Skynotes: August 2023
Upcoming events
Melbourne Sun times
| Date | Rise | Set | Day length | Solar noon§ |
|---|---|---|---|---|
| Monday 1st | 7:21am | 5:32pm | 10:11 hours | 12:26pm |
| Friday 11th | 7:10am | 5:40pm | 10:30 hours | 12:25pm |
| Monday 21st | 6:58am | 5:48pm | 10:51 hours | 12:23pm |
| Thursday 31st | 6:44am | 5:57pm | 11:13 hours | 12:20pm |
§ When the sun is at its highest, crossing the meridian or local longitude.
Moon phases
| Phase | Date |
|---|---|
| Full Moon | Wednesday 2nd |
| Third Quarter | Tuesday 8th |
| New Moon | Wednesday 16th |
| First Quarter | Thursday 24th |
Moon distances
Lunar perigee (closest to Earth) is on Thursday 31st at 357,181 km.
Lunar apogee (furthest from Earth) is on Wednesday 16th at 406,634 km.
Full Moon at Perigee
On August 2nd, the full moon will coincide with lunar perigee which means our neighbour will be slightly larger and a little brighter in the night sky, although the difference will be barely noticeable to casual observers. For full details and a comparison of full moon at perigee versus apogee, see In-The-Sky – Full Moon August 2.
Planets
Mercury will be visible in the evening from 6:50pm in the west at dusk before setting around 8pm.
Venus remains visible low in the western sky after sunset but by mid-month it will be behind the sun until later in August when it will return as the ‘morning star’ visible in the east in the dawn light just before sunrise.
Mars continues to be visible in the west from 6:30pm before setting by 8pm. The Red Planet will appear closer to the Sun over the next two months before making a slow pass behind the sun disappearing from view for several months. Once it returns to our skies it will rise in the east shortly before dawn.
Jupiter is emerging from its recent pass behind the sun. It will be visible early in the month from 1:45am low in the north-east before fading in the north in the dawn light by 6:50am. As the month goes by the Jovian Giant will be seen a little earlier each night.
Saturn is about to reach opposition - directly opposite the Sun from our view on Earth. It will be visible in the east from 8pm, reach its highest point by 1am in the north before fading in the west by 6.30am. During the month it will be seen slightly earlier each night. On the 27th Saturn will reach opposition.
Over the next three months, as we overtake Saturn in our inner faster orbit, it should be a beautiful planet to observe through a telescope with a partly open view of its vast rings.
These Hubble Telescope Wide Field Planetary Camera views of Saturn from 1996-2000 show its changing appearance. With the planet’s axis of rotation tilted 27 degrees from its orbital plane, we enjoy different perspectives of its rings. This month’s opposition should be similar to the second from the left with the ring system partly open. Image: NASA and The Hubble Heritage Team.
Explore:
EarthSky – Saturn at Opposition
Meteors
This month’s major meteor shower is the Perseids which peaks on the 13-14th although not strong in the southern hemisphere. They are fast, bright, can leave persistent trails, and come from a point below the north-east horizon in the northern constellation of Perseus. These meteors result from Comet Swift-Tuttle which passed near the Sun in 1991 leaving a trail of particles for the Earth to regularly pass through.
Stars and constellations
In the north
This month’s evening skies show Virgo and Spica (Alpha Virginis), the 15th brightest star at night and 262 light years away, have moved towards the west, while Leo has largely disappeared below the north-western horizon. However, Libra (the weighing scales) is high in the north and in the north-east is Aquila (the eagle) with its principal star Altair (Alpha Aquilae), the 12th brightest star at night and 17 light years from us.
In the east
Very high in the east after sunset and slowly moving overhead during the night as our planet rotates to the east is Scorpius with its impressive curving line of stars. The central star of the three that form the scorpion’s body is the red giant Antares (Alpha Scorpii) at 34 light years and 16th brightest star at night. Rising behind and following during the night is the centaur Sagittarius with its bow and arrow forming the famous Teapot asterism.
In the south
Standing high in the south-west is Crux, or the Southern Cross. On a moonless night, and certainly away from city lights, can be seen the dark patch known as the Coal Sack nebula, a vast region of interstellar dust that blocks our view of more distant stars. To its left are the Pointers (Alpha and Beta Centauri), the brightest and second brightest stars in the constellation of Centaurus which is the other horse-human hybrid from ancient Greek myth.
