Guides / Star Charts
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Lyrids meteor shower peaks on the night of April 21st / 22nd, 2018
The annual Lyrids meteor shower peaks during the night of April 21st / 22nd. This year's event promises to be reasonably good as the first quarter Moon sets a couple of hours after midnight and won't significantly interfere. Normally, you would expect to see up to 20 meteors per hour under ideal conditions. However, if you're lucky you might even spot a couple of fireballs. Occasionally the shower produces a few, that brilliantly streak through the sky, casting shadows as they disintegrate in the upper atmosphere.
The Planets this Month - April 2018
Mercury
Mercury passes inferior conjunction on April 1st, but it doesn't take long before the planet rises out of the Sun's glare. It should be visible, low down above the eastern horizon before sunrise from tropical and southern latitudes by about the middle of the month. The planet subsequently brightens and climbs higher in the sky each morning until it reaches a peak altitude on April 29th, the date of greatest elongation west (27 degrees from the Sun). On this day, from latitude 35S (approx. equal to Sydney, Cape Town and Santiago), Mercury shines at mag. +0.3 and appears 17 degrees above the horizon, 45 minutes before sunrise. The very thin waning crescent Moon passes 4 degrees south of the planet on April 14th. On the 23rd, Mercury reaches aphelion when it's 0.467 AU (approx. 69.9 million kilometres or 43.4 million miles) distant from the Sun.
From northern temperate latitudes, this is not a great apparition due to the shallow angle of the ecliptic to the horizon and even at greatest elongation the planet appears low down. Observers will struggle to easily spot it.
Algol eclipse dates and times for April 2018
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 63 - M63 - The Sunflower Galaxy (Spiral Galaxy)
M63, also known as the Sunflower Galaxy, is a beautiful and spectacular spiral galaxy in the constellation of Canes Venatici. Along with M51, M94 and M106, it's one of four Messier galaxies located in the constellation. Of these, M51 or the Whirlpool Galaxy, is a much-studied interacting grand design spiral that claims the title of finest galaxy in Canes Venatici. However, M63 is only marginally fainter and not far behind its more illustrious neighbour. In addition, M63 and M51 are gravitationally bound and along with at least 6 other smaller galaxies they form the M51 Group of galaxies.
M63 is best seen from the Northern Hemisphere during the months of March, April or May.
Messier 97 - M97 - The Owl Nebula (Planetary Nebula)
M97, also known as the Owl Nebula, is a famous planetary nebula located in the constellation of Ursa Major. It was discovered by Pierre Mechain on February 16, 1781 and is one of only four planetary nebulae listed in the Messier catalogue. Although not particularly bright at magnitude +9.9, it's a superb object and regarded as one of the most complex examples of its type. The name Owl Nebula was first coined in 1848 by William Parsons the 3rd Earl of Rosse, who noticed owl-like "eyes".
Locating M97 is easy as it's positioned only 2.5 degrees southeast of bright star Merak (β UMa - mag. +2.3). This is the southwest corner star of the bowl of the famous Plough or Big Dipper asterism of Ursa Major. In the same wide field telescope field of view, 50 arc minutes northwest of M97, is barred spiral galaxy M108 (mag. +10.2).
The Owl Nebula is best seen from Northern Hemisphere latitudes during the months of March, April and May. From latitudes north of 35N, it's circumpolar and therefore never sets.
Polaris - Alpha Ursae Minoris - α UMi
Polaris is only the 46th brightest star in the night sky, but it's an important one that's been of immense value to navigators. This star is the current Northern Pole Star since it's positioned only three quarters of a degree from the North Celestial Pole. Polaris is edging closer still and on March 24, 2100 it will be less than half a degree away, before starting to slowly drift away.
Polaris is a multiple system located 434 light-years away that shines with a combined magnitude of +1.97. The dominant main component, α UMi Aa, is usually referred to as simply "Polaris" and is a type F7Ib yellow-white supergiant. It's a classical Cepheid variable with a period of slightly more than 4 days. There is evidence that the brightness variation has changed over recent times. Before 1960, it was about 0.15 magnitudes but a few years later it was down to 0.05 magnitudes. Now it appears to be back on the rise and with modern imaging and measuring techniques, it will be interesting to see how it changes in the coming years. Since one of the nearest Cepheid's, Polaris has been heavily studied by astronomers. The main star is 2,300 more luminous than the Sun and 46 times larger.
NGC 4631 - The Whale Galaxy - Barred Spiral Galaxy
NGC 4631, also known as the Whale Galaxy, is a magnitude +9.3 edge-on barred spiral galaxy in the constellation of Canes Venatici. It has a high surface brightness and therefore is a good target for small scopes. Larger instruments reveal numerous dust clumps and mottling. The central region of NGC 4631 is a starburst region, where intensive star formation is currently taking place.
William Herschel discovered the Whale Galaxy on March 20, 1787. It's located 28 million light-years away and is best seen from northern latitudes during the months of March, April or May.
Finder Chart for NGC 4631 - pdf format (credit:- freestarcharts)
NGC 2403 - Intermediate Spiral Galaxy
NGC 2403 is an intermediate spiral galaxy located in the faint northern constellation of Camelopardalis. This superb mag. +8.4 object is about 10 Million light-years distant and is an outlying member of the M81 group of galaxies that also includes M81 "Bode's Galaxy" and M82 "the Cigar Galaxy". Since it's relatively near and almost face-on from our perspective, NGC 2403 displays intricate details in its spiral arms especially through large amateur scopes.
NGC 2403 was discovered on November 1, 1788 by William Herschel and is best seen from northern latitudes during the months of January, February and March. It's number 7 in the Caldwell catalogue.
NGC 2419 - The Intergalactic Tramp - Globular Cluster
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.
