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Mercury remains a morning object for observers in the tropics and Southern Hemisphere for about the first 10 days of July. The nearest planet to the Sun may be spotted about 45 minutes before sunrise in the twilight sky low down above the east-northeastern horizon; brightening from magnitude -0.1 to -0.9 during this time period. Mercury is then unobservable for the remainder of the month as it moves closer ever in the sky to the Sun. The planet reaches superior conjunction on July 23rd.
From northern temperate latitudes Mercury is unobservable during July.
The diagram below shows the June / July morning apparition of Mercury from a latitude of 35S (approx. equal to Sydney, Cape Town and Santiago). Positions of the planet are displayed 45 minutes before sunrise.
NGC 2506 is a magnitude +7.6 rich open cluster located in the constellation of Monoceros. Although its member stars are faint the cluster itself appears quite bright and can be seen with a pair of binoculars. Through telescopes it's an impressive object and of all the Monoceros open clusters it's probably the finest. With an age of 1.1 billion years old this is an old cluster. For comparison, M45 (The Pleiades) in Taurus is a youthful 115 million years old with the Hyades cluster 625 million years old. However, NGC 2506 is not nearly as old as the 4 billion years of M67 in Cancer.
William Herschel discovered NGC 2506 on February 23, 1791. Locating the cluster can sometimes be a bit tricky as it's positioned in an area of sky devoid of bright stars. It can be found 5 degrees east-southeast of alpha Mon (α Mon - mag. +3.94) the brightest star in Monoceros. Located 19 degrees southwest of NGC 2506 is the brightest star in the sky, Sirius (α CMa - mag. -1.46). Although α Mon and Sirius are the brightest stars in their respective constellations the difference in apparent brightness between them is enormous, more than 100x.
Lynx is home to the fascinating globular cluster NGC 2419. Although visually faint and small what makes NGC 2419 special is its distance; at 275,000 light-years it's one of the furthest known Milky Way globulars. In fact, twentieth century American astronomer Harlow Shapley nicknamed it "The Intergalactic Tramp" believing it to have possibly broken away from the Milky Way and headed off into deep inter galactic space. However, recent observations indicate Shapley hypothesis was incorrect and NGC 2419 is still gravitationally bound to the Milky Way just moving in a highly eccentric orbit.
NGC 2419 or Caldwell 25 was discovered by William Herschel on December 31, 1788. It's located 275,000 light-years from the Solar System and about 300,000 light-years from the galactic centre, almost twice as far away as the Large Magellanic Cloud. At such a distance it's estimated NGC 2419 will take about 3 billion years to complete a single orbit around the centre of the galaxy.
NGC 2419 is positioned 7 degrees north and slightly east of Castor (α Gem - mag. +1.58) the second brightest star in Gemini. About 4 arc minutes west of NGC 2419 is a mag. +7.2 star with a double star of mag. +7.9 a few more arc minutes further west. Even Herschel with his super telescopes of the time couldn't resolve NGC 2419 into stars. William Parsons, the 3rd Earl of Rosse, using his 72-inch (1.83 m) reflecting telescope at Birr Castle in Ireland - the largest optical telescope in the world at the time - was first the first to do so in 1850.
NGC 4236 is a tenth magnitude barred spiral galaxy in Draco that's visible through small telescopes, although best seen with larger instruments. The galaxy was discovered by German born British astronomer William Herschel on April 6, 1793 and is a member of the Ursa Major or M81 group of galaxies that contains at least 34 galaxies, including spectacular M81 (Bode's galaxy) and M82 (Cigar galaxy).
NGC 4236 is located in the far northern constellation of Draco about 15 degrees north of the seven stars that form the famous "Plough" or "Big Dipper" asterism of Ursa Major. The galaxy is positioned two-thirds of the way along an imaginary line connecting stars lambda Dra (λ Dra - mag. +3.8) and kappa Dra (κ Dra - mag. +3.9). Star HD 106574 (mag +5.7) is 0.75 degrees directly north of NGC 4236.
