From: TerryMoselat

Date: 6 May 2008 02:28:07 BST

Subject: Competition link, Mercury, Occultation, ISS, ESA, Ionosphere, 


Hi all,


1. CASSINI COMPETITION: There was a problem with the link to the Cassini comp in the last email: there should be a letter 'l' at the end of the url, as follows:

Thanks to Danny Collins for pointing that out. 


2.  MERCURY & MOON: If you want to spot Mercury, perhaps for the first time, there's a great chance to find this elusive little planet quite easily on the evenings of 6 & 7 May, when the crescent Moon will act as a guide.

  On the evening of the 6th, the very young Moon will lie just 2 degrees above and right of Mercury in the evening twilight. Start looking about 10-12 degrees above the horizon just N of West from about 21.45 BST using wide-field binocs and you should have found it by about 10 p.m. if the sky is clear. If not, keep trying - even up to 10.15 it should be quite easy: after that it may be getting a bit low down in horizon cloud or haze. If you can spot Capella much higher up, drop down vertically from Capella towards the horizon - at about 10.15 the Moon will be about 25 degrees almost vertically below Capella. (For those in the west of Ireland take about 10 mts later for all those times),

   Next evening (May 7) the Moon will have moved well to the upper left of Mercury: you'll find the innermost planet 13 degrees below and right of the Moon at about the same time that evening.


3. OCCULTATION OF MARS: Fancy a challenge? On 10 May, the 69% crescent Moon will occult Mars, but in broad daylight! Worse, the Moon & Mars will still be rising in the East, while the Sun will be near culmination, and therefore highest and brightest, at the time of the occultation! Mars will be quite faint, at magnitude +1.3. Even the Moon will not be easy to find, as the surface brightness of the crescent will be quite low at that phase.

   You'll need a very transparent sky, and good clean optics, with good tube baffling if you're using a refractor. Both Mars and the Moon will be very difficult to see in those conditions, but have a go if you relish a challenge! Here are details for various locations in Ireland. Times of occultation are given to the nearest minute - obviously you'll want to start observing well before those times, and you should aim to have found the Moon & Mars at least 5 mts before these times.

   Once you've found the Moon, whose 'horns' will be pointing to the lower left (ignoring whatever inversion your telescope may give to the image!), mentally 'complete the circle' to envisage the whole disc of the Moon. Mars will disappear behind the dark, and hence invisible, limb of the Moon, in the NE quadrant, roughly at between '10.0 o'clock' and '11 o'clock' on a clock face on the Moon's disc.

   If you have setting circles, or an aligned GoTO telescope, Mars will be at RA 8h 11m 50", Dec + 21 deg 46'.


BELFAST:  13.24 BST, Mars: altitude 26 deg 46'; azimuth 89 deg 34'.

DUBLIN:  13.19 BST: Mars: altitude 25 deg 50'; az = 87 deg 40'

CORK: 13.14 BST: Mars: altitude 23 deg 38'; az = 84 deg 19'

GALWAY: 13.19 BST: Mars: alt 24 deg 09'; az = 85 deg 27'

LIMERICK: 13.17 BST: Mars: alt 24 deg 03'; az = 85 deg 07'

WATERFORD: 13.16 BST: Mars: alt 24 deg 20'; az = 85 deg 43'.

   To find where Mars is about 10 minutes BEFORE the occultation times, it will be about 1 deg 30' of arc lower, and about 2 degrees further to the LEFT, than the position at the time of occultation.

   The crescent of the Moon will be about 0.5 degrees above right of those positions for Mars

    To help in locating it, note the exact position of the East point (90 degrees azimuth) on your local horizon, and then offset to the left by whatever few degrees are appropriate for your location at whatever time you start observing. Then sweep vertically upwards by the required amount.

   Mars will reappear from behind the bright limb of the Moon between 20 and 40 minutes after disappearance, depending on your location, but this will be much harder to see, as Mars will be much fainter than the bright edge of the Moon at that point.

   I suggest using a medium magnification to try to see Mars: too low, and the sky will appear too bright; too high and you'll probably have bad 'seeing', and Mars' disc will appear fainter, with less contrast against the sky.

   Good Luck! If you have any success, tell me, or report the observation to iaa2000at, or


4. ISS: The now much enlarged and brighter International Space Station is now starting another series of morning passes over Ireland. See the excellent, free, for details of predictions for your own location, and lots more besides.



    The European Space Agency is looking for third-level students to take part in a Space Station Design Workshop next July. Two teams will compete against each other and the competition is open to anyone studying up to masters level. See:

6. EXPLORE THE IONOSPHERE: The ionosphere is our planet's "final frontier." A realm of dancing auroras, radio-bending plasma bubbles and dangerous ultraviolet rays, it is the last wisp of Earth's atmosphere that astronauts leave behind when they enter space. Now you can explore the ionosphere from the safety of your own home.  Recently, NASA-supported researchers unveiled a "4D" computer model for the general public. Download a few files and presto--you're flying through the ionosphere. The model shows the ionosphere as it is right now; it's a real-time display based on current solar activity and atmospheric conditions.  Visit to get started.


Clear skies,


Terry Moseley