Archive for the ‘Astronomy blog’ Category

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The evolution of a large sunspot from early February to late March 2014. Sketch and copyright Harry Roberts ©, all rights reserved

On the first of January 2014 a great sunspot swept around the Sun’s eastern limb. It was big even when first seen, almost edge-on, at the limb: “helio” freeware showed it was 800 units in area; there were many ‘follower’ (f) spots in its wake. It was dubbed AR11944.

This was the beginning of an exciting time for sun-watchers, as the big preceding (p) spot and its train of followers began their transit of the visible disc – a transit that was to be the first of four ‘visits’ by the big (p) spot.

Synoptic Map: while sunspots are relatively fixed at their point of emergence, the rotation of the spherical Sun gives a constantly changing perspective of any feature under study. In order to clarify the evolution of the big spot and it attendants, several logs were mapped onto a flat plane, in a synoptic configuration, revealing changes in area, shape and heliocentric latitude and longitude over time (Fig). Logs 2 and 3 were incomplete, due to cloud – and the missing detail (dotted) is taken from SDO satellite records. Log 5 is wholly courtesy of the SDO imaging team.

As well, sunspot magnetic polarity, courtesy of Mt Wilson 150’ solar telescope, © Regents of Univ. of California, L.A., was added showing changes in the polarity of spots as they emerged – and in one case merged –producing a Hale Delta class spot group. Log 6 is also from Mt Wilson due to heavy cloud in Nowra.

While the big spot first appeared in January, it survived to return twice in the month of February, each time gaining a new NOAA active region number.

Note that the events shown in the synoptic map all occur essentially at the same point on the Sun’s surface, despite the apparent rotation of the disc. What does the map reveal?

Proper Motion: as the big spot and its group rotated into view fully-formed, no prior motion of the (p) spot is known, and its site at -8º,103º (i.e. lat 8ºS, long. 103º) is used as the ‘origin’ of the plot (Fig). Relative to this point the (p) spot moved just 1 or 2 degrees westward during its transit from E to W limbs (Fig2), with perhaps 1 degree of southward motion. Most (p) spots move a little towards the equator during their transit – but, unusually, the AR11944 (p) spot seemed to move polewards.

This motion was confirmed when the (p) spot returned (Figs 3 to 5). Five degrees of southward motion had occurred between days 3 to 34, as well as 4º of westward motion. Over the next 21 days (to day 56) there was little further change. Whatever drove the southward motion had now ceased.

Polarity changes: Mt Wilson’s workers have their own problems with weather – and detailed polarity change is incomplete. Nevertheless, the overall picture is fairly clear.

AR11944 was a new large group when it came into view (Logs1 and 2) with very strong 2700G field in the big (p) spot – and mixed (Delta class) polarity in some followers. One X1.2 flare erupted in the group on the 7th and many M-class. The group simplified as it neared the western limb.

On return only the big (p) spot of 1944 remained but it was not alone. While all its (f) followers were gone, a new dipole was in the act of emerging in front (i.e. due west) of the old (p) spot. Over the first days of Feb the new dipole grew bigger and Hale-Nicholson forces caused the new follower spot to drift east while the old (p) moved westwards – and the two spots merged into a rare bilobate [divided into two lobes] shape of Delta magnetic class (logs 3 and 4). The opposed spots became more distorted over following days until the group passed behind the western limb. Strangely, no major flares resulted.

On its third return only the old (p) remained, but it contained smaller umbrae of opposite sign – and while rounding the east limb the big single spot unleashed a GOES X4.9 flare– a bright and long-lasting event, reported earlier: the third strongest flare of SC24 and the strongest for a southern group thus far.

Delta reversed: The group now (log 5) held the old (p) spot with R2400G polarity and small umbrae of V1900G, and soon after new violet preceding (p) spots began emerging ahead of the old spot – changing the group into Hale Delta class with reversed polarity, i.e. violet spots preceding and the ‘old’ red spot following! Strong flaring in the group abruptly ceased and the small (p) spots came and went until the group (now AR11990) rotated out of view.

Fourth return! When the region returned ~March 24th heavy cloud prevented viewing at Nowra, but Mt Wilson drawings showed no spots at the old site. However, on March 27 they logged two tiny spots at the exact site (Fig, log 6): a small R1500 umbra at –14, 108 and a V1400 spot preceding. NOAA assigned AR12020 to the small reversed beta class pair. Since spots cease to be visible when fields fall below 1500G, as the site transited the disc its spots faded then reappeared on successive days – until final disappearance around Mar 31.

The ‘old’ red (p) spot of AR11944 had survived to make a fourth appearance on the disc, still in ‘following’ position! It seems the now separate spots are the two mixed polarity umbrae from the single Delta penumbra of AR11990, the penumbra having faded away.

