Spring Equinox

Here in the southern hemisphere we are about to experience Spring Equinox (or Vernal Equinox from the Latin ver for spring-time, a period of new growth). This is when day and night are effectively the same length. This will be Sunday 22nd and marks the end of winter and beginning of spring in the southern hemisphere, and end of summer and start of autumn in the northern hemisphere.

At the equator at an equinox the noon sun sits directly overhead and both hemispheres receive equal hours of daylight. However, away from the equator the sun’s path in the sky is midway between its high long summer arc and its low short winter one.

The main reason for the seasons lies in our planet’s titled axis of rotation which is 23.5 degrees with respect to its orbit around the sun. At an equinox neither hemisphere leans toward or away from the sun.

However, local day and night are not exactly equal at an equinox. Astronomical timings are based on how long the centre point of the Sun’s disc is above the horizon. A local day effectively starts when the ‘leading edge’ or limb of the Sun broaches the eastern horizon and ends when its ‘tailing edge’ or limb drops below the western horizon.

There is also a terrestrial effect as well. The Earth’s atmosphere refracts or bends light from the Sun so that at sunrise we get the first glimpse of the Sun before it physically crosses the local horizon. The reverse occurs at sunset when we see the Sun for a few minutes after it has already sunk below the western horizon.

Perigee Full Moon

This month, on Wednesday 18th, our lunar neighbour will be at full moon at the same time it is closest to Earth in its orbit (perigee). This will make the moon slightly larger and slightly brighter than other full moons that occur when at its furthest distance (apogee). Coincidentally, a partial lunar eclipse will briefly interrupt the full moon, but that will not be visible from Australia.

The moon has an average distance from Earth of 384,000 km. However, its orbital eccentricity or variation from a perfect circle, means its distance actually varies from perigee to apogee by about 50,000 km.

Explore:

Close and far moons – earthsky
September Equinox - time and date
Sunrise Sunset Refraction – HK Observatory
Spring Equinox – time and date
Day and Night - the conversation

---

Melbourne Sun times

Date	Rise	Set	Day length	Solar noon*
Sunday 1st	6:41am	5:59pm	11:17hours	12:20pm
Wednesday 11th	6:26am	6:07pm	11:40hours	12:16pm
Saturday 21st	6:11am	6:15pm	12:04hours	12:13pm
Monday 30th	5:57am	6:23pm	12:26hours	12:10pm

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

---

Moon phases

Phase	Date
New Moon	Tuesday 3rd
First Quarter	Wednesday 11th
Full Moon	Wednesday 18th
Third Quarter	Wednesday 25th

Moon distances

Lunar apogee (furthest from Earth) is on Friday 6th at 406,211 km.

Lunar perigee (closest to Earth) is on Wednesday 18th at 357,286 km.

---

Planets

Mercury continues not visible this month as it is remains too close to the Sun.

Venus is now the “Evening Star” low in the west just after sunset. It can be seen from 6:20pm setting around 8pm early in the month but will rise and set a little later each evening during the month.

Mars is visible early in the month from 2.30am rising in the east before fading in the dawn light by 6am. As the days pass it will appear slightly earlier each morning.

Jupiter is rising around 1.30am before moving across the northern sky and then fading from view by 6am.

Saturn is visible rising in the east from 6.45pm before it too moves to the north and is then lost in the west by 5.40am.

---

Meteors

While not a good time for meteors this month the Southern Piscids will peak from 11th to the 20th. They usually number only a few per hour and appear in the constellation of Pisces, the fish, which rises in the north-west from midnight.

Find out more about these space visitors at NASA Asteroids, Comets and Meteors

---

Stars and constellations

In the north

High in the north are Sagittarius (the archer centaur). Its bow and arrow forms the famous asterism The Teapot, the spout of which leads across the zenith to the curving tail of nearby Scorpius.

Lower in the north sits Aquila (the eagle) with Altair or Alpha Aquilae, the 12th brightest star at night. And quite low in the north is Lyre (the lyre) and its principal star Vega or Alpha Lyrae which is the 5th brightest star at night.

