Archive for the ‘Astronomy blog’ Category

The 2016 Australasian Sky Guide is available now.

Published by Sydney Observatory on November 30, 2015 No Comments

Dr Andrew Jacob

This annual publication, written by former MAAS curator Dr Nick Lomb, has been providing stargazers with everything they need to know about the southern night sky for the past 26 years. The 2016 guide contains monthly astronomy maps, viewing tips and highlights, and details of the year’s exciting celestial events. It also provides information on the solar system, updated with the latest findings from spacecraft. The Sky Guide (RRP $16.95) is available from the MAAS Store, Sydney Observatory, selected bookstores or online at Powerhouse Publishing. The guide is also available as an ebook.

Watch out for these highlights in 2016:

  • Venus approaches Saturn in January
  • Mercury and Venus close in May and July
  • Mars at opposition in May
  • Venus and Jupiter conjunction in August

Moon Landing Hoax

Published by Melissa Hulbert on November 26, 2015 2 Comments

Liam Birchall is an astronomy guide at Sydney Observatory. Below he discusses the lunar landing hoax.

As the clouds clear and our companion moon is waxing itself into the eastern sky, we here at Sydney Observatory have been hearing once again rumblings about the Moon Landing “Hoax” on commercial radio and thought to revisit some of these spurious claims.

According to the hoax view, NASA did not land on the moon in July 1969 as many believe. It was staged in a film studio and was a public relations coup in the midst of the cold war. The USA desperately needed ‘a win’ after the Soviets had scored a number of ‘firsts’. After Sputnik became the first satellite to orbit the earth in 1957 and Yuri Gagarin became a national hero in Russia by successfully becoming the first person to orbit the earth in 1961, US president Kennedy ambitiously proclaimed that astronauts would go to the moon.
Continuing with this rendition of events, when the United States realised that they could not follow through with such an ambitious enterprise and, unable to admit failure to the world, they travelled to a Hollywood back lot and staged the entire thing.

Well, now that we have identified a credible motive, we will try to ignore for the time being, the somewhat mammoth logistical exercise that such a mass deception would require.
Apart from the footage of Neil Armstrong and Edwin ‘Buzz’ Aldrin on the Moon which, I’m sure, would have been a blast, thousands of colluding actors would need to be reading from the same script. Leaders, politicians and bureaucrats as we know too well, have understandable difficulty in controlling their message.
This incredible feat of convincing an unsuspecting public of the veracity of this hoax is equally as impressive as setting feet on the lunar surface.

A popular film documentary exposé entitled “Conspiracy Theory: Did We Land on the Moon?” hosted by X-Files actor Mitch Pileggi in 2001 has allowed conspiracy minded individuals to flourish on the World Wide Web.
This film refutes the landing with a litany of irrefutable pieces of evidence that can, upon closer inspection be refuted easily. Of course it is hard to admit these realities if one approaches it with a deep distrust of big government malfeasance. The moon really is a different place to our planet earth and the so-called flaws in the imagery are a further testament to this.
We run into trouble when we examine the filming ‘flaws’ that are used as evidence to support the moon landing hoax. These ‘flaws’ in the images just doesn’t stack up to basic scientific scrutiny and the physical reality of the lunar environment. Yes different optical physics are at play in the airless low gravity world of our moon.

Some of the perceived discrepancies in the footage don’t even need an awareness of how a world without a true atmosphere behaves. For example, it is asked, ‘why are there no stars visible behind the astronauts?’ Well, to be clear, the moon itself has a bright reflective surface as do the astronaut’s bright reflective suits. Any type of camera in a light rich environment, both on earth or the moon is required to restrict the amount of light that the film is exposed to, to obtain a clear image. A quick shutter speed in photography will limit the amount of luminous objects that will be perceived. Stars, sadly, because of their great distance from us will always be the first lights sources that struggle to be perceived or detected.
According to theorists, this is only one, of a multitude of flaws in the moon landing footage. Flaws such as; Why does the flag wave if there is no wind? and Why is there is no blast crater?
I have started with the most glaringly flawed rationale for the hoax. We will address these issues further in our next post.
Stay tuned.

Regular solar observer & correspondent Harry Roberts reports on a Delta group of sunspots, AR12443, that didn’t flare strongly.

