The Backyard Universe

Multicultural stargazing & astronomy experiences in South Australia

Heysen Trail & Fleurieu Peninsula shuttle bus services

Nature, scenery, geology, winery & day tours

The Director's Commentary

Some behind-the-scenes views....

Why we don't do tours during full moons.
Some non-astronomy things we've seen during tours.
Naming of stars.

Why we don't do Fleurieu Stars during full moons

(unless there's a lunar eclipse that evening)

So you've been looking at our Fleurieu Stars tour calendar for a night that's not booked out.
Or you're wanting a private night sky tour for your group. Or a private tour at some other location.
And then you see it, there in our tour calendar, an interval of 6 or 7 consecutive nights when Nobody Has Booked A Tour.
So you're thinking...


    ** BUT **

There's a very good reason for that interval of no bookings -- the full moon. Its light blots out almost everything else we want to show you during Fleurieu Stars tours. Such as the Milky Way. And every other galaxy. And nebulae. And most star clusters. And the thousands of stars you would be able to eyeball if that bright moon wasn't there, ruining the experience. Just compare these two photos, taken before and after a bright moonrise in the Australian Outback.

before and after moonrise

Years ago we used to do tours during bright moons but those nights produced frequent complaints of "I can't see anything!" So we stopped doing tours during bright moons which ended those complaints.

We've confirmed our decision with calculations of the number of stars you could eyeball at our Forktree tour location during various moon phases. This is based on our measurements of the local night sky brightness over many years at various moon phases, together with the apparent brightness of every star visible from our latitude. And we've done similar measurements for Adelaide city and Adelaide's outer southern suburbs. The results are graphed below.
For comparison we've also added moonless-night star numbers for Forktree and for the Ikara-Flinders Ranges National Park (an iconic we-can-see-zillions-of-stars-out-here Outback holiday destination).

graph of visible stars versus moon phase

As expected the moon phase makes almost no difference to the view from Adelaide city because there's so much light pollution there already. Not just from the city centre but also from the ~1 million residents and ~200 thousand street lights in the surrounding Adelaide metropolitan area. The moon phase has more of an effect in Adelaide's outer suburbs. But even there the view on a moonless night is no better than our view during a 3/4 full moon. So we decided if you're going to be travelling from Adelaide (or McLaren Vale or Victor Harbor) to do our tour, the least we can do is schedule it for an evening when you can see more stars here than you can from the suburbs.

And note that on our moonless tour evenings you can eyeball practically the same number of stars as you can from the Outback.

During most years we don't run Fleurieu Stars during the Easter long weekend, because the date of Easter Sunday is controlled by a full moon. Specifically, Easter is the first Sunday after the first full moon that occurs on or after March 21. But if that full moon occurs on a Sunday, then Easter is the following Sunday. Unfortunately the Christian churches use an ecclesiastical -- not astronomical -- moon calendar which consists of 29 day and 30 day months repeating on a 19 year cycle. For a longer explanation of this calendar's history and its Easter date calculations, see Wikipedia. The ecclesiastical calendar doesn't correspond exactly to the astronomical times of moon phases. And it doesn't account for modern time zones.

For example the 2019 ecclesiastical calendar lists full moons on March 20 and April 18. In Australian timezones the actual astronomical full moons occurred on March 21 (at 12:12 Adelaide time) and on April 19 (at 20:42 Adelaide time). So an astronomical interpretation of the 2019 Easter date for Australia would start from the Thursday March 21 full moon, and pick Sunday March 24 as Easter. But the ecclesiastical calendar used its Thursday April 18 "full moon" instead and picked Sunday April 21 as Easter.

In 2021 the (astronomical) full moon occurred 6 days before Easter so we were able to schedule tours throughout the weekend that year. But most years we're not that lucky; for example in 2022 there was a full moon on the Easter Sunday and we lost the entire long weekend.
To cure this problem forever, we reckon Easter should be redefined as the second Sunday after the March full moon -- which would ensure moonless evenings and tours throughout every Easter long weekend 🙂

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Some non-astronomy things we've seen during tours

In order of decreasing altitude:

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Naming of stars

Episode 1: How it's officially done

Cultures and civilisations throughout human history had their own names for the bright stars visible in their skies. But many of these traditional names have been lost, forgotten, or actively suppressed (by conquest or genocide). Rediscovery of these star names is a slow and ongoing process combining astronomy, anthropology, archaeology, linguistics, ethnography, and archival research. And everyone involved in this rediscovery knows it will never be complete :-(