In the east

Directly east this month is a trio of adjacent constellations. In the centre is Aquarius, the water bearer while above is Capricornus (the goat), to its left sits Pisces Austrinus (Southern Fish) containing its main star and the 18th brightest star at night, Formalhaut (Alpha Piscis Austrinus).

In the south

Low in the south-west can easily be seen two of the brightest stars in the night sky, Alpha and Beta Centauri. These are the two brightest stars in the constellation of Centaurus (the centaur) with Alpha Centauri also known as Rigel Kentaurus (foot of the centaur). Together these two stars are referred to as The Pointers as they lead directly to the unmistakable diamond shape of Crux or Southern Cross. Crux is the smallest of the traditional 88 constellations astronomer use and is an easy feature of the night sky to observe, even in city surroundings.

In the south-east is the 10th brightest star, Achernar in the long constellation Eridanis (the river) that winds its way down to the horizon.

In the west

High in the west sits the curving tail, body and pincers of the scorpion, Scorpius. Within its body you should see red giant star Antares which will appear more orange than red in light polluted skies. In front of the Scorpion’s wide head and closer to the horizon sits Libra (the scales).

---

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 of the brightest and highest in elevation this month:

Evening

Monday 2nd 6:46pm-6:52pm West-South-West to North-East

Morning

Wednesday 18th 5:30am to 5:36am North-West to South-East
Saturday 21st 4:39am to 4:42am South-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 to first enter your location under ‘Configuration’.

---

On this day

1st 1939, Americans J Robert Oppenheimer and Hartland Snyder publish the first paper that describes the gravitational contraction of a star which later led to the modern concept of black holes.

1st 1859, Carrington Event, most powerful geomagnetic storm ever recorded. Now understood as a Coronal Mass Ejection (CME) from the Sun that hit Earth’s magnetosphere inducing strong northern auroras almost to the equator, and telegraph interference in Europe and North America with operators receiving electric shocks, poles sparking, and signals sent despite power cut off.

1st 1979, Pioneer 11 (USA) made the first flyby of Saturn returning the first close-up images of the planet. It was the second probe to pass the asteroid belt and Jupiter and to reach solar escape velocity. Last routine contact was on 30 September 1995 and final data received was on November 1995.

5th 1977, Voyager 1 (USA) is launched to explore the outer Solar System. After 42 years it continues sending data and is the most distant probe at 21.8 billion km (146 AU). It entered interstellar space in 2012 and its power supply may last until 2025.

8th 2004, Genesis (USA) probe crashes in Utah while returning samples of solar wind particles. Some collecting panels survived impact and were recovered giving successful scientific results.

11th 1985, the International Cometary Explorer or ICE (USA) became the first spacecraft to encounter a comet by flying through the dust tail of Comet Giacobini-Zinner.

14th 1959, Luna 2 (USSR) was the first craft to fly to and impact another body, in this case the Moon. It released sodium gas to allow visible tracking, used radio for telemetry transmission, and crashed into Mare Imbrium (the Sea of Rains).

17th 1976, NASA unveils its concept for a Space Transportation System, a rocket launched and glider return orbiter known as the Space Shuttle.

17th 1857, birth of Konstantin Tsiolkovsky, a pioneering Russian then Soviet teacher whose theoretical work on aerodynamics and rocketry influenced all who followed. He advocated spaceflight and believed humans would colonise the galaxy.

18th 1977, Voyager 1 (USA) sends the first image of Earth and Moon together taken, from a distance of 11.6 million km while on its way to Jupiter.

21st 1633, the Roman Catholic Inquisition begins its trial of Galileo for heresy in publishing and advocating a heliocentric or Sun-centred solar system contrary to church doctrine, dogma and scripture.

23rd 1846, Neptune, first predicted by Urbain Le Verrier (France), is discovered by Johanne Gottfried Galle (Germany) with John Couch Adams (UK) recognised for an independent discovery.

27th 1905, Albert Einstein published his paper containing the famous equation E=mc2 (energy equals mass multiplied by the speed of light squared), meaning a small amount of matter is equivalent to, or can be converted into, a great deal of energy.