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Algol eclipse dates and times for July 2019
Algol (β Per) is a bright eclipsing binary system located in the northern constellation of Perseus and one of the best-known variable stars in the sky. Often referred to as the "Demon Star", most of the time it shines at mag. +2.1 but every two days, 20 hours and 49 minutes it suddenly dips in brightness to mag. +3.4, remaining dim for about 10 hours before returning to its original state.
Why the brightness change. The Algol system consists of at least three-stars (β Per A, β Per B and β Per C) with the orbital plane of Algol A and B directly in line with the Earth. The regular dips in brightness occur when the dimmer B star moves in front of and eclipses the brighter A star. There is also an extra dimension in that a secondary eclipse occurs when the brighter star occults the fainter secondary, resulting in a very small dip in brightness that can be detected with photo-electrical equipment.
Messier 40 - M40 - Winnecke 4 (Double Star)
M40 is one of three curiosities in the Messier catalogue (along with M73 and M102). It's a faint double star in the constellation of Ursa Major that was discovered by Charles Messier on October 24, 1764. Messier was searching for a nebula reported in the area by Johann Hevelius. Although he didn't see any nebula, Messier catalogued this double star instead. However, despite no nebulosity existing, the double star remained on the list.
American astronomer Robert Burnham called M40, "one of the few real mistakes in the Messier catalogue". He faulted Messier for including it, when he found no trace of a nebula and all he saw was a double star. In 1863, it was rediscovered by Friedrich August Theodor Winnecke and hence is sometimes referred to as Winnecke 4 or WNC 4. M40 is best seen from the Northern Hemisphere during the months of February, March and April.
Messier 27 - M27 - The Dumbbell Nebula (Planetary Nebula)
The Dumbbell Nebula or M27 is a showpiece object that's a popular visual and imaging target for amateur astronomers. It's arguably the finest planetary nebula in the night sky and was the first of its type to be discovered. The name derives from its resemblance to a dumbbell shape, but it has also been compared to an apple core and an hourglass figure. With a mag. of +7.4, M27 is the second brightest planetary nebula in the sky. Only the Helix Nebula (NGC 7293) in Aquarius is brighter. However, the Dumbbell Nebula has a higher surface brightness and therefore the easier of the two targets to spot.
Jupiter reaches opposition on June 10, 2019
Jupiter, in Ophiuchus, is a dazzling object this month and on June 10th the planet is at its best for the year when opposition is reached. On this day, it will shine at mag. -2.6 and be visible all night long. It rises in the east at sunset, reaches its highest point in the sky around midnight before setting in the west at sunrise. The planet is unmistakable to the naked eye, and easily brighter than any night time star. Due to its declination of -22 degrees, Jupiter is currently better seen from southern rather than northern latitudes.
At opposition, Jupiter is located 4.285 AU (641 million kilometers or 398 million miles) from Earth. Its apparent size spans an impressive 46.0 arc seconds. Of all other planets, only Venus can exhibit a greater apparent size than Jupiter.
Messier 57 - M57 - The Ring Nebula (Planetary Nebula)
M57, the Ring Nebula, is a showpiece planetary nebula located in the constellation of Lyra. It's probably the most well-known, studied and photographed object of its kind and a perennial favourite with amateur astronomers. The nebula is relatively bright at magnitude +8.8 and easy to locate. It can be found about 40% the way along an imaginary line connecting stars, Sheliak (β Lyr - mag. +3.5) and Sulafat (γ Lyr - mag. +3.2). For Northern Hemisphere observers, it appears high in the sky during the warm summer months although from southern latitudes it appears much lower down.
M57 was discovered by Antoine Darquier de Pellepoix in January 1779.
Algol eclipse dates and times for June 2019
Algol (β Per) is a bright eclipsing binary system located in the northern constellation of Perseus and one of the best-known variable stars in the sky. Often referred to as the "Demon Star", most of the time it shines at mag. +2.1 but every two days, 20 hours and 49 minutes it suddenly dips in brightness to mag. +3.4, remaining dim for about 10 hours before returning to its original state.
Why the brightness change. The Algol system consists of at least three-stars (β Per A, β Per B and β Per C) with the orbital plane of Algol A and B directly in line with the Earth. The regular dips in brightness occur when the dimmer B star moves in front of and eclipses the brighter A star. There is also an extra dimension in that a secondary eclipse occurs when the brighter star occults the fainter secondary, resulting in a very small dip in brightness that can be detected with photo-electrical equipment.
Algol is located in Perseus among the stars of the northern Milky Way. It's positioned west of mag. +0.1 Capella (α Aur) and southeast of the well known "W" of Cassiopeia. The finder chart below shows the position of Algol along with magnitude data of some surrounding stars for comparative purposes.
