The Earth turns once every 23 h 56 m, so the whole sky drifts westward at about 15° per hour — at 200× magnification an untracked object crosses the eyepiece in seconds. A tracking mount cancels this drift by turning the telescope the opposite way at the sidereal rate.
There are two mechanical ways to do it:
A GoTo mount has encoders that report where its two axes point — but at power-up it has no idea how those axes relate to the sky. Alignment builds that missing link, the pointing model: a coordinate transform between "axis angles" and "sky positions" (RA/Dec).
Rule of thumb: more alignment points, better pointing accuracy — but only if the stars are well separated in azimuth and not too close to the zenith or each other.
Enter date, time and location on the hand control (SCOB's mounts have no GPS — the saved Singapore location just needs confirming), then centre any three bright objects — you don't need to know their names; even a planet or the Moon can be one. The hand control measures the angles between them and searches its database for the only trio of bright objects that fits that triangle, identifying them automatically and solving the model.
Best all-round choice for public sessions: no star names needed, works with the initial tube in any position. Pick objects spread widely apart and avoid two objects of similar brightness close together.
Centre one star you can name; the mount then chooses and slews to a suitable second star itself — you just re-centre it. Faster than full two-star since the mount does the star-picking geometry for you.
Handy in Singapore where the classic northern "first star" (Polaris) is unusable — pick anything bright you recognise (Vega, Altair, Antares…).
You choose and centre two named stars from the hand-control list. Two well-separated stars fully constrain the model, so this gives very reliable GoTos — the traditional method experienced operators still prefer.
Choose stars 40°–120° apart in azimuth, ideally 20°–60° high, on the same side of the meridian for EQ mounts.
Centre a single named star; the mount assumes its base is level and solves the rest from time and location. Pointing is approximate, but tracking near that part of the sky is fine.
Great for a fast "Moon & Saturn only" deck setup while the queue is forming — the target you aligned on tracks well; far-away GoTos will be sloppier.
Same idea as One-Star, but aligns on the Moon, a planet, or the Sun — the only bright things visible before dark. This is how a scope can track Venus at 7:15 pm before any stars appear.
⚠️ Only select the Sun with a certified solar filter fitted — the hand control hides the Sun by default (enable it in the Utilities menu).
Quick Align trusts time + location + a level, index-marked start position and skips stars entirely. Last Alignment restores the previous session's model — perfect for a mount that hasn't been moved, like a pier-mounted scope or a dome instrument re-powered mid-session.
For long-exposure imaging an alt-az fork needs an equatorial wedge, and the polar axis must physically point at the celestial pole. ASPA does this using any bright star: after a normal GoTo alignment the mount slews to where the star should be if the wedge were perfect, and you correct the difference with the wedge's mechanical knobs (not the hand control).
In Singapore the pole sits on the horizon, so ASPA — which never needs to see Polaris — is effectively the only practical way to polar-align here.
| Method | You centre | Speed | Accuracy | Use at SCOB when… |
|---|---|---|---|---|
| SkyAlign | 3 unnamed objects | ●●○ | ●●○ | default for deck CPCs at public sessions |
| Auto Two-Star | 1 named + 1 auto | ●●● | ●●● | operator knows one star; mount finds the rest |
| Two-Star | 2 named stars | ●●○ | ●●● | best GoTos for the whole night |
| One-Star | 1 named star | ●●● | ●○○ | fast setup for one bright target |
| Solar System | Moon / planet / Sun* | ●●● | ●○○ | twilight starts, Venus & Moon before dark |
| Quick / Last Align | nothing | ●●● | ●●○ | scope hasn't moved since last time |
| ASPA | 1 star + wedge knobs | ●○○ | imaging | long-exposure astrophotography on a wedge |
* Sun only with a certified solar filter.
On the hand control: Menu → Tracking → Rate. Planets are close enough to sidereal that the normal rate is fine visually.
| Mount | Type | Alignment / tracking approach |
|---|---|---|
| Deck Celestron CPC 8–11" & C6 | alt-az GoTo fork | Manual date/time entry (no GPS module) + SkyAlign / two-star as above; both axes computer-driven; field rotation irrelevant for visual queues. |
| 40 cm main telescope | English yoke equatorial (permanent) | Polar-aligned once during installation — the yoke's axis is fixed parallel to Earth's axis, so it tracks with a single constant-rate drive; no nightly alignment, only pointing calibration ("sync") on a known star. |
| German equatorial (imaging rigs) | GEM | Polar alignment (ASPA or drift method here at the equator) + 2–3 star model; meridian flips when crossing south. |
| Dobsonian (portable) | manual alt-az | No motors — the observer nudges the tube; "push-to" digital circles need a simple 2-star init. Great for teaching the sky's real motion. |
| Seestar S30 Pro | smart scope | Fully automatic plate-solving — the camera photographs the field and matches star patterns to its database — every time it slews; in EQ mode it also tracks on one axis to avoid field rotation during 30-s subs. |