THE SKY AT A GLANCE - APRIL 2008

Summer Time in the UK commenced on 30 March 2008 .

MERCURY passes through superior conjunction on 16 April and remains too close to t5he Sun for observation until the last few days of the month, when it will becomes visible low in the west-north-western sky at the end of evening civil twilight. During this short period its magnitude fades from -1.2 to –0.9. For observers in northern temperate latitudes this will be the most favourable evening apparition of the year.

VENUS , magnitude -3.9, is already too close to the Sun for observation from the latitudes of the British Isles .

MARS continues to move direct in the constellation of Gemini. Towards the end of the month it will be seen to the south of Castor and Pollux. Mars is visible in the western sky in the evenings, its magnitude fading from +0.8 to +1.2.

JUPITER , magnitude -2.2, is slowly brightening though still three months from opposition. It remains visible as a bright object in the constellation of Sagittarius. The planet is now crossing the meridian before dawn, near overhead for those in low southern latitudes, but only at a low altitude for those in the latitudes of the British Isles .

SATURN , magnitude +0.5, continues to be visible as an evening object in Leo until after midnight.

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BAA electronic bulletin No. 00336 http://www.britastro.org/
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On Friday night, 2008 April 11, at around 20:49:30 UT (21:49:30 BST), the 20km asteroid (1886) Lowell is predicted to occult the naked eye star 4.8 magnitude HIP 63355 (36 Comae Berenices).

The latest update (March 28) shows the shadow track crossing from east to west almost centrally over Edinburgh, Glasgow and surrounding towns. The star will be at an elevation of about 38º, in azimuth 119º
(ESE). The Sun will be 13º below the horizon, and there will be minimal interference from the Moon. The maximum duration will be only 1.7 seconds, but the star will disappear completely for those inside the shadow track.

As with all predictions of this type, there is some uncertainty in the precise location of the track. Taking into account the formal errors, the probability of observing a positive event is around 15% within the shadow track, decreasing to 7% at the 1 standard deviation limits. The latter are around 50 miles north and south of the centre line and enclose parts of the Tayside, Fife , Central, Strathclyde, Lothian, and Borders Regions (using pre-1996 boundaries for simplicity).

To see the detailed track, click on the link below to display Derek Breit's high precision plot of the event on a Google Map, and zoom in to Scotland :-

http://www.poyntsource.com/New/Google/20080411_13468.HTM

The predicted centre line is shown in green, the shadow track edges in blue, and the 1 standard deviation track in red. (Ignore the movable grey lines.)

Although theoretically visible to the naked eye, observers may prefer to use binoculars or a telescope to see the event.

Scientifically valuable information can be obtained from accurate timings of the disappearance *and* reappearance of occulted stars. A single positive timing can yield a position relative to the star of several times higher precision than standard astrometry. Combined timings from observers distributed across the track can yield the size and shape of the asteroid. Of course, occultations involving bright stars give the opportunity for many more observers to take part.

Observers wishing to make serious visual timings (to better than 1 second) will need a multi-lap stopwatch or a voice recorder linked to an accurate time signal. Those with sensitive enough video cameras, camcorders or webcams may also be able to record the events, but will need an accurate method of time-stamping the video. This is a red star (Mr=4.0) which CCD video cameras are more sensitive to.

Serious timings of positive occultations would be welcomed by the undersigned, as would definite negative events from within the predicted shadow track. It is normal practice to observe or record for 2 minutes either side of the predicted central occultation time above. A specimen report form can be found at:-

http://astrosurf.com/eaon/Report%20form.htm

Please email any reports to me, or contact me if you need assistance completing the form. Accurate latitude and longitude (WGS84 datum) can be obtained from the Google Map, before or after the event. Elevation above mean sea level is also required.

New Moon: 6 April 03:55 hrs
First Quarter: 12 April 18:32 hrs
Full Moon: 20 April 10:25 hrs
Last Quarter: 28 April 02:57 hrs

The safest and cheapest way to observe is with Baader AstroSolar Safety Film.  This is available from D Hinds and comes in a 8 x 12 inch sheet and is enough to cover both telescope objective and finder.

Picture 1 shows a filter made to fit my 10 inch LX200.  This is made of hardboard for the front mask and cardboard for the outer rim.  Double sided tape was used to stick the solar film to the mask and then the rim to the mask.  An inner ring was then made to fit inside and seal the solar film secure.

Pictures 2 and 3 show the filter fitted to the telescope.  The sheet of Baader Solar Film is enough to make a 7 inch off axis mask and to cover the telescope finder as well.  This is shown in Picture 4.

The cost of the Baader Solar Safety Film is around £15 including postage.  I had some hardboard and cardboard so the cost for me was just the cost of the safety film.  I expect that buying all the materials would cost about £20 to £25. 

I have tested this safety film and it gives about 99.99% rejection rate and good quality images.

Picture 1

Picture 2

Picture 3

Picture 4

Now that you have made your filters, use the following downloadable files to record your observations.  Acrobat Reader is required to view the files.