The Planets: Finding Uranus

This is a particularly easy time to find Uranus because it is in a field where there are few other stars to cause confusion.

Uranus Rings by David A Hardy image courtesy: Dakota’s Weird Blog

(CALGARY, Alberta) - The solar system has eight “official” planets although some still consider Pluto to be a planet. Looking only at the “official” list, from the Sun outwards, there is Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.

All eight are readily visible to the naked eye or binoculars Right now Mercury, Venus, Mars and Saturn are too close to the Sun to be visible. Venus is bright enough so that if you know where to look it can be spotted with the naked eye during the day.

I know this is possible, because I have done it. Venus’s maximum magnitude is about the same as the International Space Station when it is fully lit by the Sun.

My focus in this article is to help you find Uranus, which is currently very close to Jupiter.

Finding Jupiter is dead easy. At midnight Salem time, it’s due south, very high in the sky. But you don’t have to stay up late, at 9pm it’s very high in the SE and the brightest object in the sky. You can’t miss it.

Finding Uranus is similarly easy. You don’t even need a really dark sky. I find it easily from my apartment balcony in downtown Calgary.

If you can get to a place away from lights, it will be easier for you to find. Outside the city is best.

Jupiter and Uranus are less than 2º apart and, depending on the power of your binoculars, they could both be in the field of view at the same time.

Uranus is at magnitude 5.7 and Jupiter at –2.9; Jupiter is 2,755 times brighter than Uranus.

This is a particularly easy time to find Uranus because it is in a field where there are few other stars to cause confusion.

In principle, Uranus is visible to the naked eye.

This is not possible in this example because Jupiter is so bright, it will drown out Uranus’s feeble light.

The star map shows the magnitude of seven stars in the field. Uranus is easily found in this uncrowded star field.

On to Neptune

Neptune is more of a challenge and will require familiarity with, and use of a star chart. It is much fainter than Uranus, at 7.9, Uranus being about 7.5 times brighter.

Neptune is very close to Mu Capricorni,—about a quarter of a degree away. With a star chart, you can navigate in the region until you find Mu Capriconi and Neptune is close. A pair of 7x50 binoculars should be adequate. The faintest magnitude under ideal conditions with 7x50 binoculars is 9.5 so that under ordinary dark skies, you should be able to see Neptune. Mu Capricorni is about 13 times brighter than Neptune.

A note about magnitude for the mathematically inclined Magnitude is obviously the brightness of a celestial object. The idea originated with the ancient Greeks who divided the stars visible to the naked eye into six magnitudes where the brightest stars were at magnitude 1 and the faintest stars visible to the naked eye were 6. Using this classification, the higher the magnitude, the fainter the object.

In the nineteenth century this was formalized to mean that a 1st magnitude star was 100 times brighter than a 6th magnitude star. Each magnitude is 2.512 times brighter than the next; eg., from 1st to 2nd magnitude.

The system is no longer limited to six numbers and objects brighter than the brightest stars are given negative magnitudes. The Sun, for example, has a magnitude of –26 and the moon –12. The Sun is a `bout 400,00 times brighter than the full moon. Sirius (the Dog Star), the brightest star in the sky, is 23 times brighter than Polaris (the North Star).

For the mathematically inclined, the magnitude scale is logarithmic and comparisons are calculated using the ratio 2.512 as the base. For example, the magnitude of Jupiter is –2.9 and Uranus is 5.7. The variation in brightness is found with this formula where x is the power to use.

x = Magnitude of brighter object minus magnitude of dimmer object
For Jupiter and Uranus, x = (-2.9) – 5.7 = 8.6
variation = 2.512^8.6 = 2,755
for Neptune and Mu Capricorni x = 5.09 – 7.9 = 2.81
variation = 2.512^2.81 = 13.306
For the Sun and the moon x = (-12.74) – (-26.74) = 14
variation = 2.512¹⁴ = 398,359