90 MilliMeters

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

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