Skynotes: June 2025
Upcoming events
Finding fainter exoplanets – a new approach
A new technique announced last month may enable discovery of harder to detect exoplanets. In simulations it was able to identify and separate the light of a planet from the glare of its parent star.
To date, among several methods used to find exoplanets, two have proven very successful in detecting almost 6000 planets. Radial velocity analysis infers the presence of a planet by its effect on a star’s movement towards or away from Earth which subtly shifts its observed light wavelengths, and the transit method relies on changes in a star’s brightness as a planet passes in front briefly reducing the total light received by a telescope. Repeated detections using such methods are needed to establish the existence of an orbiting planet. And recently direct detection of light from an exoplanet has added more, but the problem remains that many exoplanets thought to exist are still too faint to see or detect. The new approach lowers the detection threshold.
Using a mask or coronagraph can block out the intense light of the star to reveal much fainter bodies in orbit. This is how our Sun’s faint corona has been studied. But, at the extremely faint levels, coronagraphs are plagued by light interference causing diffraction that obscures vital details. However, an Arizona University team has developed a new approach using star masking combined with a two-step ‘spatial mode sorting’ process to reveal fainter planetary signs. Their new technique may also prove useful in analysing magnetic or gravitational fields, and in medical imaging and optical communications.
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Winter Solstice Comes Around Again
The mid-year Solstices for 2025 fall on the 21st of this month; Summer Solstice for the Northern Hemisphere and Winter Solstice for the Southern Hemisphere. On that day in the South the sun rises and sets at its most northerly points on the horizon, its path is the lowest of the year giving us our shortest day, and its warming rays arrive at their shallowest angle giving the least energy per square metre. We are in the depths of winter.
Solstice comes from the Latin sol (sun) and sistere (stand still). At the winter solstice the Sun is said to briefly pause at its northernmost extreme and then begins its daily southwards rising and setting with its path lengthening and days becoming longer until we reach the spring equinox – halfway to summer. This daily shift and the solstices and equinoxes result from the Earth’s rotational axis being at a fixed angle or tilt of 23.5 degrees in relation to its orbit around the Sun.
Winter Solstice Animation
This NASA visualisation shows how the Earth’s tilt leans the Southern Hemisphere away from the Sun in winter (and the Northern Hemisphere towards the Sun for its summer). Earth and Sun are not to scale, and at NASA Solstice Animations solstices can be run for either hemisphere, with or without labels. Credit: NASA Goddard Space Flight Center / Krystofer Kim / Joy Ng.
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Melbourne Sun times
| Date | Rise | Set | Day length | Solar noon1 |
|---|---|---|---|---|
| Sunday 1st | 7:26am | 5:09pm | 9:42hours | 12:17pm |
| Wednesday 11th | 7:32am | 5:07pm | 9:35hours | 12:19pm |
| Saturday 21st | 7:35am | 5:08pm | 9:32hours | 12:21pm |
| Monday 30th | 7:36am | 5:11pm | 9:34hours | 12:23pm |
1 When the sun is at its highest, crossing the meridian or local longitude.
Moon phases
| Phase | Date |
|---|---|
| First Quarter | Tuesday 3rd |
| Full Moon | Wednesday 11th |
| Third Quarter | Thursday 19th |
| New Moon | Wednesday 25th |
Moon distances
Lunar perigee (closest to Earth) is on Monday 23rd at 363,178 km.
Lunar apogee (furthest from Earth) is on Saturday 7th at 405,554 km.
Planets
Mercury has moved from behind the Sun but is not yet visible as a night time object.
Venus as the ‘morning star’ can be seen from 3:40am shining brightly in the east before finally fading in the north-east by dawn.
Mars is still an evening object and can be seen in the north at twilight around 6pm before setting by 10:15pm.
Jupiter is not visible this month as a night time object as it is about the pass behind the Sun for its solar conjunction.
Saturn has returned from its solar conjunction and can be seen in from around 1am in the north before slipping from sight in the north-west in the early dawn light.
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.
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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 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.
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 passes expected this month over Melbourne:
Morning
Wednesday 4th 6:15am to 6:20am West-South-West to North-North-East.
Thursday 5th 5:29am to 5:32am North-East to North-East.
Evening
Friday 13th 6:52pm to 6:55pm North-West to North
Monday 16th 6:03pm to 6:09pm West-North-West to South-East
Heavens Above gives predictions for visible passes of space stations and major satellites, live sky views and 3D visualisations. Be sure first to enter your location under ‘Configuration’.
On this day
1st 2002, Czech Republic becomes the first country to ban light pollution.
2nd 1966, Surveyor 1 (USA) lands on 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 (USSR) carries the first people to a space station (Salyut 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 European Space Agency (ESA).
15th 763 BCE, Assyrians record a total solar eclipse which has helped in dating other events in Mesopotamian history.
16th 1911, a meteorite weighing 772g strikes a barn in rural Wisconsin (USA).
16th 1963, Valentina V. Tereshkova (USSR) is 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 (USSR) descends into Venus’ dense atmosphere sending data before being crushed by rising pressure.
18th 1983, Sally Ride is 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) launched as 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 explained the creation of elements in stars, promoted the steady state universe, and coined the pejorative term ‘big bang’ for the rival model of the universe’s creation.
29th 1818, Angelo Secchi born, one of the first astronomers to believe the Sun is a star.
29th 1995, Space Shuttle Atlantis (USA) – first docking at Russia’s Mir Space Station.
30th 1908, 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) was the only mission to visit the first space station Salut 1 (USSR) after which its crew of three became the only humans known to have died in space when their cabin depressurised prior to re-entry.