The Planets this Month - June 2019
Mercury
Mercury passed through superior conjunction during the second half of last month. The fast-moving planet reappears at the beginning of this month, low down towards the west after sunset. It remains visible throughout June, reaching its highest altitude above the horizon at greatest elongation east on June 23rd. During the visibility period Mercury dims in brightness. On June 1st, it shines at magnitude -1.1. By June 15th, it has reduced to magnitude -0.1 and by month end magnitude +0.9. Its angular size increases from 5.5 to 9.2 arc seconds during June.
On June 18th, Mercury passes just 1/5 of a degree north of fainter Mars (mag. +1.8). It's worth comparing the colour similarity of the two planets.
Venus
Venus, mag. -3.8, remains a morning object throughout June. However, the planet is now closing in on superior conjunction, which it attains in August. From southern locations, Venus rises 90 minutes before the Sun on the first day of the month. However, by month's end it rises only 50 minutes before the Sun. For northern based observers, the visibility period is even shorter.
On June 1st, the waning crescent Moon passes 3 degrees south of Venus.
Mars
Mars remains visible as an early evening object in western twilight throughout June, although from mid-latitude northern locations it will become increasingly difficult to spot during the second half of the month. The Red planet sets about 2 hours after the Sun at month's start, reducing to about an hour or less by month's end. Mars is long past its best and shines at only magnitude +1.8 with an apparent diameter of less than 4 arc seconds. Initially found in Gemini, it moves into Cancer on June 28th.
On June 5th, the waxing crescent Moon passes a couple of degrees south of the Moon. As previously mentioned, Mercury passes close by Mars on the 18th.
Messier 4 - M4 - Globular Cluster
M4 is a magnificent large apparent size globular cluster located amongst the rich Milky Way star fields of the constellation of Scorpius. With an apparent magnitude of +5.6, it can be spotted with the naked eye from dark sites. Even the simplest optical aid reveals an obvious non-stellar fuzzy object. In addition, not only is M4 bright but it's also one of the easiest globulars to find. It's located just 1.3 degrees west of striking red giant Antares (α Sco – mag. +1.0), the brightest star in Scorpius.
M4 was discovered by Philippe Loys de Chéseaux in 1746, who listed it as number 19 in his catalogue. It was also included in Lacaille's catalogue as Lacaille I.9 and subsequently added by Charles Messier to his famous list on May 8, 1764. M4 holds the distinction of being the first globular cluster ever to be resolved into stars by a telescope. Messier himself achieved the task, describing it "as a cluster of very small faint stars". Incidentally, this was the only globular cluster he could manage to resolve with his modest instruments.
Scorpius is best seen from tropical and Southern Hemisphere latitudes where it appears high in the sky during May, June and July. At least part of the constellation can be seen from most Northern Hemisphere latitudes, but it never rises particularly high above the horizon.
Messier 13 - M13 - Great Hercules Globular Cluster
M13 is a spectacular globular cluster and the best example of its type in the northern section of sky. It's the standout deep sky object in the constellation of Hercules and is sometimes referred to as the Great Hercules Globular Cluster. At mag. +5.8, it's just about visible to the naked eye and an easy binocular target. The popularity of M13 is mainly due to its declination; it lies at 36N and from northern temperate latitudes is well placed high in the sky during summer months. There are many other globulars larger and brighter than M13, but all are located in the southern section of the sky. As a result, they either never rise or appear low down from most North America, European and Asian locations. Hence, M13 is perhaps the most observed and studied globular cluster of all.
M13 was discovered by the Astronomer Royal, Sir Edmond Halley in 1714. He described it as "a little patch, but shews itself to the naked eye, when the sky is serene and the Moon is absent". Fifty years later, Charles Messier catalogued it on June 1, 1764.
Finder Chart for M13 - pdf format (credit:- freestarcharts)
The globular is easily found on the western side of the Hercules "Keystone" asterism, 2.5 degrees south of Eta Herculis (η Her) and along a line connecting Eta Herculis (η Her) with Zeta Herculis (ζ Her). When viewed through 10x50 binoculars, it appears as bright fuzzy ball with a well-defined center that's obviously non-stellar but without resolution. The cluster forms a right angled triangle with two nearby 7th magnitude stars. An 80 mm (3.1-inch) telescope shows M13 as a uniform extended hazy disk about 8 arc minutes across. At magnifications of about 100x, it looks like a zoomed in version of the binocular view. A 100mm (4-inch) telescope will resolve some of the outer stars, with many more visible in 150mm (6-inch) and 200mm (8-inch) instruments. The brightest star in M13 is variable star V11 (apparent mag. +11.95).