How Far Away Is That?       How Far Can Your Telescope See ?
How Big Is It Compared To Earth?       How Many Moons Does It Have?

by: Larry McNish
Page last updated April 26, 2023
(Page originally created Apr 14, 2004)


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I often get asked these questions when showing family, friends and the general public celestial targets in my telescope.
Keep these tables handy and you'll never struggle for an answer again!


1. How Far Away Is That?

The following table lists many Solar System objects by distance:

For the solar system objects the distance given is an approximation based on the differences of the semi-major axes of their orbits. For the inner planets this is too "near" given that they are in inferior conjunction when this happens - you may wish to use a different number - somewhere between inferior conjunction and perhaps greatest elongation. (See the diagram in Section 8 below.) For the outer planets, this is also too "near" given that this only happens at opposition. Pluto's distance is also adjusted considering it's current position at nearly the distance of Neptune.

However, the people asking the question are not usually seeking an explanation of solar system geometry, but a simple "guesstimate".

Object A.U. Miles Say. . . Kilometers Say. . . Light Time
Sun192,955,807.2705493 Million mi 149,597,870.696150 Million km8.31 min
Moon0.00257238,917240 Thousand mi384,500400 Thousand km1.282 sec
Mercury1-0.39 = 56,730,00057 Million mi91,500,00092 Million km5.08 min
Venus1-0.72 = 26,040,00026 Million mi42,000,00042 Million km2.33 min
Mars1.5-1 = 46,500,00047 Million mi75,000,00075 Million km4.17 min
The average asteroid  (Ceres) 2.767-1 = 164,331,000160 Million mi265,050,000265 Million km14.73 min
Jupiter5.2-1 = 390,600,000390 Million mi630,000,000630 Million km35.00 min
Saturn9.6-1 = 799,800,000800 Million mi1,290,000,0001 Billion km71.67 min
Uranus19.1-1 = 1,683,300,0002 Billion mi2,715,000,0003 Billion km2.51 hr.
Neptune30.0-1 = 2,697,000,0003 Billion mi4,350,000,0004 Billion km4.03 hr.
Pluto39.5-1 = 3,580,000,0004 Billion mi5,760,000,0006 Billion km5.33 hr.
Orcus (2004 DW)39.4-1 = 3,570,000,0004 Billion mi5,745,000,0006 Billion km5.32 hr.
Varuna (2000 WR106)43.1-1 = 3,913,000,0004 Billion mi6,298,000,0006 Billion km5.83 hr.
Haumea (2003 EL61)43.3-1 = 3,930,000,0004 Billion mi6,328,000,0006 Billion km5.86 hr.
Quaoar (2002 LM60)43.5-1 = 3,950,000,0004 Billion mi6,358,000,0006 Billion km5.89 hr.
15760 (1992 QB1)43.7-1 = 3,970,000,0004 Billion mi6,388,000,0006 Billion km5.91 hr.
Makemake (2005 FY9)45.7-1 = 4,160,000,0004 Billion mi6,687,000,0007 Billion km6.19 hr.
Eris (2003 UB313)67.7-1 = 6,200,000,0006 Billion mi9,978,000,00010 Billion km9.24 hr.
Sedna (2003 VB12)494.5-1 = 45,900,000,00046 Billion mi73,830,000,00074 Billion km68.36 hr.
The average meteor50-100 Km (in the Earth's atmosphere)
The Shuttle350 Km
The International Space Station380 Km
Geostationary satellites35,790 Km (about 100 times further than the ISS but only 1/10 the way to the Moon)
The average comet100,000,000 miles (~1 A.U.)


Also see: The Solar System for comparisons of Solar System bodies
Also see: The Kuiper Belt home page
Also see: Trans-Neptunian Objects at Wikipedia.
Also see: New Horizons - NASA's Pluto-Kuiper Belt Mission
Also see: Discovery of Eris (formerly nicknamed Xena)
Also see: Discovery of Dysnomia (formerly nicknamed Gabrielle - Eris' moon)


2. How Far Can Your Telescope See ?

The following table lists some deep sky objects by distance:

