Sky ArchiveTonight

Southern Cross: A southern sky signpost

Southern Cross and southern Pointer stars.
View larger. | Here’s the Southern Cross as seen from Manila – latitude 14 degrees north of the equator – in 2012. The photo is from EarthSky Facebook friend Jv Noriega.

For our friends in the Southern Hemisphere, we’re paying tribute today to the Southern Cross, also known as the constellation Crux. No matter where you live in the Southern Hemisphere, look in your southern sky for the Southern Cross as soon as darkness falls.

At temperate latitudes in the Southern Hemisphere, where it’s now late autumn, we astronomers say the Southern Cross swings to upper meridian transit – its high point in the sky – at early evening, or somewhere around 7 to 8 p.m. local time.

The photo below is from the Philippines also. It’s from Dr Ski, who posts frequently to EarthSky Community Photos:

The Southern Cross, seen from the Philippines, with bright stars to left and right of it.
View larger at EarthSky Community Photos. | Dr Ski caught the Southern Cross – aka Crux – in late March 2019, around the time of its midnight culmination (in other words, around the time it was crossing the meridian – highest in the sky – around midnight). He wrote: “Alpha and Beta Centauri are the bright stars on the left. Lambda Centauri and Eta Carina nebulae are on the right.”

Because the Southern Cross is circumpolar – always above the horizon – at all places south of 35 degrees south latitude, people at mid-southern latitudes can count on seeing the Southern Cross all night long, every night of the year. Watch for the Southern Cross to move like a great big hour hand, circling around the south celestial pole in a clockwise direction throughout the night. The Southern Cross will sweep to lower meridian transit – its low point in the sky – around 7 to 8 a.m. local time tomorrow.

If the Southern Cross is circumpolar in your sky, then the Big Dipper never climbs above your horizon.

Conversely, if the Big Dipper is circumpolar in your sky, then the Southern Cross never climbs above your horizon. Additionally, the W or M-shaped constellation Cassiopeia is also circumpolar at northerly latitudes. See the animation below.

Animated diagram of the Big Dipper and the W-shaped constellation Cassiopeia circling around Polaris.
In the Northern Hemisphere, the Big Dipper and the W-shaped constellation Cassiopeia circle around Polaris, the North Star, in a period of 23 hours and 56 minutes. The Big Dipper is circumpolar at 41 degrees north latitude, and all latitudes farther north.

However, if you live in the tropics, there are times when you can actually see the Big Dipper and the Southern Cross in the same sky together. In early June, for instance, the Southern Cross and Big Dipper reach upper transit – their high point – at virtually the same time.

You have a better chance of seeing the Southern Cross and the Big Dipper in the same sky right now from the southern tropics. That’s because the late autumn season in the Southern Hemisphere ushers in an earlier sunset time than at comparable latitudes in the northern tropics, where it is now late spring.

Diagram of intersecting dotted lines from Crux and pointer stars to location of South Pole.
Star-hopping to south celestial pole via the Southern Cross and the bright stars Alpha Centauri and Hadar.

Bottom line: A tribute to the Southern Cross, also known as the constellation Crux.

June 7, 2019
Sky Archive

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Bruce McClure

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