AR12443: Delta group ‘that didn’t’

Of the four Hale magnetic classes of sunspots, Delta is known to be the most active for solar flaring.  Weather permitting, Delta’s are watched closely for such events: most put on an impressive show; but there are exceptions.

AR12443 was first seen at the Sun’s east limb on Oct29, a pair of large round penumbral spots, separated by just three degrees of solar longitude, at 7ºN latitude. It was a new group, although the writer first thought it was a return of AR12414 (a southern group at the same longitude). The two big spots were shown by Mt Wilson to both have violet polarity – and had likely arisen earlier as a single large spot that split apart. Next day showed a scatter of tiny spots of opposite ‘sign’ following (f) the large pair some 8º to the east. In H-alpha several active filaments linked the (p) and (f) spots and the GOES X-ray flux began to log minor flares: all suggesting that a highly active group approached.

On Oct30, in white light, an amazing sight was seen. Overnight a large amount of new flux had emerged following (i.e. easterward of) the two big spots: a dense ‘chain’ of new spots now stretched across some 15º of solar longitude – reminiscent of AR 11429 in 2012. “Helio” freeware now gave 12443 an area about 600 units. While recording it in detail a small but bright C5 flare erupted (Fig1, in red).


The Delta group AR12443 that did’t flare as strongly as expected. Sketch and copyright Harry Roberts ©, all rights reserved.

Delta class. Mt Wilson’s log for Oct31 showed a mix of polarities in the following chain of spots (Fig1, underlined): the Delta configuration.

Delta groups are fairly rare: with ~40 out of 1400 groups thus far in SC24 – or about 3%. Yet all the strong flares of SC24 have occurred in Delta groups.

Inversion line. Both Mt Wilson and SDO HMI logs showed an irregular separation or ‘inversion line’ between the densely ‘packed’ preceding (p) and (f) polarities (Fig1, in blue). The C5 flare likely arose along that ‘line’ and spread out from there.

Flaring. To erupt, strong flares seem to need at least three things: the Delta mix of fields in one penumbra, as well as strong umbral fields (>2400G say) – and a mysterious factor termed ‘helicity’, i.e. the degree of twist in the emerging flux. Despite its promising ‘looks’, AR12443 apparently lacked some of these: its strongest flare seems to have been an M3.7 on Nov5 (at 00:43UT) – a paltry effort!

Solar Cycle 24. AR12443, a northern hemisphere group, at 7º north latitude –was fairly close to the solar equator. Meanwhile, current southern spots tend to be further from the equator, suggesting that the northern hemisphere cycle of spot generation (by subsurface magnetic ‘currents’) is now much more advanced than is its southern counterpart. In fact, the two ‘currents’ are now known to be some years ‘out of synch’.  Statistics shows that we are now, in late 2015, well past the overall SC24 sunspot activity peak, which was reached in 2014 (Fig2).


Hemispheric sunspot number for solar cycles 23 and 24. Bold curves are smoothed data, fine curves are monthly numbers. Total (grey), northern (blue) and southern (red) numbers are plotted.

But remember, in SC23, flare activity peaked some years after the peak of sunspot count and SC24 may do likewise. So keep the solar ‘scopes at the ready: anything can happen!

Harry Roberts is a Sun and Moon observer, a regular contributor to the Sydney Observatory blog and a member of the Sydney City Skywatchers.

Unlocking Ancient Astronomical Knowledge

Published by Melissa Hulbert on November 5, 2015 No Comments

Brenan Dew is an astronomy guide at Sydney Observatory and is currently working on his PhD at Macquarie University. Below he discusses ancient astronomy and the Egyptians.

In our modern society it is well known that the Earth is constantly spinning on its axis, completing one revolution in approximately 24 hours. This means that once the sun drops below the western horizon in the evening, it is only a matter of time before the Earth revolves into such a position that the sun will rise the following morning, in the eastern sky. This current understanding was foreign to many ancient cultures who had their own mythologies to explain the fundamentals of night and day as well as the extended world around them.

