M105 (NGC 3379) in Leo: Visual Star-Hop with a 200 mm Telescope

Before you start

Use a telescope in the 200 to 300 mm range, such as a Dobsonian reflector, for the view described here. A 130 mm reflector can show the galaxy from a suburban site, but the glow will be faint and hard to hold steady. Binoculars are unlikely to show it under suburban skies.

Bring three items. The first is a finder with a field of about 6 to 8 degrees. The second is a low-power eyepiece that gives a field of roughly 1.5 to 2 degrees, which you will use for the hop. The third is a medium-power eyepiece in the 100 to 150x range for the core. Adjust magnification to suit your telescope's focal length and your eyes.

Use a star atlas or a planisphere that shows stars to about magnitude 7. Check the chart before you go out so that you know which stars to expect in each stage.

Allow your eyes 15 to 20 minutes to adapt to the dark. Use a red light for reading charts, since white light resets your night vision. In a suburban sky, the naked-eye limit is about magnitude 5. You will see Regulus, Denebola, Zosma and Chertan, but the faint stars between them may not show. For this reason, the route relies on bright anchors and on counting field widths.

Where M105 sits in Leo

Leo is easiest to find by its sickle, a curved group of stars that forms the lion's head and chest. Regulus, the brightest star in Leo, lies at the base of the sickle. Denebola marks the tail, far to the east of Regulus. Zosma and Chertan lie between Denebola and the head, forming a rough triangle with Denebola.

M105 lies about 10 degrees east of Regulus and slightly north of it. It lies about 15 degrees west of Denebola and a little south. These positions are approximate, so confirm them on your chart before you start.

Star-hop route from Regulus and Denebola

This route uses three stages. Each one ends on a bright star or on a point you can check against the chart.

Stage one: Regulus to Denebola

1. Center Regulus in your finder. Confirm that the star sits at the bottom of the sickle, with the curve of faint stars above it.
2. Sweep east along the same band of sky toward Denebola. Denebola lies about 25 degrees east of Regulus, which is roughly four finder fields. Move in steps of about 5 degrees and check each field for bright stars.
3. Center Denebola in the finder. It marks the end of the lion's tail and is clearly brighter than the stars around it.

Stage two: Denebola to Chertan

1. From Denebola, move about 9 degrees west, with a slight tilt north, toward Chertan. This distance is more than one finder field, so take it in two steps of about 4 to 5 degrees.
2. Center Chertan in the finder. It is a third-magnitude star and forms one corner of the triangle with Denebola and Zosma. If you see Zosma as well, the triangle is a good check that you are in the right place.

Stage three: Chertan to M105

1. From Chertan, move about 6 degrees west and about 3 degrees south. This is a west-southwest direction. Move in two steps, and check the field at each stop for a faint glow in the eyepiece.
2. Center the point at the end of the move. M105 should be within a fraction of a degree of that point.
3. Switch to a medium-power eyepiece and look for the glow again. Use the checks in the next section to confirm the object.

Shortcut from Zosma

If you can find Zosma first, use it as the starting point. Zosma lies about 5 degrees north of Chertan. Move 5 degrees straight south from Zosma to reach Chertan, then continue with step 6. This shortcut skips the long sweep from Regulus to Denebola, so it is faster when you know where Zosma sits.

Confirming you have arrived

Center the patch at the end of the route in your lowest-power eyepiece first. Look for a soft, faint patch with no sharp star at its center. A galaxy looks like a diffuse glow, whereas a star looks like a point, even at low power.

Next, switch to the medium-power eyepiece. Look for the galaxy's core, which appears as a brighter central region within the glow. The glow should look slightly oval rather than perfectly round.

Use averted vision. Look slightly to one side of the glow, so the light falls on a more sensitive part of your eye. The glow often becomes easier to see this way. Gently nudge the telescope and check that the glow stays in the same place relative to nearby stars. A star or a reflection in your optics will move or change differently.

Check the surrounding field for two spiral galaxies. They lie roughly 1 to 1.5 degrees to the west and southwest of M105, within a field of about 2 degrees. In a suburban sky they may appear as faint smudges. If you see them, M105 should lie to the east-northeast of them. Finding them confirms that you are in the right region, even if M105 itself is hard to see.

If you cannot confirm the glow, go back to Chertan and check that you identified it correctly. Confirm the position against your chart. Then repeat the final move with a slower sweep. A small error at Chertan produces a large error at the target, because the final move covers several degrees.

What to expect

Under a suburban sky, M105 appears as an oval glow with a brighter core. Its apparent size is about 4.9 by 4.3 arcminutes, roughly one-sixth the width of the full Moon. In a 200 to 300 mm telescope, the glow is small and faint. Its shape is easier to judge at medium power than at high power, because high power spreads the light and makes the glow dimmer.

Do not expect the galaxy to show spiral arms, dust lanes or fine detail. An elliptical galaxy has a smooth, featureless structure. Its glow is the same kind of signal you would see from a faint nebula or a faint star cluster in a good sky, but it is more subtle than either.

Try different magnifications and see which one gives the clearest view on the night. Keep the telescope cool and collimated, and allow it to settle before you look. A telescope that has not reached the outside temperature often gives blurry images.

Hemispheres and altitude

M105 is visible from both hemispheres. Its maximum altitude is 68 degrees at 35 degrees north, 53 degrees at 50 degrees north, and 42 degrees at 35 degrees south. At 35 degrees north, the galaxy climbs high in the sky and is easy to reach. At 50 degrees north, it is still well placed but lower. At 35 degrees south, it stays comparatively low and culminates in the northern sky, so you need an open view toward the north.

The best months for observing M105 are April and May. Plan your session so that Leo is well above the horizon when you begin. This matters most in the south, where a low altitude makes the glow harder to see through haze and light pollution.

The route is the same in both hemispheres because the stars and the galaxy keep their positions on the sky. What changes is how the pattern appears in your view. Check your chart in the orientation that matches your location and the time of night.