Aries
Arietis
Ari
The Ram

Introduction

Aries "the Ram" is a medium sized northern constellation of the zodiac that lies in a rather barren part of the sky. It contains mostly faint inconspicuous stars and is bordered by Taurus to the east, Perseus and Triangulum to the north, Pisces to west and Cetus to the south. The constellation was one of the original 48 constellations plotted by second century astronomer Ptolemy and today remains as one of the modern 88 constellations defined by the IAU (International Astronomical Union).

In Greek mythology, Aries represents the golden ram that was sent to rescue Phrixos and Helle, the children of King Athamus of Boeotia and his first wife Nephele. The King's second wife, Ino, was resentful and wanted the children, in particular, Phrixos killed. She induced a famine in the Kingdom and then falsified a message to the King indicating Phrixos must be sacrificed in order to save the land. Athamus was about to sacrifice his son when Aries - sent by Nephele - arrived. The ram managed to rescue Phrixos but Helle didn't survive. Phrixus then sacrificed the ram to Zeus with its Golden Fleece presented to King Aeëtes of Colchis. In a later myth, Jason and the Argonauts who actively sought the fleece, eventually managed to steal it. In ancient Egyptian astronomy, Aries was associated with the god Amon-Ra, who was depicted as a man with a ram's head and represented fertility and creativity. The Arabs knew Aries as a sheep and the Chinese as a dog.

The constellation contains a single second magnitude star, a third magnitude star, three fourth magnitude stars and over a dozen fifth magnitude stars. It contains no Messier objects and no bright deep sky objects. However, in its boundaries are numerous faint galaxies within the range of medium/large amateur scopes. For small scopes there are a handful of nice double stars with some bright ones.

Two thousand or so years ago Aries contained the vernal equinox, the point where the Sun annually passes from south to north across the celestial equator. This occurs on or about March 20th and signals the start of spring in the Northern Hemisphere and autumn in the Southern Hemisphere. Due to precession - the slight wobble of the Earth in space - the Vernal Equinox has now moved into neighbouring Pisces.

Aries covers 441 square degrees of sky ranking it 39th in overall size. It's best seen from Northern Hemisphere latitudes during October, November and December. There are several meteor showers that radiate from Aries, including the Daytime Arietids and the Delta Arietids.

Aries Star Chart

Aries Star Chart - pdf format

Interesting Stars

Brightest Stars

Hamal (alpha Ari) – at mag. +2.01 is the brightest star in Aries. It's a K2 orange giant about twice as massive as the Sun that's located 66 light-years distant. The star is variable although the range is extremely small (mag. +1.98 to +2.04). From 2000 BC to 100 BC, Hamal was positioned at the Vernal Equinox.

Sheratan (beta Ari) – is a spectroscopic binary system located 59.6 light-years from Earth. The primary star is a white A5V type main sequence star that completes a highly elliptical orbit with its companion every 107 days. The secondary star is intrinsically fainter and although its spectral type has not been accurately determined it could be F type or even G type similar to the Sun. The stars shine with a combined magnitude of +2.64.

Double Stars

Mesartim (gamma Ari) – is a striking double star consisting of equally bright (mag. +4.5) white-blue components. With a separation of 7.6 arc seconds the two stars are resolvable with any size scope and are widely considered to be one of the prettiest equal pairs. The combined magnitude is +3.9 and the stars lie about 164 light-years away.

Mesartim was one of the first double stars to be telescopically identified. English scientist Robert Hooke accidentally stumbled across it while searching for a comet in 1664.

Epsilon Ari (ε Ari) – is a challenging double of two almost equally bright white stars. Together they shine at magnitude +4.6 but are separated by only 1.4 arc seconds. Telescopes of 100mm (4-inch) should split them but nights of steady transparency are required. A magnification of 200x or so should suffice.

The Epsilon Ari system is located 330 light-years distant. Both stars are classified as A2 V with the primary at magnitude +5.2 and the secondary magnitude +5.6. When first identified as a double by F.G.W. Struve in 1827 the two stars were separated by just 0.5 arc seconds.

Lambda Ari (λ Ari) – mag. +4.8 is located 2 degrees west of Hamal (α Ari). This wide separated double (40 arc seconds) is easily split with small telescopes. The primary star is white (mag. +4.9) and the fainter secondary yellow (mag. +7.7). The pair can be resolved with 7x50 binoculars although the task is much easier with 10x50 models due to increased magnification.

Lambda Ari is located 129 light-years distant.

Pi Ari (π Ari) – is a multiple star system about 800 light-years distant. The main star is a magnitude +5.3 blue giant star that's separated by 3.3 arc seconds from its magnitude +8.5 companion. For small telescopes owners this is a challenging split due to the faintness of the secondary and the closeness of the pair. A good quality 100mm (4-inch) refractor on good nights should do the trick but needs to be pushed towards the higher end of its magnification range.

