Color coded field

Number Density of Stars along the Ecliptic

large_field1.gif (4451 bytes)

Image 1

number density	color
<=800	black
800-1000	red
1000-1200	yellow
1200-1400	blue
>=1400	white

large_field2.gif (4328 bytes)

Image 2

number density	color
<=800	black
800-1000	red
1000-1200	yellow
1200-1400	blue
>=1400	black

large_field3.gif (4320 bytes)

Image 3

number density	color
<=800	black
800-1000	yellow
1000-1200	yellow
1200-1400	yellow
>=1400	black

Field Number	1	2	3	4
R.A.	3h40m-5h30m	7h20m-8h40m	14h30m-17h00m	20h00m-21h20m

Table 1

Month

Field1

Field2

Field3

Field4

Table 2

o : observable

+ : barely observable (less than two hours)

These color coded images use the stars from USNO catalog within ±5 degree of ecliptic. The ecliptic coordinate running from right to left in a conventional way (0 - 359 degree). The spacing between ticks is 10 degrees .

In Image 3, we coded star number density from 800-1400 stars per square degree (corresponding to 2400-4200 stars per 3 square degree) with yellow. We can easily find that there are NOT many fields can be used as our target fields along the ecliptic. Those black area are either with too few stars or too many stars which are not suitable for our purpose. Fields with reasonable number density are concentrated near the intersection between galactic plane and ecliptic plane.

In Table 1, we designate four groups of fields in Image 3 from right to left.The estimated width of each field was also listed.

From Table 2, we can easily tell that there are at least TWO groups of fields observable in each month.