Download Targets for Small Telescopes

Targets for Small to
medium Telescopes
IISAC October, 2009
Prepared by: John Bambury
NGC 6752
(The Starfish or Pavo Globular)
Image Credit: Anglo-Australian Observatory/David Malin
Constellation:
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TYPE:
Visual Magnitude
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Distance:
Pavo
19h 10’ 51.8”
-59 58 55”
Globular Cluster
5.3
29’
~13,000 ly
General Object Information

NGC 6752 is known as “The Starfish” or the “Pavo
Glob” . It is also catalogued as Caldwell 93. The
globular was discovered in 1827 by James Dunlop. The
apparent size of this globular is somewhat open to
discussion, O’Meara lists it as 29’ but some other
reputable sources, including Hartung and Burnham, list
it as 15’. The Central Core of NGC 6752 is very small
and compressed and covers an apparent diameter of
2.5’. The stars external to the core extend outwards in
looped arms and resemble a Starfish. Some see it as
resembling a butterfly, which in my opinion it does
somewhat more so than M6, the Open Cluster so
named.

NGC 6752 is one of over 20 Milky Way Globular
Clusters which have undergone a “core collapse”. NGC
6752 is one of the closest and brightest globulars to us
and is one of the easiest to resolve in small telescopes.
An attractive double star h 5085 is also included within
the outliers. This was one of Hartung’s favourite targets
and without doubt makes the top 10 globulars list. It is a
wonderful target in any instrument over about 4”
aperture.

It is visible naked eye under excellent sky conditions.
NGC 2070
(The Tarantula Nebula)
Image Credit: R Jay GaBany.
Constellation:
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Dorado
5h 38.6m
-6905
Emission Neb + Cluster
~4.0-5.3
30’x20’
~170,000 ly
General Object Information

NGC 2070 is known as the Tarantula Nebula. It is also
catalogued as Caldwell 103. Also sometimes known as 30
Doradus. It was discovered in ~1751 by Lacaille. It is a
massive and luminous HII region, located within the Large
Magellanic Cloud. It is the largest known HII region within
the local group of Galaxies. The entire nebula spans 3,000
ly, which compares to the Orion Nebula spanning 40 ly.
The Star Cluster at the Centre of the Nebula (also NGC
2070), spans 250 light years. If the nebula were contained
within our own Galaxy it would fill the entire constellation
of Orion (30 degrees of sky) and darkness as we know it,
would not exist..

The cluster contains a very large number of type O3 blue
supergiants. These are generally smaller than their red
counterparts, but are amongst the hottest and most
luminous stars known. The Clusters’ mass is over 200,000
suns, with the stars gravitationally bound. It is believed
with this much mass NGC 2070 could harbour a globular
cluster in the making.

Telescopically the Tarantula Nebula is one of the night
Sky’s stunning targets. Any telescope over 3” aperture will
reveal its swarms of knots and loops together with the
central star cluster. The telescopic view of the nebulosity
itself is enhanced with a UHC or OIII filter, but these filters
dampen the starlight from the central cluster.

This is an easy naked eye target under dark skies.
NGC 104
(47 Tucanae)
Image Credit: Emmanuel BEAUDOIN
Const:
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Tucana
Globular Cluster
3.9
0h 24’ 5.2”
-72° 4’ 51”
50’
~14,700 ly
General Object Information

NGC 104 is known as 47 Tucanae. It is also catalogued as
Caldwell 106. It was discovered in 1751 by Lacaille. It is
located 2.5° off the Western edge of the Small Magellanic
Cloud. It is the second brightest globular in the sky (.2 mag
behind Omega Centauri) and 3 times brighter (1.25 mags)
than the brightest Messier Globular (M22). The Cluster
spans 214 light years.

47 Tuc contains a large number of blue stragglers. One of
these, BSS-19, is the first blue straggler whose mass has
been recorded. Recent data from the Hubble Faint Object
Spectrograph in respect of BSS-19 indicates a slow merger
of a binary pair has occurred, as opposed to a collision
resulting from a core collapse.

47 Tuc is one of the night Sky’s stunning targets. In my
opinion it is the finest globular cluster in the entire sky. Any
telescope over 4” aperture will resolve it to the core. It
contains a very bright blazing condensed core, with a soft
radiating glow as you move away from the core. Many
people see colour in 47 Tuc. Some see it having a soft
yellow appearance. Others see it with a pinkish hue. I have
seen both in varying apertures.