Alpha Centauri is also known as Rigel Kentaurus (‘foot of the centaur’) and is the 4th brightest star in the night sky. Until very recently it was thought to be our sun’s nearest neighbour at 4.37 light years. We see what appears to be one star but a modest telescope will reveal it is in fact two, Alpha Centauri A (aCen A) and Alpha Centauri B (aCen B) in close orbit around their barycentre or common centre of mass.
However, bound to these two stars but at a considerable distance is the faint small red-dwarf star Proxima Centauri, known also as Alpha Centauri C. Our nearest star system is therefore a triple system.
Proxima, as the name suggests, is currently the closest star to our sun at 4.24 light years and hosts at least two planets. The first planet Proxima Centauri b (discovered in 2016) is a little over Earth mass, orbits swiftly much closer than Mercury does to our sun, and is presumed to be tidally locked with only one face turned to its star. The second planet Proxima Centauri c (discovered in 2016) is about seven Earth masses, lies further out in a 5-year orbit, and may possess a ring system.
Explore:
EarthSky – Alpha Centauri System
ESO – Family Portrait Alpha Centauri System
Low in the south-east is the 10th brightest star Achernar (in the constellation of the Eridani, the river) which sits at 144 light years from Earth, and in the south-west lies the 2nd brightest star Canopus in the constellation of Carina (the keel) at 313 light years. From our southern latitude both of these stars never disappear below the horizon.
In the west
Low in the north-west is Arcturus, the 3rd brightest star at night and 37 light years from us in the constellation of Bootes (the herder or plower).
Corvus (Latin for crow) sits squarely in the west in the evening this month. In ancient Greek mythology, however, this sacred bird is a raven that perches on the back of Hydra (the sea serpent). The serpent’s nearby head is a little higher up in the west and marks one end of a long narrow body that snakes to the horizon in the longest of the traditional 88 constellations.
International Space Station
At a distance of about 400km the ISS completes an orbit every 90 minutes and appears as a bright object that moves slowly across the night sky. There will be many visible passes this month over Melbourne and Central Victoria. Here are two expected to be the brightest and highest in elevation:
Morning
Tuesday 8th, 5:31am – 5:34am South-East to North-East
Evening
Wednesday 16th, 6:52pm – 6:54pm North-West to East-South-East
Heavens Above gives predictions for visible passes of space stations and major satellites, live sky views and 3D visualisations. Be sure to first enter your location under ‘Configuration’.
On this day
3rd 2004, the MESSENGER (USA) mission to Mercury was launched.
4th 2007, Phoenix (USA) Mars lander was launched.
5th 1998, NASA Near Earth Object Program is created to detect and catalogue asteroids that approach Earth.
5th 1939, first person to walk on the moon, American Neil Armstrong, is born.
6th 2012, the Mars rover Curiosity lands on the red planet.
6th 1996, a meteorite from Mars discovered in Antarctica is said by NASA to contain possible microfossils of bacteria.
7th 1959, Discoverer 1 (USA) returns the first satellite images of the Earth.
10th 1675, Royal Greenwich Observatory is established east of London.
10th 1990, Magellan (USA) arrives at Venus and begins radar mapping of its surface.
12th 1877, Astronomer Asaph Hall at the US Naval Observatory discovers Mars’ tracks are clearly eviden.t 12.6km diameter moon Deimos.
13th 1898, Eros, the first near-Earth asteroid is found by Carl Gustav Witt.
17th 1970, Soviet probe Venera 7 is launched to Venus and will send first pictures from the surface of another planet after landing on December 15th.
18th 1877, Mars’ 22.5km diameter moon Phobos is discovered by Asaph Hall.
18th 1868, new element ‘helium’ is found by Pierre Janssen from analysis of the Sun’s spectrum. It is now known to be the second most abundant element in the universe after hydrogen.
19th 1960, two dogs, Belka and Strelka, are launched aboard Sputnik 5 (USSR), and successfully returned to Earth.
19th 1646, birth first Astronomer Royal John Flamsteed who catalogued 3000 starts.
20th 1975, launch of Viking 1 (USA), first probe to land on and study Mars.
20th 1977, Voyager 2 (USA) launched to the planets of the outer Solar System.
22nd 1989, Voyager 2 (USA) discovers positive evidence for Neptune’s rings.
24th 2006, first formal definition of ‘planet’ is debated and vote upon by International Astronomical Union in Prague resulting in dwarf planet status for Pluto.
25th 1609, Galileo demonstrates to the Venetian Doge and officials his improved version of the newly invented telescope.
31st 1913, birth of famous British radio-astronomer Bernard Lovell.