Vitello – a strange crater on the moon

If you have a small telescope or a friend with one that you can use, it is worth while examining the moon. Huge amount of details are visible and the features change in appearance as the lunar day progresses. Most detail is visible when the moon is at first (or last) quarter as that is when the Sun is just rising (or setting) in the areas at the centre of the visible disc and is casting deep shadows.

Amateur astronomer and member of the Sydney City Skywatchers Harry Roberts does exquisitely detailed drawings of the moon. Here is his drawing and description of a crater named Vitello:

Scattered around the “shoreline” of Mare Humorum are several unusual lunar craters. The most conspicuous is gigantic Gassendi to the north, and opposite it on the southern “shore’ is Doppelmayer, looking like a half size copy of Gassendi. Both are shallow craters with a central mountain range and a network of rilles and ridges on their floors. Both give the impression that their floors are convex. Close to Doppelmayer we find Vitello, looking like a quarter size version of Gassendi, a family of crater “clones”!

Vitello’s most eye-catching feature is a near circular bright rille that encloses the brilliant chain of central peaks. I have oriented the sketch to give an astronauts-eye view into the crater from overhead. Vitello has the looks of a crater three times its size, but in fact is only 42 km across. The bright rille arises at a small crater or vent just inside the northern rim, and after meandering south for 10km sweeps around the crater floor in a near perfect curve to terminate near the central peaks.

Wood tells us that these flat-floored craters surrounding Humorum are floor-fractured craters (FFC’s, Charles Wood “Modern Moon etc.” p85). He suggests such craters have been uplifted by lava from below.

Vitello was Erazmus Witelo, 1225 – 1290, a Polish mathematician and physicist who worked in Padua, Italy. The Moon is covered with craters of all kinds, and Vitello is one of the stranger ones. Take a close look at Mare Humorum, and see the shallow fractured floor craters that surround it. It’s an extraordinary sight.

Enjoy moon watching.

The newest globular cluster – seen!

Globular clusters are roughly spherical collections of old stars that circle around the centre of the Galaxy. Some like Omega Centauri are massive objects with hundreds of thousands of stars. Others like the just announced AL 3 are faint and have relatively few stars. Amateur astronomer extraordinaire Les Dalyrmple in his latest observing report claims to have made the first visual detection ever of AL 3. Here is his story:

Those who know me, know I have a soft-spot for globular clusters. As of 29 June 2006, the “official tally” of G.Cs attached to our galaxy stood at 153. The next day it ticked up to 154 with the announcement that a previously identified open cluster candidate — AL-3 had now been positively identified as a globular from it’s colour-magnitude diagram which clearly shows the hallmarks of a G.C — a short main sequence, strong sub-giant branch and most importantly a distinct, blue horizontal-branch. The “discovery” paper is here.

A POSS II image is above. The image looks like a huge maze of teeny dots with a marginal overabundance of dots in small zone at centre.

Actually, when printed in negative, it instantly reminded me of a visit I made to a vocational guidance counsellor when I was in high school. It looks like one of those sheets of dots and blotches that supposedly contain a hidden picture or pattern of some sort (no, not the more recent 3-D art), that they’d show you after the IQ test while asking what thing you could see amid the dots. Depending on our response (or lack of), they could then determine with great accuracy whether we were headed for a career in brain surgery, advertising or ditch digging etc.

Come to think of it I can’t remember what fate the vocational guidance cousellor pronounced on me all those years ago back in high school. All I can remember upon being shown the dot mazes in succession was answering “… a star”. “… a telescope”, “… Saturn”, “… a galaxy” etc etc. Despite that I don’t think he said “… Astronomer” at the end. But, I digress …

So, armed with the approppriate maps and a POSS II image of the newcomer, off I went in search of it with the thought that I just might be the first person on the planet to make a _visual_ detection of it.

This was my proceedure — my 46cm dob is equiped with Argonavis DSC with 8192 tic encoders, and stellarcat dual axis drives ( upon which I had performed a “local sync” on NGC 6528 which is only 2.5 degrees away) — and then went to the RA and Dec for AL – 3. The pointing should have been very accurate (in my experience somewhat better than 5 arc-mins error in local sync mode with this ‘scope). I then looked for the East – West running “droopy bow-tie” type asterism made up by GSC 6855:396 and GSC 6855:1804 at the eastern end, SAO 186501 at the “knot” and GSC 6855:864 and GSC 6855:790 at the W end (visible in the pic not far below centre). This asterism is only 3.5 arc-mins long and the brightest star at “the knot” is magnitude 8.9. After the slew, that asterism happened to land esentially dead centre in a x185 27 arc-min true field of a 12mm T II Nagler. It took quite a while to actually recognise that asterism because, couter-intuitively, dead-centre of the field was the last place I looked!

