Expert: Tom Whiting - 6/2/2009

Question
QUESTION: What stars can be seend from both the southern and northern hemispheres

ANSWER: Hi Susan from Australia,
The easy, but less accurate answer is....that part of the sky
in the middle, or the equatorial regions of the sky.  It's just the celestial polar regions that each of us can't see.

The accurate answer is...it's based on your latitude.  Up here at 40 N. Latitude in the northern half of the USA, we can't see your famous Southern Cross, the bright stars Canopus (Alpha Carinae) and Achernar (Alpha Eridani), or any of the sky south of those stars.
This includes Alpha and Beta Centauri, and your famous Magellanic
clouds down near the South celestial pole.  That part of the sky
never climbs up above our far southern horizon.
So it's 90 degrees - 40 degrees N. Latitude...we can't see any of
your sky south of Declination -50 degrees in the sky, so 40 degrees
of your southern sky we forever can't see, unless one travels south.

And assuming you live around the Sydney region at about -35 degrees
S. Latitude, then you can't see any farther north than 90 - 35 or
55 degrees North Declination. So there is 35 degrees of our
far northern sky you can't ever see, unless you travel northward. So you can never see our Big and Little Dippers, the North Star Polaris (Alpha Ursae Minoris), or Draco or the "big W" the constellation called Cassiopeia.  You get to see our 2 brightest stars, Vega in August and Capella in February, only very low in the north, whereas those two stars go right through our zenith (overhead point) in those months.
So we both get to see all the Zodiac constellations...Leo, Scorpius,
Aries, Taurus, Gemini, etc...We get to see them high in our southern
sky while you are watching them high in your northern sky.
Oh, when you are facing north, you watch the sky appear to move
right to left (east to west) but we up here, facing south, watch
the sky appear to move from LEFT to RIGHT (again, east to west).

Also, you see the constellations "upside down" from us...up here
Leo looks like a backward question mark, whereas from Australia,
Leo looks more like a dangling fish-hook.  You can see it the way
we see it by facing south, then bending your neck and head all the way back as you look at Leo...be careful, don't hurt yourself trying!
To us, Sagittarius looks like an upright "teapot" but to an Aussie
facing north, it's an inverted teapot. (But if you view it facing
south, then you see it oriented the way we do. Hercules is inverted to us, he's standing on his head; but to you, Hercules is upright and normal.  {Actually they are all just area's of the sky...I don't
even know why I'm calling them men, objects, and animals...as today
they are simply designated area's of the sky, and should be learned
that way...simple areas and that's all.- since 1930, but that's
another story.}

Obviously, the two extremes are.....only a person living on, or very near the equator can see both ends of both hemispheres.  And a person living at the North or South Pole would only ever see his half of the sky, and never the other half. This is why we prefer to
put our large major telescopes on or near the Earth's equator as
practically as possible. Then you get to see both the south and north
ends of the entire celestial sphere...the entire sky.

Hope this helps,
Clear Skies,
Tom Whiting
Erie, Pennsylvania  USA


---------- FOLLOW-UP ----------

QUESTION: Hi Tom from Pennsylvania. Thanks so much for your answer. I have a follow-up question. From New York, what is the brightest star looking south that can also be seen from Melbourne, where I live. Why do I ask? I'm writing a novel that has an Australian biotech company in the story. I want to give the company that star's name. Australian scientists and business people are always trying to get noticed in the US. So the brightest star in the south that someone in the Northern US and ssouthern Australia can see would be a nice metaphor
Many thanks again and best wishes
Susan

Answer
Hi Susan,Thanks for writing again.  Well, I'm very close to New York's latitude, so the New Yorkers and the Pennsylvanians see the samebright southernmost star for both of us....Fomalhaut (or Alpha Piscis Austrini, the southern fish) in our Autumn - that's Sept and October up here -early evening sky.  (Slightly German sounding name).Fomalhaut is the bright star that goes nearly through your zenith(overhead point) in late September at 11 pm your local time inMelbourne.  (Well, exactly 8 degrees from your zenith accordingto my Skyglobe computer program-- just north of your zenith).If that name turns you off, you can use the reverse...YOUR Northernmost star just 6 degrees above your northern horizon at11 pm On January 15-20...Capella, which is going through ourzenith at that same time.  (It's also our northernmost bright startoo)!  "Capella Corporation" or Capella Limited as the Brits liketo say (fake of course), sounds much better than Fomalhaut Corporation, unless it's an original German corporation in your fiction story.  Capella is the more famous star up here...and much brighter, as it's a zero magnitude star whereas Fomalhautis much dimmer at 'only' first magnitude.  And Fomalhaut is alwayslow in the south for us, and never up, above our southern horizon for more than about 4 hours.(It's a reverse scale, the lower the magnitude number, the brighterthe object...see, there is a lot to learn in astronomy). ;-) You may have never seen bright Capella because it is so very lowin the north for you in Melbourne, and then only for a few months; It's only above your far northern horizon for about an hour a night,reaching a maximum height of only 6 degrees (about one fist-widthat arm's length) above your far northern horizon.It's at 46 N. declination, so add your 38 S Latitude and you get84 degrees.  90 - 84 = 6 degrees high at it's maximum height in  your far northern sky....during your summer months.  (Of course inlate January, we're in the depth's of winter with several feetof snow on the ground, sometimes much more.)Other bright zero magnitude or brighter stars we both see are Siriusthe Dog Star, Rigel in Orion, Arcturus and Vega, both far north foryou, but you can see them. Other first magnitude names are Antares,Aldebaran, Regulus, Pollux, Procyon, Spica, Betelgeuse in Orion,Deneb, and Altair.  In fact, the only 2 very bright stars that youcan see way to the south, that we can't, are Canopus and Achernar. You can see ALL of our bright stars...Capella being your mostdifficult, as explained above.Hope this helps,Clear Skies,Tom

FOLLOW UP:Oh, that star Capella by the way, is probably the most widely reported "UFO" in Australia, because it being so low in the north during your summer months and with all the horizon haze, it would twinkle wildly and change colors dramatically do to low horizon haze interference. You rarely would see it as a steady, bright pinpoint
of light, like we do at our zenith.
Best wishes,
Tom