Observing Skills · 6 of 11

Planning a Night

What should you check before you go out to look?

Plan an observing night in the order you live it: the Moon and the clouds, then north, south and east, a first star-hop, the night as a graph, and what to pack.

You’ll be able to plan an observing night around the Moon, the weather and what is up.

9 steps · about 7 min

Before this: Measure the Sky with Your Hand (5 min), Understanding Star Brightness (10 min), Dark Skies, Dark Eyes (6 min)

Where and which night

Working out when this is best placed from where you are…

Where

Which night

Date

Time

Kept for this guide only, until you change it here — your map settings, and every other guide, stay as they are.

Print, play outside or present

Present on a big screen

Scan with a phone's camera, or open

Sources

Bortle, "The Bortle Dark-Sky Scale", Sky & Telescope, February 2001 — the nine classes and their naked-eye limits
Kasten & Young, Applied Optics 28, 4735 (1989) — the airmass formula behind the numbers on this page
Clark, Visual Astronomy of the Deep Sky (CUP 1990) — planning around the Moon and dark adaptation in the field
HYG stellar database v4.2 — star positions and magnitudes

← GUIDES

More below ↓

With a keyboard, focus the sky, aim it with the up and down arrow keys, and press Enter to drop the pin at the centre of the view; or press Show me.

You are here

Settings

Screen

Night mode Turns every page red, to keep your eyes adjusted to the dark.

High contrast Bolder constellation lines, larger and brighter names on the sky, and stronger text and edges everywhere. Starts on if your device asks for more contrast.

Reduce motion The camera cuts to where it is going instead of flying there, and panels and sheets appear without sliding. Starts on if your device asks for less motion.

Battery saver Draws the sky thirty times a second at most: smoothness traded for battery.

Night brightness Dims the screen below your phone’s lowest setting, down to a fifth, while night mode is on.

Clock and voice

Clock How every time is written. Until you choose, your language’s own clock decides.

D describes What D says about the view on the sky: one sentence, or in full with the field, the constellation and five names.

Sounds Quiet tones as you use the map: a tick as you drag the clock past a mark or dusk, a chime for the star you pick — higher for hotter stars — and a low swell while a figure is out of the dome. Made in your browser, and off until you turn them on.

All settings and your progress

Before you pick a site, pick a date, and start with the Moon. This is the next full Moon: up all night, it turns a Bortle 3 site into a Bortle 6, and faint galaxies and nebulae are gone.

The next new Moon, the same site: no Moon all night, and the Milky Way is back. For faint things pick the week either side of it. Then, the day before, check the clouds: the Tonight page has a forecast for your site.

On the night, face north first. Stars near the pole never set, and north of about 41° nor does the Big Dipper: the place to practise. Then read the altitude on Polaris: north of the equator, that is your latitude.

Face south. Everything that rises crosses the here, at its highest and through the least air. At 30° up you look through twice the air overhead, at 20° three times, each extra layer dimming a star by over a quarter of a magnitude.

Face east to plan the rest of the night. Everything here is on its way up as the sky turns 15° an hour: a star rising due east now crosses the south six hours later. So work west to east — western targets while they last, eastern ones once they have climbed into good air.

Now navigate. Never start from a faint target: start from a shape you are certain of and hop outward. From Vega and Deneb, go south to the third corner of the Summer Triangle.

The whole night as a graph: the three stars and the Moon, height against the clock. The top of each curve is its transit, the meridian crossing from three steps ago: the time to look. The Tonight page draws this for your own targets.

Pack: a dim red torch, more layers than feels sensible, a chair, binoculars, and this map in night mode. On site, give your eyes 30 minutes before you judge the sky, and start from a shape you know.

The night's plan, on the Triangle you started from. Check the Moon, then start in the west.

The Moon picks the date: new, not full
Catch each target near its highest
Hop out from a shape you know