Night Sky September 2021
To use the star chart: print it out and then use it to locate the planets and constellations at night by holding it above your head and pointing the 'South' pointer of the chart southwards.
Ian Morison tells us what we can see in the Northern Hemisphere night sky during May 2021.
- Jupiter: As May begins and given a low horizon towards the southeast, Jupiter, rising at 03:36 BST around 2 hours before the Sun, may be glimpsed just before dawn shining at magnitude -2.2 and having an angular size of 37.44 arc seconds. By month's end, it rises at 01:43 BST, about three hours before the Sun, when its magnitude will have increased slightly to -2.4 and its angular size to 41.2 arc seconds. Sadly, its low elevation of ~20 degrees as dawn approaches will somewhat hinder our view of the solar system's giant planet.
- Saturn: Saturn precedes Jupiter into the sky, rising at ~03:00 BST at the beginning of the month. A low horizon towards the south-east will be needed to see them both. It is then shining with a magnitude of +0.71 and its disk is 16.7 arc seconds across with the rings spanning some 39 arc seconds. By month's end, it rises at 01:00 BST with a slightly increased brightness of magnitude +0.57 and a 17.6 arc second disk. We will have to wait a while to see this most beautiful planet at its best.
- Mercury: This month Mercury has its best evening apparition of the year. The planet is at its brightest, at magnitude-1, at the start of May. It then lies just below the Pleiades cluster in Taurus having an angular size of ~6 arc seconds. From the 3rd to the 6th it lies within a binocular field of view of 2.8 magnitude Alcyone in the cluster's centre. Its greatest elongation east is on the 17th when it stands about 11 degrees above the north-western horizon around 45 minutes after sunset. It will then have a magnitude of +0.41 and an angular diameter of just over 8 arc seconds. It then falls back towards the horizon passing very close to Venus on the 28th.
- Mars: Mars passed into Gemini on the 23rd of April and starts the month with a magnitude +1.56 It will be best seen in the west at an elevation of ~24 degrees soon after nightfall. Reducing in brightness to +1.74 by month's end, it will still be visible in the evening sky until August before it passes behind the Sun in October.
- Venus: At the start of May Venus, at magnitude -3.88 and having an angular size of ~10 arc seconds, will only have an elevation of ~6 degrees at sunset towards the northwest. By month's end, its elevation at sunset will have increased to ~11 degrees and its magnitude reduced very slightly to -3.85. Venus will grace the evening sky for the rest of this year and reaches its greatest elongation east from the Sun on October the 29th but will be highest in the evening sky at the beginning of December.
Highlights of the Month
- May 13th - after sunset: Mercury and a thin crescent Moon: If clear this evening, Mercury will be seen up to the right of a very thin crescent Moon. One might also spot Venus down to the right of the Moon.
- May 13th - early evening: Mars and a thin crescent Moon: If clear this evening, Mars will be seen up to the left of a thin crescent Moon. One might also be able to spot Mercury down to the right of the Moon.
- May26th - late evening: A supermoon: On the night of the 26th, the Moon will be at Perigee - its closet point to the Earth - and its angular size will be 33.6 arc minutes across compared to its average diameter at full moon of 31 arc minutes - so 8% larger in diameter. As the Moon is then as bright as it can ever be, it is called a 'supermoon'. Sadly, due to Covid, one could not now fly to New Zealand or Eastern Australia where at ~11:19 UT a brief total eclipse of the Moon could be seen.
- May28th - after sunset: Venus and Mercury: After sunset on the 28th, if clear, one would be able to see Mercury (at magnitude 2.3) around half a degree away from Venus some 300 times brighter. Mercury presents a tiny crescent but Venus a nearly full disk - with both being around 10 arc seconds across.
- May 31st - before dawn: Jupiter, Saturn and a thin crescent Moon: Before dawn on the 31st, low in the southeast, Jupiter, over to the left, and Saturn, above, a very thin crescent Moon.
