A guide to sidewalk astronomy

“When you’re in love,” said Carl Sagan, astronomer and co-founder of The Planetary Society, “You want to tell the world.”

This is the impulse that leads people to bring their telescopes outside, set them up in public, and offer passersby a glimpse of the Cosmos. Though it may sound modest, sidewalk astronomy reaches hundreds of thousands every year. Many people get their first sight of Saturn’s rings or the craters of the Moon while out on the street, where a moment’s pause on an evening walk can spark a lifelong curiosity about the Universe.

If you own a telescope and want to give sidewalk astronomy a try, it comes with a few best practices. These range from the practical (how do you share an expensive piece of equipment with lots of people, some of whom may not know how to use it?) to the more strategic (how can you best draw a crowd?). Here are our top tips on hosting your own sidewalk astronomy event, drawn from both personal experience and that of The Planetary Society’s members. 

This article is about sidewalk astronomy, specifically. For a full guide on how to enjoy the night sky, check out Stargazing 101 on The Planetary Society’s online member community. Not yet a member? Join today.

1) Choose the right spot

• Follow the foot traffic. Sidewalk astronomers often set up at street fairs, outdoor events, nightlife hotspots, or by any venue where a lot of people tend to pass by. If you want to set up at an event, check to see if you need permission from its organizers. 
• Make sure you have an open view overhead. Broad streets, parks, and parking lots can offer good views of the sky above. If you do set up on a narrow street or near tall buildings, check early on whether your target will be visible.
• Stay away from bright lights. If you’re in a city, there may be only so much you can do. Still, there is a big difference between the view from directly under a streetlight versus from a dozen feet away. Putting a building or tree between your telescope and a bright light will also improve the quality of what you see.
• Set up on grass, if you can. Materials that retain heat, like asphalt, are less ideal. They will lead to greater temperature differences around the telescope that could distort your view. Do not set up your telescope on a wooden deck, either, or any surface that will vibrate with footfalls.

2) Bring some not-so-obvious equipment 

• Put up a sign. People will be more willing to approach if they can see at a glance that you are offering views of Saturn, say, or the Moon, and that you are offering them for free. 
• Use a green laser pointer* to point out night sky objects. The laser will help attract people to your setup and give you an easy way to indicate to others where the telescope is pointed. It also helps for indicating constellations and planets to those waiting in line for their turn.
• Bring a cardboard tube. If you expect small children to come by, they may struggle to focus their gaze through the eyepiece. Having them look through a roll of toilet paper or paper towels at the eyepiece can make it easier for them to focus their eyes through the lens, instead of at it.
• A stepladder or stool with a handle on it can be a lifesaver. Kids and shorter people will be able to see better, and if you instruct people to grasp the handle as they approach the telescope (even if they’re not using the ladder), it subtly redirects them from grabbing at the eyepiece without having to warn them explicitly.

*If you use a laser, make sure it is of a class and optical output that is legal to point at the sky. Never point lasers at people, airplanes, or any other vehicles. Do not use lasers if you are stargazing near an airport.

3) Prepare your telescope for a crowd

• Make sure your telescope can’t easily be tipped or tripped over. You may want to lay down a tarp and place your telescope in the middle of it — people will recognize the change of color at their feet and know to tread carefully. You can also mark your telescope’s legs with glow-in-the-dark tape or weigh them down.
• Choose your eyepieces wisely. If your telescope doesn’t automatically track, consider using a low or mid-power eyepiece with a wider field of view so that you won't have to reposition as much. Consider keeping your nicest eyepieces packed away if you’ll be hosting children or anyone wearing eye makeup (like at Halloween), since they may touch or damage the lens coatings. And if you can, use an eyepiece with long eye relief. It will make it easier for people to spot your target and allow anyone who wears glasses to keep them on. That way, the telescope focus can stay roughly the same between observers.
• Check your focus often between stargazers. Some star party hosts like to lock the focus knob so no one can mess with it, while others like to give their guests the option to adjust as they see fit. If you do want to let people adjust their own focus, make sure those with astigmatism still keep their glasses on. 
• Start with a bright target, instead of a deep sky object. Unless you’re somewhere darker or have done sidewalk astronomy before, you’ll likely have an easier time wowing people with one of the mainstays of stargazing: the Moon, Jupiter, or Saturn. They are visible in all their glory with a relatively small telescope, even in the heart of a major city.

4) Pick your moment 

• Take advantage of holidays. People will generally have more free time to be out and about, and certain holidays — like Halloween — fill the streets.
• Check the Moon’s phase. When observing the Moon, aim for a night when the Moon is only partly full, so that the three-dimensional relief at the terminator is visible. A waxing Moon will generally be more visible during the evening. If you’re trying to observe fainter objects, aim for waning or new Moons.
• Consult an astronomical forecast. Be on the lookout not only for clouds, but also for high winds or poor “seeing” (atmospheric stability) that could blur your views. Cold temperatures might also keep people indoors. 
• Keep an eye out for big celestial events. Things like meteor showers, eclipses, novae, and comets are great opportunities to introduce others to stargazing. Even when the event is not visible from your location, it might be in the news cycle and getting people thinking about astronomy.

5) Have your talking points prepared

• Have a fact or two ready about whatever you're looking at. Consider keeping it simple by describing the size and distance of your target. If you’d like to go into more detail, pointing out major craters or where the Apollo missions landed are great standbys when observing the Moon. When showing someone Jupiter and Saturn, being able to describe exactly which moons are visible (e.g., “The one on the left is Europa”) and what they are like (a volcanic world, icy, etc.) can also add a great deal to the experience. 
• Expect to talk price tags. If someone asks how much your telescope costs, consider a tactful redirection, especially if you have a telescope more advanced than entry-level. A common response is to focus less on the cost of your particular telescope and more on the cost of solid beginner telescopes and binoculars. 

6) Cover the practicals

• Never leave your telescope unattended. Someone might knock over, damage, or (worst-case scenario) steal your equipment.
• If you go big, look into permits. A small informal gathering on a sidewalk should not generally require dealing with any red tape, but if you plan to host something larger, you may require a permit.
• Ask for help. It can be a lot of work to play the telescope assistant, tour guide, and friendly neighborhood stargazer all at the same time. With a friend willing to share the load, you can take breaks, engage more people at a time, and let yourself get carried away in a conversation with a new friend every once in a while. It’s also always good to have two adults present whenever you expect kids at your event.

For our full guide on how to enjoy the night sky, check out Stargazing 101 on The Planetary Society’s online member community. Not yet a member? Join today.