Skynotes September 2009

Month Highlights

Jupiter is looking stunning this month, rising in the north-east at sunset. It is easily recognised as the brightest object in the northern sky. The first week of the month is also a great time to see Mercury. The faintest of the naked eye planets, it can be seen above the western horizon at sunset. Saturn lies just below Mercury but quickly disappears in the glow of twilight. Mars and Venus can both be found in the north-east sky before sunrise.

Planetarium Events

The planetarium is hosting two special events this month.

• Cracking the Einstein Code – 6:30pm, Friday 11th Sept. A talk by Professor Fulvio Melia, a world expert on black holes from the University of Arizona.
• Copernicus: the story of the man who reshaped the Universe – a theatrical play under the dome, Sept 16th - Oct 4th. This special event is presented by Transit Theatre and Scienceworks as part of the International Year of Astronomy and the Melbourne Fringe Festival.

September School Holidays

Scienceworks will be opened daily from 10am–4:30pm during school holidays (19th September – 4th October). Planetarium session times are:

12pm & 2pm: The Search for Life: are we alone?
1pm: Tycho to the Moon
3pm: Our Living Climate – a stunning new show exploring the science of Earth’s climate.

See the Melbourne Planetarium's What's On listing for more details.

Sunrise & Sunset Times

 Moon Phases

The Moon will be at apogee (furthest from Earth) on Monday 28th at a distance of 404 431 km.

The Moon will be at perigee (closest to Earth) on Wednesday 16th at a distance of 364 053 km.

Let the Moon Be Your Guide

The Moon can be used as a pointer to find other objects in the sky.

• After sunset on the 2nd the waning gibbous Moon sits above Jupiter.
• On the morning of the 11th the Moon sits near the brilliant star cluster Pleiades.
• Before sunrise on the 14th the waning crescent Moon can be found below the red planet Mars.
• On the morning of the 15th the Moon forms a line with the twin stars of Gemini, Castor and Pollux.
• On the 17th, low to the eastern horizon and just before sunrise, the thin crescent Moon sits above the bright star Regulus (Leo, the lion) and to the right of Venus.
• After sunset on the 21st, the waxing crescent Moon sits above Spica (Virgo).
• On the evening of the 24th, the Moon has a close encounter with Antares (Scorpius).
• During the night of the 29th the waxing gibbous Moon is back above Jupiter.

Planets

Mercury can be found at its highest point above the western horizon just after sunset at the start of the month. However, it is slowly drifting back towards the horizon and by the middle of the month it will become too close to the Sun to be seen.

Venus is in the morning sky, sitting low to the north-east horizon. At the start of the month the twin stars of Gemini, Castor and Pollux, lie to the left of Venus. On the morning of the 17th the thin crescent Moon can be found to the right of Venus with Regulus (Leo, the lion) sitting below. In the following days, Regulus can be seen rising higher, leaving Venus behind.

Earth days are warming up again as we pass the Spring Equinox on Wednesday 23rd. At 7:18am the Sun crosses the celestial equator and moves into the southern sky. While it is often thought that day and night are equal on the Equinox, this is not the case. It is only the centre of the Sun that is above the horizon for exactly 12 hours; our day is slightly longer at 12 hours and 9 minutes. The reason why? We calculate sunrise and sunset as being when the edge of the Sun first appears above or disappears below the horizon (not the Sun’s centre). What’s more, the Earth’s atmosphere adds its own strange effect – it bends light from the Sun so that at sunrise we happen to see the Sun before it physically crosses the horizon. The reverse occurs at sunset, we continue to see the edge of the Sun for several minutes after it has actually sunk below the western horizon. As a result our equal day and night occurs before the Equinox on Saturday 19th.

Mars continues to shine in the early morning sky, high above the north-east horizon. On the morning of the 14th it sits above the crescent Moon. By the end of the month Pollux (Gemini, the twins) can be seen below Mars.

Jupiter is the planet dominating our skies this month. At sunset it can be found shining brightly in the north-east. Jupiter has two encounters with the Moon this month. One on the evening of the 2nd, and the other on the 29th.

Saturn is only visible for the first week of the month, low to the western horizon. The planet Mercury can be found sitting above Saturn. Saturn will disappear below the horizon and won't be seen again until October when it reappears in the morning sky.

Meteors

September is a poor month for meteors. The Southern Piscids is the most active shower and while it has an extended peak which runs from the 11th to the 20th, it only produces about 5 meteors per hour. The meteors appear near the constellation of Pisces (the fish) which can be found in the north-west from midnight until dawn.

Stars & Constellations

In the early evening, the Southern Cross can be seen in the south-west, tipped over on its side, with the Two Pointers almost vertical above it.

Turning towards the south-east we see the bright star Achernar, which marks the end of the river, Eridanus, and also Fomalhaut, the brightest star in Piscis Austrinus. High in the north are the three main stars of Aquila, the Eagle, including the bright star Altair, while low to the horizon is Vega, the fifth brightest star in the night sky.

Directly overhead at sunset, the curl of the Scorpion’s tail can be seen near the teapot shape of Sagittarius.

Above the western horizon sits the star Spica in the constellation of Virgo and in the north-west is the orange giant star Arcturus that belongs to Boote, the herdsman. The Milky Way spans the sky overhead, running almost north-south.

International Space Station

The ISS orbits the Earth every 90 minutes at an average distance of 400 km. From Earth, it appears as a bright star that steadily moves across the sky. It can often be seen from Melbourne, for example at:

5:52am – 5:59am, Sunday 13th September.

The space station will appear in the north-west and travel directly overhead before disappearing towards the south-east.

Predictions of when to see the ISS can be obtained from the Heaven's Above website.

On this Day

1st 1939, Oppenheimer and Snyder publish the first paper that describes black holes.

1st 1979, Pioneer 11 (USA) made the first flyby of Saturn and returned the first close-up images of the planet.

5th 1977, Voyager 1 (USA) was launched to explore the outer Solar System.

8th 1966, First episode of Star Trek shown.

9th 1839, John Herschel takes the first ever glass plate photograph.

11th 1985, ICE (USA) became the first craft to encounter a comet (Comet Halley).

14th 1959, Luna 3 (USSR) became the first craft to fly to and impact another celestial body, the Moon.

15th 1997, the Mars Global Surveyor (USA) discovers a weak magnetic field around Mars.

18th 1977, Voyager 1 (USA) returned the first image of the Earth and the Moon together.

23rd 1846, Neptune was discovered by Johann G. Galle (Germany).

27th 1905, Albert Einstein submits the paper containing the famous equation E=mc².