Archive for the ‘Astronomy blog’ Category

November 2015 night sky guide and sky chart

Published by Melissa Hulbert on November 1, 2015 4 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.

SEE THE SKY CHART
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)

(more…)

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
2015Oct12ar12422_sep28

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.

2015Oct12ar12422_limb

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.

2015Oct12ar12422flarex4

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!

 

Venus hides behind Moon at dawn, Friday Oct 9, 2015

Published by Andrew Jacob on October 8, 2015 No Comments
The eastern sky from Sydney on October 9, 2015 at 5:31 am AEDT

The Moon occults Venus. The eastern sky from Sydney on October 9, 2015 at 5:31 am AEDT. Image made with Stellarium.

 

This Friday, October 9, at dawn the Moon will move in front of Venus and hide, or occult, it. These occultations of Venus are visible from Earth once or twice per year, yet from any one location, such as Sydney, it can be about 5 to 10 years between occurrences. This occultation is visible from most of Australia except Western Australia.

All times below are in AEDT and are specific for Sydney

To see this event look towards the eastern sky before dawn. The Moon rises at 4:12am with Venus, hot on its heels, rising at 4:16am.

At 5:31 the Moon moves in front of Venus and the occultation begins. Venus is very bright at present so should be visible to the eye beside the Moon. However, binoculars will provide a fantastic view of this event. Venus is in its crescent phase and so you will see the crescent Venus disappear behind the bright edge of the waning crescent Moon!

At 6:54am Venus reappears from behind the Moon, this time against the dark edge of the Moon. However, sunrise is at 6:23am so this reappearance is in full daylight and more difficult to observe.

*If you are using binoculars to view the reappearance please take great care not to look at the Sun! Viewing the sun with binoculars may result in permanent & irreversible eye damage. If you use binoculars to view the reappearance ensure you and the binoculars are within the shadow of a house or other object while looking toward the Moon and Venus.

If the weather is cloudy and you miss this occultation we only have to wait, this time, until September 18 in 2017 for the next one.

For locations other than Sydney Ian Musgrave has provided a table of disappearance and reappearance times but note the times are all in standard time – add an hour if you are in daylight saving time.

Ian Musgrave reported his observations.

 

October 2015 night sky guide and sky chart

Published by Melissa Hulbert on October 1, 2015 No Comments

Orionids meteor shower expected to peak on 21 October

Dr Andrew JacobTo help you learn about the southern night sky, Sydney Observatory provides a written guide and a sky map or chart each month. This month’s guide is presented by Dr Andrew Jacob (pictured, right), Curator of Astronomy at Sydney Observatory.

This month, find out how to find the South Celestial Pole, and where to find stars and constellations including Crux (the Southern Cross) and the Pointer stars, the Large and Small Magellanic Clouds, the bright star Antares at the heart of Scorpius. Andrew also tells us about some good photo opportunities from the 10th and particularly the 26th onwards with Jupiter, Mars, Venus and the Moon in the pre-dawn sky. And of course, there is the Orionids meteor shower to look out for during the nights and pre-dawn during October.

For all this and more read the transcript below.

SEE THE SKY CHART
We provide an embedded sky map (below) and a October 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 Oct 2015

BUY THE BOOK
Our annual book, ‘The Australasian sky guide’, by Dr Nick Lomb has more information and star maps for months from December until December inclusive, plus information about the Sun, twilight, the Moon and tides, and a host of other fascinating astronomical information. You can purchase it ($16.95) at Sydney Observatory and Powerhouse Museum shops or other good bookshops, or online through Powerhouse Publishing (additional packing/postage costs apply). You can buy the 2015 book now, or wait until November and buy the 2016 edition.

READ THE TRANSCRIPT (after the jump)

(more…)

Outburst_in_action.ESA

A short-lived outburst from Comet 67P/Churyumov–Gerasimenko on 29 July 2015. The jet lasted barely 30 minutes. Image © ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA.

As Comet 67P/Churyumov-Gerasimenko reaches its closest point to the Sun, perihelion, on August 13, its activity is increasing. This short lived jet was spotted by the narrow angle camera on board ESA’s Rosetta spacecraft. Heating from the Sun, and the rotation of previously dark areas into sunlight result in an increased release of dust and gas as the comet approaches the Sun. From Earth comets are often most easily seen after their “perihelion passage”.

The gas released is mostly carbon-dioxide. But many other organic molecules are also released. What would it smell like? The smell has been described as a combination of: rotten-egg smell, horse-stable odor, almond and vinegar!

If you want to experience the smell for yourself book in for Warwick Holmes full-sensory presentation, “Philae and the Rosetta Comet Encounter” during Sydney Science Festival at the Powerhouse Museum, Thursday August 20.

August 2015 night sky guide and sky chart

Published by Melissa Hulbert on August 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 Astronomy Programs Coordinator.
Mel suggests stars and constellations to look out for this month include Scorpius, with the red star at its heart, Antares; Sagittarius (which looks more like a teapot than a centaur); Crux – more commonly known as the Southern Cross; and Ophiuchus, the 13th sign of the zodiac! Mel also tells us the best times and dates to try to see the planets Venus, Saturn, Jupiter, Mars and Mercury.

SEE THE SKY CHART
We provide an embedded sky map (below) and an August 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 Aug 2015

BUY THE BOOK
Our annual book, ‘The 2015 Australasian sky guide’, by Dr Nick Lomb has more information and star maps for months from December 2014 until December 2015 inclusive (next year’s, likely to be available from November, will have months from December 2015 to December 2016), plus information about the Sun, twilight, the Moon and tides, and a host of other fascinating astronomical information. You can purchase it ($16.95) at Sydney Observatory and Powerhouse Museum shops or other good bookshops, or online through Powerhouse Publishing (additional packing/postage costs apply).

READ THE SKY GUIDE (after the jump)

(more…)

WarwickHolmeswithComet67P

Warwick Holmes holds aloft a 3D printed model of comet 67P/Churyumov–Gerasimenko. The real comet is even darker than this model. Photo Andrew Jacob © MAAS, Sydney.

Warwick Holmes worked for over four years at the European Space Agency (ESA) on the Rosetta/Philae mission to comet 67P/Churyumov–Gerasimenko. He recently visited Sydney Observatory and brought along his model of the comet. It is difficult to photograph because it is jet black. The real thing is blacker still!

Warwick will present an insider’s view of the mission, including the spacecraft design and the images and the science acquired, during Sydney Science Festival, Thursday August 20, 6:30-8:00pm. Booking required. 

Aroma Festival Comes to Sydney Observatory

Published by Melissa Hulbert on July 24, 2015 No Comments

Aroma Festival

Coffee/tea and astronomers have long had a symbiotic relationship – there is nothing like a good cuppa at 2am with still a few more hours of observing to go!

With that in mind, this Sunday (26th July) is The Rocks Aroma Festival of which Sydney Observatory is a part.

From 10am-4pm our barista, Jan, will be brewing the finest blend on a unique coffee bike/cart.

With every day tour ticket purchase enjoy a Cosmic Coffee, Aromatic Black Hole Tea or a Solar Hot Chocolate and a star-inspired chocolate treat.

With sunshine forecast, what better way can you spend a relaxing Sunday then by enjoying a tour, a brew and views from Sydney Observatory?

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