Conclusion: It has been an amazing saga of sunspot evolution. The one constant over the three-month period (i.e. 4 Carrington rotations) was the persistence of the original strong ‘red’ (p) spot of AR11944: while smaller spots of violet polarity, and some red, came and went on its east and west sides. With just two tiny spots to mark the original site the saga is, apparently, over. In H-alpha some large filaments persist in the area – and ‘spotless’ flares at the site are a possibility.

Vale great red spot!

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

Daily cosmobite: Spica

Published by Nick Lomb on 1 Comment

9_Artists impression of Spica_4shared_Manuel Perez de Lema LopezVisible in the eastern sky in the early evening, this is the brightest star in the constellation of Virgo. Spica is at a distance of 250 light years and consists of a pair of hot, massive stars whirling around each other every four days. As the two stars are so close, they distort each other into football-like shapes.

Artist’s conception of the two components of Spica. Courtesy of Manuel Perez de Lema Lopez

Mars opposition, images, canals and HG Wells

Published by Nick Lomb on April 8, 2014 2 Comments

Mars_4 April 2014_Anthony Wesley

Mars imaged on the early morning of Wednesday 5 April 2014 by Anthony Wesley, one of Australia’s leading amateur astronomers, using his self-built 40-cm reflecting telescope. Image and copyright Anthony Wesley ©, all rights reserved. Used with permission

Today (8 April 2014) Mars is at opposition, that is, on the opposite side of the Earth to the Sun. Mars oppositions occur at roughly two year intervals when the Earth laps Mars in their perpetual race around the Sun. Due to the oval-shaped nature of the path of Mars around the Sun, the distance between the two planets is still lessening with the closest distance in six days’ time on 14 April 2014.

The current opposition is not a particularly favourable one as the distance between the planets is 0.621 AU (the distance of the Earth to the Sun). Compare this with the distance at the next favourable opposition on 27 July 2018 when Mars’ minimum distance will be 0.386 AU.

Anthony Wesley has produced some unbelievably clear images of Mars during this current opposition, such as the one above. A few years ago such an image could only have been produced by the Hubble Space Telescope or other space-based instruments. To produce such an image takes the right equipment, experience, great skill and considerable dedication. Anthony says of the image, “Syrtis Major is visible at lower right, and it will become more central over the next few days from here. The north polar cap is visible at top as well as a cloud-filled Hellas basin at bottom.”

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Drawings of Mars by Walter Gale on 6 August 1892 at 12:30 am Sydney Mean Time (SMT) and 7 August at 11:15 pm EST. From the Illustrated Sydney News of 18 February 1893 p18

Before spacecraft and skilled amateurs with the right equipment, astronomers laboriously sketched the planet while waiting for momentary clear views through the Earth’s turbulent atmosphere. One of those who sketched the planet was the Sydney astronomer Walter Gale, two of whose images from the favourable Mars opposition of 1892 are shown above. The 154-km wide crater on Mars where the Mars Curiosity rover landed in 2012 is, of course, named after Gale.

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North polar cap drawn at Lowell Observatory in 1905. From Percival Lowell’s book, Mars and its Canals. Courtesy Archives.org

American astronomer, Percival Lowell, set up an observatory specifically to study Mars in Flagstaff Arizona. Lowell, building on earlier observations at the favourable Mars opposition of 1877, was a great believer in Martian canals, that is, artificial water ways criss-crossing the planet. He thought that Mars was a parched and dying world whose inhabitants cooperated to create these mammoth canals to transport scarce water where it was most needed. Observing Mars by eye through a telescope is never easy and under the influence of his own ideas Lowell kept seeing numerous canals on the planet. Sadly, as can be seen in Anthony Wesley’s image at the top of this post and in spacecraft observations these canals do not exist and were just a trick of the eye. Still Lowell’s ideas led to great interest in the planet and helped to inspire the English writer HG Wells to write his famous book, the War of the Worlds.

Although the current opposition is not favourable, it is still worthwhile observing Mars with the unaided eye when it appears as a bright red object low in the eastern sky in the early evening or through a telescope at Sydney Observatory or elsewhere.

8_Mars-oppositions-2003-to-20181Every two years or so, the Earth catches up with slower-moving Mars so that the red planet is on the opposite side of the Earth to the Sun. At these times the planet is at its closest, its brightest and is visible all night. This is not a favourable opposition, but it is still worth looking for the planet low in the east in the early evening.

The paths of Mars (outer) and the Earth (inner) with the dates of the oppositions of Mars from 2003 to 2018 indicated. Diagram Nick Lomb

Daily cosmobite: Jupiter and the Moon

Published by Nick Lomb on April 7, 2014 No Comments

7_Jupiter and the Moon_18 March 2013_Nick LombDid you see a bright object near the Moon last night? That was the giant planet Jupiter. Tonight the Moon is at first quarter phase and is still near Jupiter; it is above and to the right or east of the planet. Enjoy the views of Jupiter for at the beginning of July it will move out of our view into the twilight.

