, a red giant @0.42 mag and Rigel, a blue giant @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 0.34 and Sirius – in the Big Dog. @-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. Which means that it goes around in circles in 23 hours and 56 minutes, riding something that is like a pod on the 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.
Circumpolar objects to New Zealand
There are some stars that will always be in our skies. These are called circumpolar. From Wellington, they cover declinations from – 50 degrees to 90 although they would be too close to the horizon to be seen at -50 so more realistically you will see stars around -55, for instance Achernar is -57 and very bright.
Circumpolar stars rotate in 23 hours and 56 minutes thus they appear to be in different positions in the sky – so take that into account when you look for the Southern Cross.
Binocular objects in April
- M44 – the beehive cluster and the surroundings in Cancer
- M42 – in Orion
- Tarantula Nebula
- Eta Carinae
- Omega Centauri – these are all really high around the South Celestial Circle
- Southern Pleiades
- Jewel Box
- Centaurus A
- Alpha Centauri
Telescope Objects in April
nice and high
- M83 – southern Pinwheel
- Sombrero Galaxy – M 104
- M 68 lovely globular cluster
- Leo Triplet
- M80, M4, M7 in Scorpius