Sir Isaac Newton - PowerPoint PPT Presentation

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Sir Isaac Newton

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(Universal Law of Gravity), where F = gravitational force; G = universal constant ... Lick Observatory image of Neptune and two of its moons ... – PowerPoint PPT presentation

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Title: Sir Isaac Newton


1
Sir Isaac Newtons laws of planetary motion and
his Universal Law of Gravity allow astronomers to
calculate the position of celestial objects (and
spacecraft and satellites!) at any time in space.
This is referred to as Newtonian Celestial
Mechanics. F G x m1 x m2 r2 (Universal
Law of Gravity), where F gravitational force G
universal constant of gravitation m1 and m2
the masses of two bodies and r the distance
between them. Two bodies attract each other
with a force that is directly proportional to the
product of their masses and inversely
proportional to the square of the distance
between them.
2
U.J.J. Leverrier
Neptune was discovered by pencil and
paper!!! 1790 Delambres calculations of orbits
of Uranus based on Newtonian Celestial Mechanics
are up to 2 minutes of arc off from observation.
Was Newton wrong??? 1841 Graduate student J.C.
Adams noted that in the first quarter of the 19th
century, Uranus seemed to be accelerating
slightly, in the second quarter slowing down
could be explained by gravitational perturbations
from 8th, previously unknown planet beyond the
orbit of Uranus. Adams predicted its position in
the sky, but Royal Astronomer Sir Airy ignored
Adams. 1846 Leverrier suggested that an 8th
planet deflected Uranus from its orbit. Predicted
its position in sky and wrote to astronomer J.J.
Galle. September 23, 1846 J.J. Galle received
the letter from Leverrier and found Neptune the
same night!!!
3






4
Lick Observatory image of Neptune and two of its
moons
5
January 23, 1989, images of Neptune, 2 hours
apart, taken by the approaching Viking
spacecraft. Moving across the planet at 30 S
latitude is a bright cloud feature.
6
High-altitude cirrus-like clouds in Neptunes
atmosphere 50 150 km wide and maybe 50 km
above main clouds
7
Hubble and Keck views of Neptune, showing storms
with Equatorial winds of 1,400 km/hour
8
Neptunes Great Dark Spot (Scooter) moving east
around planet, driven by strong, 700 miles/hour
west winds
9
Relative cloud motion in Neptunes atmosphere
10
Neptunes Dark Spot (Scooter) and smaller Dark
Spot 2 moving eastward around the planet at
different speeds
11
Neptunes Great Dark Spot (Scooter) and white
cirrus-like clouds
12
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13
Magnetic field of Neptune. For comparison, the
magnetic field of earth is 0.35 Gauss
14
The 2 most prominent, clumpy rings of Neptune
(clumping of material) discovered by Voyager.
Neptune is overexposed to show rings.
15
New moon of Neptune, 1989N1, discovered by
Voyager. The large crater is 400 km in diameter.
16
Crescent of Neptune with its moon Triton in the
background
17
Neptunes moon Triton is 2,705 km in diameter.
Bright ice cap in southern hemisphere (top)
(notice black streaks), and dark terrain with
highways below.
18
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19
Dark, active nitrogen geysers on Triton constant
direction of streaks hints at a very thin
atmosphere
20
Cantelope terrain on Triton hints at tectonic
processes
21
Possible frozen lakes (of water, ammonia and
salts?) on Triton
22
Neptunes moon Triton Imaged by Voyager 2 in
1989 Triton moves around Neptune opposite to the
planets rotation and movement around the Sun,
but synchronous, i.e., the same side of Triton
always faces Neptune The diameter of Triton is
2,705 km, 3/4 the size of our Moon It was
probably captured, just like Pluto Its surface
is made of solid methane (CH4) and N2, with T -
400 F Its pinkish color is due to organic
compounds that formed from CH4 and N2 There are
no large impact craters hence, the surface is
young (constantly being resurfaced) The albedo
is very high, 0.80 and, hence, the moon is bright
(presence of ices) S pole region has N2
fumaroles ejecta are wind-blown, thus, there is
a tenuous atmosphere The density 2.1 g/cm2,
hence, there must be ices present
23
Neptunes moon Nereid is 340 km in diameter. It
has the most eccentric orbit of any moon in the
Solar System. Separation from Neptune varies from
1.4 to 9.6 million km
24
Neptunes moon Nereid Discovered in 1949 Not
well imaged by Voyager 2, but the spacecraft
discovered 6 smaller moons Most eccentric orbit
of any moon in the Solar System, hence, it was
probably also captured like Triton and
Pluto Nereid is 340 km in diameter Its albedo
is low, 0.15, so Nereid is dark like our Moon
25
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