After traversing across the sky during the day, the ancient Egyptians of the New Kingdom (16th -11th Century BCE) believed that the sun deity Re entered the so-called “Duat” or “Netherworld” which it would cross in a journey throughout the night. The ancient Egyptians believed that while in the Netherworld, the sun would encounter many forms of chaos culminating in a confrontation between Re and the snake-shaped deity Apophis. For the sun to rise the following day, Re must overcome Apophis as well as other hardships encountered on this journey. Therefore the very act of the sun rising in the morning was heavily intertwined with the religion and actions of ancient Egyptian deities.

The enigmatic nature of the Duat, and other Netherworldly locations, are described in detail within various texts that many modern tourists will have encountered lining the walls of the royal tombs within Egypt’s Valley of the Kings. By translating and investigating these so-called “Books of the Netherworld” my PhD research will straddle the disciplines of history and astronomy, in order to gain a better understanding of how the ancient Egyptians understood the world around them, particularly that beyond the physical borders of their known world.

A section from the “Book of the Caverns” - a modern title given to one of the ancient cosmographic texts from the New Kingdom, belonging to the tomb of Ramesses V. Attribution: See page for author [Public domain], via <a href=""> Wikimedia Commons</a>

A section from the “Book of the Caverns” – a modern title given to one of the ancient cosmographic texts from the New Kingdom, belonging to the tomb of Ramesses V.
Attribution: See page for author [Public domain], via Wikimedia Commons

What’s Flying Out There in Space Right Now?

Published by Melissa Hulbert on November 4, 2015 No Comments

Tiffany Day is one of our astronomy guides and in this post she discusses robotic explorers of our Solar System and beyond.

If you’ve been paying attention to recent space news, you would have heard that the New Horizons space probe completed a successful flyby of Pluto – our first ever high resolution view of the planet in the history of our species – back in July of this year, or that the Curiosity rover successfully landed on Mars three years ago, and has just recently provided the first hard evidence of liquid water on Mars.

But how many space craft do we actually have out there in the Solar System right now?

The list is quite extensive, but it depends on whether we count space craft from which we are no longer receiving data or not. If we count only active probes and rovers, this handy little graphic from provides a comprehensive list at a glance.

Here we see that the planet Mars is by far the object we’ve visited the most, with two active rovers – Opportunity and Curiosity – and three orbiting satellites currently sending data from the rusty planet back home to Earth. Our own Moon is the next most actively observed object, with three orbiting satellites collecting data. Voyager 1, launched in 1977, is our winning space craft in terms of distance from Earth, now just leaving our Solar System for the first time ever in history.

Voyager 1 Spacecraft. Image courtesy of NASA/JPL

Voyager 1 Spacecraft. Image courtesy of NASA/JPL

Harry reports on coronal loops in the sunspot group AR12422

Published by Andrew Jacob on November 2, 2015 No Comments

Post flare loops in H-alpha above AR12422. Sketch and copyright Harry Roberts ©, all rights reserved.

Regular solar observer & correspondent Harry Roberts previously reported on the complex Delta Group of sunspots, AR12422. Here he follows up with a report on the group’s coronal loops.

AR12422: Coronal Loops.                                                           Harry Roberts.

Recently, when AR12422 hosted a GOES M5.5 flare, a fine display of post flare loops (PFL) ensued: we followed their development over just 8min. While they occur at every major flare, such loops are rare as they can only be seen at the Sun’s limbs, against the dark background of space. For this reason Hale Delta class spots are watched closely as they approach the Sun’s limbs.

Coronal loops. Post flare loops are a special kind of coronal loop. Coronal  loops form above most big spot groups as magnetic flux ‘ropes’ emerge from the solar interior, forming the sunspots. While much bigger than PFL, coronal loops are invisible in any spectral band unless they are filled with plasma. Since they are so large they occupy the corona from the so-called ‘Transition Zone’ at  ~2Mm high to the corona above 100Mm. This is a hot but tenuous atmospheric region, at ~106K, and little or no H-alpha light is emitted. Yet extreme UV light is emitted – and of the various bands sampled by satellites, that of Fe IX at 171Å (T=6.3×105K) seems to best reveal coronal loops. Other bands at 304Å HeII, etc. show lower structures.

