The sky of April – a rope of stars

This month is fantastic for viewing Jupiter, Saturn and Mars. Pluto is also in a good position to spot, though at a visual magnitude of 14.3 you’ll need a reasonable telescope. The other highlight for the month is that 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 spectical 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

April is a Latin name, Aprilis, Prier (in Dacian), very likely having 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, or according to some, it might be derivative from Aphrodite, original Greek name of Venus (still flowers stuff). Pri (pre) si a prefix that means “before” – “primavara” (prima vara – before summer) means spring, which comes before summer. Of course, for those in the Southern Hemisphere, at mid latitudes, it’s the month of the leaves falling off trees and 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, perfect for the season of the planets!

What’s the Sun up to?

April is more or less the month of the zodiacal constellation of the Ram (Aries). That means the Sun is transiting the constellation of Aries and so we cannot see the constellation, because (1) the stars that make it are well behind the Sun and (2) it’s dangerous to look into the Sun. For the first part of the month the Sun is in Pices. 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. Given we’re close to the solar minimum there’s not much happening on the surface of the sun at the moment but you can still see the odd flare or prominence occasionally.

However, because the Sun is in Aries, it means that almost 180 degrees on the other side of the zodiacal band, (remember the zodiacal band is an imaginary circle stuck to the celestial hemisphere) is Scorpius. This means Scorpius is opposite the Sun, which is visible in the night sky. Scorpio’s is quite high in the late evening by th end of the month – meaning that Sagittarius and the galactic centre is 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 Zenith. What else is better than that? Plus it might remind people to be more sensible about lighting so we can preserve dark skies.

I can still remember the first time I fully appreciated the Milky Way in the Southern Sky, 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. This time of the year, just after sunset, I can let my eyes wander looking at its rising core, all the way to its setting edge — from Scorpius to Taurus in one glorious panorama… In April, the City of Stars stretches through the night sky southeast to northwest. 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.

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, 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. This is also where you’ll see Jupiter this month, siting nice and high in the sky in Libra and then further along the Ecliptic around Sagittarius you’ll find Saturn, Mars and Pluto.

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 @0.86 magnitude. Then hot white Castor and orange Pollux – in Gemeni @ 1.93 / 1.14 mag, followed by blue-white Regulus @1.36 in Leo – almost due North, and blue-white Spica 0.98 in Virgo, in North East. Then in Libra is another very bright object, this time not a star, but the planet Jupiter which is getting high enough by the middle of the month to give some great views from about 10:30pm. Just rising near the centre of the Galaxy, is another red giant, Antares, @1.06 M, and at 604 light years from us. By the middle of the month Saturn and Mars will be rising about 10:30pm not far behind Antares.

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Other bright stars throughout the Galaxy

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 the celestial Ferris Wheel of the Southern Skies, a giant wheel that never stops, day after day, in a sidereal time cycle, as long as the Earth is turning.

Crux

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.

The Rope of Stars

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. For Māori they are also known in a different time of the year as the rope of an anchor and I can’t stop but thinking that this is the end of my rope of stars. If I let it go now, I will fall into the center of the galaxy which is slowly and majestically climbing on the Eastern Horizon. Here in Aotearoa, the Māori 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.

Lower on the horizon, at a magnitude of +0.95 red giant Antares shines as the brightest star in Scorpius. Right next to it, you can sometimes see its rival, Ares by its Greek name, or Mars as we all know it better, is challenging the giant’s red hue with its own red glimmer. This is how Antares got its name, as being the rival of Ares, Ant-Ares, the rival of Mars.


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Zodiacal  band

This is the Zodiacal band, an awesome drawing by Eugene Georgiades. Since one thousand years ago, when people stopped taking precession into account, the zodiacal constellations have shifted.