What can you see naked? – Our Wide Sky

What can you see naked?

October 15, 2017

The best place to get started with astronomy is Naked Eye Observing. For a beginner astronomer the sky is out there waiting to be discovered. Just go outside and look up. You don't need to buy any equipment, and you don't have to take off your clothes. Just you, your eyes and the sky. 

Learn everything you can about what you are looking at. Get to know your local observing places and start naming the things you can see. It's only in the past 400 years or so that people have used equipment to see more details in the sky. As a Naked Eye Observer you will be in good historical company.

The first patent for a telescope was lodged in 1608 by Hans Lippershey. Before that glass makers had probably figured out that glass objects of certain shapes, aligned in a tube, can make you see further, but Lippershey was the first to claim it.

In 1609 Galeleo Galilee pointed it at the sky and made the first discoveries that would change astronomy forever.

Before that all the observations were done with the naked eye. Here are some examples of advanced in astronomy made before telescopes:

  • Stonehenge was built sometime near 2500BCE, it predicts the rising and setting of the sun at the solstices.  
  • In around 700 BCE the Babylonians predicted a solar eclipse.
  • 350 BCE Aristotle argues that the celestial bodies are spheres.
  • 280 BCE Aristarchus describes a heliocentric (revolving around the sun) model for the solar system and figures out some relative dimensions for the solar system.
  • In 140 Ptolemy starts his star catalogue which also includes star brightness.
  • In 1054 the Chinese make records of a supernova, and in 1066 Halleys Comet is visible. 
  • 1420 Ulugh Beg creates a star catalogue.
  • In 1609 Galileo pointed one of Lippershey's telescopes to the night sky and changed the world.

Science is stepping stones, one discovery builds on previous discoveries. In astronomy Naked Eye observations were the foundational stepping stones.

And Now?

The work of astronomy is done with technology that can see further and deeper and in different ways, but Naked Eye Observations are still useful for science

Naked eye astronomy is what you can do at night when you walk outside. It's what you can do from a faraway beach when you are on vacation. You can look up on any clear night and see what is out there. It can make the time waiting for a bus pass more quickly, and it can be a way to meet people, share your love of astronomy and learn something new.

The best naked eye astronomers can point our the large and small constellations. They know the names of the bright stars and can give you a tour of the night sky at any time of the year.

To get started you don't need much. A curious mind and a place dark enough to see the sky.

What can I see?

The short answer is - it depends. What you can see depends mainly on the quality of your sky. Is it dark? Is it unobstructed? Is it clear?

And the long answer? I'll get right on to that...

With a dark sky, on a clear, moonless night, far from light pollution and when the air is dry and cool you will see the Milky Way stretching across the sky, bright in parts, billions of stars, with dark clouds of gas blocking the view to billions more stars behind them. When your eyes have adjusted you will see faint, tiny fizzy spots. These will be nebulae, or galaxies, or globular clusters. You won't see the colour of these objects, but you will see that they are not stars.

In the northern hemisphere you'll have a view to Andromeda, a galaxy only 2.5 million light years away. It is in the east in September, October and November. It will be a large fuzzy patch. You need a dark sky to see it well.

In the southern hemisphere you'll see the 2 Magellanic Clouds. These are 152,000 light years away. They are faint cloudy patches in the sky. Visible in the southern sky from December to April.

As you approach cities with streetlights, and polluted skies, you will see less and less, but don't let this stop you. There is still a lot to see.

At worst you will only see the moon, and the sun during the day, and maybe some of the brightest stars, such as Sirius or Antares on a moonless night. You may see Venus early with the sunrise or sunset. Mars, Jupiter and Saturn may also be visible when they are high in the sky.

You can see atmospheric phenomena if you know what to look for, and you may see the ISS passing overhead if you know where and when to look.

Limiting Magnitude

Each object in the night sky has a magnitude. This indicates how bright it looks from Earth. Closer objects look brighter, so it is not an indication of size.

Magnitudes are expressed on a logarithmic scale. This means that magnitude 2 is not twice as bright as magnitude 1. And to confuse us even more the magnitude scale is reversed. This means that magnitude -2 is brighter than magnitude -1, and a lot brighter than magnitude 1.

There is a limit to how many stars you can see with your Naked Eye. There are a number of factors that limit the magnitude of stars you can see unaided. The first is the actual number of bright stars. 

