Galaxy Background Generator

Make a galaxy or space background for a desktop, a phone or a design: glowing nebula clouds, a field of stars and, if you like, a spiral galaxy. Pick a preset or set your own: how strong the nebula is and how big its clouds are, how many stars and how large, the number of spiral arms, how tightly they wind, the tilt and the turn. Every picture comes from a seed number: the same seed and size always give the same picture, and New seed gives you a fresh sky. Choose desktop, 4K, phone, tablet, square, banner or your own size up to 4096 pixels; the stars and clouds sit at the same places in every size, so a desktop and a phone picture from one seed match. It is artwork drawn from maths, not a photograph. Download a PNG or JPG. Nothing is uploaded.

100% private — everything runs in your browser. Everything runs in your browser; nothing is uploaded.

How to make a galaxy background

1. Pick a preset, or keep the seed and change the controls.
2. Press New seed until you like the sky.
3. Set the nebula strength, cloud size and the number and size of stars.
4. Tick the spiral galaxy and set its arms, pitch, size, tilt and turn.
5. Choose a size: desktop, 4K, phone, tablet, square, banner or your own.
6. Download the PNG or JPG.

What you can use it for

• Desktop and phone wallpapers
• Backgrounds for slides, videos and streams
• Covers, posters and album art
• Game, story and classroom space scenes
• Website hero images
• Matching desktop and phone pictures from one seed

The 14 presets

Preset	Colours	Nebula	Stars in the sky	Spiral galaxy	Size	Stars in the picture
Blue-violet nebula with stars	Deep blue and violet	90	1,400	–	1920 × 1080	799
Spiral galaxy, two arms	Deep blue and violet	35	1,100	2 arms, pitch 14°, tilt 50°	1920 × 1080	610
Spiral galaxy seen face-on, four arms	Violet and pink	25	1,200	4 arms, pitch 18°, tilt 0°	1920 × 1080	675
Tilted spiral galaxy	Teal and blue	30	1,300	2 arms, pitch 12°, tilt 75°	1920 × 1080	742
Pink and violet nebula	Violet and pink	85	1,200	–	1920 × 1080	681
Ember-red nebula	Ember red and orange	80	1,000	–	1920 × 1080	554
Teal nebula, dense stars	Teal and blue	65	2,600	–	1920 × 1080	1,464
Rose galaxy with three arms	Rose and indigo	45	1,300	3 arms, pitch 16°, tilt 40°	1920 × 1080	736
Star field only	Deep blue and violet	0	2,200	–	1920 × 1080	1,216
Quiet sky, few stars	Black and white	15	500	–	1920 × 1080	297
Black and white galaxy	Black and white	20	1,500	2 arms, pitch 22°, tilt 45°	1920 × 1080	871
Dusk sky with a faint nebula	Dusk (lighter sky)	40	700	–	1920 × 1080	374
Tightly wound six-arm galaxy	Deep blue and violet	20	1,000	6 arms, pitch 9°, tilt 20°	1920 × 1080	559
Phone wallpaper: galaxy low on the screen	Violet and pink	50	1,500	2 arms, pitch 15°, tilt 50°	1170 × 2532	678

Worked out by the tool. The stars are spread over a square the width of the long side, so a wide picture shows about half of them.

One seed, every size

Size	Pixels	Width ÷ height	Stars in the picture (preset Spiral galaxy, two arms)
Desktop	1920 × 1080	1.778	610
4K	3840 × 2160	1.778	610
Phone	1170 × 2532	0.462	516
Tablet	2048 × 2732	0.750	834
Square	2048 × 2048	1.000	1,100
Banner	1500 × 500	3.000	365

Worked out by the tool: the same sky in every size, cropped to its shape.

Arm pitch and how fast the spiral opens

Pitch	b = tan(pitch)	Radius × per full turn, e^(2πb)	Turns to double the radius
5°	0.0875	1.73	1.26
9°	0.1584	2.71	0.70
14°	0.2493	4.79	0.44
18°	0.3249	7.70	0.34
22°	0.4040	12.66	0.27
30°	0.5774	37.62	0.19
40°	0.8391	194.85	0.13

Worked out from the spiral rule r = a e^(bθ) that the tool draws.

What downloads

Download	What is in it
PNG	The picture at the full size you chose, every pixel exactly as drawn
JPG	The same picture as a smaller JPG (quality 92)

To change the size of a picture afterwards, use the Image Resizer; for a smooth colour background, the Mesh Gradient Generator.

Which tool to use

You want	Use
A nebula, star field or spiral galaxy background	Galaxy Background Generator (this page)
A planet with rings, on its own	Planet Generator
Flames or embers	Fire Background Generator
Smooth colour blends	Mesh Gradient Generator

Other tools: the Planet Generator for planets, and the Phone Wallpaper Maker for photo wallpapers.

Frequently asked questions

Is this a real photo of space?

No. Every star, cloud and arm is drawn by our own code from the seed: it is artwork made from maths, not a photograph or a telescope image.

How is the nebula made?

From noise: a smooth random pattern added up at six sizes, each half as strong as the one before, and gently warped. Where it is above a level, it glows in a mix of the two nebula colours, more strongly with a higher nebula setting.

How are the spiral arms drawn?

Each arm follows a logarithmic spiral, r = a e^(bθ), where b is the tangent of the pitch angle you set. A small pitch winds the arms tightly; a large one opens them up. The table below shows how much each turn widens the spiral.

What does the seed do?

It fixes where every star and cloud goes. The same seed and size give exactly the same picture, pixel for pixel, so you can come back to a sky you liked or share the seed with someone.

Why do the stars line up between sizes?

Every star and cloud is placed as a fraction of the picture’s long side, measured from the centre. A phone picture from one seed is the same sky as the desktop one, cropped to the tall shape.

Which size should I pick for my phone?

Phone 1170 × 2532 suits most current phones; for anything else choose Your own size and type the pixels. The picture is drawn at that size, not stretched.

What do the spikes on bright stars do?

They add four thin rays to the brightest stars for a sparkle. Untick them for plain round stars.

Is it free?

Yes. There is no sign-up, no watermark and no limit.

Is anything uploaded?

No. Every pixel is worked out by JavaScript in your browser. Nothing you type is sent anywhere or saved when you close the page.