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
Near the end of June is one of the major turning points in our celestial calendar – the Winter Solstice for the Southern Hemisphere. This occurs on June 21st in 2017. On this morning the sun with rise at the furthest point north for the year and after this date the days will start getting longer again.
The 3rd Asteroid Day is being held again on 30th June. It’s a day to raise your awareness about asteroids in general, not just about the hazards they pose to Earth. Think of it as an opportunity for you to learn what won’t happen! The official site is at asteroidday.org.
Dates of interest
4th – Moon to right of Jupiter, evening sky
9th – Moon above Saturn, evening sky
15th – Saturn at opposition (opposite the Sun)
21st – Crescent Moon above Venus, morning sky
21st – Solstice
30th – Asteroid Day
Planets to look for
The two biggest planets are together in the evening sky now. Jupiter is high in the north as the sky darkens. It finishes its annual loop of retrograde motion early in June and will start to move back towards the bright star Spica in Virgo. Saturn is further eastwards, but should stand out brightly as it reaches opposition on the 15th of June. This is when it is opposite the Sun from Earth and the best viewing for the year is to be had. The rings are wide open at the moment and should be easy to see in small telescopes. The Moon will be near Saturn on the evening of the 13th.
Venus is lighting up the cold winter mornings, rising around 3.30am. Having your camera at the ready on June 21st when the waning crescent Moon joins it for a photo opportunity.
Two planets are largely out of sight this month –Mercury and Mars. Mercury is dipping down towards the Sun in the morning sky as the month begins, then will be out of sight in the Sun’s glare until July. Mars is also slowly sinking into the Sun’s glare on the evening side, where only the most dedicated of observers will want to chase this small dot that is now on the far side of the solar system to us. It really will pay to be patient now, as this time next year Mars will be at the best it’s been since 2003.
Constellation of the month
Canes Venatici, the Hunting Dogs
The Hunting Dogs were added to the sky by Johannes Hevelius in 1687. They are usually depicted as two greyhounds with leashes held by Boötes. They even have names! The southern dog is Chara, which is Greek for Joy, and Asterion, meaning 'little star'. Although they are low to the north for us here in Perth (if you are in the north of WA you'll have no trouble seeing them) they contain some famous objects that are worth a look even if they don't present at their best.
The brightest star is named Cor Caroli, the “Heart of Charles.” This was to honour the memory King Charles I, as the star was said to be particularly bright during the Restoration of Charles II. It is a double star with two white components of magnitude 2.9 and 5.5. It is often reported that a purple tinge may be seen in this pair, but I have not noticed this in my observing experience.
Y Canes Venaticorum is a variable star that is also known as La Superba because of its deep red colour. If you have trouble trying to see any colour in Cor Caroli drop further north and check this one out instead.
There are many galaxies in Canes Venatici as well, but the most well-known is the Whirlpool Galaxy. Read on below for more information.
Canes Venatici is a faint constellation representing two greyhounds between Leo and Boötes, low to the north in southern Australia.
Objects for the small telescope
The Whirlpool Galaxy
The Whirlpool Galaxy, also known as Messier 51 and NGC 5194, was the first galaxy to be observed and drawn in the classic spiral shape. If you have done any observing with a small telescope you may be aware that most galaxies just appear as small fuzzy blobs; it is actually quite hard to see much detail. Galaxies also used to be known under the umbrella term of “nebula,” meaning “cloud” in Latin, as most deep sky objects looked fuzzy and cloud like in early telescopes. Today we use nebula to define a cloud of dust and gas in space, whereas galaxies are regions that may contain many different kind of nebulae. When Lord Rosse built his giant 72” telescope, the “Leviathan of Parsonstown” in 1845, he was the first to see the fuzzy blob had structure , and a whole new universe was revealed.
Sketch of M51 by Lord Rosse in 1845.
The Whirlpool Galaxy is an active galaxy, with many star forming regions along it’s arms (the bright pink patches) and has a black hole at it’s centre. Thanks to three recent supernovae observed in it, in 1994, 2004 and 2011, we know that it is only 23 million light years away, and probably only about 35% as big as the Milky Way. The smaller galaxy just behind it has recently interacted with it, so they are connected and it is not just a line of sight coincidence.
The Whirlpool Galaxy as imaged by the Hubble Space Telescope. By NASA/ESA.
While this object is very low to the north for observers in southern Australia, it is an achievable and rewarding challenge. It is close to Alkaid, the end of the handle of the Big Dipper or Plough asterism in Ursa Major, which just sticks up above the horizon for us in the south, but you may need to star-hop your way down with the aid of a map if you are not sure you can see it.
M51 lies closest to the star Alkaid in Ursa Major (the end of the handle of the Big Dipper or the Plough,) although you may have to star-hop your way down from Cor Caroli if it’s too low to the north.
The European-Extremely Large Telescope
On May 26th the first stone was laid in the construction of the European-Extremely Large Telescope, or E-ELT. There has been drawings of concepts of enormous sized telescopes being presented for several years but now one is becoming a reality, and first light is expected in 2024.
The top of 3, 060 m high Cerro Armazones in Chile was blasted away and levelled for the foundations of what will be the biggest telescope ever built. The primary mirror will be 39.3 m across and even its second mirror at 4.2 m will be larger than many other telescopes as well. It will be 100 million times more sensitive than the human eye and is expected to be able to image exoplanets directly and even study their atmospheres. It should also be able to study the first galaxies, which will complement work done by the Square Kilometre Array Radio Telescope.
An artist’s concept of the E-ELT in operation on a clear night.
By ESO/L. Calçada