Schrijver & Zwaan: “Solar and Stellar Magnetic Activity” P189 state: “It is remarkable that no bright coronal loops end in the dark cores of spot umbrae; some bright loops appear to end in umbral light bridges. Penumbral fields, in contrast, lie at the base of bright loops”

Post flare loops. While of the same origin, the difference between a PF loop and a coronal loop is one of altitude and temperature. The PFL’s are seen when a solar flare heats a ‘bubble’ above a spot group at an altitude where H-alpha plasma can condense on the (otherwise invisible) coronal loops – making them briefly visible. In contrast to Ha (6563Å) with ionization T ~5000K, EUV 171Å, at higher temperature and altitude, reveals taller bigger loops that extend over vast areas above the spot group (Fig2).

M5.5 flare. Our earlier discussion of PFL’s above this flare (on 2015 Oct2 ~00:11UT) showed four configurations of loops to a height above the limb of ~22Mm: while dark loop arches faintly seen against the disc suggested a total height above loop footpoints (amid the sunspots) of 66Mm. A further log (Fig1) made at 00:34UT, about 15min later, shows complex multiple loops now 78Mm above the spot group. Note, this group is still some 20° of longitude from the limb and the loops are not yet tangential to our line-of-sight. This height, 78,000 km (~6 Earth diam.) is typical of PFL’s.


Coronal loops above AR12422. Sketch and copyright Harry Roberts ©, all rights reserved.

Coronal loops. What did the SDO AIA 171Å show of coronal loops above the site? Fig2.1 shows 171Å images of the region above the site soon after the flare (28min later) and ~45hr later (Fig2.2) when the spot group has rotated out of sight. Note the 171Å images show coronal loops to be much higher than the PF loops:  a at 60Mm high, b at 93Mm and c at 156Mm. Note the sites of AR12422 (p) and (f) spots plotted on the disc below the loops. The ‘a’ coronal loops are twice the height of our H-alpha PF loops. The coronal loops are filled with plasma and persist much longer than the PF loops. Note that the SDO images have been rotated in Po to match the H-alpha record. At times, H-alpha PF loops show well on SDO AIA 304Å HeII images.

So the H-alpha band shows events of the chromosphere, and at times up to ~100Mm altitude: the writer once followed an Moon-sized globule of ejecta to a height of 600Mm from the limb – but now realizes such events are very rare. In EUV the drama doesn’t end with the loops seen in 171Å: indeed it’s only the beginning. The coronal loops often form the base for helmet streamers that then flow deep into the solar system as a solar wind, and the tenuous heliosphere.

Harry Roberts is a Sun and Moon observer, a regular contributor to the Sydney Observatory blog and a member of the Sydney City Skywatchers.

November 2015 night sky guide and sky chart

Published by Melissa Hulbert on November 1, 2015 2 Comments

To help you learn about the southern night sky, Sydney Observatory provides a guide and a sky map or chart each month. This month’s guide is presented by Melissa Hulbert, Sydney Observatory’s Astronomy Programs Coordinator.
In the November sky guide, as well as showing us where to find the constellations Pegasus, Orion and Taurus, and the star clusters, Hyades and Pleiades, Melissa tells us the best times to see the dawn celestial gathering of the planets Venus, Mars and Jupiter with the Moon.

We provide an embedded sky map (below) and an November 2015 night sky chart (PDF) which shows the stars, constellations and planets visible in the night sky from anywhere in Australia. To view PDF star charts you will need to download and install Adobe Acrobat Reader if it’s not on your computer already.

Star Map Nov 2015

READ THE SKY GUIDE (after the jump)


Calling All Early-Birds: Dawn Planetary Gathering

Published by Melissa Hulbert on October 30, 2015 1 Comment

November has a spectacular treat in store for all of you early-birds!
During late October, Venus has been dancing in the pre-dawn sky with Jupiter and Mars. This dance continues in early November, with Venus and Mars at their closest on November 3 and 4, after which Venus slowly starts to retreat towards the east horizon. Jupiter is rising just ahead of Venus and Mars and on November 7, the 25-day old waning crescent Moon joins in, and is just below Jupiter. November 8, finds the 26-day old waning crescent Moon between Venus and Mars. It is well worth hopping out of bed early and finding a good view to the east on both mornings for what promises to be a wonderful pre-dawn sight!

