Guides / Star Charts

Contributions

If you like the website and want to contribute to the running costs then please do so below. All contributions are most welcome.

PayPal - The safer, easier way to pay online.

Jupiter, in Libra, is a dazzling object this month and on May 9th the planet is at its best for the year when opposition is reached. On this day, it will shine at mag. -2.5 and 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 -16 degrees, Jupiter is currently better seen from southern rather than northern latitudes.

Jupiter as imaged by Hubble Space Telescope on April 21, 2014 (credit:- NASA, ESA, and The Hubble Heritage Team (STScI/AURA))

Mercury

Mercury reached greatest elongation east at the end of April, and from southern and equatorial latitudes the planet remains well placed for observation in morning twilight during the first half of May. On May 1st, it rises some 2 hours before the Sun. The period of visibility then decreases slightly each subsequent morning, until the planet is lost to the bright twilight sometime during the third week of the month. Between May 1st and 15th, Mercury's brightness increases from magnitude +0.3 to -0.3. On the morning of May 14th, the thin waning crescent Moon, Mercury and Uranus (mag. +5.9) will be within 5 degrees of each other. Keen eyed observers may be able to spot all three objects in the same binocular field of view, although Uranus will be challenging since it's over 250x fainter than Mercury. Of course, please take extreme care when using binoculars at this time of day, and always ensure that the Sun is below the horizon before looking.

From northern temperate locations, Mercury is not well placed for observation but may be glimpsed low down above the western horizon during the first few days of the month.

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 System (credit:- Dept. of Physics and Astronomy - Univ. of Tennessee at Knoxville)

M82 is a superb irregular galaxy located in the constellation of Ursa Major. It has an apparent magnitude of +8.4 and is visible with binoculars. Separated by only 38 arc minutes from M82 is an even brighter and equally stunning galaxy, M81. However, they are very different objects. M81 (mag. +6.9) appears almost face-on, is of a grand spiral deign and therefore exhibits prominent near perfect and well defined spiral arms. On the other hand, M82 (mag. +8.4) is edge on, appears long and thin and is known as the Cigar galaxy. It's classified as the prototype starburst galaxy in which stars are forming at exceptionally high rates.

These two objects are the largest members of the Ursa Major or M81 group of galaxies, which at a distance of 11.7 million light-years is one of the closest groups of galaxies beyond the Local Group. Spatially, M81 and M82 are close and are physically separated by only about 150,000 light-years. When seen through binoculars and telescopes at low powers they form a striking pair.

Both M81 and M82 were discovered by Johann Elert Bode on December 31, 1774. Pierre Mechain then independently rediscovered them in August 1779. He reported his observations to Charles Messier, who added both galaxies to his catalogue on February 9, 1781. Finding M82 is not particularly difficult as the Plough asterism of Ursa Major can be used as a starting point. First focus on Dubhe (α UMa - mag. +1.8) the northwest corner star of the bowl. The M81 / M82 pair is located 10 degrees northwest of this star, with M82 positioned directly north of M81.

The galaxies are best seen from the Northern Hemisphere during the months of March, April and May. From locations north of +21 degrees they are circumpolar and always visible.

M81, also known as Bode's galaxy, is a large bright spiral galaxy located 11.8 million light-years away in the constellation of Ursa Major. With an apparent magnitude of +6.9, it's easily visible with binoculars and is a superb target for all sizes of telescopes. This galaxy is a striking example of a grand design spiral and exhibits near perfect and well defined spiral arms.

In the same binocular and low magnification telescope field of view as M81 is another prominent galaxy, M82. At mag. +8.4, M82 is fainter than M81 and a very different type of galaxy. It's a starburst galaxy, in which stars are been formed at exceptionally high rates. Also known as the Cigar galaxy, M82 is the prototype object and provides a striking contrast to the near perfect spiral shape of M81. Together, they form a popular visual and imaging target for amateur astronomers.

Both M81 and M82 were discovered by Johann Elert Bode on December 31, 1774. Pierre Mechain independently rediscovered them in August 1779. He reported his observations to Charles Messier who added them both to his catalogue on February 9, 1781.

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.

View towards the east just after midnight on April 22, 2018 from northern temperate latitudes (credit:- stellarium/freestarcharts)

Unlike sporadic meteors that originate from anywhere, periodic meteors can always be traced back to the same part of the sky, known as the (radiant). Therefore, spotting this type of shooting star should be easy; just look directly at the radiant. The problem is although the meteors do originate from the radiant, they almost always streak many degrees from away in a different part of the sky. Therefore a good tip is to lie down on a reclining chair, look skywards and scan a large area of sky surrounding the radiant, without looking directly at it.

The Lyrids radiant is located inside Hercules. It's positioned close to the border with Lyra and only 6 degrees from Vega (mag. 0.0), the 5th brightest star in the sky. The best time to observe is around midnight and during the early hours of the morning.

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 (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 System (credit:- Dept. of Physics and Astronomy - Univ. of Tennessee at Knoxville)

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.

M63 The Sunflower Galaxy (credit:- GALEX/NASA)