diff --git a/CHANGELOG.md b/CHANGELOG.md
index dac3da6..f88544e 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -23,6 +23,16 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - `Skymap::Catalog::ConstellationNames` gives the English name of each of the
   88 IAU constellations
 
+### Changed
+
+- `Skymap::Canvas` raises an `ArgumentError` when the padding is negative or
+  leaves no room for the sky
+
+### Fixed
+
+- The catalogs give an enumerator when `each` is called without a block,
+  instead of raising a `LocalJumpError`
+
 ## [0.2.0] - 2026-10-27
 
 ### Added
diff --git a/lib/skymap/canvas.rb b/lib/skymap/canvas.rb
index 40cdcd9..c64a12d 100644
--- a/lib/skymap/canvas.rb
+++ b/lib/skymap/canvas.rb
@@ -2,6 +2,15 @@
 
 module Skymap
   Canvas = Data.define(:size, :padding) do
+    def initialize(size:, padding:)
+      unless padding >= 0 && padding < size / 2.0
+        raise ArgumentError,
+          "padding must not be negative and must be less than half the size"
+      end
+
+      super
+    end
+
     def center
       Point.new(x: size / 2.0, y: size / 2.0)
     end
diff --git a/lib/skymap/catalog/constellation_boundaries.rb b/lib/skymap/catalog/constellation_boundaries.rb
index b50da15..6d7282d 100644
--- a/lib/skymap/catalog/constellation_boundaries.rb
+++ b/lib/skymap/catalog/constellation_boundaries.rb
@@ -13,6 +13,8 @@ class ConstellationBoundaries
       )
 
       def each
+        return enum_for(:each) unless block_given?
+
         CSV.foreach(PATH, headers: true).chunk_while do |previous, row|
           previous["border"] == row["border"]
         end.each do |rows|
diff --git a/lib/skymap/catalog/constellation_lines.rb b/lib/skymap/catalog/constellation_lines.rb
index f4abab9..036df7f 100644
--- a/lib/skymap/catalog/constellation_lines.rb
+++ b/lib/skymap/catalog/constellation_lines.rb
@@ -13,6 +13,8 @@ class ConstellationLines
       )
 
       def each
+        return enum_for(:each) unless block_given?
+
         CSV.foreach(PATH, headers: true) do |row|
           yield line_from(row)
         end
diff --git a/lib/skymap/catalog/stars.rb b/lib/skymap/catalog/stars.rb
index 38dd1a3..80f6f83 100644
--- a/lib/skymap/catalog/stars.rb
+++ b/lib/skymap/catalog/stars.rb
@@ -10,6 +10,8 @@ class Stars
       PATH = File.expand_path("../../../data/stars.csv", __dir__)
 
       def each
+        return enum_for(:each) unless block_given?
+
         CSV.foreach(PATH, headers: true) do |row|
           yield star_from(row)
         end
diff --git a/spec/skymap/canvas_spec.rb b/spec/skymap/canvas_spec.rb
index 57d7ac4..0a7afbf 100644
--- a/spec/skymap/canvas_spec.rb
+++ b/spec/skymap/canvas_spec.rb
@@ -1,6 +1,24 @@
 # frozen_string_literal: true
 
 RSpec.describe Skymap::Canvas do
+  describe ".new" do
+    it "accepts no padding" do
+      canvas = described_class.new(size: 400, padding: 0)
+
+      expect(canvas.radius).to eq(200)
+    end
+
+    it "rejects a negative padding" do
+      expect { described_class.new(size: 400, padding: -1) }
+        .to raise_error(ArgumentError, /padding/)
+    end
+
+    it "rejects a padding that leaves no room for the sky" do
+      expect { described_class.new(size: 400, padding: 200) }
+        .to raise_error(ArgumentError, /padding/)
+    end
+  end
+
   describe "#center" do
     it "is the middle of the canvas" do
       canvas = described_class.new(size: 400, padding: 1.5)
diff --git a/spec/skymap/catalog/constellation_boundaries_spec.rb b/spec/skymap/catalog/constellation_boundaries_spec.rb
index 78cff61..905606c 100644
--- a/spec/skymap/catalog/constellation_boundaries_spec.rb
+++ b/spec/skymap/catalog/constellation_boundaries_spec.rb
@@ -9,6 +9,14 @@
     expect(count).to eq(266)
   end
 
+  it "gives an enumerator without a block" do
+    catalog = described_class.new
+
+    first = catalog.each.next
+
+    expect(first).to be_a(Skymap::ConstellationBoundary)
+  end
+
   it "reads the two constellations a border separates" do
     catalog = described_class.new
 
diff --git a/spec/skymap/catalog/constellation_lines_spec.rb b/spec/skymap/catalog/constellation_lines_spec.rb
index ba800a3..5aec685 100644
--- a/spec/skymap/catalog/constellation_lines_spec.rb
+++ b/spec/skymap/catalog/constellation_lines_spec.rb
@@ -9,6 +9,14 @@
     expect(count).to eq(752)
   end
 
+  it "gives an enumerator without a block" do
+    catalog = described_class.new
+
+    first = catalog.each.next
+
+    expect(first).to be_a(Skymap::ConstellationLine)
+  end
+
   it "reads the constellation, ends and weight of each line" do
     catalog = described_class.new
 
diff --git a/spec/skymap/catalog/stars_spec.rb b/spec/skymap/catalog/stars_spec.rb
index a75ffae..75e96d6 100644
--- a/spec/skymap/catalog/stars_spec.rb
+++ b/spec/skymap/catalog/stars_spec.rb
@@ -9,6 +9,14 @@
     expect(count).to eq(9096)
   end
 
+  it "gives an enumerator without a block" do
+    catalog = described_class.new
+
+    first = catalog.each.next
+
+    expect(first.hr).to eq(1)
+  end
+
   it "reads the identifier, J2000 coordinates and magnitude of each star" do
     catalog = described_class.new