An interesting additional target for larger scopes is NGC
121. This is an 11.2 magnitude globular cluster located 30’
north northeast of the central core. It is small at 1.5’ x 1.5’
but should be visible in medium apertures under good skies.

This is an easy naked eye target under regional skies.
M11
(Wild Duck Cluster)
Image Credit: NASA
Const:
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Scutum
Open Cluster
5.8
18h 51’ 6”
6° 16’ 12”
13’
~5,460 ly
General Object Information
 M11 is known as The Wild Duck Cluster.
It is also catalogued as NGC 6705. It
was discovered in 1681by Gottfried
Kirsch. It is located 2° southeast of Beta
Scuti. It sits in a notch in the north edge
of the Scutum star cloud.
 The cluster contains about 680 stars,
400 of which shine at brighter than 14th
magnitude. The cluster spans 20 light
years. This is a very compressed open
cluster and the nucleus reminds me of a
globular cluster falling apart.
 Unlike the summer, autumn and winter
skies, the spring sky is a little light on for
bright open clusters. This is one of the
better ones. It is an easy naked eye
target under dark skies.
NGC 7293
(The Helix Nebula)
Image Credit: NASA, WIYN, NOAO, ESA, Hubble Helix Nebula
Team, M. Meixner (STScI), & T. A. Rector (NRAO)
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Aquarius
Planetary Nebula
6.0~7.3
22h 29’ 38.4”
-20° 50’ 13”
12’ x 10’
~522 ly
General Object Information

NGC 7293 is known as the Helix Nebula. It is also catalogued
as Caldwell 63. It is one of the largest examples of a
planetary nebula visible in amateur telescopes. Its true size
is 1.5 x 1.2 ly. It is located 11° north west of Pisces Austrini
(Fomalhaut). It was discovered ~1874 by Friedrich von
Auwers

It is bright at ~ 6th magnitude, but it's light is spread over a
large area, giving it a low surface brightness which can make
it reasonably dim in the telescope eyepiece. In addition, there
is a big hole in the middle which causes many people to miss
it.

It is easily visible in binoculars and finder scopes and more
so, with an OIII or UHC filter attached to the objective of the
instrument. A low power view with binoculars or the
telescope reveals the annular nature of the object.

It makes a fine photographic target and is one of the most
photographed of all targets. It has been the subject of some
Hubble Space Telescope images that have revealed gaseous
knots with comet-like tails at the inner edge of the annulus.

There are a number of field stars involved with this object
and the mag 13.4 central star should be visible in mid to
large apertures using medium to high power.

The brightness of the nebulosity is not even around the
annulus. It is brighter in the north-east and south-west
sections. The nebula responds well to narrowband filters, in
particular the OIII type.

A hand full of observers, including O’Meara, have been able
to observe this target naked eye from high quality observing
sites, with good altitude.
NGC 7009
(The Saturn Nebula)
Credit: Bruce Balick (University of Washington), Jason Alexander
(University of Washington), Arsen Hajian (U.S. Naval Observatory),
Yervant Terzian (Cornell University), Mario Perinotto (University of
Florence, Italy), Patrizio Patriarchi (Arcetri Observatory, Italy),
NASA/ESA
Const:
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Aquarius
Planetary Nebula
8.0
21h 4’ 11”
-11° 21’ 49”
.7’ x .4’
~1,400 ly
General Object Information

NGC 7009 is known as the Saturn Nebula. It is
also catalogued as Caldwell 55. It is one of the
brightest planetary nebula at Mag 8.0. It is
located 1.25° due west of Nu Aquarii, 3° from
the Capricornus border. It was discovered in
1782 by William Herschel.

It is easily visible in small telescopes but
requires a telescope of about 10” aperture to
begin detection of the nebulous extended
lobes.

Unlike most planetary nebula, the central star
is visible in smaller telescopes. It is located in
the centre of a bright elliptical bubble and
shines at Mag 11.5

Hubble Space Telescope images have
revealed gaseous knots at each end joined to
the cavity within the bubble of gas. Deep
photographs of this nebula are giving
researchers a good insight into how a one
solar mass star transforms into a white dwarf.

