The Mars Hoax

Transcription

The Mars Hoax
The Mars Hoax
Every two years or so, email accounts bristle
with messages breathlessly announcing that
observing Mars this fall will be a once in a
lifetime experience.
This email was close to the truth in 2003, but
has morphed into a series of claims that
have no basis in fact.
 The email claims are
in areas with the
original background.
 The facts of Mars in
are in this background.
Check it out, guess no one will get much sleep in
August.
Mars

The Red Planet is about to be spectacular!
Not so fast…
The Earth revolves around the Sun faster than Mars, passing
by Mars every 780 days. This means that there are some
calendar years without a close approach to Mars. The
years 2013, 2015, 2017, and 2019 have no close
approaches to Mars.
The last opposition of Mars was on March 3, 2012 and the
next one will be April 8, 2014. None of these are
particularly close
 This month and next, Earth is catching up with Mars in
an encounter that will culminate in the closest approach
between the two planets in recorded history.
 The next time Mars may come this close is in 2287.
 Due to the way Jupiter's gravity tugs on
Mars and perturbs its orbit, astronomers can only be
certain that Mars has not come this close to Earth
in the Last 5,000 years, but it may be as long as
60,000 years before it happens again.
The encounter will culminate on August 27th when
Mars comes to within 34,649,589 miles of Earth and
will be (next to the moon) the brightest object in
the night sky. It will attain a magnitude of -2.9
and will appear 25.11 arc seconds wide.
 At a modest 75-power magnification, Mars will appear
through a telescope, the same size as the Full moon to the
naked eye.
Let’s look at these claims one at a time:
Claim:
 This month and next,
Earth is catching up
with Mars in
an encounter that will
culminate in the
closest approach
between the two
planets in
recorded history.
Fact:
 For any reasonable
interpretation of
“recorded history,” the
closest approach
between Mars and
Earth was on August
27, 2003.
Claim:
 The next time Mars may come
this close is in 2287.
 Due to the way Jupiter's
gravity tugs on
Mars and perturbs its orbit,
astronomers can only be
certain that Mars has not
come this close to Earth
in the Last 5,000 years, but it
may be as long as
60,000 years before it
happens again.
Fact:
 The first claim is true, as we will
see in the next slide. The
second claim is in contradiction
with the first. The closest
distance between Earth and
Mars will be in 2287 or will not
happen for another 60,000
years.
 In fact, the opposition on August
28, 2287 will be 0.11% closer
than in 2003.*
*data from Guide 8.0 software (www.projectpluto.com)
Claims:
The encounter will
culminate on August
27th when
Mars comes to within
34,649,589 miles of Earth
and will be (next to the
moon) the brightest object
in the night sky. It will
attain a magnitude of -2.9
and will appear 25.11 arc
seconds wide.
Facts:
 On Aug. 27, 2012, Mars
will be 140 million miles
from Earth. The following
slide clarifies the situation
with a diagram of the inner
solar system on that date.
At that time, Mercury,
Venus, and the Sun are all
closer to the Earth than
Mars.*
*data from Guide 8.0 software (www.projectpluto.com)
This diagram was derived from NASA / JPL’s Small-Body
Database Browser. This JAVA applet will build an interactive
simulation of the inner solar system and any known asteroid or
comet. Click on Orbit Diagrams, near the bottom of the page.
Claims:
The encounter will culminate
on August 27th when
Mars comes to within
34,649,589 miles of Earth
and will be (next to the
moon) the brightest
object in the night sky. It
will attain a magnitude of 2.9 and will appear 25.11
arc seconds wide.
Facts:
On Aug. 27, 2012, Mars is
visible to the naked eye in
the west. An hour before
sunset, Saturn is 1.5x
brighter than Mars. In fact
there will be 4 stars visible
at that time that are
brighter than Mars.*
*data from Guide 8.0 software (www.projectpluto.com)
Claims:
The encounter will culminate
on August 27th when
Mars comes to within
34,649,589 miles of Earth
and will be (next to the
moon) the brightest object
in the night sky. It will
attain a magnitude of -2.9
and will appear 25.11 arc
seconds wide.
Facts:
 One arc-second is an
exceedingly small angle. A
full Moon is about 1,800
arc-seconds in apparent
diameter. On August 27th,
2012, Mars subtends an
angle of 5 arc-seconds.
That night Moon will
appear 310 times larger in
the sky and only 1/4th the
claimed angular diameter.
*data from Guide 8.0 software (www.projectpluto.com)
