The Abell catalogue is an all sky catalogue of galaxy clusters. It contains 4,073 rich clusters with a nominal redshift of z less than or equal to 0.2. Each galaxy cluster must meet certain criteria of richness, compactness, distance and galactic latitude to be included.

For example, to meet the richness criteria a cluster must contain at least 30 galaxies within a set magnitude range. There are six groups defined:
Group 0: 30-49 galaxies
Group 1: 50-79 galaxies
Group 2: 80-129 galaxies
Group 3: 130-199 galaxies
Group 4: 200-299 galaxies
Group 5: more than 299 galaxies

The original Northern Survey was published in 1958 by George O. Abell and contained 2,712 clusters of rich galaxies. A later Southern Survey added a further 1,361 clusters. The catalogue is of interest to amateur astronomers with large aperture scopes since it contains challenging galaxies that require dark locations.

Hubble Frontier Fields view of Abell 2744 (NASA, ESA, and J. Lotz, M. Mountain, A. Koekemoer, and the HFF Team (STScI))

Glossary A B C D E F G H I J K L M N O P Q R S T U V W X Y Z


Sky Highlights - February 2017

Comets
Comet Encke (2P/Encke) now visible in the western sky during evening twilight
Now is the last good chance to see comet 45P/Honda-Mrkos-Pajdusakova before it dramatically fades

Conjunction
Mars passes less than 1 degree north of Uranus on February 27th

Minor Planet
Vesta now visible with binoculars and small telescopes.

The Planets
This Month's Guide

Algol Minima
Algol eclipse dates and times for February 2017

Northern Hemisphere
Evening
Southwest:- Venus (mag. -4.8), Mars (mag. +1.1 to +1.3), Uranus (mag. +5.9)
Midnight
East:- Jupiter (mag. -2.1 to -2.3)
Morning
South:- Jupiter
Southeast:- Saturn (mag. +0.6)

Southern Hemisphere
Evening
West:- Venus, Mars, Uranus
Midnight
East:- Jupiter
Morning
North:- Jupiter
East:- Saturn, Mercury (mag. -0.2 - first half of month)

Deep Sky
Naked eye / binoculars:-
Messier 45 - M45 - The Pleiades (Open Cluster)
The Hyades - Open Cluster
Messier 44 - M44 - The Praesepe (Open Cluster)
Messier 35 - M35 - Open Cluster
Messier 42 - M42 - The Great Orion Nebula (Emission/Reflection)

Small telescopes:-
Messier 36 - M36 - Open Cluster
Messier 37 - M37 - Open Cluster
Messier 38 - M38 - Open Cluster

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Current Moon Phase

CURRENT MOON

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