This planetary shows distinct colour when
observed in amateur telescopes. Some see it
as green. Many see it as blue.
M33
(Pinwheel or Triangulum Galaxy)
Image Credit: Giovanni Benintende
Const:
Type:
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DEC:
Diameter:
Distance:
Triangulum
Spiral Galaxy
5.7
1h 33’ 50.8’
+30° 39’ 37
71’ x 42’
~2.3 million ly
General Object Information

M33 is known as The Pinwheel Galaxy. It is also catalogued
as NGC 598. It was discovered in 1764 by Messier. It is
located 4° west northwest of Alpha Trianguli. M33 is a member
of the local group of galaxies. It is 50,000 ly in diameter,
making it about 1/3rd the size of M31. It has about 1/15th the
mass of M31 or 1/7th the mass of the Milky Way. M33 may be
a satellite galaxy of M31.

M33 is easily observed in small to medium power binoculars,
which are a good instrument to observe it with, due to its large
angular size of over 1° .

Outside of the Magellanic Clouds, M33 is the easiest of all
galaxies to resolve. A modest aperture at low power will reveal
the clockwise sweeping spiral arms. A 10” or larger telescope,
under dark clear skies, will reveal several of the embedded
nebulae and their associated stellar regions.

An interesting challenge for small telescopes (under 6”) is to
observe NGC 604. This is a massive HII region within M33. It
is located 12’ northeast of the nucleus and 1’ northwest of a
10.5 magnitude star. NGC 604 has been observed in 3”
refractors from high altitude northern hemisphere locations. It
should be fairly easy in any telescope of 8” or larger aperture.

This is a very difficult naked eye target and the naked eye
observing challenge for IISAC 2009. I have observed it on a
couple of occasions naked eye from Coonabarabran under
exceptional conditions. What makes it a very difficult naked
eye target from the Southern Hemisphere is its low altitude.
Our skies are certainly dark and clear enough to see it.
M33
(Pinwheel or Triangulum Galaxy)
M31
(Andromeda Galaxy)
Image Credit: Tony Hallas
Const:
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Visual Mag:
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Diameter:
Distance:
Andromeda
Spiral Galaxy
3.4
0h 42’ 44”
41°16’ 6”
190’ x 62’
~2.3 million ly
General Object Information

M31 is known as The Andromeda Galaxy. It is also
catalogued as NGC 224. It was discovered in the 10th century
by the Persian Astronomer Alsufi. It is located 1° west of Mag
4.5 Nu Andromadae in the Chained Maiden’s Belt. M31 is a
member of the local group of galaxies. It is 130,000 ly in
diameter and contains 300 billion suns. It is easily the largest
galaxy in the local group and has twice the mass of our own
milky way. The stars in the nucleus of M31 are so tightly
packed it is thought that a black hole resides at the heart of
the nucleus

M31 is easily observed in small to medium power binoculars,
which are a good instrument to observe it with, due to its large
angular size of over 3° in length.

M31’s two neighbouring satellite galaxies (M32 and M110) are
easily observed in small telescopes, where they appear as
featureless fuzzy glows. In binoculars M32 and M110 appear
stellar.

M31 is a very easy galaxy to resolve in small instruments.
Numerous nebulous regions and about 10 globular clusters
can be resolved in 6” or larger telescopes. A 10” or larger
telescope, under dark clear skies, will reveal several of the
embedded nebulae and their associated stellar regions.

An interesting challenge for medium telescopes (under 10”) is
to observe NGC 206. This is a massive star cloud close to the
galaxy’s southwestern edge.

M31 is an easy naked eye target under regional skies.
M31
(Andromeda Galaxy)
NGC 253
(Silver Coin Galaxy)
Image Credit: National Optical Astronomy Observatory (NOAO)
Const:
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Sculptor
Mixed Spiral Galaxy
7.3
0h 47’ 33”
- 25°17’ 15”
29’ x 7’
~9.8 million ly
General Object Information

NGC 253 is known as The Silver Coin Galaxy. It is also
catalogued as Caldwell 65. It was discovered in 1783 by
Caroline Herschel. It is located 2° northwest of the South
Galactic Pole and 7.5° south southeast of Beta Ceti. NGC
253 is a member of the Sculptor group of galaxies which is
the closest system to our own local group of galaxies. It is
54,000 ly in diameter and contains 75 billion suns. It is 2.5
times smaller and 4 times less massive than M31.

NGC 253 is a starburst galaxy, which means its nucleus is
hosting rapid and massive bursts of star birth. Each
massive outburst creates a “superwind” which ejects vast
amounts of energy and mass streaming into the
intergalactic medium in large arcs and loops. Some of
these features are 1,000 light years long.