- May 2nd and 18th, evening: The Hyginus Rille: These evenings, should it be clear, are a superb time to view the Hyginus Rille as it will lie close to the terminator. For some time a debate raged as to whether the craters on the Moon were caused by impacts or volcanic activity. We now know that virtually all were caused by impact, but it is thought that the Hyginus crater that lies at the centre of the Hyginus Rille may well be volcanic in origin. It is an 11 km wide rimless pit - in contast to impact craters which have raised rims - and its close association with the rille of the same name associates it with internal lunar events. It can quite easily be seen to be surrounded by dark material. It is thought that an explosive release of dust and gas created a vacant space below so that the overlying surface collapsed into it so forming the crater.
Haritina Mogosanu and Samuel Leske from the Carter Science Centre in New Zealand speaks about the Southern Hemisphere night sky during May 2021.
Kia Ora from New Zealand, this is Haritina Mogosanu And Samuel Leske from Wellington New Zealand, we are here with the night sky in May 2021.
If we look at the night sky long enough to observe changes in the patterns of stars, we notice that these patterns shift ever so slowly westwards. The reason for that is our vantage point from where we are looking at the stars behind our Solar System, our galactic immediate neighbours, that vantage point changes every day by about one degree. From Earth, it seems like the same stars come up every day about 4 minutes earlier. But that’s not true for all stars. There are some stars that in New Zealand, never set or rise, their light just gets washed away by the Sun when it rises. These stars move around in circles and we call them circumpolar. The point that is visible from New Zealand around which stars rotate is called the South Celestial Pole. There are some stars that we never see from New Zealand, such as Polaris, the North Star, most of the big dipper stars, Casiopeea and so on, we don’t see them here because they are hidden by the Earth.
So if you ever buy a star and you wish to observe it, here’s something you need to keep in mind. Do you travel much around the Earth? Because except if you are on the equator, where if you are patient and can spare a few months waiting then you can see most of the stars in ideal conditions (I am accounting here for stars that are too low on the horizon) then everywhere else on Earth there are places where you see some stars and some you don’t. And if you decide to move at one of the poles forever, then every night you will see all the stars in your half of the sky and you will never see the other half.
So when we talk about what is in the sky in New Zealand, there are stars that are always in the sky here, these are the circumpolar stars. The bulk of them make a beautiful big circle in the southern part of the sky. The most famous of them is the Southern Cross and the two pointers, beautiful and bright, located straight in the Milky Way. If you ever get lost in New Zealand and you can see the Milky Way, just follow that and somewhere along the way is the Southern Cross. This works anytime on a clear sky night from a dark sky location (which is about 80% of New Zealand by the way). This time of the year, after sunset, the Southern Cross is up high, which means it is in a good position to observe. Around the Southern Cross is the famous asterism, invented by a bunch of Christchurch kids, of The Frying Pan. The two pointer stars are the handle of the frying pan and the stars in Centaurus that surround it are the pan. The southern cross, they said, is the Fish in the Frying Pan. Maori call the dark patch, the Coalsack around the Southern Cross, they call it the Flounder.
An asterism, just like a constellation, means a grouping of stars, but the word constellation is used now for the official sectors in the sky so to describe everything else that is unofficial asterism is the better definition. If you want to make the asterism of The Wok instead of a frying pan, we use the amazing Omega Centauri globular cluster as the pointy bottom of The Wok. Omega Centauri is also in a good position to observe this time of the year, finally!
First identified as a non-stellar object by astronomer Edmond Halley in 1677, Omega Centauri is about 5000 parsecs or 17 thousand light years away from us, and is the most massive globular cluster in the Milky Way, with a diameter of 150 light years across. It has about 10 million stars, weighing almost as much as the supermassive black hole at the centre of the Milky Way, that is about 4 million times more massive than our Sun. Omega Centauri is visible with the naked eye, in binoculars and in a telescope, the bigger the better the view. It is spectacular. What makes it very special other than it’s lace appearance and size is that at it’s centre, Omega Centauri has its own black hole, and it is believed it might have originally been a dwarf galaxy just like the Magellanic Clouds that was eaten by the Milky Way.
