A Tour of the Messier Catalog

~~ in ~~

Eight Spellbinding and Enlightening Episodes

~~ This Being Episode Six ~~

Voyage to the Center of the Galaxy

M11 – Open ClusterConstellation – Scutum

Right Ascension 18 : 51.1 (h:m)

Declination -06 : 16 (deg:m)

Distance 6.0 (kly)

Visual Brightness 6.3 (mag)

Apparent Dimension 14.0 (arc min)

• “Wild Duck Cluster”

• One of the richest and most compact open clusters

• About 3,000 stars

• An observer in the center of the cluster would see about 40 stars from 3 to 50 times brighter than Sirius in the night sky! And several hundred 1st

magnitude!Brian Kimball

M26 - Open ClusterConstellation – Scutum

Right Ascension 18 : 45.2 (h:m)

Declination -09 : 24 (deg:m)

Distance 5.0 (kly)

Visual Brightness 8.0 (mag)

Apparent Dimension 15.0 (arc min)

• Tight, bright cluster of about 90 –100 stars

• Has a small, 2’ circular dark ‘gap’in the center – most probably intervening dark matter

Brian Kimall

NOAO/AURA/NSF

M16 – Open ClusterConstellation – Serpens

Right Ascension 18 : 18.8 (h:m)

Declination -13 : 47 (deg:m)

Distance 7.0 (kly)

Visual Brightness 6.4 (mag)

Apparent Dimension 7.0 (arc min)

• Cluster is associated with the Eagle Nebula

• Early observers didn’t detect the nebula, only the cluster!

• A small scope will reveal about 20 stars in the cluster, which were formed from the nebula

• Burnham also calls it the ‘Star-Queen Nebula’ – see the dark throne in the center with the Queen sitting on it?

• Nebula was subject of the famous Gas Pillars photo from Hubble

NOAO/AURA/NSF

M17 – Emission NebulaConstellation – Sagittarius

Right Ascension 18 : 20.8 (h:m)

Declination -16 : 11 (deg:m)

Distance 5.0 (kly)

Visual Brightness 6.0 (mag)

Apparent Dimension 11.0 (arc min)

• Also called the Swan or Horseshoe or Omega Nebula

• Both emission and reflection nebula

• Visually, you can see a loop off of the main bar that makes it look like an Omega shape, or a swan’s neck.

NOAO/AURA/NSF

Joseph Liu

Brian Kimball

M18 – Open ClusterConstellation – Sagittarius

Right Ascension 18 : 19.9 (h:m)

Declination -17 : 08 (deg:m)

Distance 4.9 (kly)

Visual Brightness 7.5 (mag)

Apparent Dimension 9.0 (arc min)

• Very loose cluster, only about 20 stars

• And because these are hot, bright stars, it is a very young cluster, only about 30 million years old

NOAO/AURA/NSF

M24 – Star CloudConstellation – Sagittarius

Right Ascension 18 : 16.9 (h:m)

Declination -18 : 29 (deg:m)

Distance 10.0 (kly)

Visual Brightness 4.6 (mag)

Apparent Dimension 90.0 (arc min)

• The Sagittarius Star Cloud

• Located between the Swan Nebula – M17, and the Lagoon Nebula – M8

• A very rich 2° x 1° field near the galactic center

• Contains the open cluster NGC 6603, and is viewed through gaps - or a ‘hole’ in the intervening dust clouds

• Lies in the next spiral arm in towards the center of the galaxy – the Sagittarius-Carina Arm

NOAO/AURA/NSF

M25 – Open ClusterConstellation – Sagittarius

Right Ascension 18 : 31.6 (h:m)

Declination -19 : 15 (deg:m)

Distance 2.0 (kly)

Visual Brightness 4.6 (mag)

Apparent Dimension 32.0 (arc min)

• A bright cluster, but did not get included in the General Catalog of John Herschel, so it is the only Messier object that does not have an NGC ID, only an IC – or Index Catalog - number

• Contains about 50 stars brighter than 12th magnitude

NOAO/AURA/NSF

M23 – Open ClusterConstellation – Sagittarius

Right Ascension 17 : 56.8 (h:m)

Declination -19 : 01 (deg:m)

Distance 2.15 (kly)

Visual Brightness 6.9 (mag)

Apparent Dimension 27.0 (arc min)

• A bright, rich, irregularly shaped cluster

• One of Messier’s authentic discoveries

• Contains about 150 members, and is about 200 million years old

• Many different lines and shapes can be traced out with the brighter stars

NOAO/AURA/NSF

M21 – Open ClusterConstellation – Sagittarius

Right Ascension 18 : 04.6 (h:m)

Declination -22 : 30 (deg:m)

Distance 4.25 (kly)

Visual Brightness 6.5 (mag)

Apparent Dimension 13.0 (arc min)

• Fewer than 60 stars, but concentrated in the center

• Less than a degree from the TrifidNebula

• Very young – less than 5 million years

NOAO/AURA/NSF

M20 – Emission NebulaConstellation – Sagittarius

Right Ascension 18 : 02.6 (h:m)

