Skynotes: September 2020
Telescopes in Danger
You may think of telescopes as located safely on mountains or high altitude plains or in the far outback, and they are there for good reasons; to avoid radio interference or light pollution, for example, or to have clear dry air to observe the universe. But there can be danger too.
Many telescopes across the world are large, with ever larger ones planned or underway, but they can also be exposed to extreme elements like storm or fire, or can at times suffer catastrophic structural failure.
Melbourne sun times
| Date | Rise / Solar noon* / Set (day length) |
|---|---|
| 1st | 6.41am / 12.20pm / 5.59pm (11.17 hrs) |
| 11th | 6.26am / 12.16pm / 6.07pm (11.40 hrs) |
| 21st | 6.11am / 12.13pm / 6.15pm (12.04 hrs) |
| 30th | 5.57am / 12.10pm / 6.23pm (12.26 hrs) |
*When the Sun is at its highest crossing the meridian or local longitude.
Moon phases
| Phase | Date |
|---|---|
| Full Moon | Wednesday 2nd |
| Third Quarter | Thursday 11th |
| New Moon | Thursday 21st |
| First Quarter | Thursday 24th |
This month’s Moon apogee (furthest from Earth) is on Sunday 6th at 405,607 km and perigee (closest to Earth) is on Sunday 18th at 359,082 km.
Planets
Mercury is visible from around 7pm above the western horizon but will set in the west by 8:00pm.
Venus can be seen as the ‘morning star’ as it rises this month at around 4.30am but will fade by 6am in the early morning light.
Earth days in the southern hemisphere are starting to warm up as we experience the Spring or Vernal Equinox. This will be on Sunday 22nd at 11:30pm when the Sun crosses the celestial equator heading southwards (or northwards for the northern hemisphere and its Autumn equinox). It is often said that day and night are equal on the equinox, but this is not quite so. Only the centre of the Sun is above the horizon for 12 hours, making our day slightly longer at 12 hours and 8 minutes. Not only does the day start with the first appearance of the Sun, but there’s another strange effect occurring as well. The Earth’s atmosphere bends light from the Sun so that at sunrise we are able 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 even though it has already sunk below the western horizon. When is day and night equal? That will be on Saturday 19th, a few days before the equinox with sunrise at 6.14am and sunset at 6.14pm, 12 hours later.
Mars rises in the east at around 10pm, reaches its highest elevation by 3am after which it will disappear in the north west by 6am in the early light.
Jupiter is bright and easily seen in the north east from 6.30pm and will be visible until 3am when it sets in the south west.
Saturn with its characteristic yellow tinge is high in the eastern sky from 6.30pm and will reach its highest position in the north by 9pm, and then setting in the west by 3am.
Meteors
September is unfortunately a poor month for meteors. The Southern Piscids is the most active shower peaking during the period 11th to the 20th but only produces a few meteors per hour. They appear near the constellation of Pisces, the fish, which is in the north-west from midnight onwards.
Stars and constellations
In the early evening, the Southern Cross can be seen in the south-west, tipped over on its side, with the Two Pointers (Alpha & Beta Centauri, the brightest and second brightest stars in Centaurus) almost vertically above.
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. The rich expanse of the Milky Way spans the sky overhead running almost north to south, with its dark dust clouds forming an emu in many First Nations traditions. Its head is the Coal Sack nebula beside the Southern Cross while its dark body stretches to the tail of the scorpion. Learn more at the aboriginalastronomy.com.au.
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 and Central Victoria:
Evening
- Saturday 5th: 7.03am–7.08am, South-West to East
Morning
- Thursday 24th: 5.28am–5.34am West-North-West to South-East
- Friday 25th: 4.42am–4.46am North-North-West to South-East
- Sunday 27th: 4.43am–4.47am West-South-West to South-East
For predictions go to the Heavens-Above website.
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.