Astronomy on cruise ships

This page is being developed to provide information related to providing astronomy talks or observing sessions on cruise ships. Such activities are relatively popular (as opposed to activities like identifying marine algae on pier pilings at your ship’s dock) and cruise lines are looking for ways to provide astronomy experiences on their ships.

I have already prepared a lengthy webpage about traveling for land-based astronomical observations that discusses light pollution, climatological cloudiness and other factors that will affect your travel plans. The material below is focused on astronomical observations on cruise ships – and is intended mostly for the lecturer that might want to present such nighttime viewing sessions and related daytime subject matter talks.

Some background

I have been an amateur astronomer since elementary school days and currently have two telescopes (Celestron 8 and 11 inch). The smaller Celestron we took with us on travel to South Africa and to Australia to see features of the Southern Hemisphere night sky that cannot be seen from the US. I taught Earth Science courses at a community college while I was in graduate school in Tallahassee, Florida in the early 1980’s. These courses included Astronomy as one of the four main topics in the course (the other three were geology, meteorology, and oceanography). More recently, I volunteered with public viewing sessions at the very nice 3RF Astronomy campus in rural Texas, about 200 miles from where we live. Dark skies there justified the long drive on cloud-free weekends.

My wife Rosario next to our Celestron 8 inch telescope in the Tanqua Karoo National Park in South Africa. This scope also went to Australia.

There is an excellent online forum for amateur astronomers (those who observe the sky as a hobby) called Cloudy Nights. A specific forum on Cloudy Nights motivated me to prepare this webpage. It was about what was needed for teaching a nighttime session aboard a cruise ship. The replies to the initial question (posted from a lecturer on a cruise ship) are valuable to read – from a potential astronomy lecturer’s point of view.

In summary, the main comments were as follows:

  1. A green laserpointer is the most essential item to have. Human eyes are very sensitive to their green light and the beam can be seen easily by people when you point to objects in the night sky. They are dangerous in the hands of children – never loan one, even very briefly, to anyone else.
  2. binoculars are needed to go beyond pointing out the basic constellations or bright parts of the Milky Way. Anyone with them should be encouraged to bring them to an astronomy night viewing session.
  3. Telescopes of almost any kind are not very feasible due to the ship’s motion – at least while the ship is underway. In addition, a telescope will generate a long, slow moving line that most people won’t appreciate – especially if it is cold.
  4. Some app for smartphones that shows the location of features in the night sky would be useful. The app may work better on an iPad or similar larger-screen than on a small phone screen – at least the items shown will be easier to see.

While most sessions to view the stars will be held on sea days with the ship in motion, it is possible to observe when the ship is in port on overnight stays. However, the sky will likely not be very dark as overnight port calls are mostly at large towns or cities with plenty of light pollution.

Some important considerations

Consider the phase of the moon. An observing session during a full moon will not be very productive in showing the Milky Way or any dimmer objects. It may be satisfactory for showing the location of planets, the moon and some of the brighter stars and constellations. You cannot change the scheduling of a cruise ship, but you can predict quite accurately the phase of the moon and it’s rise or set for each evening of your cruise.

Consider your latitude and the amount of night you will have. Summer cruises to Antarctica or the Arctic (including Norway, Iceland, the Baltic Sea etc) will not have dark conditions until very late in the evening – if at all. There is no point having an astronomy observing session if the sky isn’t dark. The farther the cruise date gets from the solstice (June 21 in Northern Hemisphere, Dec 21 in Southern Hemisphere) the more hours of darkness there will be. Remember, the time the sun is below the horizon isn’t the only factor – how far below it is is what determines how dark it will get. When looking at tables of sunrise/sunset/ be sure to look for the time when “Astronomical twilight” ends and begins. This is when the sun is greater than 18 degrees below the horizon. This can be much less time in higher latitudes than when the sun is just below the horizon. For example, there is no real darkness (sun lower than 18˚ below the horizon) at Oslo, Norway (about 60˚N) between about April 22 and August 22 – a period of 4 months!

Definitions of the various twilight conditions (from website

Consider cloudiness. Scattered clouds like trade-wind cumulus can be present all night in the tropics but you may be able to see well during periods of fewer clouds. More widespread cloudiness will force an impromptu talk on some astronomical subject – such as where astronomical observatories are located around the world – and why (answer: places with little cloudiness).

The average daytime cloudiness based on about 7 years of daily satellite imagery.  The image's contrast and brightness has been adjusted for easier viewing of the main patterns.  Bright areas are where there is more frequent cloud cover (or snow over land areas) and darker areas over the ocean are where there is less cloudiness.  Nighttime cloudiness is not too different over the ocean areas, so the darker areas are those that are more favorable for astronomical sessions from a ship at sea.
The average daytime cloudiness for the May-October period, based on about 7 years of daily satellite imagery. The areas of frequent cruise ship activity during this time of year have been highlighted by the dashed curves or lines. Alaska (A) and the north Atlantic (C) are relatively cloudy regions, while the tropical Pacific south of the Equator (B) and the Mediterranean (D) are relatively less-cloudy. The image’s contrast and brightness has been adjusted for easier viewing of the main patterns. Bright areas are where there is more frequent cloud cover (or snow over land areas) and darker areas over the ocean are where there is less cloudiness. Nighttime cloudiness is not too different over the ocean areas, so the darker areas are those that are more favorable for astronomical sessions on a ship at sea. Click on the image for a larger view.

