M71 in Sagitta: A Star-Hop Route for Visual Observers

Before you start

Choose a night with a dark, steady sky and a clear view toward the southeast-to-northeast quarter where Aquila and Sagitta sit. Light pollution from streetlights and nearby buildings will wash out the faint glow of M71, so turn lights away from your observing position and give your eyes at least fifteen minutes to adjust.

Use a finder with a wide field, such as a 10x50 binocular or the finder of your telescope, for the first part of the hop. Set up your main instrument, a 70-90 mm refractor or a similar telescope, with a low-power eyepiece that gives a field of roughly 2 degrees or wider. Most observers find that a magnification of 20x to 40x shows the cluster best, because it is spread out and does not reward very high power.

Check your star chart or planetarium software for the current position of Altair, since the sky shifts through the evening. Altair is the anchor for the whole route, so make sure you can identify it before you move on.

Star-hop route from Altair

Step 1: Find Altair

Altair is one of the brightest stars in the summer sky. It is the bright star in the middle of the Summer Triangle, with two fainter stars on either side of it in a rough line. Once you have found it with your eyes, look through your finder to confirm it.

Step 2: Move about 10 degrees north

From Altair, move your telescope roughly 10 degrees north. A useful check is that your outstretched fist held at arm's length covers about 10 degrees. Move your view straight north on that scale, or use the finder's field to sweep across the sky until you reach the small arrow-shaped figure of Sagitta.

Sagitta is a compact group of stars, much smaller than the constellations around it. It is easy to miss if you go past it, so slow down as you approach and look for a small, bent arrow of stars with a shaft and a short head.

Step 3: Locate Gamma Sagittae

At the eastern end of the arrow, look for Gamma Sagittae. It is one of the brighter stars in the figure and makes a clear reference point. Center it in your finder, then look through the main eyepiece to confirm that it is a single star with a few fainter companions nearby.

Step 4: Hop about 1.4 degrees to the west-southwest

From Gamma Sagittae, move about 1.4 degrees toward the west-southwest. In practice this is about a quarter of the width of a 5-degree binocular field, so you can judge the move by eye. M71 lies in this direction, within the same wide field as Gamma Sagittae when you use a low-power eyepiece.

Move slowly and scan the area. You are looking for a faint, soft, round patch of light that does not have the sharp point of a star. Use averted vision, which means looking slightly to the side of the spot, because the cluster will often appear more clearly when you do not look straight at it.

Confirming you have arrived

Several checks will help you tell M71 apart from a faint star or a random patch of haze.

First, look for a round, soft glow rather than a point. A single star stays pinpoint no matter how you move your eye, but M71 looks like a fuzzy ball with a slightly brighter center.

Second, compare the patch with the stars around it. Mark the bright stars you can see in the field and check that none of them is the glow you are following. A faint star with a halo can look like a cluster at low power, so confirm that the patch remains a soft ball when you change eyepieces.

Third, make small taps or movements of the telescope. Stars jump in the eyepiece, but a cluster stays put. This is also a good way to check that you have not drifted off the target.

Finally, increase the magnification modestly to see whether the glow changes in size. M71 is small, so it will look more spread out at moderate power and will become fainter as you go higher. If you can see a soft patch at 20x to 40x that gets fainter but remains round at 60x, you have almost certainly found the cluster.

What you will see from a suburban sky

M71 has a magnitude of 6.1, which is fainter than the naked-eye limit of a suburban sky, roughly magnitude 5. You will not see it without optics. With a 70-90 mm refractor, the expected view is an easy, round, softly glowing ball. Its apparent size is 6.9 arcminutes, which is roughly a fifth of the width of a full moon.

The cluster is not very compact, so its edge looks soft and its center is not a sharp point. Do not expect to resolve individual stars in a suburban sky with this aperture. Some stars near the edges may flicker in and out of view as you change the angle of your eye, but the overall impression is a faint, smooth glow.

Binoculars can show a faint fuzzy patch in the same area, but it will be less clear than the refractor view. If you are using binoculars, look for the patch near Gamma Sagittae using averted vision, and be patient. Hold the binoculars steady, preferably braced against a wall or a stable support.

Views from different latitudes

The altitude figures in the facts table show how high M71 rises at each latitude. These heights affect how much atmosphere you look through and how easily you can find the cluster.

At 35 degrees north, M71 reaches about 74 degrees above the horizon. It is high in the sky, so the air is thin and the view is steady. Star-hopping is easier from here because the route runs close to the overhead region.

At 50 degrees north, the cluster reaches about 59 degrees. It is still well placed, but you will be looking through more air, so the view may be less crisp. Plan your session for the time when the cluster is highest, and use a low-power eyepiece to keep the view bright.

At 35 degrees south, M71 reaches only about 36 degrees above the northern horizon. From here, the cluster is low, and you look through much more of the atmosphere, so the glow will look fainter and less steady. Observe it when it is at its highest, and pick a night with good transparency. The route from Altair still works, but you will need to look toward the northern part of the sky, and the hop may take a little longer to set up.

Equipment and eyepieces

A 70-90 mm refractor is a sensible instrument for this target. A larger reflector will show more of the cluster's extent and a slightly brighter glow, but a small refractor with a low-power eyepiece is already enough to see the round ball clearly.

Use a wide-field eyepiece to make the hop easier. A field of around 2 degrees helps you keep Gamma Sagittae and M71 in the same view. Once you have confirmed the cluster, you can switch to a moderate eyepiece to check its shape, but return to low power for the best view.

Keep a red-filtered flashlight or a dim red light nearby so you can read your chart without losing dark adaptation. A small notebook or a sketch pad is useful for recording the position of nearby stars, which will help you find the cluster again on later nights.