The Sky Tonight is a monthly update of the amazing things you can find when looking up from here in Western Australia. This section is written by Jacquie Milner, resident astronomer at the Scitech Planetarium.
The casual observer
The big astro event for August will undoubtedly be the total solar eclipse crossing from coast to coast over the continental United States on 21st August. This is the first time in 38 years a total solar eclipse has been visible from the lower 48 states, which is actually rather a long break between events for them, and the first for the digital age, so it should be very well covered on social media. If you already know about this and are travelling that way to experience it, good luck! The main information page from NASA is at eclipse2017.nasa.gov/. Here in Australia we will have to wait a bit longer for another total solar eclipse – the last one was only in 2012, the next one will brush the Northwest Cape and Exmouth in 2023. The next significant event will traverse the greater metropolitan area of Sydney in 2028. Check out all the possibilities at NASA’s Eclipse Website or Eclipsewise.com
August 20th will be the 40th anniversary of the launch of Voyager 2 in 1977, the spacecraft that completed the “Grand Tour” of the outer planets: Jupiter, Saturn, Uranus and Neptune. It’s still going, along with Voyager 1 – our Canberra Deep Space Communication Complex at Tidbinbilla still communicates with it each week, the weak whisper of a radio signal taking over 31 hours to reach Earth. Check the Deep Space Network Now page to see which dish is talking to what spacecraft when!
The trajectory of Voyager 2’s “Grand Tour” of the outer planets; an artist’s impression of Voyager 2 in space, sending data back to Earth. Credit 1; Credit 2:
The Perseid meteor shower is active this month and you may hear about it in your social media feeds, but for most of us in southern Australia, it’s just not visible. The further north you are (e.g., the Pilbara, Kimberley, Top End of the NT and Far North Queensland) the better the chance you have of seeing some, but even then it will be much less than what the northern hemisphere will see. If you would like to learn more about this shower and how to see it from Australia go to meteorshowersonline.com/perseids.html
However, you should still keep an eye on the sky at any time, you never know when a big, bright sporadic meteor might streak through above you!
Dates of interest
3rd – Moon under Saturn, evening sky
8th – Partial lunar eclipse, morning sky
19th – Moon above Venus, Morning sky
25th – Crescent Moon under Jupiter, early evening sky
30th – Moon under Saturn, evening sky
Planets to look for
Mercury continues its best evening apparition for 2017 during the first half of August, but if you’d like to see this fast moving planet it recommended that you be fast moving yourself and see it as soon as possible. As the days go on it will move back towards the Sun and become harder to find, with no bright stars or the Moon nearby to point the way, either. By mid-month is it lost in the Sun’s glare again.
Jupiter is getting lower in the northwest now, too, still in Virgo, and it should start to noticeable move back towards Spica as the month progresses. The will be a nice line up with the Moon on August 25th – Spica up high, Jupiter below, then the Moon underneath them all.
Saturn is pretty much overhead as darkness falls, which actually makes it a bit awkward for telescopic viewing – even though this is the best place in the sky to be viewing planets! The Moon passes by it twice this month: once on the 3rd August and then again on the 30th. Saturn’s bright yellow colour in Ophiuchus, an area where there aren’t any bright stars, should make it easy to find.
Early morning observers can watch Venus glide through Gemini this month. The brightest planet starts August near the foot of Castor and the top of Orion’s club and continues towards the southeast from there. The Moon joins it on the morning of the 19th.
Constellation of the month
Pavo the Peacock
When we look at the constellations around the southern pole, it’s obvious there is a flock of exotic birds clustered there, introduced to the sky by the Dutch navigators Pieter Dirkszoon Kayser and Frederick de Houtman (yes, the man the Houtman Abrolhos is named after!) There is Apus, the Bird of Paradise, Toucana the Toucan, the Phoenix in flames, and Pavo the Peacock, with his splendid tail.
Peacocks are the sacred bird of Hera, the wife of Zeus, and those fabulous tail feathers came about as a sad reward for loyalty to Hera. Hera set the monster Argus Panoptes (Pan-“all”; optes – “eyes”) to watch over Io, who Zeus had turned into a white heifer to keep her safe, but Hera was suspicious. Argus had 100 eyes with which to watch, and only two slept at any one time, so he was always awake and alert. Zeus sent Hermes to rescue Io from Argus; he played his lyre and sung and eventually all 100 eyes of Argus closed, and Hermes was able to slay him and take Io away. Distraught at such trickery, Hera put the eyes of Argus on the peacock’s tail, so he could continue to serve her.
The brightest star in Pavo is known as Peacock. It only gained this name during the 1930’s to aid with aerial navigation, but it was ratified as a proper star name earlier this year by the IAU.
To find Pavo, look south of the Teapot asterism of Sagittarius and the curving crown of Corona Australis. The star Peacock marks the bird’s eye and head, he has a foot to the west and his big, showy tail spreads around up towards Ara the Altar.
Objects for the small telescope
The Starter Cluster
To the south of Sagittarius lies the constellation of Pavo the Peacock. It’s not an easy constellation to find, with only one bright star but it is worth the effort to search it out for the objects within it. It contains a number of galaxies that experienced observers might enjoy but there is also a bright globular star cluster known as the Starfish Cluster that is within easy reach of small telescopes. Binocular observers may also pick the location of this object up, but you will need a telescope to see any detail.
Also known as NGC 6752, this globular cluster lies about 15,000 light years away. Take a while to look at this cluster – careful inspection should reveal how it gained its name. Imagine a starfish with a small centre and long thin arms curving and curling around it.
A careful star-hop is required to find the Starfish cluster (NGC 6752) in Pavo the Peacock.
Partial Lunar eclipse, 8th August 2017
As a prelude to the total solar eclipse on the 21st August, we get to see a partial lunar eclipse on the morning of Tuesday 8th August, Australian time. The Moon will only dip about a quarter of itself into the shadow of the Earth before skipping back out, so it won’t be all that spectacular to see. The whole event will take five hours from start to finish, so if you’re out and about for whatever reason that morning, it might be handy to know what’s going on.
If you want to get straight to the good part, mid eclipse, when the Moon will be deepest into the umbra, or Earth’s shadow, will be 2.21am WST, so it will be starting to descend into the western sky by then.
Going back to the beginning, the Moon starts to enter the penumbra, or partial shadow of the Earth, around 11.48pm on the 7th, when it will be high overhead. You probably won’t notice anything happen for a while, not until the Moon gets close to entering the umbra, at 1.22 am. It should look darker on one side as it touches the edge of the umbra. Between 1.22am and mid-eclipse at 2.21am WST you should notice one side of the Moon looking distinctly dark grey – but don’t expect the nice coppery-red colour associated with a full lunar eclipse, the Moon probably isn’t going far enough into the umbra to show this effect this time.
About an hour later the Moon will be back out of the umbra, at 3.19am, and will make its way through the penumbra until the eclipse is all over at 4.53am.
If it doesn’t sound exciting enough to set the alarm for, don’t worry – the next total lunar eclipse for Australia is coming up on January 31st 2018, and it’s in the evening, too!
A visual summary of the partial lunar eclipse on the morning of the 8th August for Australia. The white area on the chart shows where the eclipse is visible. The red circle represent the umbra, the full shadow of the Earth, and the grey circle around it the penumbra, the partial shadow. The Moon will only dip briefly into the umbra during this partial lunar eclipse.