Following the Milky Way, in the constellation Carina there is a hypergiant star, Eta Carinae. Eta Carinae is about 2,300 parsecs or seven and a half thousand light years away. It has at least two stars of a combined luminosity five million times greater than the Sun. For three days in 1843 it became the second brightest stars in the sky, brighter than Canopus (officially the second brightest star in the sky) then faded away so it could not be seen with the naked eye and finally now has come back to being visible and is around magnitude 4-4.3, which means it can be seen with the naked eye if you know where to look. Better though, in a telescope Eta Carinae is spectacular, it has an orange tinge and there are beautiful nebulae surrounding it, it’s one of my favourite telescope objects in the entire night sky. Eta Carinae nebula is also home to WR25, one of the most luminous stars known in our galaxy.
Two open clusters, both great in binoculars but even better in telescopes are nearby the Southern Cross, these are the Jewel Box (on the same side with the pointers) and the Pearl Cluster (NGC 3766), on the opposite side. They are both really beautiful open clusters of stars and you can see blue and red giants in those clusters when you look at them through the telescopes. Pearl Cluster is also very close to Lambda Centauri that is home of the Running Chicken nebula, which is only a good object for astrophotography as it’s very hard to see otherwise.
Right by the Diamond Cross, a good binocular object is the Southern Pleiades. These are also very high in the sky, and good that they are because the Northern Pleiades, also known as the Pleiades are now very close to the Sun and so we can’t see them for a couple of months.
And finally, by the False Cross, in Vela, the Omicron Velorum star cluster or IC 2391 only about 500 light years from Earth and NGC 2516 are also objects we look at on a regular basis, every weekend, this time of the year. NGC 2516 is also known as the Southern Beehive - because it is thought it resembles the real Beehive cluster M44. This proves once again, Sam’s point that astronomers are really really good at naming stars.
The two neighbouring galaxies, the Large and Small Magellanic clouds are now a bit harder to observe because they are in the lower third each side of the axis that goes from the Southern Cross to Achernar - also a circumpolar star. After sunset of course, the Large Magellanic cloud is the patch to the west and the Small Magellanic Cloud is the patch to the east of that axis. Just pick up a pair of binoculars and enjoy them. They are not so much visible with the naked eye as you would expect so we always use peripheral or averted vision to see them better. From Wellington’s botanical gardens or on a full Moon night, you can just barely see them. Now because they are lower onto the horizon, we are observing them through a layer of atmosphere which is okay for visual observations but not good for deep sky astrophotography.
As the Earth orbits the Sun, it also spins on its axis. The extension of this axis to infinity gives us the South Celestial Pole and the North Celestial Pole. The height of the celestial pole in the sky gives you the latitude that you are on Earth. The lower the Celestial Pole in the sky, the smaller the circumpolar region and the other way around. In New Zealand, the South Celestial Pole is at approximately 40 degrees in the sky, which is also the radius of the circumpolar zone. Canopus is also circumpolar and is in the sky here all night long.
The circumpolar stars are always in the sky and depending on how much moisture is there in the sky from your observing place or how much light pollution you can enjoy very many of these objects all year long and all night long.
The circumpolar zone is fascinating, if you have one, you can almost learn to use it as a clock for time keeping. The stars rotate in 23 hours and 56 minutes so every day they shift a bit. The ancient Egyptians called these stars “indestructible” (never go away) and aligned their pyramids and temples with them. They also believed their pharaohs became stars of the circumpolar region after they died so by aligning the pyramids to the Pole star the souls of the dead had direct passage north Unfortunately we cannot see those pharaoh that became stars from New Zealand as it just so happens the North Circumpolar Region is hiding right behind Earth as observed from here.
While the Ancient Egyptians saw circumpolar stars "Ikhemw-sek" as indestructible and imperishable they thought that the rest of the stars were "Ikhemw-wredj" unwearying. Kondo. This is alluding to the fact that even though they had a longer path to travel than the circumpolar stars, the other stars still kept coming back up from behind the horizon.
