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 latest sunrise occurs in early July, as the Earth reaches aphelion on July 4th. Sunrise times will start to get earlier after this date. The Earth’s orbit is slightly elliptical, as all orbits are to some degree, and aphelion is the point when it is furthest away from the Sun in its orbit. The closest point, perihelion, is in early January.
July has five moon phases, with two First Quarter moons on the 1st and the 31st of the month
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
If you have a clear, low, western horizon, keep an eye out for Mercury in the evening sky, especially during the second half of July, as it makes its best evening apparition in the southern hemisphere for 2017. There is a lovely set up of the new crescent Moon under the inner-most planet on the evening of the 25th, right next to the bright star Regulus, too! A good one for the photographers.
Jupiter continues to shine out in Virgo, not moving very far, but now getting towards the north-west in the evening, and Saturn, just past opposition, is an easy target in the east. The nearly full Moon will be just below Saturn on the evening of the 7th.
If you are up early and watch the morning sky, Venus will slide past Taurus during July. It will line up on the other side of the V-shape of the Hyades cluster from Aldebaran on the morning of the 13th. It will probably still be quite photogenic for a couple of mornings after that as well.
Mars is currently on the other side of the Sun from the Earth. It will remain in this situation for several months – best to wait until this time next year to view it when it is at opposition – behind Earth from the Sun – when it will be at its closest since 2003.
Constellation of the month
Virgo the Maiden
Jupiter is currently in Virgo and will remain travelling through this area of sky for most of the year. It’s a good time to take a closer look at this large and famous constellation while there is a bright light to guide you to the right direction in the sky.
Virgo is the second largest constellation in the sky. Virgo is said to represent a young woman and often associated with the harvest season – two thousand years ago the Sun was in this part of the sky during the end of the northern hemisphere summer, when crops were being gathered in. Spica, the brightest star in Virgo, means “ear of wheat’ and Virgo is often drawn with her hand upraised holding some of this important grain. Her other hand is represented by eta Virginis, also known as Vindamiatrix, the Grape Gatherer. The cluster of grapes she is reaching for is represented by the faint but large open cluster in the middle of another constellation, Coma Berenices.
Some people draw Virgo as the goddess of justice, holding the scales of Libra in her hand. In this form she represents Astrea, the Roman goddess of justice.
In these modern times Virgo is better known for the galaxies found within its borders. The Virgo Supercluster is a large cluster of galaxies, so large it also attracting other galaxies toward it! You will need a telescope to see these galaxies, but some are relatively bright and will only need a small telescope to detect their light, which is travelling from around 55 million light years away.
Virgo is hosting Jupiter in 2017. Use it to guide you towards finding the shape of the Maiden in the sky.
Objects for the small telescope
The constellation of Virgo is famous for its galaxies. As we look towards this direction in the sky we are looking out towards what is known as the Virgo Supercluster. Our own Milky Way galaxy is part of this large conglomerate of star cities. On the border of Virgo and Coma Berenices is a galaxy described as a “supergiant elliptical” as it contains more mass than most galaxies in the Supercluster – Messier 87.
It’s also known as Virgo A as it is a very strong source of radio signals and its known to have a supermassive black hole in the centre of it that projects a massive jet of gas from its core. It even has 12,000 globular clusters circling around it – compare that to only 120 or so that the Milky Way is known to have. Yes, everything is super massive about M87!
The jet of gas shooting out of the super massive black hole in the middle of M87. By NASA and The Hubble Heritage Team (STScI/AURA)
It is 53.5 million light years away, which isn’t too far in galactic terms. It lies about half way between Vindamiatrix in Virgo and Denebola, the star that marks the tail of Leo the Lion to the west. Nearby is an interesting line of galaxies known as Markarian’s Chain, which is a popular target for photographers. You won’t be able to see the jet of gas yourself, but the large fuzzy halo of M87 should be easy to pick up, as are the brighter members of Markarian’s Chain.
M87 is about half way between Vindamiatrix in Virgo and Denebola in Leo. The curve of galaxies known as Markarian’s Chain is nearby.
Two More Moons for Jupiter
Our solar system is a busy place. In early June astronomers announced that while they were searching for the elusive Planet 9 they also managed to find two more moons circling Jupiter. Tiny and faint, perhaps only a kilometre or two across, they bring the total number of moons for the gas giant to 69. They don’t have names yet, just a number designation to say which year they were found in – S/2016 J1 and S/2017 J1.
TIn some ways this is no surprise, as most of Jupiter’s moons orbit in retrograde motion – against the spin of the planet – indicating they were captured by the huge mass of Jupiter when they passed too close at some time in the past. Jupiter has a big influence on any asteroid or comet that passes near it, giving them a nudge in a different direction and changing their orbits.
So, time to grab your pencils and update your text books with the latest numbers of the major planets moons:
Mars – 2
Jupiter – 69
Neptune – 14
If you want to include the dwarf planet then Pluto has five, Haumea has two, and Eris and Makemake have one each. And it’s not uncommon for asteroids to have their own moons either! Yes, it pays to keep your eyes and cameras on the alert out there, you never know what you might see next.
This enhanced-color image of Jupiter’s bands of light and dark clouds was created by citizen scientists Gerald Eichstädt and Seán Doran using data from the JunoCam imager on NASA’s Juno spacecraft. Credits: NASA/JPL-Caltech/SwRI/MSSS/Gerald Eichstädt /Seán Doran