A third fainter star with a separation 25.2 arc seconds (mag. +10.8) is visible in larger scopes. In addition, the primary itself is a spectroscopic binary making this a 4 star system.

30 Ari – a 6th magnitude wide double for small scopes. Both stars are white in colour (mag. +6.5 and +7.0). With a separation of 38 arc seconds they are resolvable with any size scope. The primary component is also a spectroscopic double itself and therefore it's a triple star system.

33 Ari – consists of a primary pure white star of magnitude +5.4 with a magnitude +8.4 companion separated by 24 arc seconds. With a combined magnitude of +5.3, it's just about visible to the naked eye. A small scope 80mm (3.1-inch) scope at about 50x magnification will easily split the pair.

41 Ari – at mag. +3.6 is the brightest star that makes up a small faint naked eye triangle along with 35 Ari (mag. +4.7) and 39 Ari (mag. +4.5). This grouping formed the basis of the short-lived and now obsolete constellation of the "Northern Fly" Musca Borealis. The fly hovered over the back of Aries was finally swatted for good at the beginning of the 20th century when the modern 88 constellations were defined.

A number of faint stars surround 41 Ari making it a multiple star but all except one are due to line of sight effects. The only true companion is separated from the main star by just 0.2 arc seconds and can't be seen visually but can be detected by spectroscopic methods.

The fainter surrounding stars visible through medium sized amateur scopes are of magnitudes +8.8 (sep. 121 arc secs), +10.6 (sep. 27 arc secs) and +11.0 (sep. 33 arc secs).

Variable Stars

U Ari – is a Mira type variable star that varies between magnitudes +7.2 and +15.2 over a period of 371 days. At its brightest it's easily visible with 7x50 or 10x50 binoculars. When faintest, a minimum 300mm (14-inch) scope is recommended to spot it.

It's located 1630 light-years distant.

R Ari – is another Mira type variable star that's 4100 light-years away. It varies between magnitudes +7.4 and +13.7 over 187 days. When at its brightest and like U Ari the star is easily visible with 7x50 or 10x50 binoculars.

SX Ari (56 Ari) – is an unusual variable star worth mentioning. It varies in brightness by only 0.1 magnitudes over a period of about a day. What makes this star interesting is it's a rotating helium variable star and the prototype of its class. About 50 such stars have so far been identified.

With an apparent magnitude of +5.8, SX Ari is faintly visible to the naked eye but the brightness variations are far too small to be noticed visually.

Deep Sky

Galaxies

NGC 772 – is the largest and brightest of the galaxies in Aries. It's a magnitude +10.3 type SA(s)b unbarred spiral galaxy visible in small scopes and in total spans 7.2 x 4.3 arc minutes of apparent sky. Located 105 million light-years from us, NGC 772 is an extremely large galaxy with an actual diameter of 220,000 light-years. For comparison this is twice the size of our Milky Way and 1.5 times the size of the Andromeda Galaxy (M31) the largest Local Group galaxy. NGC 772 is estimated to contain at least 1 trillion stars.

Locating NGC 772 is quite easy. The galaxy is positioned 2 degrees east-southeast of Mesartim (γ Ari) and forms a small right-angle triangle with Mesartim and Sheratan (β Ari). A 100mm (4-inch) telescope at low powers reveals a faint oval misty patch of light spread over 3 arc minutes. On nights of good seeing the nucleus appears well defined and surrounded by a hazy nebulosity representing the spiral arms. It's possible to glimpse the spiral arms using a 200mm (8-inch) scope but they are much easier to see in larger backyard scopes of 300mm (12-inch) aperture or more.

As a result of gravitational tidal forces probably from nearby satellite galaxy NGC 770 one of the spiral arms in NGC 772 is more developed that the others. It appears longer and slightly elongated in shape and as a result Halton Arp included NGC 772 in his Atlas of Peculiar Galaxies as Arp 78.

To date, two supernovae SN 2003hl and SN 2003iq have been observed in NGC 772.

NGC 772 Unbarred Spiral Galaxy (Stephen Leshin - sleshin.startlogic.com)

NGC 770 – observers with very large backyard scopes maybe able to spot NGC 770 in the same field of view as NGC 772. This is the largest satellite galaxy of NGC 772 but its small and faint, shining at a feeble magnitude +14.1 and spanning only 1.1 x 0.8 arc minutes. A 400mm (16-inch) scope reveals an object that looks like an out of focus star. At high magnifications it’s possible to notice a small amount of detail such as the nucleus.

