Published: September 03, 2009 08:53 pm      

How would we look to people out in space?

Most telescope guides describe how the bright planets appear in our skies, both by eye and through a telescope. How would the Earth and Moon appear to future space explorers on or around our neighbor worlds? Would you want to wait for possibly five decades for the actual images?

Let’s just first consider the planets now easily seen from Earth. The very bright steady point of light seen as it gets dark in the southeast is the planet Jupiter. Tonight the moon is about 45 degrees to the left of Jupiter. (Look for the moon about 9 p.m.)

Jupiter has a magnitude of -2.7, three times brighter than any night star. Jupiter is now about 383 million miles from Earth, more than four times as far as Earth is from the sun. A telescope magnifying 40 power will show Jupiter’s disk about the width that our moon appears to the eye. Tonight you will see Jupiter’s two biggest moons, Callisto and Ganymede (in that order) on the east side of Jupiter through a telescope or binoculars held steadily.

The next planet to appear in the night sky is Mars, now in eastern Gemini, and rising in the East about 1:15 a.m. Mars is rather dull, being about 140 million miles away from Earth. Mars has a magnitude of 0.8, being outshone by the two brightest stars of the nearby star group Orion (to the right of Mars). Three hundred power will be needed to show Mars as large as our moon appears to the eye.

At about 4:15 a.m., Venus, the queen of the planet rises in the East. Venus is now in front of Cancer, one of the dimmest zodiac star groups. Venus is now about 130 million miles from the Earth.

Venus’ magnitude is -4, more than three times as bright as Jupiter and ten times as bright as the brightest night star. Both Venus and Mars are best viewed in the dawn around 6 a.m. when both will be sufficiently above the horizon to have clear telescopic views.

Now consider how the Earth would appear from the planets Mercury, Venus and Mars. From the giant planets, Jupiter, Saturn, Uranus and Neptune, the Earth would be lost in the glare of the sun, if we were to view the sky from one of the moons of these planets. All four of the giant planets have no solid surface, dense cloud cover and only an ocean of liquefied air under immense pressures far greater than the Earth’s surface.

Mercury has an orbit about three eighths the size of our own orbit about the sun. At an average close approach to Earth, Mercury would be 57 million miles away. To have the best view of Earth, we would have to be on the night side of Mercury where the temperature drops to -300 F!

The Earth would be a magnificent white-blue point of light, even brighter than Venus appears in our skies. Up to a quarter of a degree away would be our moon, nearly lost in the Earth’s glare. (A penny or dime held at arm’s length is about 2.5 degrees wide, so a quarter of a degree would be a tenth as wide as a penny).

If from Mercury we would use a telescope magnifying 240 power, then the Earth’s disk would appear to be four times as wide as our moon does to our eye. This magnification would show our moon as large as it appears to our eyes on Earth.

Venus has an orbit about .7 the size of Earth’s orbit around the sun. At an average close approach to the Earth, Venus would be 26 million miles away. Since Venus is sheathed in a dense atmosphere, we would have to observe Earth from an orbiting space station around Venus.

But the Earth would appear 5.6 times brighter than it appears from the surface of Mercury. Our moon could be seen out to an angle of a half degree from the white-blue Earth. At a magnification of 240 power, the Earth would appear to be eight times as wide as our moon appears to the eye. (This is the angular width of a 1-foot wide classroom globe at 13.6 feet away.) Our moon would appear to be twice as wide as it appears to our eyes at this magnification.

Mars has an orbit about 50 per cent larger than our own orbit about the sun. At an average close approach to the Earth, Mars would be 48 million miles away. But at each close approach, the Earth is lost in the sun’s glare. Also, the night side of the Earth then faces Mars.

So a much better time to observe the Earth from Mars would be when Earth makes its greatest angle from the sun (about 41 degrees) as seen from Mars. Earth would appear a little bit dimmer than Venus (appears in our skies). The Earth would then be 106.5 million miles away from Mars.

Our moon’s angle from the Earth would be one eighth of a degree, likely swallowed in Earth’s glare. Then telescope views of Earth would show a half Earth (viewing half of the day side and half of the Earth’s night side) and a half moon. A telescope magnifying 240 X would show the Earth as being about 1 degree across, about twice as wide as our moon appears to our eyes. Those observing Earth from Mars will have to deal with Mars’ cold average global temperature of -60 F!

Frostburg State Planetarium resumes its Sunday programs today at 4 p.m. and 7 p.m. Our September program is “White-Blue Ball and Pale Grey Dot,” the Earth and moon as seen from other planets. The Planetarium is in Tawes 302. Call (301) 687-4270 for road directions.

The moon is now rising later each night, moving from Pisces (tonight and tomorrow), Aries (Tuesday and Wednesday) and Taurus (Thursday and Friday). By then the moon will appear half full in the morning sky. The brightest points in the evening sky in order are: Jupiter (south), Vega (high in the west) and Capella (low in the northeast).

Bob Doyle invites comments and questions from readers; call (301) 687-7799 or email rdoyle@frostburg.edu .