Object Distance
The Pleiades M45 380 LY (Light Years)
The Dumbbell nebula M27 1,250 LY
The Orion Nebula M42, M43 1,600 LY
The Ring Nebula M57 2,300 LY
The Lagoon nebula M8 5,200 LY
The Crab nebula M1 6,300 LY
Globular Cluster M13 25,000 LY
The Andromeda Galaxy M31,M32,M110  2.9 Million LY
Galaxies M81, M82 12 Million LY
The Whirlpool Galaxy M51 37 Million LY
The Sombrero Galaxy M104 50 Million LY
Stars within the galaxy Thousands of Light Years
Messier objects Closest M45=380 LY, The most distant Messier objects=60 Million LY
The Finest 110 NGC objects Closest NGCxxx =? the most distant (NGCxxx) =?
Other Galaxies Hundreds of Millions of Light Years
Quasars Billions of Light Years


3. How Big Is It Compared To Earth?

The following table shows Solar System objects (o) relative to Earth (e) by Diameter and Volume:

Object Diam (km) Do/De Diameter Comment Vo/Ve Volume Comment
Earth127561 1 
Moon34750.272421 1/4 of Earth0.0203 50 times smaller
Sun1392530109.1667 110 times1,300,979 a million times larger
Mercury48790.382487 1/30.0562 18 times smaller
Venus121040.948887 a tiny bit smaller0.857 a little smaller
Mars67920.532455 1/20.151 about 7 times smaller
Jupiter14298011.20884 11 times1,321.33 1300 times larger
Saturn1205409.449671 9 times763.59 800 times larger
Uranus511204.007526 4 times like Neptune63.08 60 times larger like Neptune
Neptune495303.882879 4 times like Uranus57.74 60 times larger like Uranus
Pluto2370 0.1858 1/50.0059 a "speck" about 1% of Earth
Orcus (2004 DW)~1500 0.1176 1/90.0016 a "speck" less than 1% of Earth
Varuna (2000 WR106)~800 0.0627 1/160.0002 a "tiny speck" much less than 1% of Earth
Haumea (2003 EL61)~1500 0.1176 1/90.0016 a "speck" less than 1% of Earth
Quaoar (2002 LM60)~1260 0.09878 1/100.0010 a "speck" less than 1/10% of Earth
15760 (1992 QB1)~?    a "speck" less than 1% of Earth
Makemake (2005 FY9)~1900 0.1489 1/70.0033 a "speck" less than 1% of Earth
Eris (2003 UB313)2330 0.1827 1/50.0035 a "speck" about 1% of Earth
Sedna (2003 VB12)~1600 0.1254 1/80.0020 a "speck" less than 1% of Earth
The average asteroid   tiny  same
The average meteor   like a grain of sand  same
The average comet   tiny nucleus, huge coma   same

And a special note - all the planets could fit between the Earth and the Moon.


Yes, it's true. See: http://www.universetoday.com/115672/you-could-fit-all-the-planets-between-the-earth-and-the-moon/


Also see: The Solar System for comparisons of Solar System bodies

Also see: http://www.rense.com/general72/size.htm for a comparison between the Earth and other planets and the Sun and other stars.


4. How Many Moons Does It Have?

Object # of Moons Names (arranged closest to furthest)
Mercury0 
Venus0 
Earth1 Luna, the Moon
Mars2 Phobos and Deimos (both very small and hard to observe even with the largest telescopes)
Jupiter80 Possibly 95 moons. 4 big ones - Io, Europa, Ganymede, Callisto (can be seen in binoculars)
Saturn83 6 big ones - Enceladus, Tethys, Dione, Rhea, Titan, and Iapetus
Uranus27 5 big ones - Miranda, Ariel, Umbriel, Titania, and Oberon
Neptune14 3 big ones - Proteus, Triton, and Nereid (The 14th moon S/2004 N1 was discovererd July 1, 2013 by Mark Showalter of the SETI Institute in Mountain View, Calif. using the Hubble space telescope.
sub-total207 
Pluto5 1 big one - Charon, and 4 small ones - Nix, Hydra, "S/2011 (134340) 1" or "P4" now named Kerberos, discovered July 20, 2011, and "S/2012 (134340) 1" or "P5" now named Styx, discovered on images taken by Hubble's Wide Field Camera 3 on June 26, 27, 29, and July 7 and 9, 2012. In a February 2013 on-line poll to vote for names for the last two moons, "Vulcan" and "Cerberus" (or "Kerberos") (for P4 and P5) won the competition. The July 2, 2013 IAU official announcement of the names for P4 and P5 is here.
Ceres0 
Eris (2003 UB313)1 Dysnomia discovered on September 10, 2005
Haumea (2003 EL61)2 Hi'iaka discovered on January 26, 2005, and Namaka discovered on June 30, 2005
Makemake (2005 FY9)0 
sub-total8 
Orcus (2004 DW)1 Vanth discovered on November 13, 2005 (announced on February 22, 2007)
Quaoar (2002 LM60)1 Weywot discovered on February 14, 2006 (announced on February 22, 2007)
sub-total2 
Total217 (and counting. . .)