The other part of the sky that we see from New Zealand is seasonal. There’s a new book by famous archaeoastronomer Professor Anthony Aveni called Star Stories, where he discusses seasonality as a common theme among constellation myths. Stories progress as constellations move across the sky, he says, — It’s all about the stories and what we learn from them. “We created constellations for discourse about moral issues and social rules, about affairs both practical and spiritual, about our immediate needs and our wildest dreams” The sky is there to tell tales of moral significance for all of the cultures, he says.
Here in New Zealand, Maori, have even different names and stories for the same stars as they shift across the sky each season occupying a different position as seen after sunset, in regards to the cardinal points.
The most popular of these seasonal constellations are the zodiacal constellations. The stars that make the zodiacal constellations are those stars that are behind the path of the planets in our solar system. Nobody knows for sure who invented them or what they looked like in ancient times but we do know the Summerians left a rich artistic tradition that showed many naturalistic animals but featured prominently lions, bulls and sometimes scorpions. These same animals were pictured in the sky as the earliest zodiacal constellations: Taurus, Leo and Scorpius. (Rogers). Their stars are 3 of the 4 the Royal Stars: Aldebaran in Taurus, Regulus in Leo and Antares in Scorpius. What’s awesome about these constellations is that they are about 90 degrees apart from each other. A fourth constellation that completes the four Mesopotamian pillars of the sky is Aquarius (now set).
This time of the year,after sunset, we can see the constellation of Leo in the mid northern part of the sky while Scorpius is rising from the west.
Gemini is lying along the horizon waiting to set so not in a good position to observe.
Leo is an amazing target for telescopes and binoculars. Close to the area south of the triangle that marks Leo’s hips…M65, M66 and NGC 3628, which will be visible depending on the size of your binoculars they are also known as the “Leo Triplet”. Also in Leo, M105 is an elliptical galaxy. M96 another galaxy in Leo lies at about 35 million light years away.
To the east of Leo is Virgo, home of the 3C 273 quasar, which is a favourite observation target for us.
To the east of Virgo is Libra the scale, reinvented by the ancients by reducing the claws of the scorpion to mark the autumnal equinox when the days were equal to the nights. Hence Libra is a symbol of equality and justice. Due to precession, the equinox now occurs in Virgo. Ironically, the two brightest stars in Libra still bear the names of Northern Claw and Southern Claw, Zubenelgenubi and Zubeneschamali, a reminder of the former glory of Scorpius.
In May, we have more hours of dark than we have of light. If you are a morning bird you must wait until 7 AM for the sunrise at the beginning of the month and 7:30 at the end of the month. If you are a stargazer, then be happy, as sunset is very early in May, the Sun is going down at about 5:30 at the beginning of the month and around 5 at the end of the month. But that’s not when the darkness falls onto New Zealand, it would take two more hours for it to be well enough beyond the horizon - which is when it is officially night. So only two hours later you should be able to properly see /photograph some deep sky objects, that is if you are lucky enough to have a moonless night.
Speaking of which, here is what happens to the Moon in May:
At New Moon, the Moon rises and sets with the Sun - so is on the same line of sight as the Sun.
The next traditional phase of the Moon is the First Quarter, in May this occurs on the 20th And last but not least Full Moon is on 26 th of May. Just a note, the worst time to look at the Moon through a telescope is at Full Moon. The Moon is really bright as it has the maximum amount of surface lit from the Sun, remember the Moon reflects the light from the Sun so unless you have a Moon filter it will be a strain for the eye. If you look at it through a telescope you will lose the little dark adaptation you got throughout the night. However, the Full Moon is great to photograph through a small telescope with a normal phone camera - held by an adaptor of course or even by your hand.
No naked eye planet is visible in the evening sky but if you wait until after midnight, you will see Saturn and Jupiter and in the morning, just before sunrise they are the two bright objects in the northwestern sky.
Before we sign out, the constellation featured by Globe at Night in May is Crux. Get your observing hat on and help us measure light pollution around the world. You will see detailed instructions on our website, Look after our Night Sky, or on GlobeAtNight.org. All you have to do is count the number of stars you can measure from your street and compare these with the number of stars from Globe at Night’s maps. This is a citizen science project where anyone can participate and make a difference while you learn your stars.
Provided courtesy of: http://www.jodcast.net/