How to Observe the Herschel 400

The History

William Herschel spent decades systematically sweeping the sky with large telescopes he built himself. Between 1783 and 1802, he cataloged over 2,500 deep-sky objects — far more than had ever been recorded. His son John continued the work in the southern hemisphere.

In 1980, the Astronomical League compiled the Herschel 400 — a representative selection of 400 of William's finest objects that are accessible to modern amateur telescopes. They span all major object types: galaxies, nebulae, open clusters, and globular clusters.

What's in the List?

Minimum: 6-inch (150mm) Telescope

A 6" telescope can complete the Herschel 400 under good dark skies, but you'll struggle with the faintest galaxies. Expect to revisit some objects multiple times waiting for ideal conditions.

• • Works for brighter objects (clusters, bright galaxies, planetary nebulae)
• • Requires very dark skies (Bortle 3 or better) for faint targets
• • About 80% of the list is achievable under good conditions

Ideal: 10–12 inch Telescope

A 10" or 12" telescope makes many Herschel objects dramatically easier, turning frustrating faint smudges into clearly resolved galaxies and clusters.

• • Resolves detail in galaxies and clusters
• • Handles suburban skies (Bortle 5-6) for most objects
• • Greatly speeds up completion time

Eyepieces & Accessories

The Bortle Scale & Herschel Objects

When to Observe

• • New Moon window: The 5 nights before and after new moon are your best sessions
• • Galaxy season (March–June): Prime time for the many Virgo and Coma galaxies — the hardest part of the list
• • Summer (June–September): Clusters, nebulae, and globulars dominate — easier, rewarding sessions
• • Winter (Nov–Feb): Some fine clusters and nebulae, Orion-region objects
• • Transparency over seeing: Faint galaxies need transparent skies more than steady seeing

Work by Season & Constellation

The most efficient approach: plan each session around what's highest in the sky right now. Don't jump around the sky randomly — work a region thoroughly before moving on.

Tools for Planning

• • Stellarium (free): Plan sessions, find objects, simulate your view
• • SkySafari (app): Built-in Herschel 400 observing list with progress tracking
• • Astroplanner / Cartes du Ciel: Desktop planning with observing log integration
• • Printed charts: Sky Atlas 2000.0 (recommended) or Uranometria 2000 for challenging targets
• • SkyObs: Log each object as you observe it, track your progress and build your achievement history

The Virgo Cluster: The Big Challenge

The Virgo Galaxy Cluster contains roughly 50+ Herschel objects within a relatively small area — it's the single most concentrated region of the list. Many observers find this both the most frustrating and the most rewarding part.

• • Use a detailed chart: Galaxies are close together and easy to confuse. Print a finder chart specifically for the Virgo Cluster.
• • Anchor on M84/M86: Start at this bright pair and star-hop outward systematically.
• • Mark galaxies as you go: It's easy to lose track of which ones you've logged.
• • Expect multiple sessions: Dedicate 4–6 spring sessions exclusively to Virgo.

The Essential Skill

Most Herschel objects are too faint for GoTo mount plate-solving to be reliable in typical conditions. Star-hopping — navigating by star patterns — is the classical skill that separates intermediate from advanced observers.

1. 1. Find a bright nearby star that you can positively identify. Use a chart or app to confirm it.
2. 2. Note the chain of stars between your starting star and the target on your chart. Memorize the pattern.
3. 3. Move step by step with low power eyepiece, sweeping slowly. Each hop should be within 1–2° to keep you oriented.
4. 4. When close to the target field, look for the object directly and with averted vision (looking slightly to the side).
5. 5. Confirm the object by checking its position relative to surrounding stars on your chart before logging it.

Averted Vision: Your Secret Weapon

The edges of your retina contain more rod cells (sensitive to faint light) than the center. By looking slightly to the side of an object, you can often detect objects up to 1–2 magnitudes fainter than looking directly.

• • Look about 10–15° away from where the object should be
• • Gently move your eye or the telescope — motion helps the brain detect faint objects
• • Allow 30+ minutes for full dark adaptation before attempting faint targets
• • Never look at bright lights or phone screens during a session

Galaxies (the majority of the list)

• • Most appear as faint, elongated smudges — this is normal. Don't expect Hubble images.
• • Look for the core: a slightly brighter nucleus confirms you found a galaxy and not a faint star
• • Edge-on spirals (like NGC 891) show a distinctive thin sliver shape
• • Face-on spirals may show hints of structure in larger apertures under good skies
• • Interacting pairs: look for two smudges close together — very satisfying to resolve
• • Dark skies matter more than aperture for galaxies

Globular Clusters

• • With 8"+, most Herschel globulars will resolve individual stars around the edges
• • Increase magnification to 150–200× to bring out resolution
• • The largest (NGC 6752, NGC 5139) are spectacular showpieces
• • Summer and early fall are prime time — many lie in Ophiuchus and Sagittarius

Open Clusters

• • These are often the easiest and most immediately satisfying Herschel objects
• • Use low to medium magnification — too high and stars drift out of the field
• • Rich clusters may take a few minutes to count and verify you have the right one
• • Compare star patterns to your chart to confirm identity

Planetary Nebulae

• • Many look like stars at low power — use the "blinking technique": alternate with and without an O-III filter; the nebula blinks while stars don't
• • High magnification (200–300×) reveals disc shape in larger planetary nebulae
• • O-III filter dramatically improves contrast for nearly all planetary nebulae
• • Look for slight color: some show blue-green hues (NGC 7009 Saturn Nebula is famous for this)

What to Record Per Object

The Astronomical League requires a written observation for each object. Minimally record:

• • Object designation (NGC number)
• • Date and time of observation (UT preferred)
• • Location and approximate sky darkness (Bortle or limiting magnitude)
• • Telescope used (aperture, type)
• • Magnification used
• • Description — what you saw: size, shape, brightness, notable features

Official Certification via Astronomical League

Once you've observed all 400 objects, you can apply for the Herschel 400 Certificate and pin through your local Astronomical League club or directly through the AL.

• • Submit your observing logs to your club's AL representative
• • Logs must show a written description for each object
• • Sketches are encouraged but not required
• • Observers who complete the list twice (with a larger scope, different site, etc.) can earn the Herschel II certificate

Trying to rush the galaxy season

The spring Virgo and Coma galaxy regions require patience and multiple dedicated sessions. Don't try to blitz them in one night — give yourself a full season.

Not cooling the mirror

A warm mirror in cool outside air creates thermal turbulence that ruins fine detail. Set up your telescope 30–60 minutes before observing and never bring a warm mirror directly outside from a heated room.

Skipping the observing log

Memory is unreliable. Objects you "definitely saw" three sessions ago can become uncertain. Log in the moment with enough detail to satisfy certification requirements.

Using too much magnification on galaxies

More magnification doesn't mean more detail for faint extended objects. It spreads the light out, making them harder to see. Medium power (80–120×) is often optimal for galaxies.

Ignoring collimation

A Dobsonian or reflector out of collimation will show bloated, soft stars. Even a 10" scope poorly collimated underperforms a well-tuned 6". Check and adjust collimation every session.

Not checking the official list

Verify your target list against the official Astronomical League Herschel 400 list. Some planning apps include slight variations. Observing an object not on the official list doesn't count.