WhatTheStar

M 28 Deep sky · Globular cluster in Sagittarius · M 28 · NGC 6626

M 28

A compact globular cluster above the Teapot’s lid, and the first globular in which a millisecond pulsar was found.

Finder chart of M 28: about 6° of sky with north up and east to the left, M 28 ringed at the centre, stars to magnitude 6.5, with Kaus Borealis and Namalsadirah named, and M 22 marked. M 28Kaus BorealisNamalsadirahM 22
About 6° of sky, north up and east to the left, as you see it facing that way. Stars to magnitude 6.5.

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Type
Globular cluster
Designations
M 28 · NGC 6626
Constellation
Sagittarius
Apparent magnitude
7.7
Apparent size
11′
Position (J2000)
RA 18h 25m · Dec −24° 52′

The full Moon, about 31′ across, is 2.8 times as wide. The Sun passes 2° from it around late December, and for about 29 days of the year it sits within 15° of the Sun, lost in its glare.

Survey photograph of M 28: 19′ of sky, north up and east to the left, with the stars around it taken out
19′ of sky, north up and east to the left: the picture the sky map lays in as you zoom in, its stars taken out so the map’s own show through. Photo: DSS2 colour (STScI / Caltech / AAO; colour and HEALPix by CDS). Licence: DSS: © Caltech, AAO/UKSTU and AURA, by agreement; HiPS © CNRS/Unistra (ODbL).

When to see it

On the night of Fri 25 Jun 2027, when it is highest around midnight, on each city’s own clock:

FromRisesHighestSets
London GMT+1 21:34 01:11 · 14° 04:48
New York EDT 20:40 01:05 · 24° 05:31
Singapore GMT+8 19:19 01:16 · 64° 07:13
Sydney GMT+10 16:56 00:07 · 81° 07:18

Common questions

Can I see it from 50° north?
Yes. It rises and sets, and at its highest it stands 15° up in the south.
Can I see it from 35° south?
Yes. It rises and sets, and at its highest it stands 80° up in the north.
When is the best time of year to see it?
Around late June, when it stands opposite the Sun and is highest at midnight. It comes round about two hours earlier each month, so by late September it is highest in the early evening, and in late March not until the hours before dawn.
How bright is it?
Magnitude 7.7 in total, but that light is spread over 11′ of sky: on average 21.5 magnitudes per square arcsecond. Against a dark country sky that average stands out; a city’s glow drowns all but its brightest parts.
Naked eye, binoculars or telescope?
Binoculars. At magnitude 7.7 it is past the eye, but a 50 mm pair under a dark sky reaches about magnitude 11.0.

Look for

It sits just north-west of Kaus Borealis, the top of the Teapot. Binoculars show a small, fuzzy star.

Science

A millisecond pulsar is a dead star spun up by feeding on a companion. Crowded globular clusters, where stars pair up, are full of them.

Look for

From 50° north it climbs to 15°; from 35° north it climbs to 30°; from the equator it climbs to 65°; from 35° south it climbs to 80°.

Look for

Magnitude 7.7 against the faintest star each can show: the eye under a city sky, 4.5 (3.2 short); the eye under a dark country sky, 7.0 (0.7 short); 50 mm binoculars under that dark sky, 11.0 (3.4 to spare); a 100 mm telescope there, 12.5 (4.9 to spare). Those limits are for a point of light; its light is spread over its whole size, so it needs some of that margin in hand. Through 7×50 binoculars, whose field is about 7.1° across, it spans 3% of the field’s width; through a 100 mm telescope at 50×, a field about 1° across, it spans 19% of the field’s width.

Words used here

Its constellation

Nearby in Sagittarius

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