Deep-Sky Objects in Aries

NGC 772
Image Credit: NGC 772 by Stephen Leshin

Aries is the 39th biggest of the 88 recognized constellations, and the second smallest of the zodiacal constellations, taking up an area of just 441 square degrees of the sky. The brightest star in the constellation, Hamal (Alpha Arietis), is a K-type orange giant with an apparent visual magnitude of +1.98 from a distance of about 66 light years away, which also makes it the 48th brightest star in the entire night sky. Hamal is now perhaps best known for the fact that between 2,000 BC and 100 BC, it marked the point of the Vernal Equinox.

Aries is situated between Pisces to its west, and Taurus to its east, with the constellation visible from latitudes of between +90° and -60, although it is best seen at about 9 PM Local Time during the month of December. While Aries has no Messier objects, it does contain a small number of interesting deep-sky objects, the most notable of which are explored in this list.

NGC 772 (Arp 78)

Located about 130 million light years away, NGC 772 is an unbarred spiral galaxy that is roughly 200,000 light years in diameter, making this galaxy almost twice as big as the Milky Way. NGC 772 has a distinctive highly evolved spiral arm populated by clusters of young blue star clusters, with this single prominent feature believed to be the result of tidal interactions with one or more of its satellite galaxies, including NGC 770, a dwarf elliptical galaxy separated from the larger galaxy by a distance of 113,000 light-years.

While the galaxy’s nucleus is thought to be a star forming H II region, it is likely that the central region of the galaxy is in fact only a transient object. In 2003, there were two supernovae events seen in NGC 772 over just a three-week period, namely SN 2003 hl and SN 2993 iq.

Look for this magnitude 10.3 galaxy at RA: 01h 59m 19.6s and Dec.: +19° 00′ 27″, a short distance to the southeastward of the star Beta Arietis. Note that while the satellite galaxy NGC 770 is described as having a high surface brightness, its magnitude of 14.2 might make it difficult to spot from urban areas.

NGC 1156

NGC 1156This dwarf galaxy located around 17 million light-years away is classified as an ibm-type Magellanic-type irregular galaxy. While it has a far larger than usual core for galaxies of this type, the most notable aspect of NGC 1156 is that it contains areas of contra-rotating gas, which is thought to be the result of an interaction with a passing, gas-rich galaxy sometime in the distant past.

During a recent survey, investigators identified a possible satellite galaxy close to NGC 1156, which appears to be a dark galaxy, which are a class of galaxy that contain so few stars that they can only be identified by the large volumes of gas they contain. It is perhaps then not surprising that only a handful of so-called dark galaxies have been positively identified, since they are easy to confuse with large clouds of molecular gas and dust.

Look for the magnitude 12.3 galaxy NGC 1156 at RA: 02h 59m 42.2s and Dec: +25° 14′ 14″, a short distance to the northwestward of the star Delta Arietis.

NGC 972

NGC 972Also informally known as “The LED Lamp Galaxy”, NGC 972 has yet to be classified, although is believed to be a spiral galaxy. Recent studies have shown that it contains several active starburst regions with high rates of star formation. For instance, the rate of star formation is estimated to be 0.23 solar masses per year in the inner core, and as high as 2.1 to 2.7 solar masses per year in the innermost 3.6 kiloparsecs of the galaxy. Studies have also shown that the star formation process in the inner regions of NGC 972 is of a recent origin, with the stars in this area being only about 5.4 million years old.

Look for magnitude 12.1 NGC 972 at RA: 02h 34m 13,4s and Dec: 29° 18′ 41″. In large amateur telescopes under dark skies, the galaxy’s apparent dimensions will be about 3.3′ × 1.6′.

NGC 678

NG 678 is an edge-on spiral galaxy located around 130 million light-years from Earth that has an apparent magnitude of 13.35. It is 171,000 light-years across, with one of its distinguishing features being its prominent dust lane.

NGC 680

Also located around 130 million light-years away, NGC 680 is an elliptical galaxy that’s separated from NGC 678 by about 200,000 light-years. It is 72,000 light-years wide, and has an apparent magnitude of 12.9.

NGC 691

This spiral galaxy is notable for its multiple spiral arms, and its bright core, although being so diffuse means it has a low surface brightness. NGC 691 is 126,000 light-years across, and lies 124 million light-years away.

Other DSOs

Other notable galaxies in the constellation Aries includes the gravitationally interacting pair NGC 877 and NGC 876; and the similarly interacting NGC 935 and IC 1801. Aries also contains the elliptical galaxy NGC 821, and the dwarf galaxy Segue 2.

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