90 MilliMeters

Posts Tagged ‘Deep Sky’

Ursa Major holds a few deep sky objects for observers with small telescopes that are visible even under moderately light polluted skies. Bode’s Nebulae, better known as M81 and M82, are two such objects and both are readily visible in a low power eyepiece. Messier 81 was first discovered by Johann Elert Bode in 1774. Consequently, the pair of galaxies (M81 & M82) is sometimes referred to as “Bode’s Nebulae”. In 1779, Pierre Méchain and Charles Messier re-identified Bode’s object, which was subsequently listed in the Messier Catalogue. M81 & M82 are located approximately 10° northwest of Alpha Ursae Majoris making this an easy target to locate. You can download a Telrad finder chart here or a more detailed finder chart here.

As with any telescope at low power, the 90mm at 40x shows these two galaxies at either edge of the field of view. M81 looks like an oval of defused light radiating out from the bright center while M82 appears as a thin, elongated, evenly distributed silver of light. Increasing the power to 71x improves the contrast and I can detect a dark dust lane in M81 about half way from the center to the faint outer edge. Stepping up to the 150mm at 54x the spiral nature of M81 becomes evident. Since this object can handle higher magnifications, I dropped in my 20mm eyepiece coupled with a 2x Barlow for 76x. Now I can see greater detail in the spiral arms of this grand galaxy. Amazing how just a small amount of magnification can improve the view.

In the 150mm at 38x, M82 is an elongated glow that is brighter toward the western edge. I bumped the power up to 76x for a better view but was unable to detect any detail. The light is more evenly distributed across the surface at this power and the galaxy fills the eyepiece.

If you observe from an urban location where light pollution is an issue, such as here at the 90mm observatory, these objects will benefit from using a narrow-band filter. Narrow-band filters pass the critical hydrogen-beta and ionized oxygen wavelengths, while blocking out the remainder of the visual spectrum. They also increase the contrast of emission and planetary nebulae, revealing detail that is often washed out by background sky glow.

When observing M81 & M82, as with any deep sky object, try using different eyepieces and eyepiece/Barlow combinations to see which gives the best view. Take time to study the object for a few minutes, you’ll be surprised at the amount of detail you’ll start to see. Don’t forget about averted vision. A good amount of detail can be seen with this observing technique.

Until next time, clear skies.
-Dan

[Disclosure]

I came across an article on Cloudy Nights Telescope Reviews the other day that just made me want to grab my 10×50 binoculars and go have a look. Of course, it was cloudy, so much for that good feeling. But, there is nothing like a great article about observing deep sky objects to get the juices flowing. Phil Harrington, the author of Touring the Universe through Binoculars, takes you on a tour of the famous Double Cluster in Perseus and into Cassiopeia. Read the article here. Be sure to check out Phil’s Website at http://www.philharrington.net/index.htm.

Messier 52, an open cluster located in a rich Milky Way field in Cassiopeia.

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M31 – Spiral Galaxy – Andromeda

Another look at M31 in Andromeda, this time under better sky conditions. The galaxy is elongated  NW/SE. At x40, with adverted vision, I can see some detail in M31′s southeastern side toward the center as well as the northwestern edge where a dark lane trails in toward the central glow of the galaxy. At x90 the detail becomes slighty more prominent.

M110 – Elliptical Galaxy – Andromeda.

An At x40 this galaxy is small but bright with a near stellar core. The object is elongated E/W. At x90, no additional detail is noticed beyond the hazy smudge of light.

NGC 663 – Open Cluster – Cassiopeia

This cluster seems to be clumped into 4 sections. A beautiful site at x40, about 11 tenth mag. stars with many 12th mag. stars.

Stock2 – Open Cluster – Cassiopeia

This is a very large cluster best viewed with low power. The cluster fills the entire eyepiece with around 50 tenth mag. stars.

Clear Skies.