Understanding the stars

Wadi Rum has several factors that make one of the best locations in the world for stargazing.

• Low population density limiting light pollution
• Predominantly clear skies
• Low latitudes with both significant night-time hours and increased range
• Altitude above 1000m

It is beneficial to have some basic bearings to aid you in knowing which areas of the sky to look. For reference, the direction through the valley towards the village is north. The camp has minimal light pollution and is a good open area and moving up to a higher vantage above the camp increases visibility to the east and west. Khor al Ajram is a good open location for stargazing, although it is negatively impacted by light pollution. Open areas south of Um Mugur offer ideal plains without artificial light.

Important factors to ensure no light pollution:

• Light pollution - Due to the light pollution caused by urban centres, you should plan to be at least 5km from Wadi Rum village, ideally obstructed by one of the mountains. You would need to travel even further from At Diseh, which generates significantly more light. Once in the area, you will have a sense for the light pollution after observing it on the horizon. Similarly, if there are other artificial light sources around you, they will impact your naked eye light sensitivity. Plan ahead and be aware of the location of your accommodation.
• Moon phase - If you are visiting Wadi Rum specifically for stargazing, make yourself aware of the lunar phases and ensure that you will have opportunities without moonlight to obscure your visibility. The full moon in Wadi Rum is an experience in itself, as it lights up the sandstone cliffs and provides significant night-time visibility without any artificial light. However, it is not conducive to locating stars or stellar constellations.

Apparent magnitude of stars

Star brightness is scaled in magnitude. Each point of magnitude increases references by 2.5 times reduction in brightness. The zero-reference point is the star Vega of the Lyra constellation.

• The Sun has a magnitude of -27
• PThe Moon has a magnitude of -13
  This means that the sun is 2.5^14 times brighter than the moon = 370,000+ multiples
• Venus (third brightest natural light source) -4.6
• Sirius (brightest star) -1.4
• Naked eye limit (in urban area) +3
• Naked eye limit (dark sky) +6
• Binoculars +9.5
• Hubble telescope +30
• Other planets: (they all range due to the significant variance in location in our night sky – approximate mean values given)
  Jupiter -2 / Mars, Mercury & Saturn 0 / Uranus 6 / Neptune 8 / Pluto 14

As your eye can see 3 magnitudes dimmer (or over 15 times dimmer), it means stars in dark skies will be significantly more visible. As -5 points of magnitude is equal to 100 multiples of brightness, visitors to Wadi Rum using binoculars will be able to see stars over 100 times dimmer than they will be able to see in their hometowns.

The number of stars visible at each magnitude is:

• 0 ~ 4 stars (Vega is the 5th brightest star with adjusted value at 0.03)
• 1 ~ 15 stars
• 2 ~ 48 stars
• 3 ~ 171 stars
• 4 ~ 513 stars
• 5 ~ 1602 stars
• 6 ~ 4800 stars
• naked eye limit ~ 9100 stars
• 7 ~ 14000 stars
• the Hubble telescope = several billions

For this reason, when you are star gazing it is important to not expose your eyes to artificial light. Your visibility will be reduced significantly for several minutes if you view a phone screen, look at headlights or sit near an open flame. Looking at a dimmed screen on your phone will affect your eye’s sensitivity and eliminate visibility of stars by 90 percent. For the best experience, it is best to sit in complete darkness for several minutes to allow your eyes to adjust and ensure you avoid artificial light sources to experience the best outcome.

Why is magnitude measured from Vega?

Vega is an important star for a number of reasons:

• It appears as the brightest star in the in the summer months in the Northern Hemisphere
• It is directly overhead for a large proportion of the year in the Northern Hemisphere middle latitudes making it easy to identify
• It was the north star (around 12,000BC) and therefore had great significance to ancestral people who relied heavily on the stars for navigation
• It is relatively close to us at 25 light years

With most astronomical research historically taking place in the northern hemisphere middle latitudes it became a major focus and was used to test many advancements in astronomy theories. It was also used as a reference point, not only for apparent brightness, but also for the colour spectrum of stars.

How far away are the stars?

Many star gazing applications allow you to hover over stars and get basic information including their distance from earth. However quantifying these staggering numbers is difficult. Something that puts it into perspective is yourself.

Depending on your age – light sources you can see at any given time that are younger than you (assuming perfect conditions and zero light pollution):

• 30yo – 10-20
• 40yo – 20-30
• 50yo – 30-40

There are a total of 133 visible stars within 50 light years of earth. The majority of these are very faint to the naked eye, with around half above magnitude 5. From wherever you stand on the planet, earth itself is obscuring at least half of the space around you. This means that even with perfect conditions, at most, a quarter of these stars would be visible to you.