M78 Star Hop: Finding the Reflection Nebula with a 114-150 mm Reflector

Before you start

Choose a night when Orion is high in the sky and the Moon is not bright. The Moon's glare washes out faint nebulae, and M78 has a surface brightness that is easily lost in moonlight. Let your telescope reach outdoor temperature before you begin, which reduces image shimmer and makes faint detail easier to see.

Set up with a low-power eyepiece, roughly 30 to 40 mm in focal length, which gives a wide view and makes the star-hop easier. Use a finder, such as a small red-dot or a finder scope, aligned on a star well away from Orion so that the alignment holds. If your reflector is on a manual mount, loosen the clutches and sweep slowly so you do not overshoot the field.

Keep a printed or app-based star chart showing Orion down to about magnitude 7 or 8. Charts with this depth show the faint stars you use to confirm your position.

Star-hop route from Alnitak

The hop uses bright stars and one optional landmark. Each step is a move you can check against the chart before you move the telescope.

1. Find Orion's Belt. Look for three bright stars in a nearly straight line: Mintaka, Alnilam and Alnitak. Alnitak, also called Zeta Orionis, is the belt star farthest from Mintaka, at the eastern end of the line. It is the easiest of the three to confirm by its brightness and position relative to the other two.

1. Center Alnitak. Put Alnitak in the middle of your finder and then the eyepiece. Note the faint stars around it, since you will use them later to check your position. Low-power views of Alnitak show a bright star with a few fainter companions in the surrounding field.

1. Look for the Flame Nebula. Just east of Alnitak, a short distance from the star, lies a faint glow known as the Flame Nebula. In a suburban sky, it is faint, and you may not see it at low power. If you can see it, it confirms that you are in the right region. If you cannot see it, skip it and continue to the next step. Do not spend long trying to detect it.

1. Move north-northeast. From Alnitak, move about 2.5 degrees toward the north-northeast. This is a longer hop than a single field in most low-power eyepieces, so expect one or two re-centering steps. Move in stages, first north, then east, using the faint stars in the field as markers. Check your chart at each stage to confirm you are following the line of faint stars rather than drifting into empty sky.

1. Find the faint star field. As you approach the target, the field should show a sparse scatter of faint stars. Several of these form a loose, uneven pattern around the nebula. Center the field on the pattern and look for a soft, uniform glow near the middle.

1. Center on the glow. Move the telescope slowly so that the glow sits in the middle of the eyepiece. Then increase power to about 60x to 80x only if the view is steady and the glow remains clear. Higher power spreads the light and makes the nebula fainter, so do not increase magnification past the point where the glow starts to fade.

Confirming you have arrived

A faint glow can be mistaken for scattered light, a reflection in the eyepiece, or dust on the optics. Use these checks before you accept the view.

Move the telescope slightly off target, then back. A real glow stays in the same place relative to the faint stars, and its position should not shift with the eyepiece or the telescope's movement. Tap the tube gently and watch the field. The glow should remain steady, and the stars should stay sharp. A patch that moves or changes with the tap is an artifact.

Compare the glow with a nearby empty patch of sky. Center the eyepiece on the glow, then move about a finder field away. The empty area should look darker, and the glow should be a distinct, evenly lit area rather than a set of separate points. Averted vision, which means looking slightly to the side of the glow, often brings out a faint patch more easily than looking straight at it.

Finally, check the faint stars against your chart. If the pattern of stars around the glow matches what you expect, you are on the target. If you cannot match the pattern, return to Alnitak and repeat the route, paying attention to the number of re-centering moves you made.

What you will see from a suburban sky

M78 is a magnitude 8.0 object with an apparent size of 4.5 arcminutes. At this size, it covers only a small part of the eyepiece view at moderate power. Its brightness is spread across that area, which makes it look faint even when it is correctly placed.

In a suburban sky with a naked-eye limit of about magnitude 5, you can expect a faint, grey-white glow around the illuminating star. You will not see fine structure, filaments or color. The glow is most visible when you look slightly away from it, and it is easier to find with a wide-field eyepiece than with a high-power one.

Light pollution affects reflection nebulae differently from emission nebulae. Narrowband filters are designed for emission lines and do little for reflection nebulae, so they are not a useful choice for this target. A broadband light pollution filter may improve contrast slightly by reducing the background glow, but it will not make the nebula bright. If you have a dark-sky site available, observe there, since the difference in contrast is considerable.

Equipment and eyepiece settings

A 114 mm reflector gives you a fainter limiting magnitude than a smaller scope, while a 150 mm reflector gathers more light still. Both instruments can show the glow, but the larger aperture gives a brighter, more evenly lit view. Neither will show much detail in a suburban sky.

For the hop itself, use the widest, sharpest low-power eyepiece you have. As a general guide, a magnification of about 30x to 40x gives a field that is wide enough for the star-hop and still shows the faint stars you use as markers. For the final view of the glow, about 40x to 60x is a useful range. These are typical settings for this class of instrument, not measured requirements.

Keep the telescope's optics clean and collimated. Dew can form on the corrector or the eyepiece and reduce contrast quickly. A dew shield or a heater band helps on humid nights. Check the focus at the start of the session and again after the telescope has cooled, since focus can drift as the tube temperature changes.

Hemisphere and latitude notes

M78 is close to the celestial equator, so it can be observed from both hemispheres. Its altitude depends strongly on latitude, and that changes how easy it is to see.

At 35 degrees north, M78 reaches a maximum altitude of about 55 degrees. This gives a steady, well-placed view, with the sky dark enough to show the faint glow. At 50 degrees north, the maximum altitude drops to about 40 degrees. The object sits lower in the sky, so you must observe through more atmosphere. Look for a clear horizon and a steady, transparent sky, and avoid observing when haze or low cloud is near the horizon.

At 35 degrees south, the maximum altitude is again about 55 degrees, so the view is similar to a 35-degree north site. Orion appears reversed relative to northern charts. The belt still runs in the same line, and Alnitak is still the star to start from, but the compass directions in this guide are written for a northern chart. If you use a southern chart, check the belt pattern first, then reverse north and south in the hop. The stars around the target still confirm your position.

When to observe

M78 is best observed in January and February, when Orion is well placed in the evening sky. At these times, the object is high enough for a comfortable view for observers at mid-northern and southern latitudes. Choose the early part of the evening, when the constellation is still high and the sky is dark enough for faint stars.

Outside these months, M78 is lower in the evening sky or is lost in the twilight. It still rises in the late evening or early morning in other seasons, but the view is less comfortable and the object sits lower, so the glow is harder to pick out.