Sydney Observatory is holding a special early morning viewing on Saturday 7th November. Join our astronomers and view Jupiter, Venus, Mars and the Moon through our telescopes. Afterwards enjoy a light breakfast while watching the sunrise over Sydney Harbour – what a way to start the weekend! Places are limited and bookings essential. You can book online or by calling 9921 3485.

Dawn Planetary Gathering on 7 November 2015

Dawn Planetary Gathering on 7 November 2015

Harry reports on AR12422, a complex Delta Group

Published by Andrew Jacob on October 12, 2015 No Comments

Fig 1: AR12422 on 2015 Sep 27. Sketch and copyright Harry Roberts ©, all rights reserved.

Regular solar observer & correspondent Harry Roberts reports on active region AR12422, a complex Delta Group:

AR12422: Complex Delta Group.                                                      Harry Roberts

Hale’s invention of the visual magnetograph and the Hale Classification of sunspots is a heroic tale, but we can only touch on it here. He found that spots were magnetic entities, shaped by hidden flux sources: sources that reversed polarity at successive solar cycles. And, sometime soon, current spots will be joined by others, of reversed polarity, as a new cycle begins.

Or will they? Research and data seem to show a steady decline in overall solar activity. The writer’s plot of current flaring against that of past cycles shows SC24 flaring is an order of magnitude weaker in X-ray flux than the previous three cycles (SC21-23). Yet past flare activity was seen to peak some time after the sunspot peak; i.e. peak flaring occurred some years after the sunspot maximum. We have yet to reach that point in cycle SC24. What will happen then?

With this in mind, the writer maps the more ‘active-looking’ spot groups in hope of flare activity: Delta groups are watched most closely. Sometimes nature cooperates.

Delta spots. Hale did not recognize the delta mix of fields: i.e. spots of opposite ‘sign’ in one penumbra; Künzel added that class in 1960. In white light, Delta groups may look like a blend of two bipolar groups- with say, twin (p) or (f) spots, or spots in long chains, or distorted penumbrae: kind of sunspot “train wrecks”! Not surprisingly, Delta groups are the chief ‘flarers’.  In fact, all but one of the SC24 groups, thus far, that hosted an X-class flare, were class Delta.

AR12422. The writer has few logs of it due to cloud. Sighted first on Sep. 27 (04:00UT) and logged in detail 18h later (Fig1, 27th,22:00), it looked Delta class. But what would the magnetograms show? Two kinds are posted on-line: the ‘robot’ ‘scopes (GONG, SDO, etc) log ‘global field’ in real-time –with flux range 0 – 100G using an Fe line in IR (of low spatial resolution).  Also we still have Hale’s own scope at Mt Wilson, using a red Fe line in the visual: flux range 1000-3000G+. With high spatial resolution, it gives polarity and flux in individual spot umbrae (i.e. umbral fields) – and is likely what Künzel had in mind in 1960. Global fields and umbral fields don’t always agree on a Delta classification for a given group: but they did for AR12422.

Umbral fields. On the 28th the strongest field logged at MtW was 2400G in the (f) umbrae, with 2100G in (p) spots; no Delta mix was detected by MtW, while NOAA assigned Delta by this time from SDO, GONG etc. global data. We see (Fig 1) complex (p) and (f) spot clusters with linear umbrae and spot chains attached. It was actively flaring, the strongest an M7.6 on the 28th – but the writer logged none during a 62 min patrol.


Fig 2: AR12422 at the western limb of the Sun. Sketch and copyright Harry Roberts ©, all rights reserved.

At the limb. Fig2 Shows the group 4d later (after more cloud) at the west limb, when it had grown to a huge ~20° in length! In disbelief, the log was confirmed with SDO’s HMI 6173Å continuum image. Groups this long are rare. Its (p) spots had migrated 5° west over the 4d period, while the (f) drifted just 2° eastward. Or had new (p) spots emerged ahead of the group? The spots are now in complex chains, albeit compressed by limb curvature.

Delta mix. Mixed polarity is seen in the group’s umbrae (Fig2) and MtW now assigns class delta. Flux strength is down, but measurement at the limb detects transverse components of flux; often less than vertical. Strongest field is seen in the (f) spots.


