Archive for the ‘Astronomy blog’ Category

Daily cosmobite: zodiac constellations

Published by Nick Lomb on July 15, 2014 No Comments

15_Sagittarius with nearby constellations_StellariumThese are the constellations that the Sun passes through during the course of a year. Looking from west to east in the early evening the following zodiac constellations are visible: part of Cancer, Leo, Virgo, Libra, Scorpius, Ophiuchus and Sagittarius.

The zodiac constellation of Sagittarius the Archer. Courtesy Stellarium

Daily cosmobite: Mars and Spica

Published by Nick Lomb on July 14, 2014 No Comments

14_Mars Saturn and Spica_Nick LombThe red planet Mars is high in the northern sky each evening after dark. Tonight it makes a close approach to the bright star Spica, the brightest star in the constellation of Virgo the Maiden. With less than three moon-widths separating the planet and the star it should be a great sight.

Mars, Saturn and the star Spica on the evening of 14 July 2014. Chart Nick Lomb

Daily cosmobite: most distant object

Published by Nick Lomb on July 12, 2014 No Comments

12_MACS0647_JD_HubbleAnnounced in November 2012, the Hubble Space Telescope has imaged the most distant galaxy ever seen. MACS0647-JD is 13.3 billion light years from us and we see it as it shone only 400 million years or so after the big bang. As scientists would expect with such a young galaxy, it is tiny compared to the size of our own galaxy.

MACS0647-JD1. Courtesy NASA, ESA, M. Postman and D. Coe (STScI), and the CLASH Team

Bolide over Sydney and Melbourne 10 July 2014

Published by Nick Lomb on July 11, 2014 26 Comments

Bolide 10 July 2014 path
The above map gives a rough guess of the bright meteor or fireball or bolide that passed over eastern Australia at about 9:42 pm AEST on the evening of 10 July 2014. Diagram Nick Lomb, map courtesy of Google

On the evening of 10 July at about 9:42 pm AEST numerous people in the eastern part of Australia saw a bright moving object in the sky. There were dozens of reports on the Sydney Observatory Lights in the Sky page and we thank those people who reported their sighting. As well reports were made to emergency services, news media and of course on Twitter.

Reports ranged from the vicinities of Melbourne, Sydney,Hobart, Parkes and according to one ABC reporter, Brisbane. The most credible reports gave a direction of movement from south-west to north-east. This is consistent with the rough guess for a trajectory given on the map above.

Some of the reports indicated that the object was seen for ten seconds or more which is exceptionally long for a meteor sighting and others indicated a slower speed than they had seen in previous meteor sightings. A “tail” was reported by many people; this is a dust trail or “train” left behind by the object as it moves through the atmosphere. These trains can sometimes be seen for ten minutes or more.

The object was likely to be a piece of an asteroid or space rock hitting the Earth’s atmosphere, moving almost parallel to the Earth’s surface along the above path. It would have been 100 km or so high so that it could be seen for hundreds of kilometres. As it travelled along the intense heat of friction would have broken off bits of it and this was seen, especially from the Sydney region.

A very bright object passing through the atmosphere is called a bolide or a fireball. It is the same as a meteor but brighter as it is a larger object.

An object hitting the Earth’s atmosphere must be travelling at least at the escape velocity from Earth which is 11.2 km/sec or 40,000 km/hr. When space junk reenters the atmosphere it is moving slower so the reported slow speed of Thursday evening’s bolide could indicate that it was space junk.

It would be exciting if parts of this object did survive the journey through the atmosphere and could be found. Most likely though the smaller bits that broke off the object disintegrated while the main part fell into the ocean north of Brisbane.

Update 11:20 am 11 July 2014

As indicated above, the bright object seen last night was likely to be space junk as it appeared to be travelling slower than the minimum speed of a meteor impact. Low Earth satellites circle at around 7 km/sec while the minimum speed of a meteor is 11.2 km/sec, the Earth escape velocity. In addition, the shallow impact angle of the object last night also suggested a reentry from Earth orbit.

It is now clear that the object was the third-stage rocket that helped to take Russia’s second Meteor-M weather satellite into orbit on 8 July 2014. This was a massive metal object as can be seen here so that it is not surprising that it was so bright in the Victorian/New South Wales night sky as it burned up.

The report that the rocket was seen over Brisbane is now most unlikely. There is another report that a sonic boom was heard near Cobar about 600 km to the west of Sydney suggesting that the rocket disintegrated in that vicinity. That maybe correct, but it may not as Cobar maybe a little too far from Sydney where the object was clearly seen. If metal debris from the rocket is found in the vicinity of Cobar that would be proof of the location of the rocket’s break up.

Postscript

There is a project based in Western Australia to try to find fallen meteorites, called the Desert Fireball Network. They are keen to pin down the track of the Russian rocket and possibly locate any remnants. They have an app called Fireballs in the sky for download in both the App Store and Google Play and ask people to log their observations if they’re close to where they saw the fireball and can remember in which direction they were facing. Just change the time to ~9.43pm Thursday when they’re asked to edit a sighting at the end of the process.

