Your Sky Help: Ephemeris

 

  Right
Ascension
Declination Distance
(AU)
From 47S 7E:
Altitude Azimuth
Sun 22h 45m 51s −7 50.8' 0.991 −35.046 −4.678 Set
Mercury 21h 1m 44s −17 5.4' 0.947 −20.502 −30.571 Set
Venus 19h 58m 25s −19 35.1' 1.019 −11.737 −43.547 Set
Moon 22h 16m 10s −5 52.8' 59.9 ER −36.184 −13.954 Set
Mars 9h 22m 17s +19 52.9' 0.709 19.492 155.307 Up
Jupiter 16h 50m 26s −21 40.7' 5.342 17.470 −76.684 Up
Saturn 23h 5m 13s −7 46.1' 10.652 −35.225 1.185 Set
Uranus 20h 4m 6s −20 53.8' 20.436 −11.252 −41.702 Set
Neptune 19h 45m 55s −20 39.2' 30.861 −9.324 −45.560 Set
Pluto 16h 5m 23s −6 54.5' 29.652 14.568 −95.535 Up
1995 DW1 12h 5m 24s +2 58.7' 0.456 38.069 −159.504 Up

The ephemeris shows you the positions of the principal bodies in the Solar System at the selected time, both in celestial coordinates, and as seen from your specified observing site for sky and horizon maps. If you're tracking an asteroid or comet by specifying its orbital elements, its position is given at the foot of the table. The sample ephemeris above gives positions for 00:00 UTC on March 1, 1995, while tracking the Earth-orbit-crossing asteroid 1995 DW1, whose discovery (on February 25, 1995) was reported in Minor Planet Electronic Circular 1995-E02 of 00:15 UTC, March 1, 1995, giving the orbital elements shown at the end of this page.

For each solar system body the following data are displayed: The first three items give the equatorial celestial coordinates of the object at the specified time, and its distance from the Earth. These values are independent of the observing site.

Right ascension
Hour angle at Greenwich.
Declination
Declination with regard to the equator.
Distance (AU)
Distance from the Earth in astronomical units (the Moon's distance is given in units of the Earth's radius).

The next three columns give the location of the object in the sky at the specified observing site. They are not included in displays from the Virtual Telescope, which uses celestial coordinates exclusively.

Altitude
Altitude of the body above the horizon, in degrees at the observing site. If negative, the body is below the horizon (“set”) and hence invisible.
Azimuth
Local compass bearing to the object at the observing site. Astronomers measure azimuth from the South (consistent with the convention for hour angle), with positive angles toward the West and negative angles toward the East.
Visibility
This column interprets the Altitude and Azimuth to describe what you can expect to see. Objects below the apparent horizon (taking account of the refraction of the atmosphere and the finite angular size of the Sun and Moon but not altitude of the observer) are shown as “Set” while objects clearly visible in the sky (or visible if the Sun weren't also up) are shown as “Up”. Objects that are just appearing or disappearing on the horizon are shown as “Rising” or “Setting”, and objects at culmination (crossing the local meridian) are shown as being in “Transit”. Transit times are quite accurate, but rising and setting times can be given only approximately because the altitude of the observer, local topography along the horizon, and the effects of atmospheric refraction (which, in turn, vary based upon temperature and barometric pressure) have a major influence upon when you will actually see an object appear or disappear at the horizon.

Press the button to reproduce the sample ephemeris above, using the following orbital elements for asteroid 1995 DW1:

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