Nevertheless some of these ancient star names have survived to today, although their pronunciations in modern English are sometimes very different from the original, mostly due to errors & misunderstandings in historical translations.
The earliest star maps and star catalogues were compiled (independently of each other) by Greek, Indian, and Chinese astronomers over 2000 years ago; and then copied / rewritten / translated multiple times over the subsequent centuries. One of the most influential versions -- The Book Of Fixed Stars -- was written in the 10th century by the Iranian astronomer Abd al-Rahman al-Sufi (a.k.a. "Al-Sufi"). Al-Sufi summarised most of the astronomical knowledge known in his time, including star names, all translated into Arabic. And he included beautiful maps of his constellations. Latin translations of The Book Of Fixed Stars became one of the standard astronomical references for early Medieval Europeans. And Al-Sufi's star names were copied into the classic European star atlases and catalogues of the 16th and 17th centuries.

But these atlases and catalogues also introduced some other ways to name the same stars, and so what we have today for official star names is:

The International Astronomical Union maintains the official list of internationally recognised bright star names (there's a copy of this list on Wikipedia too). And to their credit the IAU are actively soliciting official star names from non-Western cultures nowadays for the bright stars that don't already have names. For example the fifth-brightest star in the Southern Cross was originally named Epsilon Crucis (by Bayer). But as of late 2017 it's also known officially as Ginan, its name among the Wardaman people of the Northern Territory.

Episode 2: Businesses and other places 'selling' star names

There's two versions of this activity:

  1. A fund raising gimmick used by lots of astronomy clubs & observatories & planetariums. Where it's made very clear to every potential "buyer" that their money is being used for fund raising and won't confer any legal rights. For example Spend $10 to 'buy' one of the stars on this photo to help us raise $10,000 for our new telescope. Or Spend $10 to 'buy' one of the stars on this photo, we'll donate $8 of it to [a charity], and we'll give you this nice photo certificate of 'your' star. This version of 'selling' stars is not a problem. Although in Australia, don't forget to ask for a receipt of any charitable donation so that you can claim a tax deduction.

  2. The version of 'selling' stars that IS a problem are the businesses who offer, for a fee, to have a star "officially" or "exclusively" named "forever" for you in commemoration of a deceased relative or friend. Or named as a gift for someone special to you who isn't dead. Some of these businesses will also claim they're authorised by NASA or some other space agency, or show off alleged endorsements by major online stores or media outlets.
    If you paid one of these businesses then (sorry, there is no nice way to say this) -- YOU HAVE BEEN SCAMMED. You have been preyed upon while you're emotionally vulnerable. The star that's been 'sold' to you, 'officially named' for your relative or friend, can also be 'sold' again to the scammer's next victims.
    You probably received a photo of the star; sometimes including its genuine astronomical coordinates to make the 'sale' look more legitimate. The photo might be part of a 'certificate' that 'officially names' the star for you. We've seen versions that claim to be 'certificates of ownership' of the star too, supposedly signed by real astronomers or astronauts. It's still a scam.
    But it gets worse. Even with genuine coordinates there is no guarantee that we can show you this star. It may be too faint even for our big telescopes. Or it may be so far north that it never rises above our horizon.
    Are you feeling angry about this scam yet? It's been operating in one form or another for decades, and continues to thrive because most of its victims are too embarrassed to admit they were conned and so they never (knowingly) meet each other. Or demand compensation....

    But public disclosure can happen regardless. There was a school group's night sky tour we were running about 20 years ago. One pair of parents brought along a photo of a star 'named' for their recently stillborn child by Star Naming Company A. A second set of parents brought along a photo of a star 'named' for a beloved grandparent by Star Naming Company B. Both pairs of parents demanded to see 'their star'. And yes; we were shown near-identical photos of exactly the same star!

If you're really determined to have your name on a star, then change your legal name to be an actual star's existing name (see Episode 1 above). Or pick a name for your newborn child that's an actual star's name. Many of the bright stars also have traditional names from non-Western cultures too. So pick a bright star's name you like and then contact your local Births Deaths & Marriages office about How To Change Your Name. In Australia if your new legal name (a) isn't obscene/offensive, and (b) is pronounceable, then it's yours. So go for something like Alpha Orionis or Betelgeuse rather than 2MASS J05551028+0724255.
Of course, you also have the added expense of changing your name on your passport, licences, registrations, ownership documents, bank accounts, utility bills -- although if you can do this paperwork at the same time as you're getting married then you may avoid some fees.
But cheer up. At the end of this process you WILL -- officially and legally and unquestionably -- have a star that has the same name as you. And it won't matter if somebody else chooses the same star name. After all, the English-speaking world has had centuries to figure out how to positively identify a specific "John Smith"!

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