11_Orbits of Jupiter_outer moons_WikipediaThe giant planet Jupiter has a swarm of 67 moons circling around it like a mini solar system. The International Astronomical Union has named some of the moons discovered a decade ago. The names include Hegemone, Mneme, Aoede and Cyllene, who in Greek mythology are all daughters of Zeus or Jupiter.

The paths of Jupiter’s outer moons around the planet. Courtesy Wikipedia

Daily cosmobite: the nearest star

Published by Nick Lomb on July 10, 2014 No Comments

10_alphacen_orbitneg_Harry-RobertsAlpha Centauri, the brightest of the pointer stars, is high in the south. Though it is part of the nearest star system it is not the nearest star to Earth. That honour belongs to a faint, reddish and insignificant dwarf star called Proxima Centauri that is about four moon-widths below Alpha.

Alpha Centauri can be seen as a double star through a small telescope. The orbit of one of the two components around the other is shown here. Drawing courtesy Harry Roberts

Daily cosmobite: Woomera approaches

Published by Nick Lomb on July 9, 2014 2 Comments

Daily cosmobite: Woomera approachesSpace rock or asteroid 11195 Woomera circles the Sun every 3½ years between the paths of Mars and Jupiter. Discovered by amateur astronomer Frank Zoltowski in January 1999 and named after the remote site in South Australia where he lives, the asteroid is making its closest approach to the Earth for the year at a distance of 231 million km.

The path of 11195 Woomera around the Sun. Courtesy NASA/JPL

Is there life in space 2?

Published by Nick Lomb on July 8, 2014 No Comments

Aliens at Sydney Observatory_Nick Lomb

If aliens ever arrive on Earth maybe they would first contact astronomers. Here is an imaginary scene of aliens visiting Sydney Observatory. Digital mischief by Nick Lomb with help from Microsoft clipart

This is the second of two posts contemplating the possibilities of life, especially intelligent life, in space. In the first post we established that that there is a plentiful supply of organic molecules, essential for life as we know it, in the clouds of gas and dust from which stars and planets form. Also that in our galaxy there are an estimated two million Sun-like stars circled by Earth-size planets in their habitable zone, the zone in which water can exist on the surface as a liquid. Finally, we considered the seven-factor Drake equation that contains the ominous term on the lifetime of civilisations.

It is difficult to use the Drake equation to draw any conclusions on the possibility of intelligent life elsewhere as that involves making guesses about the values of the, as yet, unknown terms. A completely different approach is to use the Fermi Paradox that uses only one fact and yet gives a definitive answer.

Before considering the Fermi Paradox though let’s have a numerical interlude and consider the likely size or height (h) of any animal-like creatures on another world. A creature to lift itself above the ground must have legs of sufficient strength to support its weight. The weight of the creature will scale with its volume, that is, with h^3 and with the local acceleration due to gravity (g), while strength scales with the cross-sectional area of its legs, that is, with h^2. This gives the ratio of the weight to strength as proportional to gh and, assuming biological muscles are the same strength everywhere per unit area, we find that h ∝ 1/g. So on a rocky body the size of Earth creatures should be roughly Earth-size, on a smaller body with half the gravity they would be about twice the size and on a larger rocky body with twice the gravity they would be half the size.

Returning to the Fermi Paradox that says that let us assume that there are other civilisations in our galaxy. Some are likely to have developed much faster than on Earth, while some maybe less advanced. Those that are more advanced by, say, a million years would have technological capabilities that would be completely unimaginable to us. One capability they would have, and possibly a civilisation only a little more advanced than ours could have as well, is to be able to colonise the galaxy. This could be done, for example, by sending to a few stars autonomous machines that could find and land on suitable planets, reproduce themselves a number of times utilising available resources and then launch themselves and the copies to new stars. It does not matter if it would take, say, a 100 years to build copies, the galaxy could still be colonised within a relatively short period of a few multiples of 10,000 years.

This analysis suggests that if there are other civilisations in our galaxy at least one should have made its presence felt long ago. Since there is no evidence of any significance to suggest that we have been visited or colonised by an extra-terrestrial civilisation in the past, reluctantly we need to conclude that we on Earth are likely to have the one and only civilisation in our galaxy. Other explanations are canvassed in a recent and excellent article in the Huffington Post, but still we have yet another reason to look after our own planet.

8_Saturn and the Moon_Nick LombThe ringed planet Saturn can be seen in the north-east each evening after dusk. Tonight the gibbous Moon is below and to the right or east of the planet. We will not see the Moon cover or occult Saturn tonight; for that we need to wait until next month when there will be an occultation on the evening of Monday 4 August.

Saturn and the Moon. Chart Nick Lomb

Daily cosmobite: the Southern Cross

Published by Nick Lomb on July 7, 2014 3 Comments

7_Southern Cross_Nick LombThis constellation, known as Crux to astronomers, is high in the southern sky. Five stars are visible to the unaided eye in Crux: four mark the arms of the cross and the fifth one is inside. Seeing Epsilon, the faintest star, is getting harder from brightly lit urban areas.

The Southern Cross. Photo Nick Lomb

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