[BAA-ebulletin 00851] Mercury in the Evening Sky - Observing Opportunity

[BAA electronic bulletins service]

See Mercury in the Evening Sky

Mercury can be a difficult planet, not because it is faint, it can be an 
easy naked eye object, but rather because being so close to the Sun it only 
pops in to view for short periods in the morning or evening sky.

At the end of this month and beginning of May there is an opportunity to see 
it during its best evening apparition of the year (it reaches greatest 
eastern elongation on May 7). Also, on the evening of April 30, it passes 
within 2 degrees of the Pleiades star cluster (Messier 45) making an ideal 
observing and imaging opportunity.

To find Mercury on that date (binoculars will help here) follow the ecliptic 
down through Jupiter and Venus towards the horizon and once the Sun has set 
(around 19:20UT, 20:20BST) Mercury, shining at magnitude -0.4, will be found 
around 18 degrees up.

Do make sure the Sun has set before you scan for the planet using any 
optical aid, as even the briefest accidental view of the Sun through 
binoculars could result in blindness.

As the sky darkens Mercury should become an easy naked eye object and around 
20:00UT it will lie about 11 degrees above the horizon at an azimuth of 293 
degrees. If you use a telescope it will show a phase of 56% and a disk 
diameter of 7 arcsec. By comparison, Venus will show a diameter of 16.7 
arcsec and the giant planet Jupiter a diameter of 38 arcsec.

If you fail to see it on April 30 because of the fickle British weather all 
is not lost as Mercury and the Pleiades remain within a few degrees of each 
other for the next couple of days. On May 7, date of its greatest eastern 
elongation, at 19:30UT it will lie exactly midway between Venus and the 
point on the horizon where the Sun sets, although by now no longer close to 
the Pleiades.

If you are successful with your observations do remember to send them in to 
the BAA.

Stewart Moore