Personal Favorite Deep Sky Objects
The following deep sky objects are my personal favorites to observe for a variety of reasons. Some are bright and easy to see, some have peculiar or interesting shapes, and some are a fun challenge to observe.
All objects have a recreation of what they look like through large telescopes. The magnification and filter used, as well as the Bortle level and exit pupil, are noted.
Image previews are designed to create a useful representation of how deep sky objects appear in an eyepiece. To create the most accurate recreation of an eyepiece view first set the brightness of the screen to the highest setting and dim the screen until the gray box around the 8 is no longer visible.
All image previews are meant to recreate views from bright suburban skies. These recreations assume the viewer has dark-adapted (not looking at lights or screens) for at least 3-5 minutes. In darker skies (Bortle 4 or darker), the same views are better approximated with the object appearing twice as bright (half the listed stated exit pupil for the same magnification). For dark skies setting the screen brightness to the maximum will provide a more accurate view.
Most previews have an exit pupil of 3.2mm striking a good balance between magnification and surface brightness to accommodate most objects. A larger exit pupil will have a brighter image. The eyepiece images presented also assume some light leak typical of stock dobsonians without any added flocking and shrouding. Telescopes with flocking and or shrouds should expect the views presented with a 50% smaller than stated exit pupil or an image twice as bright at the same magnification.
How to Use Image Previews
M 57
The Ring Nebula
Type: Planetary Nebula
Magnitude: +8.8
Best Filter: UHC
Observing Months: May - November
Aperture: 100mm+
M 57 is one of the best and brightest planetary nebulae in the Northern sky. It has a high surface brightness allowing it to be easily visible in light-polluted skies. Larger apertures do improve views even in light-polluted conditions. A UHC filter improves the contrast between the nebula and the background sky.
This nebula like most planetary nebulae does well at high magnifications. An exit pupil of 3 or larger is recommended.
M 42
The Orion Nebula
Type: Emission Nebula
Magnitude: +4.0
Best Filter: UHC or Unfiltered
Observing Months: October - April
Aperture: Naked Eye
M 42 is the brightest star-forming region visible from northern latitudes. The core of the nebula is visible to the naked eye even in heavy light pollution. In brighter skies only the brighter core regions of the nebula are visible. In darker skies, the nebula fills the eyepiece at low magnifications (30x).
A UHC filter improves contrast in the nebula making the details in the gas easier to see. In sufficiently dark skies keen observers can see hints of green and pink around the core of the nebula.
Due to the large size of M42, a larger exit pupil (4+) is recommended. High magnification is not needed.
M 5
Type: Globular Cluster
Magnitude: +5.6
Best Filter: None
Observing Months: March - August
Aperture: 50mm+
M 5 may be the best globular cluster seen from mid-northern latitudes. Its large size and high surface brightness allow it to be seen in binoculars in light-polluted skies. M 5 is a moderately concentrated globular cluster, and under high magnification the cluster resolves into many easily distinguishable stars. A fuzzy glow is still visible at higher magnifications at the core of the cluster.
M 5 is best seen at high magnification due to the high number of resolvable stars and is resistant to dimming from high power. An exit pupil of 2mm is recommended to reduce the brightness of the sky background and retain surface brightness.
M 11
The Wild Duck Cluster
Type: Open Cluster
Magnitude: +5.8
Best Filter: None
Observing Months: May - October
Aperture: 50mm+
M 11 is an open cluster in the constellation Scutum. It has a high density of stars allowing it to be seen as a fuzzy ball and almost like a globular cluster at very low magnifications (10x). The stars in the cluster easily resolve at higher magnifications.
Since M11 is an open cluster and all the stars in the cluster are resolvable the object does well at higher magnifications. Larger apertures do improve views with the stars appearing brighter.
An exit pupil of 2mm is recommended to reduce the brightness of the sky background and improve contrast.
M 17
The Omega/Swan Nebula
Type: Emission Nebula
Magnitude: +6.0
Best Filter: None
Observing Months: May - October
Aperture: 50mm+, Possibly Naked Eye
M 17 is an emission nebula and star formation region in Sagittarius and has the highest surface brightness of the emission nebulae in the vicinity of the Milky Way core. The part of the nebula that has a swan or omega-like appearance is the brightest part of the nebula thus giving its name.
The brighter regions of the nebula have prominent oxygen emission allowing it to be visible in heavily light-polluted skies. A UHC or OIII filter is best to improve contrast and make the nebula pop out from the background sky. An OIII filter makes the nebula rather dim but reveals more detail. Dark adaptation and intentional light avoidance are a must for the use of an OIII filter on this nebula in light-polluted skies.
An exit pupil of 3mm or larger is recommended to allow for the use of filters to improve views.
M 27
The Dumbell Nebula
Type: Planetary Nebula
Magnitude: +7.4
Best Filter: UHC / OIII
Observing Months: April - October
Aperture: 100mm+
M 27 is a planetary nebula in the Summer Triangle in the constellation of Vulpecula the Fox. It is typically found by using the constellation Sagitta the Arrow and moving over to a set of 4 stars that make an incomplete hexagon. The nebula is believed to be around 1200 ly away.