Fig 3: AR12422 flare and filament. Sketch and copyright Harry Roberts ©, all rights reserved.

Flaring. (Fig3)32 mins into the H-alpha patrol a sub-flare erupted (00:08UT) near -25,100 and rapidly brightening to GOES M5.5 at 00:13, as flare material (ejecta?) spread to the limb at  -25,120.  At 00:14 a bright arc rose above the limb, but was dark against the chromosphere: likely an ejecting filament or post flare loop. It soon became a fine display of such loops, with footpoints that shifted about amongst the spot umbrae.  At 00:20, clumpy spray-like ejecta rose bright above the limb in places.  Motion in the ejecting filament was timed at ~200km.sec-1

                        Next day (not shown) saw the trailing 10° of AR12422 still visible, with large bright surges above the limb at the latitude of the now unseen (p) spots. Despite an 80min H-alpha patrol no other transients arose.

It is likely that remnants of the group will reappear ~2015 Oct 16. This delta group was a good example of its class, but while it hosted many GOES M-class flares, the M7.6 was strongest and no X-class were produced. We wait: hoping that the late peak in X-class flaring seen in SC23 will be repeated in coming months.

Harry Roberts is a Sun and Moon observer, a regular contributor to the Sydney Observatory blog and a member of the Sydney City Skywatchers.

Robert Thorburn Ayton Innes

Robert Thorburn Ayton Innes

What is the closest star, in the night-time sky, to Earth?

Almost everyone answers Alpha Centauri, the brighter of the pair of Pointer stars. But Alpha Centauri is in fact a system of three stars. Two orbit close together and their combined light is what our naked-eye sees as the brighter of the Pointer stars, and what most of us would call Alpha Centauri.

The third star of the system is too faint to see without a large telescope but it is the closest of the three. We call this star Proxima Centauri.

How do we know Proxima Centauri is the closest? We could measure its distance via the parallax method. Or we could measure how fast it is moving across the sky – its proper motion – and infer that it is the closest because it has the greatest proper motion.

On October 12, 1915 astronomer Robert T. A. Innes, working in South Africa, placed two glass plate negatives of the sky into a blink comparator. This device allowed him to rapidly flip between viewing one plate then the other. He noticed one faint star jumped back and forth as he blinked the plates – it had moved in the five years separating the exposure of the plates. His measurements showed its proper motion and the direction it was heading were very similar to those of the star-pair we call Alpha Centauri. It was almost certainly part of that star system and therefore nearby. Later parallax measurements, by Innes and others, proved it was the closest known star at a distance of 4.22 light years.

If you want to know what 4.22 light years feels like try walking the Solar System model on the Melbourne shoreline.

A blink comparator (H10185) used at Sydney Observatory and made by H. F. Pinnock c1960.

A blink comparator (H10185) used at Sydney Observatory and made by H. F. Pinnock c1960.

Before moving to South Africa Innes lived for several years in Australia. He arrived in Sydney in 1890, as a 28 year old, to establish a wine & spirit business. He was already an accomplished mathematician and had been appointed a Fellow, no less, of the Royal Astronomical Society at age 17. In Sydney he got acquainted with local astronomers: Henry Chamberlain Russell at Sydney Observatory, John Tebbutt at Windsor and Walter Gale (after whom Gale crater on Mars, where the Curiosity rover is presently roaming, is named). While in Sydney he observed double stars and investigated the orbital motions of planets. He also helped establish the NSW branch of the British Astronomical Association, a group that continues to meet at Sydney Observatory to this day as the Sydney City Skywatchers.

Proxima Centauri is a faint red dwarf flare star. David Malin, UKS, AAO, APOD

Proxima Centauri is a faint red dwarf flare star. David Malin, UKS, AAO, APOD

Viewing Proxima Centauri The star is too faint to view with the naked eye and it lies four Moon-widths from the star we call Alpha Centauri (the bright Pointer star). Theoretically it should be visible through a good full-size pair of binoculars from a dark site. If you want to take up that challenge this article will help you find it! However, it is easier to find with a well setup computerised telescope. From Sydney Observatory last week I used our new 16-inch diameter DFM telescope. After allowing my eyes to adjust to the dark and some careful comparison with the star map on the PC, there it was – a pale pink-red spot!




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