How to Plan an Observing Session
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Three Different Questions, Several Ways to Answer Them
"What app should I use" is really three separate questions wearing one trench coat: what's actually up there tonight, will the sky even cooperate, and how do I frame or schedule the session once I know both. Treating them as one question is how people end up with five overlapping apps and no clear workflow. ORIVON's own Sightline (see below) answers all three at once for free; the sections below break down the individual apps in case you'd rather assemble your own stack. For the fuller field guide to sky apps — including PhotoPills and Light Pollution Map for astrophotography framing and dark-sky scouting — see Best Astronomy Apps for Beginners instead.
Problem 1: What's Actually Up There — Stellarium vs. SkySafari
Stellarium is a full planetarium simulator with a genuinely capable free tier — accurate positions for stars, planets and deep-sky objects, searchable by name or catalog number. It's the tool for planning a session in advance rather than identifying something in the moment.
SkySafari takes a more premium approach: a paid app (tiered Plus and Pro versions) known for its depth of catalog data and for direct control of supported computerized mounts and smart telescopes, a feature Stellarium's mobile app doesn't match as comprehensively. Reviewers consistently frame the choice as depth versus cost — Stellarium's free tier covers the essentials, while SkySafari's paid tiers matter most once you own equipment it can directly control.
Best for: Session planning and object lookup — pick Stellarium if budget matters, SkySafari if you want deeper mount integration and don't mind paying for it.
Problem 2: Will the Sky Cooperate — Clear Outside
Clear Outside is a weather app built specifically for astronomers rather than adapted from a general forecast — it breaks down cloud cover, transparency and seeing hour by hour instead of giving a single daily summary. It's free, and arguably the most-checked app in this entire category, since no amount of planning matters if the sky doesn't cooperate.
Best for: The final go/no-go check before you commit to setting up.
Problem 3: Framing the Session
Once you know what's up and whether the sky will cooperate, the last piece is framing — knowing where a target will actually sit relative to your foreground, or how a mosaic panel lines up with the rest of a target. We cover this specific problem, along with light pollution scouting, in the full apps field guide rather than duplicating it here.
How They Fit Together
| Stellarium | Free planetarium and session planning — the default starting point. |
| SkySafari | Paid, deeper catalog and mount control — for owners of a computerized setup. |
| Clear Outside | Free, astronomy-specific sky condition forecast — checked closest to go time. |
| ORIVON Sightline | Free, built by ORIVON — combines all three signals into one recommendation instead of three separate apps. |
If juggling three separate apps feels like overkill, we also built our own tool for exactly this problem.
No signup. No download. No paid tier.
Frequently Asked Questions
Yes, in practice — they solve different problems. A planetarium app tells you what's worth looking at; a forecast app tells you whether tonight is even worth setting up for.
Mainly once you own a computerized mount or smart telescope SkySafari can control directly. For naked-eye and small-telescope planning, Stellarium's free tier covers most needs.
It's not necessarily more accurate on temperature or precipitation, but it reports the specific metrics astronomers actually need — cloud cover by altitude, transparency and seeing — which general forecast apps don't break out.