Same as previous image except for Nov-April period. Now the main ship activity is in the Caribbean Sea region (D), between Sydney and New Zealand (E), western Mexico (C), and the Antarctic peninsula region (B) (routes between Buenos Aires and Santiago). The South Pacific (A) is included because some cruises traverse this area during the period. Click on the image for a larger view.

Quick summary: High latitude cruises during the summer months are not really suitable for outdoor astronomy activities (lectures are fine) because of the combination of cloudy conditions, colder temperatures, and most importantly, the lack of fully-dark “nighttime” conditions for several months around the summer solstices.

Once the cruise ship is a few hours from port the sky should be quite dark – that is free of light pollution from cities (see the image comparison below). The main problem with be your ship’s lights. Cruise ships like to advertise themselves and are lit up everywhere for safety of passengers walking at any hour of the night. Finding a really dark location on a cruise ship is nearly impossible. But with some advanced planning, an upper deck that few people use at night can be converted into a night viewing location with minimum effort. This “minimum effort” should include covering key lights with red bags that reduce greatly, but not entirely, the lighting. A human eye’s adaption to see in the dark is much less affected by red light than by by white light.

The light dome from Oahu – mainly Honolulu – and the surrounding islands of Kauai and those near Maui. Black is dark-sky conditions while the other colors reflect increasingly poor conditions for viewing the stars. The distance from Honolulu to dark sky conditions is about 50 miles – about 2-3 hours sailing.

Consider ship noise and the ability of your audience to hear you. With any wind and engine noise, you may be hard to hear. A portable microphone can be very useful – but it needs to be requested in advance. Cruise ships have great audiovisual support for their main venues – but the top deck at night isn’t one of them! Give them plenty of advance notice to see it they can help out.

Consider the ambient conditions – especially the temperature and wind that the audience is exposed to. Astronomy observing sessions are much better when the air is warm – think 80˚F, as opposed to cold conditions – anything under 70˚F. The ship will be moving at approximately 20 miles per hour and if the ship is moving into the wind the wind the audience will feel will be very unpleasant. Protected areas on the ship – where the wind ship-relative wind is minimized, are best. You may be lucky and the ship is moving in the same direction as the wind flow so there appears to be little wind at all – but then you may end up smelling the diesel fumes from the engines!

Consider your audience

Many people in your audience for an evening astronomy session aboard ship may not be very familiar with the night sky. If they are, it will most likely be the sky that is visible from their home – which means for most cruisers -the Northern Hemisphere at latitudes between 30˚N and 50˚N. These people will not be very familiar with objects that can be seen only from lower latitudes or the Southern Hemisphere. Prominent features of the Southern Hemisphere night sky include the Large and Small Magellanic Clouds (two satellite galaxies to our own Milky Way), the Southern Cross and nearby Coal Sack (a dark nebula), the Eta Carina (bright) nebula and a variety of other objects (like the globular cluster 47 Tucana) that can’t really be seen well from the US, Europe, Japan or China.

Even people who are familiar with the night sky from their homes may only rarely have been in really dark-sky locations where there is almost no light pollution. Most of us live in, or near urban areas. You can see the light pollution where you live by looking at websites (one is here) that provide maps of light pollution. A better site where you can download a kmz file for displaying in Google Earth is here.

What “ought” to be covered in a night sky observing session

Do discuss green laser pointers and the most obvious basic constellations in the sky. Discuss original constellations, those of the Zodiac, and current astronomical constellations (88 of them).

The moon, planets, the ecliptic and the zodiac

meteors, satellites, zodiacal light, aurora etc

basics of binoculars and telescopes

light pollution

Obviously, one cannot talk about all of these subjects during a single nighttime observing session. Just be prepared to talk about something – otherwise people may not like staying up late for your presentation if the sky is cloudy!

Astronomy Talks

Ideally, nighttime observing session shouldn’t be held without some introductory material being presented first. There might, or might not, be time available for such a talk (your cruise director will know), so you should come to the observing session prepared to talk endlessly about a few key astronomical subjects. Below are a few topics I would talk about, if given the chance. Everyone’s background is different.

Just what is astronomy? How does it differ from the subject of planetary science? (They used to be grouped together- before we began to explore our solar system.)

The history of Astronomy

Telescopes and observatories

Our solar system and how we have explored it in recent decades (what our century will be remembered for a millennium from now).

Beyond our solar system, our Milky Way. What’s all this about galaxies, star clusters, nebulae and multiple stars?

The universe… Hint … it’s really big. The big bang. Black holes.

Each one of the topics above could fill an entire lecture (some topics justify an entire college course). So the lecturer needs to judge their audience and select the topics they think will be most appropriate – both educational and entertaining.

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