Jupiter and the Moon on 18 March 2013. Image Nick Lomb

Daily cosmobite: clocks go back

Published by Nick Lomb on April 5, 2014 No Comments

5_Clock face_Nick LombPeople in the south-eastern states can catch an extra hour of sleep as summer time ends at 3 am on Sunday. Until summer time recommences on Sunday 5 October, the time differences between states go back to normal, eg two hours between NSW and Western Australia.

Clock face. Image Nick Lomb

Daily cosmobite: stars in the north

Published by Nick Lomb on April 4, 2014 No Comments

4_Orion_12 March 2012_Nick LombIf we face north in the early evening we see Spica low to the far right or east. Just to the right we have Regulus and just to the left Pollux and Castor. Above them is Procyon and then Sirius, the brightest star in the sky. Further to the left or west we reach Rigel, Betelgeuse and the other stars of Orion.

The stars of the constellation of Orion. Image Nick Lomb

Daily cosmobite: Virgo the Maiden

Published by Nick Lomb on April 3, 2014 No Comments

3_Virgo and Corvus_StellariumIn the early evening this zodiac constellation is visible low down in the eastern sky. To find its brightest star, Spica, first look for a distorted rectangle of four stars that form the constellation of Corvus the Crow. Two of the stars point to Spica directly below.

The constellation of Virgo with its brightest star Spica indicated. Courtesy Stellarium

Daily cosmobite: around the galaxy

Published by Nick Lomb on April 2, 2014 No Comments

2_Artists conception of Milky Way galaxy_NASA_SSEThe Earth goes around the Sun once a year. The Sun itself is moving as it circles the centre of our galaxy roughly once every 240 million years. This may seem a long time, but during its life the Sun has completed around 20 circuits of the galactic centre. Feeling dizzy?

An artist’s concept of the Milky Way based on recent information. Courtesy NASA

End of daylight saving means end of dark mornings

Published by Nick Lomb on April 1, 2014 4 Comments

Sunrise times_Sydney_2014_Nick Lomb

Graph indicating sunrise in Sydney throughout the year. It is calculated for 2014 but there is little change from year to year except for the slight shift of the starting and ending dates for daylight saving. Diagram Nick Lomb

If you rise early whether for work, school, gym, a run or walking the dog you are probably sick of the dark mornings that crept up on us very quickly in recent weeks. In that case, help is at hand for this coming Sunday (6 April 2014) is the first Sunday in April and hence daylight saving finishes early that morning.

As can be seen on the above graph the morning before, that is, Saturday morning, is the latest sunrise for the year with the Sun rising at 7:10 am. In the depths of winter at the end of June and the beginning of July the latest sunset is only 7:01 am. So the mornings may well become cooler as the year progresses towards winter, but it is not going to become darker.

If you think that 7:10 am is late for sunrise, spare a thought for the 8000 or so people of the small town of Wentworth in the south-west of NSW. The town is approximately 9° to the west of Sydney and, as each degree of longitude represents four minutes of time, sunrise occurs about 36 minutes later than in Sydney. There the latest sunrise for the year is on Saturday at 7:47 am.

Of course, some people may be disappointed by the earlier sunrise. If you are trying to sleep in for instance you may not appreciate being woken up by light spilling through edges and gaps in blinds and curtains. Also others may have enjoyed the opportunity to see the planet Venus and other objects in the dark morning sky such as passes by the International Space Station.

The above diagram is a useful one as we can see how daylight saving acts to reduce the spread of sunrise times throughout the year. Without daylight saving in early December sunrise would be as early as 4:37 am, which could be a serious difficulty for those trying to sleep at that time.

An interesting, just released, American study suggests that at the start of daylight saving in spring there is a spike of 25% in people experiencing heart attacks, presumably due to losing one hour’s sleep. Conversely, at the end of daylight saving in autumn when the clocks are moved backwards by an hour there is a 21% decrease in heart attacks. The study is based on data from only one American state and the authors suggest that it would be worthwhile comparing the results of their study with data from a state that does not have daylight saving. Maybe a comparison could be done in Australia between hospitals in Sydney and in Perth where there is no daylight saving?

If you like you can stay up till 3 am to change your clocks on Sunday morning. For most people though it is easier and more sensible to do so before going to bed on Saturday evening. And, fortunately, these days many devices like mobile phones, tablets and computers, tend to change automatically without the need for human intervention. However you do it, enjoy the extra hour of sleep on Sunday morning and the lighter mornings from then on.

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