From: http://skyandtelescope.com/observing/objects/planets/article_827_1.asp (as of January 2006).
Two new moons for Pluto? See: ASTRONOMICAL HIGHLIGHTS for November 2005 and Astronomy Picture of the Day for 2005 November 3

Two new moons for Uranus ("Cupid" and "Mab") December 22, 2005 see: http://hubblesite.org/newscenter/newsdesk/archive/releases/2005/33/
and http://www.astronomy.com/asy/default.aspx?c=a&id=3821
Note that these two "new moons", "Mab" and "Cupid" are just "new" names for two discovered in 2003 - S/2003 U1 and S/2003 U2 - so the total is still 27 for Uranus.

Saturn - 47, 49, 50 or ?? - see the article: http://saturn.jpl.nasa.gov/multimedia/images/image-details.cfm?imageID=1700

Most Recent: http://www.skyandtelescope.com/observing/objects/planets/A_Guide_to_Planetary_Satellites.html July 2013



from: http://solarsystem.nasa.gov/multimedia/display.cfm?IM_ID=2823 Also see: The Solar System for comparisons of Solar System bodies


Other KBOs with Moons:
At least 12 KBOs have companions, and more are being discovered all the time. They are often called "binary KBOs" because the two objects have similar size, so it's not clear which is the "KBO" and which is the "moon!"
"Santa" has a moon nicknamed "Rudolph".

There are also more than 100 asteroids with moons and some "double asteroids"
see http://www.johnstonsarchive.net/astro/asteroidmoons.html

Some Asteroids with Moons:

Asteroid # of Moons Name(s)
243 Ida1 Dactyl (discovered February 1994)
762 Pulcova 1 
90 Antiope  actually a double asteroid! 
87 Sylvia2 Romulus and Remus 
2001 SN263 / 1535912 S/2008 (153591) 1 and S/2008 (153591) 2 
216 Kleopatra3 
45 Eugenia3 Petit-Prince and another designated S/2004 (45) (3rd discovered in 2007)
87 Sylvia3(2001)
93 Minerva3(2009)
3749 Balam3(2008)


5. The Brightest Asteroids
The ones brighter than about magnitude +9 can be seen with binoculars under good conditions.
The dimmer ones (higher magnitudes) will require a telescope.

   #   Name Magnitude 
4 Vesta7.6
1 Ceres8.7
2 Pallas9.1
20 Massalia10.1
11 Parthenope 10.1
3 Juno10.3
344 Desiderata10.3
51 Nemausa10.3
44 Nysa10.5
88 Thisbe10.5
5 Astraea10.5
17 Thetis10.6
89 Julia10.7
7 Iris10.7
8 Flora10.7
19 Fortuna10.8
15 Eunomia10.9
16 Psyche10.9
387 Aquitania10.9
324 Bamberga11.0


 

6. Saturn's biggest moons
Saturn's moons


7. Jupiter's biggest moons
Jupiter's moons



8. Solar System Geometry
Solar Geometry
IC- Inferior Conjunction
GEW- Greatest Elongation West
SC- Superior Conjunction
GEE- Greatest Elongation East
O- Opposition
WQ- Western Quadrature
C- Conjunction
EQ- Eastern Quadrature
Note that the distance between Earth and any other planet varies greatly.
For Mercury and Venus it ranges from IC to SC (on the other side of the Sun).
For Mars, Jupiter, Saturn, Uranus, Neptune and the Plutoids it ranges from O to C.


9. Retrograde Motion Examples:
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