Winter Solstice

Winter Solstice occurs this month in the southern hemisphere. On the 21st the sun rises and sets at its most northerly points, its path is the lowest of the year giving us our shortest day, and its rays arrive at their shallowest angle giving the least energy per square metre.

Solstice comes from the Latin sol (sun) and sistere (stand still). At the winter solstice the Sun is said to “stand still” at its northernmost extreme after which it begins its daily southwards progression to the spring equinox. This daily shift and the solstices and equinoxes result from the Earth’s rotational axis being titled at an angle of 23.5 degrees from its orbit around the Sun.

Explore more at:
Timeanddate - June Solstice
Museums Victoria - Reasons for the Seasons

Aurora Delight

Across media and online last month beautiful pictures appeared of the Aurora Australis (Southern Lights) so we prepared this brief explainer about the extraordinary phenomenon enjoyed by so many, including from metropolitan Melbourne as seen below.

Space Weather includes the effect our local star, the Sun, has on Earth. In the current Solar Maximum period in the Sun’s 11-year cycle of energy output, increased solar activity has generated higher than normal levels of solar particles in the solar wind that blows out across the solar system in all directions. This current ‘solar max’ is occurring a year earlier than predicted and is creating auroras further from the polar regions where they normally appear.

Earth’s force field

As our planet rotates its solid iron-nickel inner core and liquid iron outer core act as a massive dynamo generating electric currents which produces an extended protective magnetic field enveloping Earth. Physics has shown that an electric current in a conducting material, whether it be copper wire or an entire planet, will produce a magnetic field. The reverse is also true; a magnetic field can induce an electric current. Such is the dual nature of electro-magnetism.

Earth’s dynamic field deflects most of the high energy charged particles of protons and electrons that form the solar wind which travels at 400 to 800 km per second. Some particles, however, spiral in between field lines and are trapped over our planet’s magnetic poles. In a process not fully understood billions are released and collide with air molecules in the upper atmosphere

Colourful curtains

These particles impart energy to high altitude air molecules which become temporarily charged and then release photons of light at specific wavelengths (corresponding to the aurora colours we see) as they return to their normal un-excited state. With Earth’s magnetic field lines constantly fluctuating, the overall effect is shifting patterns of colour in the upper atmosphere, looking very often like vast curtains rippling in a gentle breeze.

Auroras typically occur at between 100 to 300 km altitude and sometimes as high as 600 km. Colours are green from oxygen, pink from nitrogen, red from higher altitude oxygen, and blue or purple from hydrogen and helium (although these last two are not easily seen). The auroras occur at all times but are best seen on clear nights when they can be a spectacular sight.

Aurora opportunities

Being Solar Maximum it is highly likely there will be more good times to observe and photograph auroras. The Australian Bureau of Meteorology’s Space Weather Forecasting Centre advises on cloud cover, aurora conditions and solar wind activity, along with useful videos: SWS - Aurora (bom.gov.au).

Explore more:
Australian Antarctic Program - Awesome Aurora
NASA - Aurora Fact Sheet

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Melbourne Sun times

Date	Rise	Set	Day length	Solar noon*
Tuesday 1st	7:26am	5:09pm	9:42hours	12:18pm
Sunday 11th	7:32am	5:07pm	9:34hours	12:20pm
Wednesday 21st	7:35am	5:08pm	9:32hours	12:22pm
Friday 30st	7:36am	5:11pm	9:34hours	12:23pm

^*When the sun is at its highest, crossing the meridian or local longitude.

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Moon phases

Phase	Date
New Moon	Thursday 6th
First Quarter	Friday 14th
Full Moon	Saturday 22nd
Third Quarter	Saturday 29th

Moon distances

Lunar perigee (closest to Earth) is on Thursday 27th at 369,286 km.

Lunar apogee (furthest from Earth) is on Friday 14th at 404,077 km.

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Planets

Mercury, after its passage behind the Sun, is not visible this month being still too close to the Sun.

Venus is not yet visible after having just completed its superior solar conjunction and passage behind the Sun.

Mars can be seen in the early morning rising in the east around 3:30am and moving to the north-east before fading from view by dawn.

Jupiter rises around 6am early in the month and a little earlier each morning before quickly fading in the early dawn light.

Saturn rises by 1am early in the month and moves across the north eastern and northern sky before fading by dawn. Mid-June it will rise at half past midnight and by the end of the month by 11:30pm.

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Meteors

There are two minor meteor showers this month. The Arietid Meteor Shower (in the constellation of Aries) occurs through to June 24 but peaks on June 11th. From Melbourne the shower is likely best seen just before dawn. Although low in number (less than 10 per hour) they can often be spectacular and bright with many displaying a yellow/orange colour.

The Bootid Meteor Shower (in the constellation of Bootes) appears late in June and into early July. The best time to see meteors is after midnight with no moon in the night sky.

Learn more at:
In-the-sky – Arietid Meteor Shower
In-the-sky – Bootid Meteor Shower

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Stars and constellations

In the west

Although Orion has disappeared below the western horizon but his two dogs Canis Major with the star Sirius (low in the west) and Canis Minor with the star Procyon (low in the north-west) are still both in our skies.

In the north

Leo the lion is still visible in the north-west with the bright star Regulus. Look for a large hook of stars, or inverted question mark, to locate his curving mane and shoulders.