Due to its high northerly declination, NGC 4236 is a Northern Hemisphere object. The best months to look for it are March, April or May although from most northern locations it's visible all year round and never sets. It can be seen from the Southern Hemisphere but only from latitudes north of 20 degrees south and even then appears low down above the northern horizon at best.
Mercury passed inferior conjunction on May 30th and was therefore positioned too close to the Sun to be observable. However, it moves rapidly out from the Sun so that two weeks later it becomes visible as a morning object for observers in the tropics and Southern Hemisphere. The planet subsequently climbs higher in the sky and brightens each day until it reaches a peak altitude on June 24th, the date of greatest elongation west (22.5 degrees from the Sun). Also on this day Mercury passes 2 degrees north of orange giant star Aldebaran (α Tau) the brightest star in the constellation of Taurus "the Bull". At magnitude +0.4 Mercury is half a magnitude brighter than the star with the pairing making a lovely early morning binocular / small telescope view.
It should also be noted that once past greatest elongation west, Mercury continues to brighten as it begins to draw into the Sun. For example, the planet shines at mag. +1.7 on June 15 but by month's end it has brightened to magnitude -0.1. From northern temperate latitudes, Mercury is a more difficult catch as it battles against the long morning twilight. The best time to try and catch it is for a few days on and around June 24th when it should be visible low down above the east-northeast horizon just before sunrise. A pair of binoculars will easily show the magnitude +0.4 planet although be careful not to confuse it with nearby Aldebaran.
NGC 2775 is a magnitude +10.5 spiral galaxy located in the constellation of Cancer, close to its border with Hydra. The galaxy is unusual in that it contains a very smooth nucleus with multiple spiral arms extending outwards from the central region. What makes the spiral arms interesting is their incredible complex detail, tightly wound structures and active star formation. Amateur astronomers should also keep their eye on this galaxy; it's been host to 5 supernovae explosions in the past 30 years and you never know when the next one will go off!
To find NGC 2775 look for the head of Hydra "the Sea Serpent". The asterism of stars that forms the head are ω Hyd (mag. +5.0), ζ Hyd (mag. +3.1), ρ Hyd (mag. +4.4), ε Hyd (mag. +3.4), δ Hyd (mag. +4.1), σ Hyd (mag. +4.5) and η Hyd (mag. +4.3). None of the stars are particularly bright but all can be seen with the naked eye. The galaxy is positioned a few degrees east and slightly north of this grouping.
NGC 2477 is a stunning open cluster located in the Milky Way rich constellation of Puppis. It's arguably the constellations finest cluster which also contains other superb examples such as M46, M47 and M93. At magnitude +5.8, NGC 2477 is faintly visible to the naked eye but easily seen with binoculars and a fantastic telescope object, especially in medium to large scopes. It's listed as number 71 in the Caldwell catalogue.
The cluster was discovered by French astronomer Nicolas Louis de Lacaille during his tour of South Africa in 1751-52. In total it contains about 300 stars packed into an area 27 arc minutes in diameter with the brightest member star shining at magnitude +9.8. The four-magnitude difference between the combined cluster magnitude and the brightest component is an indication of how rich the cluster is.
NGC 2477 is too far south to have been included in Charles Messier's catalogue, but if he had observed from a more southerly latitude than Paris he almost certainly would have noticed this striking object. Twentieth century America astronomer Robert Burnham described NGC 2477 as "probably the finest of the galactic clusters in Puppis".
NGC 188 is an open cluster located in the far northern constellation of Cepheus. John Herschel, the son of William Hershel, discovered it on November 3, 1831. He originally recorded it as h34 in his 1833 catalogue and then as GC92 in his General Catalogue of 1864. The cluster eventually became NGC 188 in John L.E. Dreyer's New General Catalogue of 1888.
NGC 188 is positioned 4.75 degrees from the North Celestial Pole and is the northernmost open cluster in the sky. It's effectively circumpolar from all Northern Hemisphere locations. However, it can never be seen from latitudes south of 5 degrees south.
Although comet Lovejoy has faded significantly since it reached naked eye brightness a few months ago it should still remain an easy telescope target during May. During the month the comet continues on its northerly path heading towards a close pass of Polaris and the North Celestial Pole.