I then located the two stars to the east of the position for the cluster that don’t quite point at it : GSC 6855:724 and GSC 6855:336 at mags 11 & 12 respectively and identified those two. The latter is somewhat less than 2 arc-mins from the position for the cluster. At the time, the field was at about 65 degrees in elevation above the ESE horizon. At that altitude the atmosphere is a negligible issue, but it is far enough from Zenith that “Dobsons hole” ought not be an issue either (and I’m only 1 step up the ladder!).

There was nothing visible after a couple of minutes of looking at x185 so I switched to the 9mm Nagler at x247. Again nothing. Then the 7mm Nagler at x317. At this magnification I spent about 5 minutes looking and was nearing the point of giving up on it, when I thought I saw a tiny patch near a mag 15 – 16 star a couple of times while I was shifting my gaze within the field of view. It would sort of turn on and then turn off almost instantly. I couldn’t quite determine at that point whether it was real or “averted imagination”.

As the seeing was very good — at a rough estimate about 0.7 arc secs or better (I didn’t attempt to verfy that with some double star splitting — it is a “guesstimate” based on experence and the appearance of the star images), I went for the doctor and slipped in the Ultima barlow with the 7mm Nagler giving x634 and a tiny 7.5 arc min field.

At that magnification, AL – 3 was intermittently visible near the mag 15 star with averted vision about 20% of the time as no more than a small, slightly less than 1 arc min diameter “field enhancement” — a tiny patch which seemed to have marginally higher surface brightness than the surrounding sky and there seemed to be a couple of 16th magnitude (or worse) sparks that were very occasionally visible at the centre. Very, very nasty indeed. Gary confirmed it’s existance and then Col & Jeff took their turn at the eyepiece. Elation!

One of the most wonderful Sydney experiences

Q. I have heard that sometimes when there is a full moon one can sit at McMahons point and watch it rise under the Harbour Bridge. I was told it is one of the most wonderful Sydney experiences. Is this the case and how often/when does it happen?

A. Yes it can happen. Measuring from a street directory the viewing angle under the Harbour Bridge from McMahons Point ranges from 104° degrees east of true north to 140°. The furthest east the moon can rise ranges from 112° to 125° east of true north. The moon cycles between these maximum values over a period of 18 years.

Over the next 12 months the rise direction of the full moon fits within the viewing angle from McMahons Point on the following dates:

Wednesday 9 August 2006 at 5:01 pm (direction 114° east of true north)
Wednesday 2 May 2007 at 4:48 pm (direction 113° east of true north)
Friday 1 June 2007 at 4:41 pm (direction 123° east of true north)
Saturday 30 June 2007 at 4:21 pm (direction 124° east of true north)
Monday 30 July 2007 at 5:23 pm (direction 114° east of true north)

The above night time picture of North Sydney has the Harbour Bridge on the right while McMahons Point is out of the picture towards the left. If anyone manages to take a picture of the rising moon on 9 August or one of dates listed for 2007, let us know and we will replace the picture above.

Mars is not approaching this August

There is an email circulating in cyberspace saying that the red planet Mars will be exceptionally close on 27 August (2006). According to one version “It will look like the Earth has two moons”!!!

Once again this is a good lesson in not believing everything on the Internet. The email is a hoax describing in a somewhat exaggerated fashion the events of 2003. On 27 August 2003 Mars was only 55.8 million kilometres away which is almost the closest possible distance it can be from Earth. To the unaided eye it looked like a shining red beacon while through a telescope a small red disc could be seen with some dark features visible. Above is a great picture of the planet by the Hubble Space Telescope taken on 27 August 2003.

In late August this year (2006) Mars is faint and just visible after sunset low in the western sky.

Weather clears for a great Festival

Sydney Observatory’s annual Festival of the Stars was held this weekend on Friday (21 July) and Saturday (22 July). The weather forecast was gloomy and sure enough there was lots of cloud for the Friday evening. However, it cleared for the Saturday evening and many hundreds of visitors had a great time looking through numerous telescopes and enjoying the numerous other activities such as the ghost tour, the 3-D theatre, short talks, the CSIRO Science show and much else.

Waiting for the rain to stop on the Friday evening by the large 67-cm telescope.

What a difference a day makes! Queuing for the same telescope on the Saturday evening.

A number of buildings and structures such as the Sydney Harbour Bridge, the Opera House and the Westpac barometer were kindly turned off to give visitors a better view of the sky during the Festival. As can be seen on the image of North Sydney though many organisations still need to be convinced to be more considerate both of stargazers and the environment. Note that strangely a number of buildings including some on this image had promised to switch off their lights but did not.

The CSIRO Science Show: starting an exciting demonstration in front of a spellbound audience of children.

Browsing one of the stalls – the Sydney City Skywatchers stall.

A figure-of-eight

Q. At 12.00 midday each day (weather permitting) I mark the shadow cast by the top corner of the building. I have been recording this since Sept 23 2005, and the shape has taken a nice elongated figure 8 shape (infinity symbol). On the 23rd June the shape bottomed out, and I expected it to continue the smooth curve as previously established. However it seem to stutter and fell back towards the building in a straight line rather than the expected curve. Now it seems to have returned to the expected curve. Please explain.