Declination -23 : 02 (deg:m)

Distance 5.2 (kly)

Visual Brightness 9.0 (mag)

Apparent Dimension 28.0 (arc min)

• The famous Trifid Nebula

• Contains both emmission (red) and reflection (blue) nebulosity

• Named by John Herschel due to the trisecting dark dust lanes

• These dark nebula were classified by Barnard as Barnard 85

• The Barnard catalog is a very interesting list of dark nebula in the plane of the Milky Way

• Lies 2° NW of its large neighbor, the Lagoon Nebula

Brian Kimball

M8 – Open Cluster & EmissionNebula

Constellation – SagittariusRight Ascension 18 : 03.8 (h:m)

Declination -24 : 23 (deg:m)

Distance 5.2 (kly)

Visual Brightness 6.0 (mag)

Apparent Dimension 90x40 (arc min)

• The famous Lagoon Nebula

• Another mix of star formation, star clusters, gas and dust – a very active stellar ‘nursery’!

• The young open cluster component is NGC6530

• The bright center of the Lagoon is called the ‘Hourglass Nebula’due to the shape of the foreground dust clouds

• Also contains ‘globules’ of protostellar clouds about 10,000 AU in diameter!

NOAO/AURA/NSF

Somebody named Olivier in Italy from the internet

M22 – Globular ClusterConstellation – Sagittarius

Right Ascension 18 : 36.4 (h:m)

Declination -23 : 54 (deg:m)

Distance 10.4 (kly)

Visual Brightness 5.1 (mag)

Apparent Dimension 32.0 (arc min)

• Probably the 1st globular cluster ever discovered

• Easy naked-eye cluster, brighter than the Hercules cluster M13

• The mighty Omega Centauri and 47 Tucanae are the only brighter globulars

• One of the closest at a little over 10,000 LY

• One of only 4 globulars known to contain a planetary nebula

NOAO/AURA/NSF

M28 – Globular ClusterConstellation – Sagittarius

Right Ascension 18 : 24.5 (h:m)

Declination -24: 52 (deg:m)

Distance 18.3 (kly)

Visual Brightness 6.8 (mag)

Apparent Dimension 11.2 (arc min)

• Smaller and more compressed than M22

• Slightly elliptical in shape

• Intervening Milky Way dust obscures its brightness by about 2 ½ magnitudes

• One of the more compact and denser globular clusters

NOAO/AURA/NSF

M69 – Globular ClusterConstellation – Sagittarius

Right Ascension 18 : 31.4 (h:m)

Declination -32 : 21 (deg:m)

Distance 29.7 (kly)

Visual Brightness 7.6 (mag)

Apparent Dimension 9.8 (arc min)

• One of the smaller and fainter of the Messier globulars

• Similar to its neighbor, M70, both discovered on the same night

• One of the metal-richest globulars, indicating old age

• Only 6200 LY from the Galactic Center

NOAO/AURA/NSF

M70 – Globular ClusterConstellation – Sagittarius

Right Ascension 18 : 43.2 (h:m)

Declination -32 : 18 (deg:m)

Distance 29.3 (kly)

Visual Brightness 7.9 (mag)

Apparent Dimension 8.0 (arc min)

• A physical neighbor of M69 –about the same distance away from us and 2° east of M69

•Close in size and magnitude to M69

• Has a very dense core

• Became famous in 1995 when Comet Hale-Bopp was discovered while Alan Hale and Thomas Bopp were observing M70 NOAO/AURA/NSF

M54 – Globular ClusterConstellation – Sagittarius

Right Ascension 187 : 55.1 (h:m)

Declination -30 : 29 (deg:m)

Distance 87.4 (kly)

Visual Brightness 7.6 (mag)

Apparent Dimension 12.0 (arc min)

• Easternmost of a row of 3 Messier globulars in the base of the Sagittarius ‘Teapot’ asterism

• Small and bright with an intense core

• 3 times further away than M69 and M70

• Discovered to be not in the Milky Way after all, but associated with the recently discovered Sagittarius Dwarf Elliptical Galaxy – a member of the Local Group of galaxies!

NOAO/AURA/NSF

M55 – Globular ClusterConstellation – Sagittarius

Right Ascension 19 : 40.0 (h:m)

Declination -30 : 58 (deg:m)

Distance 17.3 (kly)

Visual Brightness 6.3 (mag)

Apparent Dimension 19.0 (arc min)

• Large cluster, about 2/3 of the Moon’s diameter

• Fairly loose visually

• One of the nearer clusters at about 17,000 LY

NOAO/AURA/NSF

Credits & Acknowledgements:

Star Maps: Night Vision, courtesy of Brian Simpson

Text: Burnhams Celestial HandbookNational Optical Astronomy ObservatorySEDS – University of Arizona

Photos: Brian KimballNational Optical Astronomy Observatory