In the east

Scorpius is in the south-east this month with the red-giant star Antares as the middle of three stars that form the scorpion’s body. During winter the centaur-archer Sagittarius suits below the scorpion with its bow and arrow (the famous ‘Tea Pot’ asterism).

In the south

High in the south-east is Crux or The Southern Cross with the Pointers (Alpha and

High in the south-east is Crux or The Southern Cross with the Pointers (Alpha and Beta Centauri) lower down. In darker skies the two neighbouring galaxies, the Large and Small Clouds of Magellan, can be seen as small isolated patches in the south-west. From our southern latitude they are easily seen every night.

In dark locations the broad band of the Milky Way’s billions of stars and numerous interstellar dust clouds stretches across the sky from horizon to horizon. While some foreground stars in our local region of the galaxy can be seen, the dark dust clouds obscure our view further into the galaxy since our eyes and optical telescopes ‘see’ in only the visible part of the spectrum.

See NASA-JPL video Interstellar Clouds and Dark Nebulae

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International Space Station

ISS orbits every 90 minutes at an average distance of 400 km appearing like a bright star moving slowly across the night sky.

Here are some of the brightest morning and evening passes expected this month over Melbourne:

Morning

Tuesday 4th 6:19am to 6:25am South-West to North-East

Evening

Saturday 15th 6:51pm to 6:54pm North-West to South-West
Sunday 16th 6:02pm to 6:08pm North-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’.

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On this day

1st 2002, Czech Republic becomes the first country to ban light pollution.

2nd 1966, Surveyor 1 (USA) reaches the Moon as first probe to land on another body.

3rd 1965, Ed White takes America’s first spacewalk as part of Gemini IV.

6th 1971, Soyuz 11 (‘Union’ 11, USSR) carries the first people to a space station (Salyut 1 or ‘Salute’ 1).
7th 1879, Joan Voute proves with parallax that dwarf star Proxima Centauri is the same distance as Alpha Centauri binary.

8th 2004, a Transit of Venus is observed, the first in 122 years.

9th 1986, Rogers report on Space Shuttle Challenger explosion reveals solid rocket booster fault and serious management and safety problems with US program.

10th 2003, launch of Mars Exploration Rover Spirit (USA) which lands in 2004 and exceeds expectations operating to 2010.

13th 1983, Pioneer 10 (USA) becomes the first spacecraft to travel beyond the planets of the Solar System.

13th 2010, Hyabusa (Japan) craft returns the first asteroid samples to Earth.

14th 1962, European Space Research Organisation (ESRO) begins, later to be part of the European Space Agency (ESA).

15th 763 BCE, Assyrians record a total solar eclipse which helps date other events in Mesopotamian history.

16th 1911, a meteorite weighing 772g strikes a barn in rural Wisconsin (USA).

16th 1963, Valentina V. Tereshkova (USSR) becomes the first woman in space in Vostok 6, the first civilian into space, and the only woman to undertake a solo space flight.

17th 1969, Venera 6 (‘Venus 6’, USSR) descends into Venus’ dense atmosphere sending data before being crushed by rising pressure.

18th 1983, Sally Ride becomes the first American woman in space aboard Shuttle Challenger.

20th 1990, Asteroid Eureka found as part of the Trojans asteroid group orbiting at Mars’ L5 Lagrange point.

21st 2004, SpaceShipOne (USA) is launched as the first privately-funded human space flight.

21st 2006, Pluto’s small moons Nyx and Hydra are named.

22nd 1633, Galileo recants his sun-centred solar system model under threat of torture by the Catholic Inquisition.

22nd 1978, Dr James W. Christy (USA) discovers Pluto’s large moon Charon.

24th 1883, discoverer of cosmic rays, Victor Francis Hess, is born.

24th 1915, birth of Fred Hoyle, who later explains the creation of elements in stars, promotes the steady state model of the universe, and coins the pejorative term ‘big bang’ for the rival model of the universe’s creation.

24th 1997, first life-threatening space collision occurs as Russia’s Progress supply craft collides with Mir Space Station during a test docking while not using its automated docking and radar system. The ageing problem-plagued station suffers a 3cm puncture in its Spekr module which quickly depressurises. US astronaut Mike Foale evacuates from the damaged module in time and Mir spins out of control as solar power is lost. Progress rebounds but is later safely de-orbited to burn up. Control is slowly regained by cosmonaut Vasily Tsbliev assisted by cosmonaut Aleksander Lazitkin and Foale. This serious incident heightens tensions between the American space agency NASA and their Russian counterpart Roscosmos.

29th 1818, Angelo Secchi born, one of the first astronomers to believe the Sun is a star.

29th 1961, first use in space of a radioisotope thermoelectric generator (RTG) using plutonium238 which powered a US Navy NAVSAT satellite Transat4A.

29th 1995, Space Shuttle Atlantis (USA) – first docking at Russia’s Mir Space Station.

30th 1908, The Tunguska Event; a meteor several metres in size explodes over Tunguska (Russia) destroying 2,200 km2 of forest in a multi-megaton blast.

30th 1971, Soyuz 11 (USSR) is the only mission to visit the first space station Salut 1 (USSR) after which its crew of three become the only humans known to have died in space when their cabin depressurises prior to or during re-entry.