NGC 821 – is a mag. +10.8 type E6 elliptical galaxy located in the far southern section of Aries close to the border with Cetus and Pisces. It's positioned 2.5 degrees north of star ξ1 Cet (mag. +4.3) and can be spotted with 100mm (4-inch) scopes appearing as a small faint round nebulous patch of light. NGC 821 has an apparent size of 2.5 x 1.7 arc minutes. When viewed with larger backyard scopes the surface appears uneven in brightness with some mottling visible.

The galaxy is 80 million light-years distant with an actual diameter of 60,000 light-years.

NGC 972 – is an inclined spiral galaxy at the northern section of the constellation. It's positioned 3.5 degrees northwest of double star 41 Ari (mag. +3.6). Located just off an imaginary line connecting NGC 972 and 41 Ari is star 35 Ari (mag. +4.7).

At magnitude +11.4, NGC 972 is best seen with at least a medium sized scope. Through a 200mm (8-inch) instrument it appears as an elongated misty envelope of nebulosity with a brighter centre just north of a faint double star. The galaxy covers 3.3 x 1.7 arc minutes but has a reasonably high surface brightness.

NGC 1156 – is another galaxy located near to star 41 Ari but this time in the opposite direction to NGC 972. It's an irregular object positioned 3 degrees southeast of the star. At magnitude +11.7 you would probably not expect much from NGC 1156 but be in for a pleasant surprise. Even small scopes show some details including a faint ghostly like halo surrounding a brighter core with a number of foreground stars also visible in the same field of view. On nights of good seeing, a 200mm (8-inch) scope reveals mottling with larger instruments displaying subtle texture in the halo.

NGC 877 – mag. +11.8 is a spiral galaxy 1.5 degrees southeast of 19 Ari (mag. +5.7). There are two 8th magnitude stars adjacent to NGC 877 and the galaxy appears in the same low power field of view as one of the stars. A 200mm (8-inch) scope shows little detail except for a slightly brighter core. Increasing the aperture does not significantly enhance the view although the galaxy appears larger and hints at structural details. It's located 180 million light-years distant.

Ultraviolet Image of NGC 1156 (NASA/GALEX)

NGC 678 and NGC 680 – are a pair of 12th magnitude galaxies very close together in the eastern part of the constellation close to the Pisces border. They are separated by only 5 arc minutes of apparent sky, which corresponds physically to about 200,000 light-years. NGC 678 and 680 are currently interacting with each other resulting in shape distortions. They are part of the NGC 691 group of galaxies and are both located 125 million light-years away.

Of the two, NGC 680 is an elliptical galaxy and the brighter at magnitude +11.9. It measures 1.8 x 1.6 arc minutes. Although larger in both apparent and absolute size, NGC 678 is not as bright as NGC 680. This spiral galaxy shines at magnitude +12.5 with an apparent size of 4.5 x 0.8 arc minutes. It appears almost edge on from our perspective.

Both galaxies are visible in medium sized telescopes but are fairly faint. What's noticeable are the different shapes; NGC 680 is essential round, NGC 678 needle like. A prominent dust lane bisects through NGC 678 and can be seen in larger amateur scopes.

NGC 678 and NGC 680 (Adam Block/Mount Lemmon SkyCenter/University of Arizona)

NGC 697 – is a barred spiral galaxy with an apparent magnitude of +12.0 that's located 2 degrees northwest of Sharatan (β Ari). A 200mm (8-inch) scope reveals a highly inclined thin elongated patch of light. It stands out quite well due to a reasonably high surface brightness. There is a 12th magnitude star positioned at the eastern edge of NGC 697.

The galaxy NGC 674 is widely believed to be a mistake entry in the NGC catalogue and though to be the same object as NGC 697.

Meteor showers

Aries is home to a number of meteor showers including the Daytime Arietids. This is one of the strongest showers that occurs during the day and lasts from May 22nd to July 2nd. At peak on June 7th at about 50 meteors per hour can be detected using radar techniques. However, it is possible to visually spot a few meteors before dawn towards the eastern horizon.

Of the nighttime Arietids all have low peak rates of the order of a few meteors per hour. This includes the Delta Arietids in December but it can produce some bright fireballs.

