Astronomy Now Home
Home Magazine Resources Store

On Sale Now!

The October 2014 issue of Astronomy Now is on sale! Order direct from our store (free 1st class post & to UK addresses). Astronomy Now is the only astronomy magazine specially designed to be read on tablets and phones. Download the app from Google Play Store or the Apple App Store.

Top Stories

Earthshine used to test life detection method
...By imagining the Earth as an exoplanet, scientists observing our planet's reflected light on the Moon with ESO's Very Large Telescope have demonstrated a way to detect life on other worlds...

Solid buckyballs discovered in space
...Astronomers using NASA’s Spitzer Space Telescope have detected a particular type of molecule, given the nickname “buckyball”, in a solid form for the first time...

Steamy water-world gets the Hubble treatment
...Hubble Space Telescope observations of a 7 Earth-mass planet find an unusual water-rich world swathed in a thick, steamy atmosphere...

Moon occults open cluster
Posted: 24 May 2012

Bookmark and Share

M67-occultation_400x261 The waxing crescent Moon passes in front of the star cluster M67 on the evening of 26 May. AN graphic by Greg Smye-Rumsby.

The Moon's perpetual eastwards journey against the starry background will cause it to pass in front of or occult many stars with a wide range of magnitudes. Occultations of really bright stars are not as common as one would think and those involving the planets, or at least those visible from the UK, are pretty rare. But to make up for this occasionally a well-known and bright deep sky object is occulted and on Saturday evening (26th) from 10pm it's the turn of the open cluster M67 in Cancer.

As with many 'on the face of it decent events', the observing circumstances from the UK are not ideal, with a waxing 5.5 day-old Moon relatively low over the western horizon and sinking further into the mire as twilight darkens. It starts to get dark around 10pm BST and the Moon has already bitten a large chunk out of M67. It will be difficult for visual observers to see many of the fainter cluster stars disappear behind the dark lunar limb; if you have a 150-mm 'scope then around 50 stars in M67 can be seen with the number swelling to in excess of 100 in a 300-mm. Of course at this low altitude atmospheric extinction, together with the twilight and lunar glare will wipe out the fainter stars, but it still will be well worth trying to observe the disappearance of as many stars as possible.

The clusters brightest star is magnitude +7.8 HIP 43519 and this is a good target to aim for. The disappearance of this star occurs at the dark limb at 10.48pm BST from London and at this time the Moon will be 15 degrees up. From Edinburgh, the star disappears about five minutes earlier. Astrophotographers should be able to capture some of the cluster stars alongside the Moon if a site with a clear, uninterrupted western horizon can be found.

M67 M67 pictured by Greg Parker.

M67 (NGC 2682) is the second Messier open cluster in Cancer, with the limelight usually hogged by the brilliant Beehive Cluster or M44. But M67 is well worthy of attention in its own right as it shines at a healthy magnitude +6.9 and covers 25 arcminutes of sky; at its distance of 3,000 light years this equates to an actual physical diameter of 21 light years. It is an ancient open cluster, one of the oldest known and is thought to be in the region of 3.7 million years old. Furthermore, it is thought to be less than half way through it's lifespan. Due to its great age M67 contains many well-evolved stars, with around 20 red giants and over 150 white dwarfs. This great diversity of stars has lead to M67 being one of the most important photometric clusters, with many of its stars being so-called 'standard stars' for the UBVRI photometric filter system.

The Planets
From tiny Mercury to distant Neptune and Pluto, The Planets profiles each of the Solar System's members in depth, featuring the latest imagery from space missions. The tallest mountains, the deepest canyons, the strongest winds, raging atmospheric storms, terrain studded with craters and vast worlds of ice are just some of the sights you'll see on this 100-page tour of the planets.

Hubble Reborn
Hubble Reborn takes the reader on a journey through the Universe with spectacular full-colour pictures of galaxies, nebulae, planets and stars as seen through Hubble's eyes, along the way telling the dramatic story of the space telescope, including interviews with key scientists and astronauts.

3D Universe
Witness the most awesome sights of the Universe as they were meant to be seen in this 100-page extravaganza of planets, galaxies and star-scapes, all in 3D!


© 2014 Pole Star Publications Ltd.