Apparent magnitude is how bright a star looks from where we are, rather than how bright a star actually is, as seen if you were close to it. A star identical to our sun will be dim at a distance, and grow dimmer with greater distance. If all the stars in the sky were identical to our Sun we would still see only the close stars. The further away they are, the dimmer they appear to us.

There are only 2 stars in the night sky that are brighter than magnitude -0.5. These are Sirius (-1.46) and Canopus (-0.74). Canopus is in the Southern Hemisphere constellation of Carina. Sirius is in the constellation of Canis Major and is visible to most people on Earth. Canis Major means "the greater dog" which is why Sirius is also called the Dog Star.

Another 20 stars are visible brighter than 1.5 apparent magnitude. And another 263 stars are brighter than 3.5 magnitude.

If you have a dark sky location you may see up to magnitude 6.5, which is generally considered the limiting magnitude for naked eye observing. There are 8700 stars visible at this magnitude or brighter, but you will need a very dark sky and a very clear night to see stars at this magnitude.

Here is a guide on what you can see. As I said, it depends on your local conditions. It's a good experiment to figure out your limiting magnitude from  your location. Remember that seasonal changes will affect the quality of your sky, and the stars you are looking at. 

  • Bright inner city: You'll see very few stars. The naked eye planets will be visible (Venus, Mars, Jupiter and Saturn), and the brightest few stars. Your limiting magnitude will be around 2.0 on a moonless night with a clear sky. There are perhaps 22 stars with this magnitude and you'll see those visible depending on the time of year and your latitude. Buildings will likely be in the way too. Streetlights are your enemy.
  • In the suburbs: From a good site you will see around 200 stars with a limiting magnitude of about 3. Don't forget that you don't see the whole sky, so you will see only some of the 200 stars. You'll be able to identify constellations and see the difference in brightness. Get away from streetlights if you can.
  • In the dark suburbs: The further from the bright city lights you are, the better will be your view. Find a dark park and let your eyes adjust, and you may see to Magnitude 5 when there is no Moon and the sky is clear. There are over 2000 stars with this apparent magnitude. You will be able to you see a lot more and identify more constellations. You may even be able to see the Andromeda galaxy, the Magellanic Clouds and the Orion Nebula. Streetlights will limit what you can see.
  • Out in the Country. You'll see lots of stars. At a good site you'll see so many stars that identifying the constellations will be difficult. It's worth the travel though. The Milky Way from a dark site is stunning. You'll see lots of deep sky objects such as nebula and star clusters. These appear as faint fuzz patches that you almost can't see. These are harder to see and identify, and you definitely need a dark sky to see any of them with your naked eye. Did I say it was worth going to a dark site?

Even though the visible numbers are low, it is still a challenge to learn to identify these stars and name them when they are visible in the sky. Don't underestimate the complexity of the sky, even with 5 planets and 25 stars. 

The better your observing location, the more stars you will see, so get out into the suburbs, or out into the country when you can to enjoy a dark sky. 

Here are some other things you can do to improve your view of the sky:

  • Use binoculars or a telescope. This will dramatically improve your limiting magnitude and open up a whole new sky, regardless of your location.
  • Do your bit to reduce light pollution. It's amazing how much light is spilled upward in a city. The more informed you are of the ways of reducing light pollution the more you can say and do about it. Change happens slowly, and with a better informed public. We'll have more on this in later blog posts.
  • Know the Moon. The Moon is one of the biggest observing party poopers. Know when the best phases of the moon for observing are and schedule your observing then. Connect with us on social media as we share the best days for observations. On the nights when the Moon is bright it makes a good observing target. There is plenty to see with the naked eye on the Moon.

Naked Eye Observing

Of course you can see a lot more with binoculars or a telescope, but nothing is simpler than getting outside and looking up. There is still a lot to discover: planets, the changes in the Moon, the changing seasons, the Earth's atmosphere, bright stars, and constellations. You have to work a bit harder to see something that is immediately interesting. The temptation is to say, oh just a star how boring. Often it is a matter of learning more deeply about what you are looking at, learning to recognise the star or constellation and point it out in the night sky, and discovering ways to go beyond your limiting magnitudes.

Don't forget to download our Naked Eye Observer's Guide. It's packed with useful information about observing naked (without taking off your clothes).

References:

https://en.wikipedia.org/wiki/Limiting_magnitude

http://www.stargazing.net/david/constel/howmanystars.html

http://highered.mheducation.com/sites/0072482621/student_view0/astronomy_timeline.html

https://www.space.com/21950-who-invented-the-telescope.html

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