But wait, there’s more bad news…
The Earth’s atmosphere blurs fine details of
the night sky. Ellery Hale once noted that
looking at astronomical objects through the
atmosphere was like bird-watching from the
bottom of a swimming pool.
This limit in image resolution imposed by our
atmosphere, for most telescopes, is about 1
arc-second. If we blur the image of Mars
from the beginning of the file, we might see
something like this through a backyard
telescope on August 27, 2009.
Applying more magnification will
only magnify the blur, without
adding more detail.
So the images above are cheating in two ways. First, if
you magnified the image of Mars so that it looked as
large as the Moon does to your naked eye, it would not
have the claimed resolution; it would still be a blurry
mess.
Secondly, this image of the Moon is not what your
naked eye sees. This is a much higher resolution
image taken with a telescope. Look at the Moon closely
the next time you see it in the night sky for comparison.
Mars will be easy to spot. At the
beginning of August it will rise in the east at 10p.m.
and reach its azimuth at about 3 a.m.
By the end of August when the two planets are
closest, Mars will rise at nightfall and reach its
highest point in the sky at 12:30a.m. That's pretty
convenient to see something that no human being has
seen in recorded history. So, mark your calendar at
the beginning of August to see Mars grow
progressively brighter and brighter throughout the
month.
Claim:
Mars will be easy to spot. At
the beginning of August it
will rise in the east at
10p.m. and reach its
azimuth at about 3 a.m.
Fact:
 In mid-August, 2012, Mars
rises at about noon and
goes below the horizon
2 ½ hours after sunset.
 All objects have an
azimuth in the sky. If the
writer was trying to convey
the time when Mars is
visible in the night sky at
its highest point, then that
occurs at 17:30 EDT,
during daylight.
*data from Guide 8.0 software (www.projectpluto.com)
Why was 2003 so different than 2012?
In this diagram, the inner loop is the
orbit of the Earth and the larger one
is the orbit of Mars. Mars’ orbit is
not a perfect circle. (Neither is the
Earth’s but it’s pretty close to one,
with the Sun at the center.) When
Earth passes Mars in its faster,
smaller orbit, it’s called an
opposition. (The point of minimum
distance is very close to this date,
but not exactly so.)
Late in August the orbit of Mars is
closest to the Sun, at the same
time, the Earth passes a point that
is nearest to the orbit of Mars, but
usually Mars is somewhere else.
They pass each other in late August
only about once every 15 years.*
Diagram from Meeus, More Mathematical Astronomy Morsels, 2002, Fig, 36a, p. 214.
*Meeus, Mathematical Astronomy Morsels, 1997, p. 227.
Why is 2003 so different than 2012?
The next close pass will be on July 31,
2018, when Mars will appear only
3% smaller and 1% dimmer than in
August 2003.*
*data from Guide 8.0 software (www.projectpluto.com)
Diagram from Meeus, More Mathematical Astronomy Morsels, 2002, Fig, 36a, p. 214.
Is the 2003 approach as good as it gets?
No. You can find a list of close Earth-Mars approaches here. Look at the
bottom of the page for the “perihelic oppositions.” These are nearly the dates of
closest approach between Mars and the Earth in each of the above-mentioned
15 year cycles. To find the distance in miles, multiply the distance in AU’s by
92,956,000. To find the apparent diameter of Mars in arc-seconds, divide 9.35
by the distance in AU’s.
Actually things get a little better as we look into the future. The orbit of Mars
becomes more eccentric (less like a circle) until the year 24,100 A.D., allowing
the orbits of Mars and Earth to become a little closer.
The vertical axis of this plot is the minimum Earth-Mars distance in AU’s. The horizontal
axis is the year A.D. From this you can see that there are closer encounters than the
one in 2003 in the years 2287, 2366, 2571, 2650, 2729, 2808, and 2934.
It must be emphasized that the opposition in 2729 is only slightly closer than the one in
the year 30, the difference being less than 0.1% of the total distance.
Diagram from Meeus, More Mathematical Astronomy Morsels, 2002, Fig, 36b, p. 217.
Share this with your children and
grandchildren.
With this there can be no argument. Find a local astronomy
club, or visit the MacAdam Student Observatory for one of
our outstanding public presentations, and see Mars. No
matter how it appears, seeing it for yourself is a unique
experience.

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