Visual Astronomy Tools
Tonight’s Observing List
Clear sky, an hour or two free, and no idea where to point. This builds you a plan for tonight from your own back garden — what is up, how high, which direction, what magnification, and in what order, so you catch the things that are setting before they go. It works out where the Moon is and how much it is costing you, and it tells you what to skip.
Where and when
Sets your coordinates and a typical sky quality for that town — adjust both if you know better.
The plan runs from dusk on this date through to dawn.
West is negative — Ontario is around −75 to −95.
Your sky
Moonlight is added on top of this automatically from the real position and phase of the Moon — you do not need to allow for it yourself.
Your telescope and session
Trees, roofs and haze. 25° is a realistic suburban horizon.
01Tonight at a glance
Sun, Moon and the length of real darkness — computed for your coordinates, not a generic table.
02The plan
03The night, drawn
Altitude against time for everything in the plan. Tap any object above or below to trace it.
04Everything else that is up
Every target at its best moment tonight, with what the Moon is costing it.
Not tonight
05How the plan is built
Setting objects first
The most common mistake on a clear night is to start with whatever is highest. Do that and you will lose the western objects entirely — they set while you are busy admiring something that will still be there in four hours. This plan works the other way round: at each point in the night it offers you the worthwhile object with the least time left, then moves on. It is how an experienced observer works a session, and it is the single biggest improvement you can make to a night with a list.
What the Moon actually costs
Moonlight is not a simple on-or-off. Its effect on the sky background grows with the illuminated fraction, with how high the Moon is, and with how close your target sits to it. A quarter Moon low in the south-west costs you very little on an object in the north-east; a gibbous Moon overhead costs you well over a magnitude everywhere. The table in section 04 shows the cost for each object in magnitudes per square arcsecond, so you can see for yourself which targets are worth attempting and which are not.
Why the Moon does not appear in the deep-sky verdicts as a simple penalty
Some objects barely notice it. Small, high-surface-brightness targets — the Ring Nebula, the Clown Face, bright globular clusters, double stars, and every planet — punch through moonlight almost unchanged. Large faint ones — M33, M101, the North America Nebula, the Veil — are erased by a fraction of a magnitude. That is why a Moon-lit night is not a wasted night, but it is a night for different objects.
Altitude, and the atmosphere you are looking through
At the zenith you are looking through one atmosphere. At 30° above the horizon, two. At 15°, nearly four. That costs brightness through extinction and sharpness through turbulence, and both are folded into tonight’s verdicts. It is also why the same object can be a showpiece at midnight and a disappointment at nine o’clock. The horizon-limit control lets you tell the tool about your own trees and rooftops so it stops suggesting things you physically cannot see.
How accurate are the times?
Sunset, twilight, Moon phase and Moon rise and set are computed from standard low-precision solar and lunar theory, and are good to well under a minute for this purpose. Planet positions come from JPL’s approximate Keplerian elements, which are valid from 1800 to 2050 and accurate to a few arcminutes — far better than needed to tell you where to point and how high it will be. Deep-sky coordinates are catalogue J2000 positions precessed to the date. None of it accounts for your local horizon, weather, or haze, which is why the horizon-limit control exists.
What Will I Actually See?
The honest description of every object on this list, for your aperture and sky.
Double-Star & Eyepiece Calculator
Magnification, true field and exit pupil for the eyepieces you own.
Nebula & light-pollution filters
What rescues an emission nebula on a moonlit or suburban night.
All free calculators
Focus steps, flat frames, guiding, ISS passes and more.
06Questions we get asked
Why does it tell me to look at something low in the west first?
Because it is about to be gone. Anything in the west is setting, and once it drops into the haze near the horizon it is finished for the night — and for several weeks, since it sets four minutes earlier each evening. The things high overhead will still be well placed in two hours. Working west to east is how you get the most out of a session, and it is the habit that most separates a productive night from a frustrating one.
The Moon is up all night. Should I bother going out?
Yes, but change what you look at. Moonlight raises the sky background, which destroys contrast on large faint objects and does almost nothing to bright compact ones. A full-Moon night is an excellent night for the Moon itself, for Jupiter and Saturn, for double stars, for bright globular clusters, and for small planetary nebulae like the Ring. It is a poor night for galaxies. The plan reorders itself accordingly, so what you see on a bright night is a genuinely different list rather than the same list with worse verdicts.
Does it know about clouds?
No. It knows where everything is and how bright the sky will be, which is the part that is predictable. Check a forecast for cloud and transparency — and be aware that a night can be perfectly clear and still have poor transparency from high haze or smoke, which hurts faint deep-sky objects far more than it hurts planets.
Why is my favourite object missing?
The list is deliberately a curated set of about fifty of the best-known visual targets rather than a full catalogue, so that every entry can carry an honest description of what it actually looks like at your aperture. If something you observe regularly is missing and you think it earns a place, tell us — the list is ours to extend.
Can I use it outside Ontario?
Yes. The town list is Ontario-first because that is where most of our customers observe, but the custom coordinate entry and the browser location button work anywhere, including the southern hemisphere. The seasonal notes in the object descriptions are written from a northern point of view, and a handful of the southern objects on the list — M6, M7, M22, NGC 253 — will behave very differently if you are observing from below the equator.
What magnification is it suggesting, exactly?
The power that puts a sensible exit pupil on that class of object for your aperture — a large one for big faint nebulae so they stay bright, a small one for planets and tight planetary nebulae so detail is enlarged. It is capped by what tonight’s seeing can support. To turn that into an actual eyepiece, divide your telescope’s focal length by the suggested power, or use the eyepiece tab of our double-star calculator.