[BAA-ebulletin 00860] Observing opportunity. See Neptune in the morning sky

[Rick]

[BAA-ebulletin 00860] Observing opportunity. See Neptune in the morning sky
(c) 2015 British Astronomical Association    http://www.britastro.org/

Locating the outer planets , the ice giants Uranus and Neptune, can sometimes be tricky, particularly for the binocular user with no firm platform for star hopping or if using a mount without go-to or setting circles. What is needed to make things easier is a bright sky marker to act as a reference point. A few weeks ago Venus acted as such a reference beacon for Uranus and on June 9 the Moon acts as a suitable marker for Neptune.

Neptune at magnitude 7.9 and with a disk diameter of just over 2 arc seconds will appear star-like through low power binoculars, but if you are using a telescope it should show a tiny bluish disk while the stars remain as points of light - albeit slightly bloated and wobbly ones if the seeing is poor!

This activity all takes place in the very early morning so is particularly suited to insomniac observers. The start of civil twilight on June 9 is at 02:50 UT with the Sun rising at 03:37 UT (times based on my Essex village of Thorpe-le-Soken). The Moon will be 56% illuminated at this time, and Neptune will be found 2.5 degrees below it, around 17 degrees above the south-eastern horizon at 02:30 UT (03:30 BST). There will be some field stars to confuse you, in particular magnitude 3.8 lambda Aquarii which lies a similar distance below the Moon but 2 degrees to the east of Neptune (this bulletin also appears as a news article on the BAA website and a star chart of the area is given there). The position of Neptune on June 9 is RA 22h 46m 38s and Dec 8 deg 36 arcmin 29 arcsec.

Although Neptune will remain visible in the morning sky for a few more weeks the Moon will unfortunately move on and no longer point the way, so let's hope for clear skies on Tuesday morning.

Stewart Moore
BAA Council