Aries Star Data Table

Henry Draper Catalogue (HD)Hipparcos Catalogue (HIP)BayerFlamsteedStruveNameRA (J2000)Dec (J2000)Visual Mag.Var.Var. Mag. RangePeriod (days)DoubleSep. (arc secs)PA (deg.)Mag. Primary. Sec
129299884Alpha Arietis13---Hamal02h 07m 10s23d 27m 45s2.01Y2.19 -> 1.98uncertain------------
116368903Beta Arietis6---Sheratan01h 54m 38s20d 48m 29s2.64---------------------
115028832Gamma Arietis5180Mesartim01h 53m 32s19d 17m 38s3.88---------Y7.614.52 / 4.58
1851913914Epsilon Arietis48333Epsilon Arietis02h 59m 13s21d 20m 26s4.63---------Y1.42105.17 / 5.57
119739153Lambda Arietis9---Lambda Arietis01h 57m 56s23d 35m 46s4.79---------Y40444.80 / 7.70
1754313165Pi Arietis42311Pi Arietis02h 49m 18s17d 27m 52s5.26---------Y3.31215.32 / 8.50
162461218930 Arietis30400530 Arietis02h 37m 01s24d 38m 50s6.48---------Y382756.50 / 7.02
166281248933 Arietis3328933 Arietis02h 40m 41s27d 03m 39s5.30---------Y23.63565.30 / 8.40
175731320941 Arietis41---41 Arietis02h 49m 59s27d 15m 38s3.61---------Y0.2 / 121 / 27 / 33290 / 233 / 230 / 2903.63 / 8.80 / 10.66 / 11.04
19737---U Arietis------U Arietis03h 11m 03s14d 48m 00s7.20Y15.2 -> 7.2371------------
1391310576R Arietis------R Arietis02h 16m 07s25d 03m 07s7.40Y14.3 -> 7.4187------------
198321489356 Arietis56---SX Arietis03h 12m 14s27d 15m 25s5.78Y5.78 -> 5.740.73------------

Aries Deep Sky Data Table

NGCTypeRA (J2000)RA (J2000)App. Mag.App. Size (arc mins)Distance (light-years)Actual Size (light-years)
772Unbarred Spiral Galaxy01h 59m 20s19h 00m 22s10.37.2 x 4.3105,000,000220,000
770Dwarf Elliptical Galaxy01h 59m 13s18h 57m 19s14.11.1 x 0.8105,000,00035,000
821Elliptical Galaxy02h 08m 21s10h 59m 44s10.82.5 x 1.780,000,00060,000
972Spiral Galaxy02h 34m 13s29h 18m 42s11.43.3 x 1.673,000,00070,000
1156Dwarf Irregular Galaxy02h 59m 42s25h 14m 11s11.72.6 x 1.715,000,00011,500
877Spiral Galaxy02h 17m 59s14h 32m 50s11.82.4 x 1.9180,000,000125,000
678Spiral Galaxy01h 49m 25s21h 59m 51s12.54.5 x 0.8125,000,000160,000
680Elliptical Galaxy01h 49m 47s21h 58m 14s11.91.8 x 1.6125,000,00065,000
697Barred Spiral Galaxy01h 51m 17s22h 21m 28s12.04.0 x 1.3130,000,000150,000

Sky Highlights - March 2017

Comet
Comet 41P/Tuttle-Giacobini-Kresak now visible with binoculars as it heads towards perihelion

Mercury
Mercury heading towards greatest elongation east

Minor Planet
Vesta now visible with binoculars and small telescopes.

The Planets
This Month's Guide

Algol Minima
Algol eclipse dates and times for March 2017

Northern Hemisphere
Evening
West:- Venus (mag. -4.8 to -4.1 - first half of month), Mars (mag. +1.3 to +1.5), Uranus (mag. +5.9), Mercury (mag. -1.5 to -0.4 - second half of month)
Midnight
Southeast:- Jupiter (mag. -2.3 to -2.5)
Morning
Southwest:- Jupiter
Southeast:- Saturn (mag. +0.5)

Southern Hemisphere
Evening
West:- Venus (first half of month), Mars, Uranus
Midnight
North:- Jupiter
East:- Saturn
Morning
West:- Jupiter
Northeast:- Saturn
East:- Neptune (mag. +8.0 - second half of month)

Deep Sky
Naked eye / binoculars:-
Melotte 111 - Mel 111 - The Coma Star Cluster (Open Cluster)
Messier 44 - M44 - The Praesepe (Open Cluster)

Telescopes:-
Messier 67 - M67 - Open Cluster
Messier 51 - M51 - The Whirlpool Galaxy (Spiral Galaxy)
Messier 97 - M97 - The Owl Nebula (Planetary Nebula)
Messier 101 - M101 - The Pinwheel Galaxy (Spiral Galaxy)
Messier 65 – M65 – Spiral Galaxy
Messier 66 - M66 - Intermediate Spiral Galaxy
Messier 95 - M95 - Barred Spiral Galaxy
Messier 96 - M96 - Intermediate Spiral Galaxy
NGC 4244 - Spiral Galaxy
NGC 4565 - Needle Galaxy - Spiral Galaxy

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