With access to dark skies, cruise passengers have opportunities to enjoy some celestial sights they can't see at home. "Overhead at zenith will usually be quite dark as soon as you are 5 to 10 miles away from a brightly lit city," writes Bob Parks, Executive Director of the International Dark-Sky Association. "While sky glow may still be visible up to 100 miles from the source, once you are more than 25 miles away, the majesty of the Milky Way will render distant sky glow insignificant."
If you're not accustomed to a dark sky, you might be amazed at what you're able to see when you have one. In addition to the moon, as many as five bright planets (Mercury, Venus, Mars, Jupiter and Saturn) and some of the 21 brightest stars, which you're probably able to see at home, you might also be able to see the dimmer stars (up to a thousand or more at once), the bright swath of the Milky Way, dim meteors and satellites, and even the faint glow of the Andromeda Galaxy two million light-years away. You can see all this with the naked eye -- no telescope necessary! If you're a very dedicated sky-watcher, you can book a cruise to travel to the best locations to see an exceptional celestial phenomenon like an eclipse, bright comet or meteor shower.
Here are some suggestions for taking advantage of stargazing opportunities on your cruise vacation:
1. The farther you head from shoreside lights, the more celestial objects you'll see. Head to the middle of the ocean, and your cruise ship will likely be beyond the reach of land-based light pollution, allowing you to see fainter objects in the sky than you might see ashore. World cruises and ocean crossings are good bets for escaping the lights of land, but any itinerary that takes you more than a couple of dozen miles from shore might give you great stargazing opportunities.
2. Your location impacts what you see in the sky. Your latitude -- your distance north or south of the equator -- will determine which stars you see and how long you see them. You won't see the Southern Cross much farther north than the Tropic of Cancer (23.5 degrees north latitude), which runs between Key West and Cuba and also near Cabo San Lucas at the tip of Baja California. You won't see the North Star south of the equator. South of the Tropic of Capricorn (23.5 degrees south latitude), about as far south of the equator as Rio de Janeiro, you'll watch the sun, moon and planets go right-to-left across the northern part of the sky instead of the left-to-right path you see them cross the southern horizon in the mainland U.S. and Europe. A star chart will help you find the bright stars and planets. Not sure where you are? Many cruise ships have a channel on the in-stateroom TV that includes the exact longitude and latitude of the ship during the voyage.
3. When you travel makes a big difference. The time of year will determine the stars and constellations you'll see, and the time of month determines how much moonlight brightens your sky. For northern lights, choose a North Atlantic, Alaska or Scandinavia cruise after mid-August (when you once again have darkness late at night) and when there is little moonlight. A new moon, when the moon begins its new cycle and can't be seen at night, is the darkest time of the lunar cycle. (At this time, the moon turns its unlit side toward Earth and crosses the sky in the daytime with the sun.) A waxing moon, between the new and full moon, gets brighter every night and sets later after sunset. The full moon rises at sunset and sets at sunrise, shining its bright light all night long. The waning moon, between the full and new moon, is less illuminated each night and rises later after sunset. The brighter the moonlight, the fewer faint objects (including dim stars, meteors and satellites) you'll see.
4. Choose the dry season for better nighttime views. Sailing during a region's dry season (which usually coincides with its high season) will tend to have fewer clouds at night, giving a better view of the entire sky and more pleasant time on deck. Think Caribbean December through April and Mediterranean May through September.
5. Stargazing will be best from the darkest part of ship. The area forward of the bridge is always kept dark when the ship is at sea, but unfortunately most of the large ships built in the 21st century no longer have public areas and promenade decks there. (Cunard's Queen Mary 2 and Royal Caribbean ships are notable exceptions.) Even if the promenade deck goes all the way around the ship, the view may be blocked in places by an overhanging deck. Generally, positions forward will be windier, and those aft will be brighter (staircases especially will be lit for safety reasons) and may have smoke from the stacks blocking part of the sky. One other thing to note: the Deck Department will generally hose the decks down at night when they don't expect passengers to be out on deck, so watch for hoses and errant spray.
6. If you want to see a total solar eclipse, book an astronomy theme cruise. Total solar eclipses from the Arctic to Antarctica have been a staple of cruise calendars since astronomer Ted Pedas' first charter in 1972. (His chronicle of the voyage, "Saga of Launching the World's First Eclipse Cruise" is a hoot.) Total solar eclipses aren't rare -- they happen every year or two -- but you might have to wait centuries for one to come to you. Often, much of an eclipse's path is over water and accessible only by seagoing vessels, and ships have the added advantage of not being limited by roads (and traffic) if they have to maneuver to avoid clouds that threaten to hide the show. Theme cruise companies will plan specific solar eclipse cruises; look for them in our list of nature-based theme cruises.
7. Check last minute for unpredictable astronomical events. Comets and meteor showers can be spectacular when seen from a dark sky. However, not all of these celestial events can be accurately predicted far in advance. To quote famed comet hunter David Levy: "Comets are like cats; they have tails, and they do precisely what they want." Even though we may be able to accurately calculate a comet's path, astronomers can only guess at how bright it will be for Earth-bound viewers. The intensity of meteor showers, caused by the cosmic flotsam of a comet's tail, can also be notoriously hard to predict. The upshot is that cruise lines can't schedule theme cruises or arrange for onboard astronomers for these events; but if you check before your trip, you'll have a heads-up to look out for these potentially amazing celestial phenomena.
8. Seek professional help -- in book form. A good beginning astronomy book can help you understand more about what you're seeing. I'm a fan of DK Publishing's "Smithsonian Nature Guide: Stars and Planets," available in "flexiback" (a durable cover better than hardback or paperback for a field guide) and as an eBook. Its monthly sky guide shows positions of the planets through 2019 and is written for both northern and southern latitudes with sky charts designed for 60 degrees North (including Juneau, the Canadian Maritime provinces, Great Britain and the Baltic capitals) to 40 degrees South (all of Africa and Australia north of Tasmania, half of New Zealand and most of South America). Astronomy magazines and websites will let you know about upcoming notable astronomical events like meteor showers and eclipses, which planets you might see and which bright stars might appear near the moon during your cruise.
9. Seek professional help -- in human form. Find out if there is a naturalist or astronomy lecturer aboard giving enrichment presentations during your voyage. Sometimes this information is listed in advance on the cruise line's website. Cunard's Queen Mary 2, which has the only permanent seagoing planetarium, also regularly features speakers from the U.K.'s Royal Astronomical Society. Even if you can't find out ahead of time, ask when you get onboard, or check your daily program for talks. In addition to daytime presentations on sea days, shipboard astronomers often give nighttime star talks on deck, giving you the chance to see firsthand celestial sights you might never see at home. Consider it extra (and free!) sightseeing your shore excursion department could never provide.
10. Take advantage of astronomy smart phone and tablet apps. You'll find the biggest variety of astronomy apps for iPhone and iPad, but they also exist for Android, Blackberry and Windows 8 operating systems. If your device has built-in GPS, you can take advantage of applications that don't need to connect to the ship's cell phone network (at roaming rates that can be quite expensive). So-called "planetarium" apps allow users to identify stars and planets just by pointing their devices at the sky. Other handy apps can be used to identify satellites. (You need to connect to a network to download satellite orbital elements, but you can do this before your voyage or when ashore.) You can also predict northern lights activity hours or days in advance, but you will need to connect to a network for this to be useful.
--by Dan Benedict, Cruise Critic contributor