A. What you should see is an analemma. This indicates the changing elevation of the Sun above the horizon vertically during the year and horizontally indicates in minutes how much earlier or later than 12 noon the Sun is due north. See the attached horizontally exaggerated curve fom the Wikipedia entry on analemmas. A more realistic version is also attached. Of course they are upside down as they are from the northern hemisphere.

If you do not see a smooth figure-of-eight curve as above all I can suggest is that maybe you were getting a shadow of something else than the corner of the building when the Sun is at its lowest elevation for the year.

How dark can we go?

This coming Friday and Saturday evenings (July 21 & 22) Sydney Observatory is holding its second annual Festival of the Stars. The Sydney Harbour Bridge floodlights will be turned off for the events and a number of City and North Sydney buildings will be turning off their exterior signage. Maybe, maybe they they will be joined by a major Sydney landmark.

For the first time Sydney Observatory will be measuring the brightness of the night sky during the event while the lights are turned off. This is with a special Sky Quality Meter borrowed from the Sydney City Skywatchers. Last night (Monday 17 July at 9:00 pm) the reading was 17.82 magnitudes per square arcseconds. How dark can we go? Any guesses welcome – post them as comments. Note that the higher the reading the darker the sky. A really dark sky in the country is 23 mag/arcsec2, but that is not feasible in Sydney.

Double header event at Sydney Observatory on Monday 7 August

On Monday 7 August from 6:30 pm there will be a double event at Sydney Observatory.

First there will be the opening of a spectacular photographic display. This is from the 2006 “David Malin” Awards that was held during the CWAS Astrofest in July.

The Overall Winner of the Awards was Peter Ward for his picture titled; “Eclipse Sequence”. The category winners were:

Zac Pujic – Amateur: Solar System
Gary Hill – Amateur: Wide-Field
Michael Sidonio – Amateur: Deep Sky
Eddie Trimarchi – Semi-Pro: Deep Sky
Peter Ward – Semi-Pro: Solar System

Canon Australia was the major supporter of the Awards with prizes to the value of $5,000 donated.

The photo shows all the winners with world renowned astrophotographer Dr David Malin (in the blue shirt). Courtesy John Sarkissian.

The exhibition opening will be followed by an interesting talk at a meeting of the Sydney City Skywatchers. The speaker is Dave Gault from the Western Sydney Amateur Astronomy Group. He will be talking about “What’s it like to be an Umbra-Holic”:

Astronomers have been timing lunar occultations for years, trying to refine knowledge of the moon and the stars beyond. New techniques and equipment are within easy reach of the Amateur Astronomer that is revitalising the study of all types of occultations.

Using an ‘ordinary’ telescope, with a sensitive video camera, a GPS time inserter, free software and a ‘personal occulting disk’ the amateur can resolve double stars beyond the Dawes Limit. A team of like minded amateurs can measure the profile of an asteroid to a precision surpassing huge telescopes like KECK or Gemini. That’s where we are now.

Where are we going? Faster and more sensitive cameras, greater precision and the goal of measuring a chord across a Kupier Belt Asteroid beyond Pluto.

All welcome. There will be a charge of $2 for supper after the Skywatchers talk.

Just how much fun can you have in one day!

Every School Holidays we hold numerous family events. Yesterday we ran our “Lost in Space Family Fun Day”. Aimed at children, all the activities were included in the ticket price of just $10 per child. Here are some photos to show how much fun you can have in one day at Sydney Observatory.

Surge on Sun

Sunspots on the Sun indicate regions of strong activity and magnetic fields. The number of spots tends to vary with a cycle of 11-years called, not surprisingly, the sunspot cycle. In 2006 the Sun is at a minumum in the cycle and there are generally few spots visible. There are exceptions though. Over the last couple of weeks a large spot region numbered 898 moved across the Sun, going over the edge of the Sun about 12 July. The above image from NASA’s Solar and Heliospheric Observatory (SOHO) spacecraft indicates that the group was considerably larger than the Earth.

Monty Leventhal, a Sydney amateur astronomer from Sydney City Skywatchers observes the Sun regularly with special equipment that filters out all colours in sunlight except for a narrow band of colour associated with excited hydrogen atoms. On 5 July he photographed a surge – a jet of material ejected from an active region that reaches high into the Sun’s outer atmosphere or corona and then fades or returns along the same path. Monty’s image and details are as follows:

Filtergram taken on 5th July 2006 shows a large Surge below a Sunspot group in region 898.

Date:- 5-7-06
Telescope:- Meade 10″ S.C.
Filter:- DayStar 6Å T-scanner
Camera:- Olympus OM1
Film:- Kodak Tech Pan
Conditions:- Poor (4)