M68 (NGC 4590) Observing Guide — Globular Cluster in Hydra

Overview

M68 is a globular cluster in Hydra, catalogued as NGC 4590. Shining at magnitude 7.8 and about 33,000 light-years away, it is one of the southern-sky globular clusters that peaks in spring — an alternative to the summer-dominated globular calendar and a worthwhile target for observers who want globulars during the galaxy season.

Like all globular clusters, M68 is an ancient, gravitationally bound system orbiting the Milky Way's outer halo. Its loose concentration makes it one of the more resolvable Messier globulars for moderate-aperture instruments.

Basic Data

Physical Characteristics

M68 lies about 33,000 light-years from Earth and glows at magnitude 7.8. It belongs to the lower concentration classes, meaning its stars spread relatively gradually outward from the core — a feature that aids resolution with smaller instruments. Its stellar population is dominated by old red giants estimated at over 10 billion years old.

Observing Guide

Finding It

M68 sits in Hydra and transits around 8–10 PM in spring. Beta Corvi provides a useful anchor — M68 lies about 3.5 degrees to the north-northwest. The cluster is relatively low in the southern sky for northern hemisphere observers, so a clear southern horizon and timing near transit are helpful.

Observing Tips

M68's loose concentration means individual stars at the outer fringe become apparent at lower magnification than highly compressed globulars. Use the gradually widening scatter of stars from center to edge as the primary identification feature. Full dark-adaptation is essential for appreciating the outer halo extent.

Recommended Equipment

A 60mm telescope shows M68 as a bright, diffuse glow. At 100mm or more under dark skies, the outer fringe begins to resolve into individual stars. The globular's large angular size makes it amenable to moderate rather than very high magnification.

Astrophotography Tips

Prime-focus photography with a tracking setup captures M68 cleanly. Moderate individual exposures stacked in software reveal the cluster's full extent and resolved outer stars. Wide-field compositions that include the surrounding Hydra star field add context to the result.

Summary

M68 is spring's primary globular cluster offering — a loose, resolvable system in Hydra that provides a counterpoint to the galaxies that dominate the spring deep-sky calendar. Its low altitude from northern latitudes is a challenge but not an obstacle for observers who take the time to catch it near transit.