Expert: Philip Stahl - 6/30/2008

Question
Can the southern cross conselation be seen from the island of Maui????

Answer
Hello,

Maui is at latitude 20 deg 48 min North. This means any objects with a declination of 20o 48' would pass through your overhead point. Between the overhead point(zenith) and the southernmost point of your horizon would be 90 degrees. The celestial equator (at 0 degrees) is 20 o 48' south of the zenith. This leaves:

(90 deg -   20 deg 48 min) =   69 deg 12 min to the southernmost point. I.e. 69 deg 12 min BELOW (south of) the celestial equator..

That means that any object with declination LESS than (-69 deg 12 min) would not be seen.

Acrux (Alpha Crucis) the brightest star in the Southern Cross is at a declination of about - 61.5 deg. This means if you were to observe the Cross exactly when it's on your meridian, Acrux would be at an altitude of (69 deg 12' -  61 deg 30') = 7 deg 42'.

If you hold your fist out at arm's length - it would span just about 5 degrees, so the above altitude would be slightly greater.

Meanwhile, the Cross star Gacrux (Delta Crucis) is at a declination of about -56.5 deg.

Again, doing the math you can work out its altitude (maximal) when viewed from your meridian would be:

(69 deg 12'  -   56 deg 30') = 12 deg 42 '

Beta Crucis would be at about (-59 deg) declination, so again it will also be seen at about 10 deg altitude above the south horizon when on the meridian.

Bottom line, you will be able to see the Cross from Maui, but it will be difficult, and you will have to look as close to the time of meridan transit as feasible.

From my Cybersky program, using a median Right Ascension for the Cross of 12 h 30 m, this appears to be ~ 6.30 p.m. Maui local time. For which clearly there will still be too much sunlight on today's date. Part of the Cross will still be visible 2-3 hrs later, but some of it will not be seen because it is now past your local meridian.

If you do observe, be sure you have a totally unobstructed view of the southern horizon!

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Addendum: you would have been able to see the (whole) Cross at its meridian transit time had you observed on May 15, at 9.30 p.m.