If you are planning a summer vacation to a national park, be sure to schedule some time for stargazing. After a long day of hiking and site seeing, you may be more inclined to go to bed than go outside and look at stars. The view is worth it. Planning is essential, even if it’s for only 30 minutes.
Really dark skies are becoming so rare that national parks are one of the few places you can go to experience them. One fifth of the world’s population and two thirds of the US population live in areas where the Milky Way is not visible. Seeing the Milky Way under dark skies is an experience you never forget.
Here are some things to consider:
- Keep your schedule flexible. Clouds and the Moon are great at derailing the best made plans. You may find observing in pre-dawn skies can work out best. You may have to wait a day or two for clouds to clear or the Moon to move.
- Plan your trip within a few days of a New Moon. New moons are the opposite of a Full Moon. You cannot see the Moon when it is new. On the other hand full moons are up all night and very effective at wiping out a dark sky. Many campers like to camp during a Full Moon because the Moon cast enough light that you do not need flashlights.
- The latest sunsets, and earliest sunrises, occur around June 20th. If you are going to northern locations, like Glacier National Park, it never really gets dark a week or two either side of June 20.
If you are not an amateur astronomer this is probably the first vacation where you’re planning involves phases of the Moon! So how do you do that? Fortunately there are resources on the internet that can help. The nice thing, you can start understanding Moon phases, moonrise and moonset times before your vacation right from your own backyard.
A review of lunar phases may help. It takes the Moon approximately 29.5 days to go around the Earth. This cycle is divided by four events: New Moon, First Quarter Moon, Full Moon, and Last or Third Quarter Moon. Each event is roughly seven days apart. Many calendars mark the dates of these events. The best time for dark sky (no Moon) observing is between Last Quarter and First Quarter. The closer to New Moon you plan the more hours of dark Moon free sky you will have.
If you want detailed information go to http://www.sunrisesunset.com/USA/NationalParks/ or here for your own back yard. You can print out a monthly calendar for a specific location. Here is a sample for Grand Teton National Park, Colter Bay Visitor Center, Wyoming on July 26, 2014 (New Moon). Astronomical twilight is the time when the light from the Sun no longer affects the night sky.
- Astronomical twilight: 3:58 am
- Moonrise 6:03am (rises with the Sun)
- Sunrise: 6:04am
- Moonset 8:27pm
- Sunset: 8:54pm
- Astronomical twilight: 11:00pm (technically you need to get this time for the day before which is 11:02pm)
Given the data above the best time to observe the sky at its darkest on the evening of July 25-26 is between 11:02pm (July 25) and 3:58am (July 26), roughly 5 hours.
If you go one week earlier the picture changes significantly. On July 18-19 astronomical twilight starts at 11:13pm (July 18) and ends at 3:46am (July 19), a period of roughly 4.5 hours, but Moon rises at 12:42am. The darkest sky without the Moon is now between 11:13pm and 12:42am or about 1.5 hours.
Huh? I know it really looks complicated. Fortunately the Moon is very predictable and easier to understand than many think. You can read about it, but the best way to understand what the Moon is doing is to observe it for two weeks.
- Start a day or two after New Moon and observe the Moon 30 to 60 minutes after sunset. Watch the Moon move toward the east at 12.5 degrees per day, and go from a thin crescent to full.
- Or, if you are a morning person, start with Full Moon and observe 30 to 60 minutes before sunrise and watch the Moon move toward the east at 12.5 degrees per day and go from a Full Moon to a thin crescent.
- Most important is that you observe around the same time each day.
Before experiencing a dark sky here are a few things to know:
- No white lights, use red or dark green lights instead
- Give your eyes a good ten minutes to night adapt. It takes about 20 minutes to fully night adapt.
- Get comfortable! Lay on your back or in a lounge chair. Make sure you dress warmly.
- Do not try to identify constellations unless you really want to. There are far too many stars to make it easy for a beginner. It’s even difficult for us who know.
- If you have binoculars scan the Milky Way. You will find more than stars.
Many parks have “astronomy” nights were amateur astronomers bring telescopes for public viewing. Check with the park you are planning to visit. Bryce Canyon is one of the best parks for this activity.
Wishing you clear skies