Midinfrared studies have shown the nucleus to be
unusually luminous and to contain a super cluster of stars,
in addition to a diffuse envelope containing an older
population of supernova remnants and low mass stars.

NGC 253 is an easy galaxy to resolve in medium
instruments. An 8” telescope at high power will begin to
show a lot of detail in the nucleus as well as the multitude
of dust clouds in the arms. NGC 253 is easily observed in
small to medium power binoculars, although no detail is
visible.

NGC 253 has been observed by several observers naked
eye, including O’Meara, but is an exceptionally challenging
naked eye target. It is possibly beyond the normal
observing conditions of the Hunter Valley.
Gamma Delphinus
Image Credit: Sky and Telescope Magazine
Const:
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Visual Mag:
Separation:
PA:
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DEC:
Distance:
Delphinus
Double Star
3.9
9.1”
265°
20h 46’ 39”
16° 7’ 25”
~100 ly
General Object Information

Gamma Delphinus is catalogued as HR 7948, HIP
102532 and SAO 106476. It presents a lovely colour
contrast, with a Mag 3.9 yellow primary accompanied by
a Mag 5.3 pale yellow/white Secondary. Separation is
currently 9.1" making it easy to separate in the smallest
telescopes. Separation has decreased slightly from
12.0" since the first measures in 1755 to its current
separation of 9.1". The position angle (PA) of the
secondary has also decreased slightly over the same
time period from 280º to its current position of 265º. The
stars have similar proper motions and are believed to
form a long period system.

Both stars are of a similar apparent size with the
primary being slightly larger and brighter than the
secondary. Different observers see the secondary as
different colours. The colours I have mentioned
previously, Yellow and Pale Yellow/White are consistent
with the spectral types, sometimes I see the secondary
as having a pale green or emerald tone to it, depending
on conditions.

This is a showpiece double star in any size telescopes.
Beta Cygni (Albireo)
Image Credit: Centre for Astrophysics and Space Astronomy –
University of Colorado
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Distance:
Cygnus
Double Star
3.1
34.4”
54°
19h 30’ 43”
27° 57’ 35”
~390 ly
General Object Information

Albireo is catalogued as HR 7417, HIP 95947 and SAO
87301. It presents a lovely colour contrast, with a Mag
3.1 yellow/gold primary accompanied by a Mag 5.4
electric blue secondary. Separation is currently 34.4"
making it easy to separate in the smallest telescopes or
good binoculars. This double is set against the Cygnus
Star Cloud, which makes a wonderful backdrop.

Separation and PA have remained essentially
unchanged since the first measures by F Struve in 1832.
The stars have like proper motions and are believed to
be in orbit and form a long period binary system.

The primary itself was found to be a close binary pair in
1977 using speckle interferometry. It has a separation of
.39” and the magnitude difference is 1.5. It was observed
visually in 1979 by C. E. Worley using a 26” refractor.
The pair should be observable in amateur telescopes
over 25” aperture, in excellent seeing conditions.

The colours I have mentioned previously, yellow and
blue are consistent with the spectral types.

This is one of the most celebrated, if not the most
celebrated and renowned double stars in the sky. It is a
showpiece double star in any size telescope.
Theta Eridani (Acamar)
Image Credit: Unknown Source
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Distance:
Eridanus
Double Star
2.9
8.3”
90°
2h 58’ 16”
- 40° 18’ 17”
~ 160 ly
General Object Information

Acamar is catalogued as HR 897, HIP 13847 and SAO
216113.

It was described by Hartung as one of the gems of the
Southern Sky. I tend to agree with him. It is one of my
all time favourites. The primary is a pale blue/white
star of magnitude 3.2, spectral type A4III (pale blue to
white giant), with the secondary another pale
blue/white star magnitude 4.1, of spectral type A1V
(pale blue dwarf) at position angle 90° with an angular
separation of 8.3”.

I see both stars as pale blue/white in my 10” reflector,
which is consistent with their spectral types. This does
not always occur with visual observations of double
stars. Some observers see the colours as being more
white than blue, while some observers have described
both stars as having a yellowish tinge. The apparent
visual colour of stars can of course be aperture
dependant.

Since John Hershel’s original measurements in 1835,
the only change has been slow direct motion. The
stars form a long period system.

An excellent double star for any size telescope.