The brighter central region of the nebula has an apple core shape that has ionized hydrogen on its edges. A UHC filter will emphasize the apple core shape of the nebula. An Oxygen filter brings out the fainter extensions or ears of the nebula but reduces contrast in the nebula’s central region. This nebula has a rather low surface brightness compared to the other brighter planetary nebula and requires proper dark adaptation when viewed with filters in Bortle 6 or 7 skies.
An exit pupil of 3mm or larger is recommended to allow for the use of filters to improve views.
M 92
Type: Globular Cluster
Magnitude: +6.4
Best Filter: None
Observing Months: May - October
Aperture: 50mm+
M 92 is the often-looked-over globular cluster in Hercules. Its large size and high surface brightness allow it to be seen in binoculars in light-polluted skies. M 92 is more centrally concentrated than M 13 allowing it to appear slightly brighter than M 13 in bright skies. M 13 is definitely a more impressive globular cluster in darker conditions but when the sky is bright M 92’s bright core can make it more impressive than its larger neighbor.
At higher magnification, the cluster is partially resolved maintaining its fuzzy core. Larger apertures do improve views with the core appearing brighter due to its small size and high surface brightness.
An exit pupil of 3mm is recommended to reduce the brightness of the sky background and retain surface brightness.
Albireo
The Cow Star
Type: Binary Star
Magnitude: +3.18
Best Filter: None
Aperture: Single star Naked Eye, 50mm+ for split
Observing Months: April - November
Albireo, sometimes referred to as the Cow star is the second brightest star in the constellation Cygnus the Swan. The binary star is visible as an orange star to the naked eye and when magnified splits into a brighter orange (+3.3) and dimmer blue star (+5.5).
The differences between star colors can be rather subtle but when different colored stars are placed next to each other they seem to exaggerate their differences. Albireo is about 380 light-years from Earth and with a separation of 34 arcseconds between the two stars, the stars are easily split at low powers.
A standard exit pupil of 2mm is recommended to balance splitting the two stars and keeping their colors vibrant.
Epsilon Lyrae
The Double Double
Type: Binary Star
Magnitude: ~ +5.0
Best Filter: None
Aperture: Single star Naked Eye, 30mm+ for first split, 130mm+ for second split.
Observing Months: April - October
Epsilon Lyrae is a system containing at least 5 stars, 4 of which are resolvable visually. The 5th component was discovered spectroscopically. When viewed with the naked eye the entire star system appears as a single blue star.
Epsilon Lyrae 1 (left) and Epsilon Lyrae 2 (right) are both visual binaries and are believed to be part of the same system due to their common proper motion. Epsilon Lyrae 1’s visual components have a period of ~1200 years with the stars 140 AU (astronomical units) apart. Epsilon Lyrae 2’s visual components have an orbital period of about half that of Epsilon Lyrae 1.
An exit pupil of 2mm or smaller is recommended to reduce the size of the visual size of the stars from diffraction to make them easier to resolve.
M 13
Great Cluster in Hercules
Type: Globular Cluster
Magnitude: +5.8
Best Filter: None
Observing Months: May - October
Aperture: 50mm+, Possible Naked Eye
M 13 is the biggest and brightest globular cluster in Hercules. Its large size and high surface brightness allow it to be seen in binoculars in light-polluted skies. When viewed at higher magnifications with a telescope the fuzzy nature of the globular cluster fades as it resolves into countless stars.
M 13 is not a very centrally concentrated globular cluster and can be sensitive to dimming at higher magnifications in bright skies. In dark skies, high magnification can be used. Larger apertures do improve views with the resolved stars appearing brighter and the central glow being more extensive.
An exit pupil of 3mm is recommended to reduce the brightness of the sky background and retain surface brightness.
M 3
Type: Globular Cluster
Magnitude: +6.39
Best Filter: None
Observing Months: March - August
Aperture: 50mm+
M 3 is a moderately bright and moderately concentrated globular cluster. It is still one of the brighter globular clusters in the sky but is not as visually impressive as M 13 or M 5.
M 3 is one the earliest bright globular clusters of the year to be visible, able to be viewed months before the many globular clusters in late spring and summer. It has a considerable number of resolvable stars but remains a fuzzy appearance at its core even at higher magnifications.
An exit pupil of 3-4mm is recommended to keep the surface brightness of the cluster from being too dim.
M 2
Type: Globular Cluster
Magnitude: +6.6
Best Filter: None
Observing Months: July - January
Aperture: 50mm+
M 2 is a bright and moderately concentrated globular cluster visible with binoculars in bright skies. It is one of the brightest globular clusters visible in fall and is slightly more impressive than nearby M 15.
M 2 has a considerable number of resolvable stars but remains a fuzzy appearance at its core even at higher magnifications. This globular cluster has a nice appearance at both moderate and high magnifications.
An exit pupil of 3mm is recommended as a good balance between magnification and maintaining surface brightness.