Sky Notes for July 2013 with James Abbott #stargazing
Following the Summer Solstice on June 21st, the nights start to draw in again through July but only very slowly. For most of July the Sun still sets after 9 pm BST.
Venus remains visible throughout July but will always be low in the North West in the evening dusk, setting about an hour after the Sun. Although our “Sister planet” is on the far side of its orbit around the Sun from Earth, it is the brightest object in the night sky apart from the Moon and so with a clear Western horizon it should be visible in the twilight.
Saturn is still fairly well placed at the start of July but by the end of the month is starting to sink low in the sky soon after 11 pm BST. The first quarter Moon is nearby on the evening of the 16th. Full Moon is on the night of the 22nd/23rd, low down in the Southern sky.
As the Moon wanes in the last week of July and leaves the late evening skies, clear nights will reveal the Northern Milky Way almost overhead. From truly dark sites the Milky Way reveals a lot of detail but from Essex we have to cope with an often murky atmosphere and of course light pollution.
But away from streetlights in the Essex countryside it is possible to see some detail in the Milky Way. Looking at Cygnus, the individual stars we can see are almost all relatively close to us in space, typically tens or hundreds of light years away with a few exceptions such as the supergiant Deneb which is several thousand light years distant. The hazy Milky Way is made up of millions of faint stars much further away, forming the spiral arms of our galaxy. Through Cygnus, an obvious dark rift in the Milky Way can be seen, caused by huge clouds of dust obscuring the spiral arm stars.
Late July is also a good time, with hopefully some warm evenings, to watch for meteors – which are also caused by dust, but obviously much closer to home. As well as the Perseids which starts in late July there are several other showers active. Almost all meteor showers are streams of dusty debris left behind in the orbits of comets. The Earth crosses a number of these through the summer and each shower is different depending on the way in which the comet orbit intersects that of the Earth and the physical properties of the comet dust. Perseids strike our atmosphere at a velocity of 60 kilometers per second. The energy produced as the dust grains burn up means we can see them easily even though they are over 80 km up in the atmosphere.
Fragments of meteor dust drift down to the surface of the Earth and across the whole planet material from space amounts to many tonnes per day.
James Abbott is an astronomer, NEAS member and CfDS Regional Information Officer.
Posted on 8 July, 2013, in Astronomy News, Observing News, Stargazing and tagged cygnus, moon, perseids, saturn, summer triangle, venus. Bookmark the permalink. Comments Off on Sky Notes for July 2013 with James Abbott #stargazing.